www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Libraries, users, DLLs

reply "antiAlias" <gblazzer corneleus.com> writes:
Currently, D libraries are predominantly linked in a static fashion. I have
a fairly substantial OO library that I'd really like to distribute as a
dll/shared-lib, but there are apparently a number of issues that stop one
doing so. I may have all of this completely wrong, and I'm really looking
for guidance more that anything else:

1) each DLL has its own GC. Crossing DLL boundaries is a problem for memory
allocations, especially for OO libraries (new doesn't work; some methods
allocate within the DLL but the reference is held by the client instead;
etc).

2) as I understand it, Exceptions do not cross DLL boundaries correctly

One of the goals of providing a library is "ease of use" for the end user. I
don't wish to make anyone jump through hoops just to use an OO class from a
DLL, yet the library really needs to be shareable (there's potentially a
very large number of small bound clients, so one would hope to avoid
static-binding where possible). Can someone point me in the right direction?
Or can we get some support from the compiler, if it's necessary? After all,
a new language is a tough sell without good, easy to use libraries ...
right?
Aug 08 2004
parent reply Lars Ivar Igesund <larsivar igesund.net> writes:
antiAlias wrote:

 Currently, D libraries are predominantly linked in a static fashion. I have
 a fairly substantial OO library that I'd really like to distribute as a
 dll/shared-lib, but there are apparently a number of issues that stop one
 doing so. I may have all of this completely wrong, and I'm really looking
 for guidance more that anything else:
 
 1) each DLL has its own GC. Crossing DLL boundaries is a problem for memory
 allocations, especially for OO libraries (new doesn't work; some methods
 allocate within the DLL but the reference is held by the client instead;
 etc).
 
 2) as I understand it, Exceptions do not cross DLL boundaries correctly
 
 One of the goals of providing a library is "ease of use" for the end user. I
 don't wish to make anyone jump through hoops just to use an OO class from a
 DLL, yet the library really needs to be shareable (there's potentially a
 very large number of small bound clients, so one would hope to avoid
 static-binding where possible). Can someone point me in the right direction?
 Or can we get some support from the compiler, if it's necessary? After all,
 a new language is a tough sell without good, easy to use libraries ...
 right?
 
 
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but being rather difficult to use correctly and safely seems to keep most people from actually creating any. At the very least, strategies for how to overcome the problems mentioned above, should be collected (at the Wiki, I suppose). Maybe it's possible to make tools that can create the factories, stubs, etc automatically, but it sure would be nice to be able to use them the easy way. I would like to come with suggestions for how to 'fix' the DLL's, but I don't think I really have the know-how to even suggest. I *do* know though, that I would like to not have to use reference-counting. Lars Ivar Igesund
Aug 09 2004
next sibling parent "Matthew" <admin.hat stlsoft.dot.org> writes:
"Lars Ivar Igesund" <larsivar igesund.net> wrote in message
news:cf73n3$b1l$2 digitaldaemon.com...
 antiAlias wrote:

 Currently, D libraries are predominantly linked in a static fashion. I have
 a fairly substantial OO library that I'd really like to distribute as a
 dll/shared-lib, but there are apparently a number of issues that stop one
 doing so. I may have all of this completely wrong, and I'm really looking
 for guidance more that anything else:

 1) each DLL has its own GC. Crossing DLL boundaries is a problem for memory
 allocations, especially for OO libraries (new doesn't work; some methods
 allocate within the DLL but the reference is held by the client instead;
 etc).

 2) as I understand it, Exceptions do not cross DLL boundaries correctly

 One of the goals of providing a library is "ease of use" for the end user. I
 don't wish to make anyone jump through hoops just to use an OO class from a
 DLL, yet the library really needs to be shareable (there's potentially a
 very large number of small bound clients, so one would hope to avoid
 static-binding where possible). Can someone point me in the right direction?
 Or can we get some support from the compiler, if it's necessary? After all,
 a new language is a tough sell without good, easy to use libraries ...
 right?
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but being rather difficult to use correctly and safely seems to keep most people from actually creating any. At the very least, strategies for how to overcome the problems mentioned above, should be collected (at the Wiki, I suppose). Maybe it's possible to make tools that can create the factories, stubs, etc automatically, but it sure would be nice to be able to use them the easy way. I would like to come with suggestions for how to 'fix' the DLL's, but I don't think I really have the know-how to even suggest. I *do* know though, that I would like to not have to use reference-counting. Lars Ivar Igesund
If someone could right a brief - 2 page? - treatise on the current state, and their perceived problems, I'd be happy to take a look at start to digest the problem.
Aug 08 2004
prev sibling parent reply pragma <EricAnderton at yahoo dot com> <pragma_member pathlink.com> writes:
In article <cf73n3$b1l$2 digitaldaemon.com>, Lars Ivar Igesund says...
antiAlias wrote:

 Currently, D libraries are predominantly linked in a static fashion. I have
 a fairly substantial OO library that I'd really like to distribute as a
 dll/shared-lib, but there are apparently a number of issues that stop one
 doing so. I may have all of this completely wrong, and I'm really looking
 for guidance more that anything else:
 
 1) each DLL has its own GC. Crossing DLL boundaries is a problem for memory
 allocations, especially for OO libraries (new doesn't work; some methods
 allocate within the DLL but the reference is held by the client instead;
 etc).
 
 2) as I understand it, Exceptions do not cross DLL boundaries correctly
 
 One of the goals of providing a library is "ease of use" for the end user. I
 don't wish to make anyone jump through hoops just to use an OO class from a
 DLL, yet the library really needs to be shareable (there's potentially a
 very large number of small bound clients, so one would hope to avoid
 static-binding where possible). Can someone point me in the right direction?
 Or can we get some support from the compiler, if it's necessary? After all,
 a new language is a tough sell without good, easy to use libraries ...
 right?
 
 
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but being rather difficult to use correctly and safely seems to keep most people from actually creating any. At the very least, strategies for how to overcome the problems mentioned above, should be collected (at the Wiki, I suppose). Maybe it's possible to make tools that can create the factories, stubs, etc automatically, but it sure would be nice to be able to use them the easy way. I would like to come with suggestions for how to 'fix' the DLL's, but I don't think I really have the know-how to even suggest. I *do* know though, that I would like to not have to use reference-counting. Lars Ivar Igesund
Honestly, I've already surmounted a huge number of issues regarding D DLL's in my time writing DSP. I've had to devise some workarounds including, but not limited to: object proxies, pointer lists and event messaging to signal dll unloads. I like your suggestion that solutions should be up on the Wiki, and I may publish my findings there. :) Like everyone in this thread, I want more from D with regard to how libraries are handled. Here's my $0.02: What is really missing is giving the DLL's a larger role in the eyes of the garbage collector. Having a separate GC on each library works well when having D inter-operate with different languages, but within a 100% D project it can become a hinderance. Without close and careful management of where a given D object "lives", releasing a DLL mid-process can be disasterous. However, this isn't any different from what we've already come to know about C and C++, its just something we would all rather live without (what with D already making strides to overcome other problems in C++). Two years ago, I put down development of my own GC-based runtime library for C++ I came across this issue and devised some solutions for it, but was unable to implement it as my GC engine had some impossible-to-debug quirks with it. For all that effort, I did learn some rather invaluable lessons about the impact a collector has on a language. Hooking a GC into another dll isn't that hard to do, as long as one is willing to take on the notion of D-platform-dependent libraries. Ultimately, I realized that the problem regarding Dll's and GC engines is easy provided you can answer one question: Does a given pointer represent a pointer to code on a given DLL, or to a valid root in a given DLL? From this we can deduce the rest of the information we need to do everything else dynamically. If a DLL has no vtables or delegates pointing to it's code, and no pointers elsewhere to any other roots within the DLL, then there are no dependencies on that DLL and it may be dismissed. This leads up to the notion that DLL's themselves may be managed by utilizing the gc. A DLL can be treated as a collectable object, provided that its root pointers and _entire code space_ are set as roots to be scanned by the hosting process's garbage collector. Such A DLL can be unloaded from the process in a manner analagous to collection of a typical object (i.e. lazy destruction and release of resources). The result is something that is almost totally transparent to the language, provided that phobos is given some additional support (outside of std.loader) for DLLs. Careful object management and prodding the GC should be enough to get a library to release/unload/close whenever needed. By constrast an explicit and immediate unload of a DLL requires far more plumbing and participation on behalf of the library developer and library user alike. Collectable DLL's, IMO are the way forward for D. - Pragma
Aug 09 2004
parent reply "antiAlias" <fu bar.com> writes:
What you suggest sounds really promising Eric, and it would certainly help
tremendously with what I'm doing.

So, what am I doing, specifically? Well, Mango has a clustering package,
used for the caching, queuing, and execution of D classes across a LAN.
Naturally, the classes passed around at runtime must be known at
compile-time.

Within a cluster, the server (storage) nodes get around this problem by
maintaining such classes in serialized form only. That is, they deliberately
avoid instantiating an instance (otherwise they'd need to be compiled with
every single possible class that might be stored).

The cluster-clients, on the other hand, do need to know about each class ~
since they will receive and operate upon concrete class instances. These
classes must be known at compile time. For certain applications this is not
a restriction of any kind. In fact, it may actually be viewed as security
benefit.

However, most software systems evolve rather dynamically, and rebooting an
entire operational network to get some new class-instances configured into
the cluster is just not practical.

That's where DLL's (or shared libs) step in. In particular, the clustering
package would benefit greatly if the mobile classes involved were packaged
as discrete dll's. That way, it would be easy to ship them around the
cluster too (as files), and they'd 'attach' to client nodes as appropriate.
This is very similar in approach to how servlets are loaded dynamically into
a running server (and reloaded when they are seen to change).

The other factor involved in such an approach is this: these mobile classes
often need to use resources outside of their own codebase (think Mango
classes, or a database, or whatever). One does not want to bloat the mobile
dll's with such artifacts ~ they should be bound when said dll is loaded
instead. That is, the Mango library itself should be a dll.

Being able to do this cleanly, elegantly, efficiently, and robustly is
important. I think something needs to be done to bring D up-to-date in this
respect.

How about it?




"pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote in
message news:cf80ak$m3v$1 digitaldaemon.com...
 In article <cf73n3$b1l$2 digitaldaemon.com>, Lars Ivar Igesund says...
antiAlias wrote:

 Currently, D libraries are predominantly linked in a static fashion. I
have
 a fairly substantial OO library that I'd really like to distribute as a
 dll/shared-lib, but there are apparently a number of issues that stop
one
 doing so. I may have all of this completely wrong, and I'm really
looking
 for guidance more that anything else:

 1) each DLL has its own GC. Crossing DLL boundaries is a problem for
memory
 allocations, especially for OO libraries (new doesn't work; some
methods
 allocate within the DLL but the reference is held by the client
instead;
 etc).

 2) as I understand it, Exceptions do not cross DLL boundaries correctly

 One of the goals of providing a library is "ease of use" for the end
user. I
 don't wish to make anyone jump through hoops just to use an OO class
from a
 DLL, yet the library really needs to be shareable (there's potentially
a
 very large number of small bound clients, so one would hope to avoid
 static-binding where possible). Can someone point me in the right
direction?
 Or can we get some support from the compiler, if it's necessary? After
all,
 a new language is a tough sell without good, easy to use libraries ...
 right?
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but being rather difficult to use correctly and safely seems to keep most people from actually creating any. At the very least, strategies for how to overcome the problems mentioned above, should be collected (at the Wiki, I suppose). Maybe it's possible to make tools that can create the factories, stubs, etc automatically, but it sure would be nice to be able to use them the easy way. I would like to come with suggestions for how to 'fix' the DLL's, but I don't think I really have the know-how to even suggest. I *do* know though, that I would like to not have to use reference-counting. Lars Ivar Igesund
Honestly, I've already surmounted a huge number of issues regarding D
DLL's in
 my time writing DSP.  I've had to devise some workarounds including, but
not
 limited to: object proxies, pointer lists and event messaging to signal
dll
 unloads.  I like your suggestion that solutions should be up on the Wiki,
and I
 may publish my findings there. :)  Like everyone in this thread, I want
more
 from D with regard to how libraries are handled.

 Here's my $0.02:

 What is really missing is giving the DLL's a larger role in the eyes of
the
 garbage collector.  Having a separate GC on each library works well when
having
 D inter-operate with different languages, but within a 100% D project it
can
 become a hinderance.  Without close and careful management of where a
given D
 object "lives", releasing a DLL mid-process can be disasterous.  However,
this
 isn't any different from what we've already come to know about C and C++,
its
 just something we would all rather live without (what with D already
making
 strides to overcome other problems in C++).

 Two years ago, I put down development of my own GC-based runtime library
for C++
   I came across this issue and devised some solutions for it, but was
unable to
 implement it as my GC engine had some impossible-to-debug quirks with it.
For
 all that effort, I did learn some rather invaluable lessons about the
impact a
 collector has on a language.

 Hooking a GC into another dll isn't that hard to do, as long as one is
willing
 to take on the notion of D-platform-dependent libraries.  Ultimately, I
realized
 that the problem regarding Dll's and GC engines is easy provided you can
answer
 one question:

 Does a given pointer represent a pointer to code on a given DLL, or to a
valid
 root in a given DLL?

 From this we can deduce the rest of the information we need to do
everything
 else dynamically.  If a DLL has no vtables or delegates pointing to it's
code,
 and no pointers elsewhere to any other roots within the DLL, then there
are no
 dependencies on that DLL and it may be dismissed.  This leads up to the
notion
 that DLL's themselves may be managed by utilizing the gc.

 A DLL can be treated as a collectable object, provided that its root
pointers
 and _entire code space_ are set as roots to be scanned by the hosting
process's
 garbage collector.  Such A DLL can be unloaded from the process in a
manner
 analagous to collection of a typical object (i.e. lazy destruction and
release
 of resources).

 The result is something that is almost totally transparent to the
language,
 provided that phobos is given some additional support (outside of
std.loader)
 for DLLs.  Careful object management and prodding the GC should be enough
to get
 a library to release/unload/close whenever needed.

 By constrast an explicit and immediate unload of a DLL requires far more
 plumbing and participation on behalf of the library developer and library
user
 alike.  Collectable DLL's, IMO are the way forward for D.

 - Pragma
Aug 19 2004
parent reply "Matthew" <admin.hat stlsoft.dot.org> writes:
Kris,

... cough ... splutter ...

sorry.

Mr Alias

From your description of your requirements I would say that it's _possible_
that you can implement what you need by
using interfaces, and being _very_ careful with your memory management, but I
don't fancy your (or anyone else's)
chances of making such an infrastructure simply, robustly and flexibly. For my
money, I don't think D's got any kind of
acceptable answer to this issue atm.

Nomenclatural definition: I use the term "link unit" a lot. I'm sure you'll
grok the full extent of the concept when I
say that an exes and dynamic libs are link-units, and static libs are not.
Another way to think of it is link units
define a complete symbol name space. (For more on this and other fascinating
issues, please feel free to preorder a copy
of "Imperfect C++" from
http://www.amazon.com/exec/obidos/tg/detail/-/0321228774/ <g>)

I see four issues with DLLs and D. I'm interested to hear whether I've missed
any and, especially, what ideas people
have for solving these issues in a "Spirit of D" way (i.e. without all the
clodhopping nonsense that is the Java/.NET
infrastructure):

1. Sharing/managing GC - I think this is the most important in the short/medium
term
2. Being able to talk _classes_ not just _interfaces_ between link units. We
can get a long way with interfaces,
methinks, once GC sharing is handled, but still it'd be nice to work with
classes as well, if simply achievable.
3. Versioning, i.e. avoiding DLL Hell
4. Security. Is there something simple and efficient that nonetheless addresses
those handled by the heaving leviathan
that is .NET?

Ancilary issues:

1. Serialisation as a part of the language??


(Germane) thoughts everyone?

Cheers



-- 
Matthew Wilson

Author: "Imperfect C++", Addison-Wesley, 2004
    (http://www.imperfectcplusplus.com)
Contributing editor, C/C++ Users Journal
    (http://www.synesis.com.au/articles.html#columns)
Director, Synesis Software
    (www.synesis.com.au)
STLSoft moderator
    (http://www.stlsoft.org)

"Youth ages, Immaturity is outgrown, Ignorance can be educated, drunkeness
sobered. But stupid lasts forever",
Aristophenes

-----------------------------------------------------





"antiAlias" <fu bar.com> wrote in message
news:cg3pmt$2q32$1 digitaldaemon.com...
 What you suggest sounds really promising Eric, and it would certainly help
 tremendously with what I'm doing.

 So, what am I doing, specifically? Well, Mango has a clustering package,
 used for the caching, queuing, and execution of D classes across a LAN.
 Naturally, the classes passed around at runtime must be known at
 compile-time.

 Within a cluster, the server (storage) nodes get around this problem by
 maintaining such classes in serialized form only. That is, they deliberately
 avoid instantiating an instance (otherwise they'd need to be compiled with
 every single possible class that might be stored).

 The cluster-clients, on the other hand, do need to know about each class ~
 since they will receive and operate upon concrete class instances. These
 classes must be known at compile time. For certain applications this is not
 a restriction of any kind. In fact, it may actually be viewed as security
 benefit.

 However, most software systems evolve rather dynamically, and rebooting an
 entire operational network to get some new class-instances configured into
 the cluster is just not practical.

 That's where DLL's (or shared libs) step in. In particular, the clustering
 package would benefit greatly if the mobile classes involved were packaged
 as discrete dll's. That way, it would be easy to ship them around the
 cluster too (as files), and they'd 'attach' to client nodes as appropriate.
 This is very similar in approach to how servlets are loaded dynamically into
 a running server (and reloaded when they are seen to change).

 The other factor involved in such an approach is this: these mobile classes
 often need to use resources outside of their own codebase (think Mango
 classes, or a database, or whatever). One does not want to bloat the mobile
 dll's with such artifacts ~ they should be bound when said dll is loaded
 instead. That is, the Mango library itself should be a dll.

 Being able to do this cleanly, elegantly, efficiently, and robustly is
 important. I think something needs to be done to bring D up-to-date in this
 respect.

 How about it?




 "pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote in
 message news:cf80ak$m3v$1 digitaldaemon.com...
 In article <cf73n3$b1l$2 digitaldaemon.com>, Lars Ivar Igesund says...
antiAlias wrote:

 Currently, D libraries are predominantly linked in a static fashion. I
have
 a fairly substantial OO library that I'd really like to distribute as a
 dll/shared-lib, but there are apparently a number of issues that stop
one
 doing so. I may have all of this completely wrong, and I'm really
looking
 for guidance more that anything else:

 1) each DLL has its own GC. Crossing DLL boundaries is a problem for
memory
 allocations, especially for OO libraries (new doesn't work; some
methods
 allocate within the DLL but the reference is held by the client
instead;
 etc).

 2) as I understand it, Exceptions do not cross DLL boundaries correctly

 One of the goals of providing a library is "ease of use" for the end
user. I
 don't wish to make anyone jump through hoops just to use an OO class
from a
 DLL, yet the library really needs to be shareable (there's potentially
a
 very large number of small bound clients, so one would hope to avoid
 static-binding where possible). Can someone point me in the right
direction?
 Or can we get some support from the compiler, if it's necessary? After
all,
 a new language is a tough sell without good, easy to use libraries ...
 right?
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but being rather difficult to use correctly and safely seems to keep most people from actually creating any. At the very least, strategies for how to overcome the problems mentioned above, should be collected (at the Wiki, I suppose). Maybe it's possible to make tools that can create the factories, stubs, etc automatically, but it sure would be nice to be able to use them the easy way. I would like to come with suggestions for how to 'fix' the DLL's, but I don't think I really have the know-how to even suggest. I *do* know though, that I would like to not have to use reference-counting. Lars Ivar Igesund
Honestly, I've already surmounted a huge number of issues regarding D
DLL's in
 my time writing DSP.  I've had to devise some workarounds including, but
not
 limited to: object proxies, pointer lists and event messaging to signal
dll
 unloads.  I like your suggestion that solutions should be up on the Wiki,
and I
 may publish my findings there. :)  Like everyone in this thread, I want
more
 from D with regard to how libraries are handled.

 Here's my $0.02:

 What is really missing is giving the DLL's a larger role in the eyes of
the
 garbage collector.  Having a separate GC on each library works well when
having
 D inter-operate with different languages, but within a 100% D project it
can
 become a hinderance.  Without close and careful management of where a
given D
 object "lives", releasing a DLL mid-process can be disasterous.  However,
this
 isn't any different from what we've already come to know about C and C++,
its
 just something we would all rather live without (what with D already
making
 strides to overcome other problems in C++).

 Two years ago, I put down development of my own GC-based runtime library
for C++
   I came across this issue and devised some solutions for it, but was
unable to
 implement it as my GC engine had some impossible-to-debug quirks with it.
For
 all that effort, I did learn some rather invaluable lessons about the
impact a
 collector has on a language.

 Hooking a GC into another dll isn't that hard to do, as long as one is
willing
 to take on the notion of D-platform-dependent libraries.  Ultimately, I
realized
 that the problem regarding Dll's and GC engines is easy provided you can
answer
 one question:

 Does a given pointer represent a pointer to code on a given DLL, or to a
valid
 root in a given DLL?

 From this we can deduce the rest of the information we need to do
everything
 else dynamically.  If a DLL has no vtables or delegates pointing to it's
code,
 and no pointers elsewhere to any other roots within the DLL, then there
are no
 dependencies on that DLL and it may be dismissed.  This leads up to the
notion
 that DLL's themselves may be managed by utilizing the gc.

 A DLL can be treated as a collectable object, provided that its root
pointers
 and _entire code space_ are set as roots to be scanned by the hosting
process's
 garbage collector.  Such A DLL can be unloaded from the process in a
manner
 analagous to collection of a typical object (i.e. lazy destruction and
release
 of resources).

 The result is something that is almost totally transparent to the
language,
 provided that phobos is given some additional support (outside of
std.loader)
 for DLLs.  Careful object management and prodding the GC should be enough
to get
 a library to release/unload/close whenever needed.

 By constrast an explicit and immediate unload of a DLL requires far more
 plumbing and participation on behalf of the library developer and library
user
 alike.  Collectable DLL's, IMO are the way forward for D.

 - Pragma
Aug 19 2004
parent reply "antiAlias" <fu bar.com> writes:
I agree that #1 (the shared GC) is a primary issue. On the face of it, what
Eric describes (below) sounds really attractive.

Other than that, what about the exception-boundary issue?



"Matthew" <admin.hat stlsoft.dot.org> wrote in message
news:cg3ul4$2sq0$1 digitaldaemon.com...
 Kris,

 ... cough ... splutter ...

 sorry.

 Mr Alias

 From your description of your requirements I would say that it's
_possible_ that you can implement what you need by
 using interfaces, and being _very_ careful with your memory management,
but I don't fancy your (or anyone else's)
 chances of making such an infrastructure simply, robustly and flexibly.
For my money, I don't think D's got any kind of
 acceptable answer to this issue atm.

 Nomenclatural definition: I use the term "link unit" a lot. I'm sure
you'll grok the full extent of the concept when I
 say that an exes and dynamic libs are link-units, and static libs are not.
Another way to think of it is link units
 define a complete symbol name space. (For more on this and other
fascinating issues, please feel free to preorder a copy
 of "Imperfect C++" from
http://www.amazon.com/exec/obidos/tg/detail/-/0321228774/ <g>)
 I see four issues with DLLs and D. I'm interested to hear whether I've
missed any and, especially, what ideas people
 have for solving these issues in a "Spirit of D" way (i.e. without all the
clodhopping nonsense that is the Java/.NET
 infrastructure):

 1. Sharing/managing GC - I think this is the most important in the
short/medium term
 2. Being able to talk _classes_ not just _interfaces_ between link units.
We can get a long way with interfaces,
 methinks, once GC sharing is handled, but still it'd be nice to work with
classes as well, if simply achievable.
 3. Versioning, i.e. avoiding DLL Hell
 4. Security. Is there something simple and efficient that nonetheless
addresses those handled by the heaving leviathan
 that is .NET?

 Ancilary issues:

 1. Serialisation as a part of the language??


 (Germane) thoughts everyone?

 Cheers



 --
 Matthew Wilson

 Author: "Imperfect C++", Addison-Wesley, 2004
     (http://www.imperfectcplusplus.com)
 Contributing editor, C/C++ Users Journal
     (http://www.synesis.com.au/articles.html#columns)
 Director, Synesis Software
     (www.synesis.com.au)
 STLSoft moderator
     (http://www.stlsoft.org)

 "Youth ages, Immaturity is outgrown, Ignorance can be educated, drunkeness
sobered. But stupid lasts forever",
 Aristophenes

 -----------------------------------------------------





 "antiAlias" <fu bar.com> wrote in message
news:cg3pmt$2q32$1 digitaldaemon.com...
 What you suggest sounds really promising Eric, and it would certainly
help
 tremendously with what I'm doing.

 So, what am I doing, specifically? Well, Mango has a clustering package,
 used for the caching, queuing, and execution of D classes across a LAN.
 Naturally, the classes passed around at runtime must be known at
 compile-time.

 Within a cluster, the server (storage) nodes get around this problem by
 maintaining such classes in serialized form only. That is, they
deliberately
 avoid instantiating an instance (otherwise they'd need to be compiled
with
 every single possible class that might be stored).

 The cluster-clients, on the other hand, do need to know about each class
~
 since they will receive and operate upon concrete class instances. These
 classes must be known at compile time. For certain applications this is
not
 a restriction of any kind. In fact, it may actually be viewed as
security
 benefit.

 However, most software systems evolve rather dynamically, and rebooting
an
 entire operational network to get some new class-instances configured
into
 the cluster is just not practical.

 That's where DLL's (or shared libs) step in. In particular, the
clustering
 package would benefit greatly if the mobile classes involved were
packaged
 as discrete dll's. That way, it would be easy to ship them around the
 cluster too (as files), and they'd 'attach' to client nodes as
appropriate.
 This is very similar in approach to how servlets are loaded dynamically
into
 a running server (and reloaded when they are seen to change).

 The other factor involved in such an approach is this: these mobile
classes
 often need to use resources outside of their own codebase (think Mango
 classes, or a database, or whatever). One does not want to bloat the
mobile
 dll's with such artifacts ~ they should be bound when said dll is loaded
 instead. That is, the Mango library itself should be a dll.

 Being able to do this cleanly, elegantly, efficiently, and robustly is
 important. I think something needs to be done to bring D up-to-date in
this
 respect.

 How about it?




 "pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote
in
 message news:cf80ak$m3v$1 digitaldaemon.com...
 In article <cf73n3$b1l$2 digitaldaemon.com>, Lars Ivar Igesund says...
antiAlias wrote:

 Currently, D libraries are predominantly linked in a static
fashion. I
 have
 a fairly substantial OO library that I'd really like to distribute
as a
 dll/shared-lib, but there are apparently a number of issues that
stop
 one
 doing so. I may have all of this completely wrong, and I'm really
looking
 for guidance more that anything else:

 1) each DLL has its own GC. Crossing DLL boundaries is a problem
for
 memory
 allocations, especially for OO libraries (new doesn't work; some
methods
 allocate within the DLL but the reference is held by the client
instead;
 etc).

 2) as I understand it, Exceptions do not cross DLL boundaries
correctly
 One of the goals of providing a library is "ease of use" for the
end
 user. I
 don't wish to make anyone jump through hoops just to use an OO
class
 from a
 DLL, yet the library really needs to be shareable (there's
potentially
 a
 very large number of small bound clients, so one would hope to
avoid
 static-binding where possible). Can someone point me in the right
direction?
 Or can we get some support from the compiler, if it's necessary?
After
 all,
 a new language is a tough sell without good, easy to use libraries
...
 right?
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but
being
rather difficult to use correctly and safely seems to keep most
people
from actually creating any.

At the very least, strategies for how to overcome the problems
mentioned
above, should be collected (at the Wiki, I suppose). Maybe it's
possible
to make tools that can create the factories, stubs, etc
automatically,
but it sure would be nice to be able to use them the easy way.

I would like to come with suggestions for how to 'fix' the DLL's, but
I
don't think I really have the know-how to even suggest. I *do* know
though, that I would like to not have to use reference-counting.

Lars Ivar Igesund
Honestly, I've already surmounted a huge number of issues regarding D
DLL's in
 my time writing DSP.  I've had to devise some workarounds including,
but
 not
 limited to: object proxies, pointer lists and event messaging to
signal
 dll
 unloads.  I like your suggestion that solutions should be up on the
Wiki,
 and I
 may publish my findings there. :)  Like everyone in this thread, I
want
 more
 from D with regard to how libraries are handled.

 Here's my $0.02:

 What is really missing is giving the DLL's a larger role in the eyes
of
 the
 garbage collector.  Having a separate GC on each library works well
when
 having
 D inter-operate with different languages, but within a 100% D project
it
 can
 become a hinderance.  Without close and careful management of where a
given D
 object "lives", releasing a DLL mid-process can be disasterous.
However,
 this
 isn't any different from what we've already come to know about C and
C++,
 its
 just something we would all rather live without (what with D already
making
 strides to overcome other problems in C++).

 Two years ago, I put down development of my own GC-based runtime
library
 for C++
   I came across this issue and devised some solutions for it, but was
unable to
 implement it as my GC engine had some impossible-to-debug quirks with
it.
 For
 all that effort, I did learn some rather invaluable lessons about the
impact a
 collector has on a language.

 Hooking a GC into another dll isn't that hard to do, as long as one is
willing
 to take on the notion of D-platform-dependent libraries.  Ultimately,
I
 realized
 that the problem regarding Dll's and GC engines is easy provided you
can
 answer
 one question:

 Does a given pointer represent a pointer to code on a given DLL, or to
a
 valid
 root in a given DLL?

 From this we can deduce the rest of the information we need to do
everything
 else dynamically.  If a DLL has no vtables or delegates pointing to
it's
 code,
 and no pointers elsewhere to any other roots within the DLL, then
there
 are no
 dependencies on that DLL and it may be dismissed.  This leads up to
the
 notion
 that DLL's themselves may be managed by utilizing the gc.

 A DLL can be treated as a collectable object, provided that its root
pointers
 and _entire code space_ are set as roots to be scanned by the hosting
process's
 garbage collector.  Such A DLL can be unloaded from the process in a
manner
 analagous to collection of a typical object (i.e. lazy destruction and
release
 of resources).

 The result is something that is almost totally transparent to the
language,
 provided that phobos is given some additional support (outside of
std.loader)
 for DLLs.  Careful object management and prodding the GC should be
enough
 to get
 a library to release/unload/close whenever needed.

 By constrast an explicit and immediate unload of a DLL requires far
more
 plumbing and participation on behalf of the library developer and
library
 user
 alike.  Collectable DLL's, IMO are the way forward for D.

 - Pragma
Aug 19 2004
parent reply "Matthew" <admin.hat stlsoft.dot.org> writes:
"antiAlias" <fu bar.com> wrote in message
news:cg408a$2tge$1 digitaldaemon.com...
 I agree that #1 (the shared GC) is a primary issue. On the face of it, what
 Eric describes (below) sounds really attractive.
It sounds promising. I'd like to hear more fine details, though. I'd also like to hear if his ideas would require changes to std.loader (as I'm itching for an excuse to rewrite that stillborn obscenity). I'd also like to hear Walter's opinions on the matter. I think this issue is of sufficient import to be a 1.0 prerequesite, don't you?
 Other than that, what about the exception-boundary issue?
Well, D's going to have an ABI, and since all exceptions are going to co-exist memorywise (when the GC's linearised/homogenised), what's the prob?
 "Matthew" <admin.hat stlsoft.dot.org> wrote in message
 news:cg3ul4$2sq0$1 digitaldaemon.com...
 Kris,

 ... cough ... splutter ...

 sorry.

 Mr Alias

 From your description of your requirements I would say that it's
_possible_ that you can implement what you need by
 using interfaces, and being _very_ careful with your memory management,
but I don't fancy your (or anyone else's)
 chances of making such an infrastructure simply, robustly and flexibly.
For my money, I don't think D's got any kind of
 acceptable answer to this issue atm.

 Nomenclatural definition: I use the term "link unit" a lot. I'm sure
you'll grok the full extent of the concept when I
 say that an exes and dynamic libs are link-units, and static libs are not.
Another way to think of it is link units
 define a complete symbol name space. (For more on this and other
fascinating issues, please feel free to preorder a copy
 of "Imperfect C++" from
http://www.amazon.com/exec/obidos/tg/detail/-/0321228774/ <g>)
 I see four issues with DLLs and D. I'm interested to hear whether I've
missed any and, especially, what ideas people
 have for solving these issues in a "Spirit of D" way (i.e. without all the
clodhopping nonsense that is the Java/.NET
 infrastructure):

 1. Sharing/managing GC - I think this is the most important in the
short/medium term
 2. Being able to talk _classes_ not just _interfaces_ between link units.
We can get a long way with interfaces,
 methinks, once GC sharing is handled, but still it'd be nice to work with
classes as well, if simply achievable.
 3. Versioning, i.e. avoiding DLL Hell
 4. Security. Is there something simple and efficient that nonetheless
addresses those handled by the heaving leviathan
 that is .NET?

 Ancilary issues:

 1. Serialisation as a part of the language??


 (Germane) thoughts everyone?

 Cheers



 --
 Matthew Wilson

 Author: "Imperfect C++", Addison-Wesley, 2004
     (http://www.imperfectcplusplus.com)
 Contributing editor, C/C++ Users Journal
     (http://www.synesis.com.au/articles.html#columns)
 Director, Synesis Software
     (www.synesis.com.au)
 STLSoft moderator
     (http://www.stlsoft.org)

 "Youth ages, Immaturity is outgrown, Ignorance can be educated, drunkeness
sobered. But stupid lasts forever",
 Aristophenes

 -----------------------------------------------------





 "antiAlias" <fu bar.com> wrote in message
news:cg3pmt$2q32$1 digitaldaemon.com...
 What you suggest sounds really promising Eric, and it would certainly
help
 tremendously with what I'm doing.

 So, what am I doing, specifically? Well, Mango has a clustering package,
 used for the caching, queuing, and execution of D classes across a LAN.
 Naturally, the classes passed around at runtime must be known at
 compile-time.

 Within a cluster, the server (storage) nodes get around this problem by
 maintaining such classes in serialized form only. That is, they
deliberately
 avoid instantiating an instance (otherwise they'd need to be compiled
with
 every single possible class that might be stored).

 The cluster-clients, on the other hand, do need to know about each class
~
 since they will receive and operate upon concrete class instances. These
 classes must be known at compile time. For certain applications this is
not
 a restriction of any kind. In fact, it may actually be viewed as
security
 benefit.

 However, most software systems evolve rather dynamically, and rebooting
an
 entire operational network to get some new class-instances configured
into
 the cluster is just not practical.

 That's where DLL's (or shared libs) step in. In particular, the
clustering
 package would benefit greatly if the mobile classes involved were
packaged
 as discrete dll's. That way, it would be easy to ship them around the
 cluster too (as files), and they'd 'attach' to client nodes as
appropriate.
 This is very similar in approach to how servlets are loaded dynamically
into
 a running server (and reloaded when they are seen to change).

 The other factor involved in such an approach is this: these mobile
classes
 often need to use resources outside of their own codebase (think Mango
 classes, or a database, or whatever). One does not want to bloat the
mobile
 dll's with such artifacts ~ they should be bound when said dll is loaded
 instead. That is, the Mango library itself should be a dll.

 Being able to do this cleanly, elegantly, efficiently, and robustly is
 important. I think something needs to be done to bring D up-to-date in
this
 respect.

 How about it?




 "pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote
in
 message news:cf80ak$m3v$1 digitaldaemon.com...
 In article <cf73n3$b1l$2 digitaldaemon.com>, Lars Ivar Igesund says...
antiAlias wrote:

 Currently, D libraries are predominantly linked in a static
fashion. I
 have
 a fairly substantial OO library that I'd really like to distribute
as a
 dll/shared-lib, but there are apparently a number of issues that
stop
 one
 doing so. I may have all of this completely wrong, and I'm really
looking
 for guidance more that anything else:

 1) each DLL has its own GC. Crossing DLL boundaries is a problem
for
 memory
 allocations, especially for OO libraries (new doesn't work; some
methods
 allocate within the DLL but the reference is held by the client
instead;
 etc).

 2) as I understand it, Exceptions do not cross DLL boundaries
correctly
 One of the goals of providing a library is "ease of use" for the
end
 user. I
 don't wish to make anyone jump through hoops just to use an OO
class
 from a
 DLL, yet the library really needs to be shareable (there's
potentially
 a
 very large number of small bound clients, so one would hope to
avoid
 static-binding where possible). Can someone point me in the right
direction?
 Or can we get some support from the compiler, if it's necessary?
After
 all,
 a new language is a tough sell without good, easy to use libraries
...
 right?
I have to say that I agree. DLL's are supposed to be the glorious way forward (at least it is what is preached outside the D world), but
being
rather difficult to use correctly and safely seems to keep most
people
from actually creating any.

At the very least, strategies for how to overcome the problems
mentioned
above, should be collected (at the Wiki, I suppose). Maybe it's
possible
to make tools that can create the factories, stubs, etc
automatically,
but it sure would be nice to be able to use them the easy way.

I would like to come with suggestions for how to 'fix' the DLL's, but
I
don't think I really have the know-how to even suggest. I *do* know
though, that I would like to not have to use reference-counting.

Lars Ivar Igesund
Honestly, I've already surmounted a huge number of issues regarding D
DLL's in
 my time writing DSP.  I've had to devise some workarounds including,
but
 not
 limited to: object proxies, pointer lists and event messaging to
signal
 dll
 unloads.  I like your suggestion that solutions should be up on the
Wiki,
 and I
 may publish my findings there. :)  Like everyone in this thread, I
want
 more
 from D with regard to how libraries are handled.

 Here's my $0.02:

 What is really missing is giving the DLL's a larger role in the eyes
of
 the
 garbage collector.  Having a separate GC on each library works well
when
 having
 D inter-operate with different languages, but within a 100% D project
it
 can
 become a hinderance.  Without close and careful management of where a
given D
 object "lives", releasing a DLL mid-process can be disasterous.
However,
 this
 isn't any different from what we've already come to know about C and
C++,
 its
 just something we would all rather live without (what with D already
making
 strides to overcome other problems in C++).

 Two years ago, I put down development of my own GC-based runtime
library
 for C++
   I came across this issue and devised some solutions for it, but was
unable to
 implement it as my GC engine had some impossible-to-debug quirks with
it.
 For
 all that effort, I did learn some rather invaluable lessons about the
impact a
 collector has on a language.

 Hooking a GC into another dll isn't that hard to do, as long as one is
willing
 to take on the notion of D-platform-dependent libraries.  Ultimately,
I
 realized
 that the problem regarding Dll's and GC engines is easy provided you
can
 answer
 one question:

 Does a given pointer represent a pointer to code on a given DLL, or to
a
 valid
 root in a given DLL?

 From this we can deduce the rest of the information we need to do
everything
 else dynamically.  If a DLL has no vtables or delegates pointing to
it's
 code,
 and no pointers elsewhere to any other roots within the DLL, then
there
 are no
 dependencies on that DLL and it may be dismissed.  This leads up to
the
 notion
 that DLL's themselves may be managed by utilizing the gc.

 A DLL can be treated as a collectable object, provided that its root
pointers
 and _entire code space_ are set as roots to be scanned by the hosting
process's
 garbage collector.  Such A DLL can be unloaded from the process in a
manner
 analagous to collection of a typical object (i.e. lazy destruction and
release
 of resources).

 The result is something that is almost totally transparent to the
language,
 provided that phobos is given some additional support (outside of
std.loader)
 for DLLs.  Careful object management and prodding the GC should be
enough
 to get
 a library to release/unload/close whenever needed.

 By constrast an explicit and immediate unload of a DLL requires far
more
 plumbing and participation on behalf of the library developer and
library
 user
 alike.  Collectable DLL's, IMO are the way forward for D.

 - Pragma
Aug 19 2004
parent reply pragma <EricAnderton at yahoo dot com> <pragma_member pathlink.com> writes:
FYI: this is a long post, please read.  Thank you. :)

In article <cg41tm$2u6a$1 digitaldaemon.com>, Matthew says...
"antiAlias" <fu bar.com> wrote in message
news:cg408a$2tge$1 digitaldaemon.com...
 I agree that #1 (the shared GC) is a primary issue. On the face of it, what
 Eric describes (below) sounds really attractive.
It sounds promising. I'd like to hear more fine details, though.
I'll work on a more detailed treatment as soon as time permits. I'll have to first go back through my old source/notes and make sure that there's nothing that I've managed to miss. One thing I will say though: No matter how many times I revisit the problem, the businss of explicitly unloading a library at runtime has ugly consequences regardless of how the GC is hooked. Also, I blame languages like Java and C# for raising our expectations of how this should be handled. I don't think the problem can be completely solved for in-memory objects, without resorting to proxies and/or notification lists.
I'd also like to hear if his ideas would require changes to std.loader (as I'm
itching for an excuse to rewrite that
stillborn obscenity).
I think my first reaction to reading that source was: "This compiled?" (j/k) I wouldn't anticipate need to change std.loader drastically. Outside of that, I'd love to see the thread-local storage bits broken out into another library or as an extension to std.thread. ;) One question though: is all the extra ref-counting code needed for linux libraries, or does it supply some extra value to both Win32 and Linux environments?
I'd also like to hear Walter's opinions on the matter. I think this issue is of
sufficient import to be a 1.0
prerequesite, don't you?
I couldn't agree more. I too, would like to hear what direction things will take with respect to dll's.
 Other than that, what about the exception-boundary issue?
Well, D's going to have an ABI, and since all exceptions are going to co-exist memorywise (when the GC's linearised/homogenised), what's the prob?
With respect to Kris' concern about handling exceptions, its really obnoxious how an uncaught exception within a library kills your app. Aside from making all of my libraries behave like class-factories, I've taken to using methods that do this:
 int someMethod(int foo){ /* impl */ }
..to be called and exported by a dll stub function:
 export(Windows) Exception someMethod(int foo,out _returnval){
   Exception _exception;
   try{ _returnval = someMethod(foo); }
   catch(Exception e){ _exception = e; }
   return(_exception);
 }
You can use a similar stub on the calling side that wraps the function pointer that you grab from the library. Meanwhile (on a slightly OT note), I'm still working on some of the more tricky aspects of dll's in D. In particular, I've tracked one really nasty bug down to (what looks like) the digitalmars-C backend:
 // deceptively simple example.
 import std.c.windows.windows;
 void main(){
   HMODULE mod = LoadLibrary("mydll.dll");
   printf("freeing...");
   FreeLibrary(mod);
   printf("You will never see this print.\n");
 }
(Matthew, Kris, have you had this problem on your Windows machines? I've done this on two separate boxes with the same result. If you two or anyone else can confirm this, I'll go ahead and post it to the bugs NG) Basically, stdout and stdin are "automagically" set to EOF (or some similar state) after the call to FreeLibrary(): nothing goes in and nothing comes out. Everything else runs fine, no exceptions are thrown, and GetLastError() faithfully returns 0. I've been able to recreate the above in DMC, with a 100% C-built Dll using the same .def file as the mydll sample. The results are also the same when calling that dll from a host program written in MSVC6, DMD and DMC. Unless I'm horribly mistaken on how to do compose dll's using Digitalmars' technology, this is what you get the instant you unload any DMC/DMD built dll. The problem seems to only manifest when a proper DllMain() method is exported from the library. If none is provided, or if the given implementation can be optimized away, the error does not ocurr. This caused me hours upon hours of anguish trying to figure out why in my DSP/Mango server kept quietly halting on me: it was waiting for console input to terminate, but Mango's Stdin throws on EOF. :( - Pragma
Aug 20 2004
next sibling parent reply "Matthew" <admin.hat stlsoft.dot.org> writes:
I've read it once, but want to take some time to think before I respond to some
of the points.

Let me pose my question in a more direct manner:

AFAICS, one of the biggest problems is the ability to be able to use DLLs with
D in *all* of the following guises:

1. D exe, C dll. Communication by plain C-API function calls. All resources
returned whence they came.
2. C exe, D dll. Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). All
resources returned whence they came
3. D exe, D dll, Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). All
resources returned whence they came
4. D exe, D dll, Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). Memory
allocated hither and used safely thither
5. D exe, D dll, Communication via extern(C) calls and/or extern(D) calls
and/or interfaces with well-known vtable
layout (e.g. COM). Memory allocated hither and used safely thither
6. D exe, D dll, Communication via 5. + classes. (Not sure of these details.)

Note, for each of the above, you can permute by replacing exe with D client
code inside a D dll in any of cases 2-6!

Since D has, putatively at least, an ABI, all 6 (or 11) of these should, in
principle be realisable. Further,
commercially speaking, D *must* provide all of these, to not be abandoned by
developers more influenced by deadline and
pragmatism than idealism and performance - in other words, most of them.

To my mind, we have two choices. One option is that the GC and supporting
infrastructure is *always* in some DCore.dll -
i.e. there're no more statically linked programs - in the same vein as .NET.
The other option is that we come up with a
mechanism whereby each link-unit is able to detect whether the process in which
it is loaded already has a GC and, if
so, links to that, otherwise starting its own. The complication to this is that
if the first such link-unit is not the
process' exe, we have the issue whereby the GC might be prematurely unloaded
while other link-units are still depending
on it. This could, hopefully(!), be resolved be having dependent link-units
hold an independent dynamic-load reference
on the GC's owning DLL.

Thoughts?

Walter, I'd be very interested in your thoughts on this, both on my comments on
the need for this commercially, and also
on possible implementation mechanisms.




"pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote in
message
news:cg5184$c7u$1 digitaldaemon.com...
 FYI: this is a long post, please read.  Thank you. :)

 In article <cg41tm$2u6a$1 digitaldaemon.com>, Matthew says...
"antiAlias" <fu bar.com> wrote in message
news:cg408a$2tge$1 digitaldaemon.com...
 I agree that #1 (the shared GC) is a primary issue. On the face of it, what
 Eric describes (below) sounds really attractive.
It sounds promising. I'd like to hear more fine details, though.
I'll work on a more detailed treatment as soon as time permits. I'll have to first go back through my old source/notes and make sure that there's nothing that I've managed to miss. One thing I will say though: No matter how many times I revisit the problem, the businss of explicitly unloading a library at runtime has ugly consequences regardless of how the GC is hooked. Also, I blame languages like Java and C# for raising our expectations of how this should be handled. I don't think the problem can be completely solved for in-memory objects, without resorting to proxies and/or notification lists.
I'd also like to hear if his ideas would require changes to std.loader (as I'm
itching for an excuse to rewrite that
stillborn obscenity).
I think my first reaction to reading that source was: "This compiled?" (j/k) I wouldn't anticipate need to change std.loader drastically. Outside of that, I'd love to see the thread-local storage bits broken out into another library or as an extension to std.thread. ;) One question though: is all the extra ref-counting code needed for linux libraries, or does it supply some extra value to both Win32 and Linux environments?
I'd also like to hear Walter's opinions on the matter. I think this issue is of
sufficient import to be a 1.0
prerequesite, don't you?
I couldn't agree more. I too, would like to hear what direction things will take with respect to dll's.
 Other than that, what about the exception-boundary issue?
Well, D's going to have an ABI, and since all exceptions are going to co-exist memorywise (when the GC's linearised/homogenised), what's the prob?
With respect to Kris' concern about handling exceptions, its really obnoxious how an uncaught exception within a library kills your app. Aside from making all of my libraries behave like class-factories, I've taken to using methods that do this:
 int someMethod(int foo){ /* impl */ }
..to be called and exported by a dll stub function:
 export(Windows) Exception someMethod(int foo,out _returnval){
   Exception _exception;
   try{ _returnval = someMethod(foo); }
   catch(Exception e){ _exception = e; }
   return(_exception);
 }
You can use a similar stub on the calling side that wraps the function pointer that you grab from the library. Meanwhile (on a slightly OT note), I'm still working on some of the more tricky aspects of dll's in D. In particular, I've tracked one really nasty bug down to (what looks like) the digitalmars-C backend:
 // deceptively simple example.
 import std.c.windows.windows;
 void main(){
   HMODULE mod = LoadLibrary("mydll.dll");
   printf("freeing...");
   FreeLibrary(mod);
   printf("You will never see this print.\n");
 }
(Matthew, Kris, have you had this problem on your Windows machines? I've done this on two separate boxes with the same result. If you two or anyone else can confirm this, I'll go ahead and post it to the bugs NG) Basically, stdout and stdin are "automagically" set to EOF (or some similar state) after the call to FreeLibrary(): nothing goes in and nothing comes out. Everything else runs fine, no exceptions are thrown, and GetLastError() faithfully returns 0. I've been able to recreate the above in DMC, with a 100% C-built Dll using the same .def file as the mydll sample. The results are also the same when calling that dll from a host program written in MSVC6, DMD and DMC. Unless I'm horribly mistaken on how to do compose dll's using Digitalmars' technology, this is what you get the instant you unload any DMC/DMD built dll. The problem seems to only manifest when a proper DllMain() method is exported from the library. If none is provided, or if the given implementation can be optimized away, the error does not ocurr. This caused me hours upon hours of anguish trying to figure out why in my DSP/Mango server kept quietly halting on me: it was waiting for console input to terminate, but Mango's Stdin throws on EOF. :( - Pragma
Aug 21 2004
parent "antiAlias" <fu bar.com> writes:
Matthew;

As far as the GC is concerned, it would be wonderful to stuff that into a
DLL ... that would solve a major problem right off the bat. Putting Phobos
in a DLL would be a good idea also (no duplication of code across DLL
instances).

If subsequent DLL's were loaded as collectable entities (wrapped by a class;
or perhaps /as/ a class) then the GC could handle all the murky ref-counting
in its own inimitable fashion (invoking the destructor when the DLL is no
longer referenced). That would eliminate another sticky wicket; as Eric
pointed out.

Those two get my immediate support; they would help tremendously with both
Mango clustering and with the servlet-engine.

As to how one gains access to a class within the DLL ... I'd be happy with a
simple and convenient means of accessing a factory method from the DLL, and
going from there. Of course, what you are describing would be infinitely
superior; but I'd be happy to wait for it if the primary issues were taken
care of (shareable GC; DLLs as collectible entities).



"Matthew" <admin.hat stlsoft.dot.org> wrote in message
news:cg8kuk$2il8$1 digitaldaemon.com...
 I've read it once, but want to take some time to think before I respond to
some of the points.
 Let me pose my question in a more direct manner:

 AFAICS, one of the biggest problems is the ability to be able to use DLLs
with D in *all* of the following guises:
 1. D exe, C dll. Communication by plain C-API function calls. All
resources returned whence they came.
 2. C exe, D dll. Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). All
 resources returned whence they came
 3. D exe, D dll, Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). All
 resources returned whence they came
 4. D exe, D dll, Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). Memory
 allocated hither and used safely thither
 5. D exe, D dll, Communication via extern(C) calls and/or extern(D) calls
and/or interfaces with well-known vtable
 layout (e.g. COM). Memory allocated hither and used safely thither
 6. D exe, D dll, Communication via 5. + classes. (Not sure of these
details.)
 Note, for each of the above, you can permute by replacing exe with D
client code inside a D dll in any of cases 2-6!
 Since D has, putatively at least, an ABI, all 6 (or 11) of these should,
in principle be realisable. Further,
 commercially speaking, D *must* provide all of these, to not be abandoned
by developers more influenced by deadline and
 pragmatism than idealism and performance - in other words, most of them.

 To my mind, we have two choices. One option is that the GC and supporting
infrastructure is *always* in some DCore.dll -
 i.e. there're no more statically linked programs - in the same vein as
.NET. The other option is that we come up with a
 mechanism whereby each link-unit is able to detect whether the process in
which it is loaded already has a GC and, if
 so, links to that, otherwise starting its own. The complication to this is
that if the first such link-unit is not the
 process' exe, we have the issue whereby the GC might be prematurely
unloaded while other link-units are still depending
 on it. This could, hopefully(!), be resolved be having dependent
link-units hold an independent dynamic-load reference
 on the GC's owning DLL.

 Thoughts?

 Walter, I'd be very interested in your thoughts on this, both on my
comments on the need for this commercially, and also
 on possible implementation mechanisms.




 "pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote
in message
 news:cg5184$c7u$1 digitaldaemon.com...
 FYI: this is a long post, please read.  Thank you. :)

 In article <cg41tm$2u6a$1 digitaldaemon.com>, Matthew says...
"antiAlias" <fu bar.com> wrote in message
news:cg408a$2tge$1 digitaldaemon.com...
 I agree that #1 (the shared GC) is a primary issue. On the face of
it, what
 Eric describes (below) sounds really attractive.
It sounds promising. I'd like to hear more fine details, though.
I'll work on a more detailed treatment as soon as time permits. I'll
have to
 first go back through my old source/notes and make sure that there's
nothing
 that I've managed to miss.

 One thing I will say though: No matter how many times I revisit the
problem, the
 businss of explicitly unloading a library at runtime has ugly
consequences
 regardless of how the GC is hooked.  Also, I blame languages like Java
and C#
 for raising our expectations of how this should be handled.  I don't
think the
 problem can be completely solved for in-memory objects, without
resorting to
 proxies and/or notification lists.

I'd also like to hear if his ideas would require changes to std.loader
(as I'm itching for an excuse to rewrite that
stillborn obscenity).
I think my first reaction to reading that source was: "This compiled?"
(j/k)
 I wouldn't anticipate need to change std.loader drastically.  Outside of
that,
 I'd love to see the thread-local storage bits broken out into another
library or
 as an extension to std.thread. ;)

 One question though: is all the extra ref-counting code needed for linux
 libraries, or does it supply some extra value to both Win32 and Linux
 environments?

I'd also like to hear Walter's opinions on the matter. I think this
issue is of sufficient import to be a 1.0
prerequesite, don't you?
I couldn't agree more. I too, would like to hear what direction things
will
 take with respect to dll's.
 Other than that, what about the exception-boundary issue?
Well, D's going to have an ABI, and since all exceptions are going to
co-exist memorywise (when the GC's
linearised/homogenised), what's the prob?
With respect to Kris' concern about handling exceptions, its really
obnoxious
 how an uncaught exception within a library kills your app.  Aside from
making
 all of my libraries behave like class-factories, I've taken to using
methods
 that do this:

 int someMethod(int foo){ /* impl */ }
..to be called and exported by a dll stub function:
 export(Windows) Exception someMethod(int foo,out _returnval){
   Exception _exception;
   try{ _returnval = someMethod(foo); }
   catch(Exception e){ _exception = e; }
   return(_exception);
 }
You can use a similar stub on the calling side that wraps the function
pointer
 that you grab from the library.

 Meanwhile (on a slightly OT note), I'm still working on some of the more
tricky
 aspects of dll's in D.  In particular, I've tracked one really nasty bug
down to
 (what looks like) the digitalmars-C backend:

 // deceptively simple example.
 import std.c.windows.windows;
 void main(){
   HMODULE mod = LoadLibrary("mydll.dll");
   printf("freeing...");
   FreeLibrary(mod);
   printf("You will never see this print.\n");
 }
(Matthew, Kris, have you had this problem on your Windows machines?
I've done
 this on two separate boxes with the same result.  If you two or anyone
else can
 confirm this, I'll go ahead and post it to the bugs NG)

 Basically, stdout and stdin are "automagically" set to EOF (or some
similar
 state) after the call to FreeLibrary(): nothing goes in and nothing
comes out.
 Everything else runs fine, no exceptions are thrown, and GetLastError()
 faithfully returns 0.

 I've been able to recreate the above in DMC, with a 100% C-built Dll
using the
 same .def file as the mydll sample.  The results are also the same when
calling
 that dll from a host program written in MSVC6, DMD and DMC.  Unless I'm
horribly
 mistaken on how to do compose dll's using Digitalmars' technology, this
is what
 you get the instant you unload any DMC/DMD built dll.

 The problem seems to only manifest when a proper DllMain() method is
exported
 from the library.  If none is provided, or if the given implementation
can be
 optimized away, the error does not ocurr.

 This caused me hours upon hours of anguish trying to figure out why in
my
 DSP/Mango server kept quietly halting on me: it was waiting for console
input to
 terminate, but Mango's Stdin throws on EOF.  :(

 - Pragma
Aug 21 2004
prev sibling next sibling parent reply "Matthew" <admin.hat stlsoft.dot.org> writes:
I've read it once, but want to take some time to think before I respond to some
of the points.

Let me pose my question in a more direct manner:

AFAICS, one of the biggest problems is the ability to be able to use DLLs with
D in *all* of the following guises:

1. D exe, C dll. Communication by plain C-API function calls. All resources
returned whence they came.
2. C exe, D dll. Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). All
resources returned whence they came
3. D exe, D dll, Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). All
resources returned whence they came
4. D exe, D dll, Communication via extern(C) calls and/or interfaces with
well-known vtable layout (e.g. COM). Memory
allocated hither and used safely thither
5. D exe, D dll, Communication via extern(C) calls and/or extern(D) calls
and/or interfaces with well-known vtable
layout (e.g. COM). Memory allocated hither and used safely thither
6. D exe, D dll, Communication via 5. + classes. (Not sure of these details.)

Note, for each of the above, you can permute by replacing exe with D client
code inside a D dll in any of cases 2-6!

Since D has, putatively at least, an ABI, all 6 (or 11) of these should, in
principle be realisable. Further,
commercially speaking, D *must* provide all of these, to not be abandoned by
developers more influenced by deadline and
pragmatism than idealism and performance - in other words, most of them.

To my mind, we have two choices. One option is that the GC and supporting
infrastructure is *always* in some DCore.dll -
i.e. there're no more statically linked programs - in the same vein as .NET.
The other option is that we come up with a
mechanism whereby each link-unit is able to detect whether the process in which
it is loaded already has a GC and, if
so, links to that, otherwise starting its own. The complication to this is that
if the first such link-unit is not the
process' exe, we have the issue whereby the GC might be prematurely unloaded
while other link-units are still depending
on it. This could, hopefully(!), be resolved be having dependent link-units
hold an independent dynamic-load reference
on the GC's owning DLL.

Thoughts?

Walter, I'd be very interested in your thoughts on this, both on my comments on
the need for this commercially, and also
on possible implementation mechanisms.




"pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote in
message
news:cg5184$c7u$1 digitaldaemon.com...
 FYI: this is a long post, please read.  Thank you. :)

 In article <cg41tm$2u6a$1 digitaldaemon.com>, Matthew says...
"antiAlias" <fu bar.com> wrote in message
news:cg408a$2tge$1 digitaldaemon.com...
 I agree that #1 (the shared GC) is a primary issue. On the face of it, what
 Eric describes (below) sounds really attractive.
It sounds promising. I'd like to hear more fine details, though.
I'll work on a more detailed treatment as soon as time permits. I'll have to first go back through my old source/notes and make sure that there's nothing that I've managed to miss. One thing I will say though: No matter how many times I revisit the problem, the businss of explicitly unloading a library at runtime has ugly consequences regardless of how the GC is hooked. Also, I blame languages like Java and C# for raising our expectations of how this should be handled. I don't think the problem can be completely solved for in-memory objects, without resorting to proxies and/or notification lists.
I'd also like to hear if his ideas would require changes to std.loader (as I'm
itching for an excuse to rewrite that
stillborn obscenity).
I think my first reaction to reading that source was: "This compiled?" (j/k) I wouldn't anticipate need to change std.loader drastically. Outside of that, I'd love to see the thread-local storage bits broken out into another library or as an extension to std.thread. ;) One question though: is all the extra ref-counting code needed for linux libraries, or does it supply some extra value to both Win32 and Linux environments?
I'd also like to hear Walter's opinions on the matter. I think this issue is of
sufficient import to be a 1.0
prerequesite, don't you?
I couldn't agree more. I too, would like to hear what direction things will take with respect to dll's.
 Other than that, what about the exception-boundary issue?
Well, D's going to have an ABI, and since all exceptions are going to co-exist memorywise (when the GC's linearised/homogenised), what's the prob?
With respect to Kris' concern about handling exceptions, its really obnoxious how an uncaught exception within a library kills your app. Aside from making all of my libraries behave like class-factories, I've taken to using methods that do this:
 int someMethod(int foo){ /* impl */ }
..to be called and exported by a dll stub function:
 export(Windows) Exception someMethod(int foo,out _returnval){
   Exception _exception;
   try{ _returnval = someMethod(foo); }
   catch(Exception e){ _exception = e; }
   return(_exception);
 }
You can use a similar stub on the calling side that wraps the function pointer that you grab from the library. Meanwhile (on a slightly OT note), I'm still working on some of the more tricky aspects of dll's in D. In particular, I've tracked one really nasty bug down to (what looks like) the digitalmars-C backend:
 // deceptively simple example.
 import std.c.windows.windows;
 void main(){
   HMODULE mod = LoadLibrary("mydll.dll");
   printf("freeing...");
   FreeLibrary(mod);
   printf("You will never see this print.\n");
 }
(Matthew, Kris, have you had this problem on your Windows machines? I've done this on two separate boxes with the same result. If you two or anyone else can confirm this, I'll go ahead and post it to the bugs NG) Basically, stdout and stdin are "automagically" set to EOF (or some similar state) after the call to FreeLibrary(): nothing goes in and nothing comes out. Everything else runs fine, no exceptions are thrown, and GetLastError() faithfully returns 0. I've been able to recreate the above in DMC, with a 100% C-built Dll using the same .def file as the mydll sample. The results are also the same when calling that dll from a host program written in MSVC6, DMD and DMC. Unless I'm horribly mistaken on how to do compose dll's using Digitalmars' technology, this is what you get the instant you unload any DMC/DMD built dll. The problem seems to only manifest when a proper DllMain() method is exported from the library. If none is provided, or if the given implementation can be optimized away, the error does not ocurr. This caused me hours upon hours of anguish trying to figure out why in my DSP/Mango server kept quietly halting on me: it was waiting for console input to terminate, but Mango's Stdin throws on EOF. :( - Pragma
Aug 21 2004
parent pragma <EricAnderton at yahoo dot com> <pragma_member pathlink.com> writes:
In article <cg8kut$2ilc$1 digitaldaemon.com>, Matthew says...
To my mind, we have two choices. One option is that the GC and supporting
infrastructure is *always* in some DCore.dll -
i.e. there're no more statically linked programs - in the same vein as .NET.
The other option is that we come up with a
mechanism whereby each link-unit is able to detect whether the process in which
it is loaded already has a GC and, if
so, links to that, otherwise starting its own. The complication to this is that
if the first such link-unit is not the
process' exe, we have the issue whereby the GC might be prematurely unloaded
while other link-units are still depending
on it. This could, hopefully(!), be resolved be having dependent link-units
hold an independent dynamic-load reference
on the GC's owning DLL.

Thoughts?
I like the idea, but it represents quite a paradigm shift for D. Also, any time you introduce a platform library, you have the messy consequences of library versioning and which library instance (if multiple are present) is used on the search path. - Pragma
Aug 21 2004
prev sibling parent reply "Matthew" <admin.hat stlsoft.dot.org> writes:
"pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote in
message
news:cg5184$c7u$1 digitaldaemon.com...
 FYI: this is a long post, please read.  Thank you. :)

 In article <cg41tm$2u6a$1 digitaldaemon.com>, Matthew says...
"antiAlias" <fu bar.com> wrote in message
news:cg408a$2tge$1 digitaldaemon.com...
 I agree that #1 (the shared GC) is a primary issue. On the face of it, what
 Eric describes (below) sounds really attractive.
It sounds promising. I'd like to hear more fine details, though.
I'll work on a more detailed treatment as soon as time permits. I'll have to first go back through my old source/notes and make sure that there's nothing that I've managed to miss.
Ok. This is an issue that will run and run, I think. At least for a month or two, or until it's sorted, at least.
 One thing I will say though: No matter how many times I revisit the problem,
the
 businss of explicitly unloading a library at runtime has ugly consequences
 regardless of how the GC is hooked.
Can you give some more detailed examples. I'm an example kinda guy. :)
  Also, I blame languages like Java and C#
 for raising our expectations of how this should be handled.  I don't think the
 problem can be completely solved for in-memory objects, without resorting to
 proxies and/or notification lists.

I'd also like to hear if his ideas would require changes to std.loader (as I'm
itching for an excuse to rewrite that
stillborn obscenity).
I think my first reaction to reading that source was: "This compiled?" (j/k)
Can you be specific? I'm troubled by its implementations for certain reasons, but I'd like to hear your unalloyed criticisms.
 I wouldn't anticipate need to change std.loader drastically.  Outside of that,
 I'd love to see the thread-local storage bits broken out into another library
or
 as an extension to std.thread. ;)
Do you think we'll need to provide any additional mechanisms that will need to be standardised via std.loader? For example, GC-using D dlls might be required to export a specific entry point to facilitate GC-hooking, which would be built into std.loader.
 One question though: is all the extra ref-counting code needed for linux
 libraries, or does it supply some extra value to both Win32 and Linux
 environments?
Probably not for Linux, but I'm very cautious/cynical on this issue, as I've previously been bitten on some UNIXen that did not do internal ref-counting on dynamic libs. Hence, I think it's safest to do it ourselves.
I'd also like to hear Walter's opinions on the matter. I think this issue is of
sufficient import to be a 1.0
prerequesite, don't you?
I couldn't agree more. I too, would like to hear what direction things will take with respect to dll's.
I've posted another, more detailed, response on this in this thread. I'd be keen to hear your ideas on that.
 Other than that, what about the exception-boundary issue?
Well, D's going to have an ABI, and since all exceptions are going to co-exist memorywise (when the GC's linearised/homogenised), what's the prob?
With respect to Kris' concern about handling exceptions, its really obnoxious how an uncaught exception within a library kills your app. Aside from making all of my libraries behave like class-factories, I've taken to using methods that do this:
Yes, exceptions also need sorting from a multiple library point of view. As I say in the other post, I'm beginning to think that D link-units need to search each other out at runtime, and coordinate their activities somehow. We've just got to hope that it turns out to be less messy than COM or, heaven forefend, .NET!
 int someMethod(int foo){ /* impl */ }
..to be called and exported by a dll stub function:
 export(Windows) Exception someMethod(int foo,out _returnval){
   Exception _exception;
   try{ _returnval = someMethod(foo); }
   catch(Exception e){ _exception = e; }
   return(_exception);
 }
You can use a similar stub on the calling side that wraps the function pointer that you grab from the library. Meanwhile (on a slightly OT note), I'm still working on some of the more tricky aspects of dll's in D. In particular, I've tracked one really nasty bug down to (what looks like) the digitalmars-C backend:
 // deceptively simple example.
 import std.c.windows.windows;
 void main(){
   HMODULE mod = LoadLibrary("mydll.dll");
   printf("freeing...");
   FreeLibrary(mod);
   printf("You will never see this print.\n");
 }
(Matthew, Kris, have you had this problem on your Windows machines? I've done this on two separate boxes with the same result. If you two or anyone else can confirm this, I'll go ahead and post it to the bugs NG)
I confess I've done ~0 dynamic libs with D. :-)
 Basically, stdout and stdin are "automagically" set to EOF (or some similar
 state) after the call to FreeLibrary(): nothing goes in and nothing comes out.
 Everything else runs fine, no exceptions are thrown, and GetLastError()
 faithfully returns 0.

 I've been able to recreate the above in DMC, with a 100% C-built Dll using the
 same .def file as the mydll sample.  The results are also the same when calling
 that dll from a host program written in MSVC6, DMD and DMC.  Unless I'm
horribly
 mistaken on how to do compose dll's using Digitalmars' technology, this is what
 you get the instant you unload any DMC/DMD built dll.

 The problem seems to only manifest when a proper DllMain() method is exported
 from the library.  If none is provided, or if the given implementation can be
 optimized away, the error does not ocurr.

 This caused me hours upon hours of anguish trying to figure out why in my
 DSP/Mango server kept quietly halting on me: it was waiting for console input
to
 terminate, but Mango's Stdin throws on EOF.  :(

 - Pragma
Aug 21 2004
parent pragma <EricAnderton at yahoo dot com> <pragma_member pathlink.com> writes:
In article <cg8png$2ltl$1 digitaldaemon.com>, Matthew says...
"pragma" <EricAnderton at yahoo dot compragma_member pathlink.com> wrote in 
 One thing I will say though: No matter how many times I revisit the problem,
the
 businss of explicitly unloading a library at runtime has ugly consequences
 regardless of how the GC is hooked.
Can you give some more detailed examples. I'm an example kinda guy. :)
I'll take an oversimplified example from my D-Servlet Pages project. void foo(Request req,Response res){ // ServletLibrary proxies all the exports from the dll // and exposes some extra housekeeping functions ServletLibrary library = getServletLibrary("mylib.dll"); // library is queried for a servlet. The servlet is created inside the dll DSPServlet servlet = library.getServlet(); // Do some work (generate HTML, and so forth) servlet.service(req,res); // This frees the library. It is now no longer in memory library.unload(); // "servlet" is now invalid (see below) } No matter which side has the responsibility for performing GC operations and memory allocations, the V-table for any object always lives where it was created. This application in particular rebuilds dlls on demand, so references to servlets can be invalidated at a drop of a hat, across multiple threads.
 I think my first reaction to reading that source was: "This compiled?" (j/k)
Can you be specific?
Honestly, it comes down to a matter of coding style: I'm just not used to reading your code. :) You say poh-tay-toh I say po-tot-oh... But I understand why its organized the way it is, and I feel its a very solid lib. The only thing I'd have done differently would be to roll HXModule into a non-auto class that handles all the refcounting, while wrapping the linux functions with Win32-like functions (or the other way around), so there's less code in there.
I'm troubled by its implementations for certain reasons, but I'd like to hear
your unalloyed criticisms.

 I wouldn't anticipate need to change std.loader drastically.  Outside of that,
 I'd love to see the thread-local storage bits broken out into another library
or
 as an extension to std.thread. ;)
Do you think we'll need to provide any additional mechanisms that will need to be standardised via std.loader? For example, GC-using D dlls might be required to export a specific entry point to facilitate GC-hooking, which would be built into std.loader.
If we're going to go with hooking rather than a GCCore.dll-type solution (from your other post, I like that idea), then yea, that would be best served internally by loader. A non-auto class (DllModule maybe?) would be a nice touch. Also an 'event' (I guess a delegate[] in D is close enough) that is called when a dll is finally unloaded (refcount goes to zero), would be a *very* nice addition.
Yes, exceptions also need sorting from a multiple library point of view. As I
say in the other post, I'm beginning to
think that D link-units need to search each other out at runtime, and
coordinate their activities somehow. We've just
got to hope that it turns out to be less messy than COM or, heaven forefend,
.NET!
I confess I've done ~0 dynamic libs with D. :-)
Hehe.. we'll fix that. ;) Walter has made it easy as sin to create .dll's in D. What's missing is a D-standard stub that is /implicitly/ added to a library along with classinfo, exception piping, GC hooking, etc etc... one becomes painfully aware of all this only *after* you start working with dll's heavily. Its even worse coming from using Java's classloader or .NET assemblies; D has a very long way to go in this department. - Pragma
Aug 21 2004