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digitalmars.D.learn - Calling C functions

reply CrypticMetaphor <CrypticMetaphor88 gmail.com> writes:
I found this page that describes how to call c functions from D.

I found this page that describes how:
http://arsdnet.net/dtips/#cfunc

on that page he uses gcc, and I use dmc, but I get different results. 
This is what I did

// cfile.c file
extern int globalFromD;

void functionFromC(int a) {
    globalFromD = a;
}
// end cfile.c

// dfile.d
extern(C) { // this is needed to make it available from C
         int globalFromD;
}
extern(C) { // also needed when listing the prototypes for your C functions
         void functionFromC(int);
}

import std.stdio; // for writefln

int main() {
         globalFromD = 100;
         writefln("%d", globalFromD);

         functionFromC(500);
         writefln("%d", globalFromD);

         return 0;
}
// end dfile.d

I compile with:
dmc -c cfile.c
And I get  an cfile.obj, which is the object code (.o in gcc).
Then I compile the D code
dmd dfile.d cfile.obj
and I get no errors, so I run it, the result:
// start result
C:\DCode\libtest>dfile.exe
100
100

C:\DCode\libtest>
// end result

Why is it still 100? It should be 500. I don't think functionFromC( int 
) is being called, and I can't really find any other sources that 
clearly explain how to do this simple stuff, so can anyone explain how 
to fix it?
Dec 09 2010
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 09 Dec 2010 09:37:03 -0500, CrypticMetaphor  
<CrypticMetaphor88 gmail.com> wrote:


 I found this page that describes how to call c functions from D.

 I found this page that describes how:
 http://arsdnet.net/dtips/#cfunc

 on that page he uses gcc, and I use dmc, but I get different results.  
 This is what I did

 // cfile.c file
 extern int globalFromD;

 void functionFromC(int a) {
     globalFromD = a;
 }
 // end cfile.c

 // dfile.d
 extern(C) { // this is needed to make it available from C
          int globalFromD;
 }
 extern(C) { // also needed when listing the prototypes for your C  
 functions
          void functionFromC(int);
 }

 import std.stdio; // for writefln

 int main() {
          globalFromD = 100;
          writefln("%d", globalFromD);

          functionFromC(500);
          writefln("%d", globalFromD);

          return 0;
 }
 // end dfile.d

 I compile with:
 dmc -c cfile.c
 And I get  an cfile.obj, which is the object code (.o in gcc).
 Then I compile the D code
 dmd dfile.d cfile.obj
 and I get no errors, so I run it, the result:
 // start result
 C:\DCode\libtest>dfile.exe
 100
 100

 C:\DCode\libtest>
 // end result

 Why is it still 100? It should be 500. I don't think functionFromC( int  
 ) is being called, and I can't really find any other sources that  
 clearly explain how to do this simple stuff, so can anyone explain how  
 to fix it?


I'm guessing that this is a later D2 compiler?  If so, then the default  
storage for globals is in Thread Local Storage (local to each thread).   
This could explain why it doesn't work, because globalFromD is in TLS in  
D-land, but in the normal global space in C-land.  But there is no  
declaration of the global-space version then, so I'm surprised it would  
compile then.

I'm really curious why this doesn't work but does compile.

What version of D compiler are you using?

When using dmd 2.050 on linux I get this error when compiling:

steves steve-laptop:~/testd$ gcc -c testc.c
steves steve-laptop:~/testd$ ~/dmd-2.050/linux/bin/dmd testcallc.d testc.o
/usr/bin/ld: globalFromD: TLS definition in testcallc.o section .tbss  
mismatches non-TLS reference in testc.o
testc.o: could not read symbols: Bad value
collect2: ld returned 1 exit status
--- errorlevel 1

Maybe it's a bug in Windows dmd?

-Steve
Dec 09 2010
parent reply CrypticMetaphor <CrypticMetaphor88 gmail.com> writes:
On 12/9/2010 3:57 PM, Steven Schveighoffer wrote:

 On Thu, 09 Dec 2010 09:37:03 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:


 I found this page that describes how to call c functions from D.

 I found this page that describes how:
 http://arsdnet.net/dtips/#cfunc

 on that page he uses gcc, and I use dmc, but I get different results.
 This is what I did

 // cfile.c file
 extern int globalFromD;

 void functionFromC(int a) {
 globalFromD = a;
 }
 // end cfile.c

 // dfile.d
 extern(C) { // this is needed to make it available from C
 int globalFromD;
 }
 extern(C) { // also needed when listing the prototypes for your C
 functions
 void functionFromC(int);
 }

 import std.stdio; // for writefln

 int main() {
 globalFromD = 100;
 writefln("%d", globalFromD);

 functionFromC(500);
 writefln("%d", globalFromD);

 return 0;
 }
 // end dfile.d

 I compile with:
 dmc -c cfile.c
 And I get an cfile.obj, which is the object code (.o in gcc).
 Then I compile the D code
 dmd dfile.d cfile.obj
 and I get no errors, so I run it, the result:
 // start result
 C:\DCode\libtest>dfile.exe
 100
 100

 C:\DCode\libtest>
 // end result

 Why is it still 100? It should be 500. I don't think functionFromC(
 int ) is being called, and I can't really find any other sources that
 clearly explain how to do this simple stuff, so can anyone explain how
 to fix it?


 I'm guessing that this is a later D2 compiler? If so, then the default
 storage for globals is in Thread Local Storage (local to each thread).
 This could explain why it doesn't work, because globalFromD is in TLS in
 D-land, but in the normal global space in C-land. But there is no
 declaration of the global-space version then, so I'm surprised it would
 compile then.

 I'm really curious why this doesn't work but does compile.

 What version of D compiler are you using?

 When using dmd 2.050 on linux I get this error when compiling:

 steves steve-laptop:~/testd$ gcc -c testc.c
 steves steve-laptop:~/testd$ ~/dmd-2.050/linux/bin/dmd testcallc.d testc.o
 /usr/bin/ld: globalFromD: TLS definition in testcallc.o section .tbss
 mismatches non-TLS reference in testc.o
 testc.o: could not read symbols: Bad value
 collect2: ld returned 1 exit status
 --- errorlevel 1

 Maybe it's a bug in Windows dmd?

 -Steve


Yeah I am using D2

dmc version: 8.42n
dmd version: 2.050

Windows XP. But yeah, it compiles

here is a screenshot:
http://img813.imageshack.us/img813/8230/testu.gif

So I gotta read more about threads eh? But that's all the way at the end 
of the book :-(

But anyway, it should not compile right?

Should I submit a bug report or something?
And how I supposed to call the c function?
Dec 09 2010
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 09 Dec 2010 10:15:59 -0500, CrypticMetaphor  
<CrypticMetaphor88 gmail.com> wrote:


 On 12/9/2010 3:57 PM, Steven Schveighoffer wrote:

 On Thu, 09 Dec 2010 09:37:03 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:


 I found this page that describes how to call c functions from D.

 I found this page that describes how:
 http://arsdnet.net/dtips/#cfunc

 on that page he uses gcc, and I use dmc, but I get different results.
 This is what I did

 // cfile.c file
 extern int globalFromD;

 void functionFromC(int a) {
 globalFromD = a;
 }
 // end cfile.c

 // dfile.d
 extern(C) { // this is needed to make it available from C
 int globalFromD;
 }
 extern(C) { // also needed when listing the prototypes for your C
 functions
 void functionFromC(int);
 }

 import std.stdio; // for writefln

 int main() {
 globalFromD = 100;
 writefln("%d", globalFromD);

 functionFromC(500);
 writefln("%d", globalFromD);

 return 0;
 }
 // end dfile.d

 I compile with:
 dmc -c cfile.c
 And I get an cfile.obj, which is the object code (.o in gcc).
 Then I compile the D code
 dmd dfile.d cfile.obj
 and I get no errors, so I run it, the result:
 // start result
 C:\DCode\libtest>dfile.exe
 100
 100

 C:\DCode\libtest>
 // end result

 Why is it still 100? It should be 500. I don't think functionFromC(
 int ) is being called, and I can't really find any other sources that
 clearly explain how to do this simple stuff, so can anyone explain how
 to fix it?


 I'm guessing that this is a later D2 compiler? If so, then the default
 storage for globals is in Thread Local Storage (local to each thread).
 This could explain why it doesn't work, because globalFromD is in TLS in
 D-land, but in the normal global space in C-land. But there is no
 declaration of the global-space version then, so I'm surprised it would
 compile then.

 I'm really curious why this doesn't work but does compile.

 What version of D compiler are you using?

 When using dmd 2.050 on linux I get this error when compiling:

 steves steve-laptop:~/testd$ gcc -c testc.c
 steves steve-laptop:~/testd$ ~/dmd-2.050/linux/bin/dmd testcallc.d  
 testc.o
 /usr/bin/ld: globalFromD: TLS definition in testcallc.o section .tbss
 mismatches non-TLS reference in testc.o
 testc.o: could not read symbols: Bad value
 collect2: ld returned 1 exit status
 --- errorlevel 1

 Maybe it's a bug in Windows dmd?

 -Steve


 Yeah I am using D2

 dmc version: 8.42n
 dmd version: 2.050

 Windows XP. But yeah, it compiles

 here is a screenshot:
 http://img813.imageshack.us/img813/8230/testu.gif

 So I gotta read more about threads eh? But that's all the way at the end  
 of the book :-(


No, not really.  TLS is related to threads, but you don't really have to  
understand how threads work to understand where things are stored.

I don't know where it is in the book, but try looking for Thread Local  
Storage in the index?


 But anyway, it should not compile right?

 Should I submit a bug report or something?


Yes please, and be sure to specify that it correctly does not compile on  
linux. http://d.puremagic.com/issues/enter_bug.cgi


 And how I supposed to call the c function?


Mark the extern(C) integer as __gshared in D.  That will put it in the  
global namespace instead of TLS.

e.g.:

extern(C) { // this is needed to make it available from C
   __gshared int globalFromD;
}

-Steve
Dec 09 2010
next sibling parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
I know I prefer using shared() when interfacing with C.

I've tried using __gshared once when interfacing with C code. But I
had crashes all the time, using shared instead made my app stable
again. It might be related to the way the C code worked, since
multiple threads were involved. Anyway.. that's my experience with
gshared..

On 12/9/10, Steven Schveighoffer <schveiguy yahoo.com> wrote:

 On Thu, 09 Dec 2010 10:15:59 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:


 On 12/9/2010 3:57 PM, Steven Schveighoffer wrote:

 On Thu, 09 Dec 2010 09:37:03 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:


 I found this page that describes how to call c functions from D.

 I found this page that describes how:
 http://arsdnet.net/dtips/#cfunc

 on that page he uses gcc, and I use dmc, but I get different results.
 This is what I did

 // cfile.c file
 extern int globalFromD;

 void functionFromC(int a) {
 globalFromD = a;
 }
 // end cfile.c

 // dfile.d
 extern(C) { // this is needed to make it available from C
 int globalFromD;
 }
 extern(C) { // also needed when listing the prototypes for your C
 functions
 void functionFromC(int);
 }

 import std.stdio; // for writefln

 int main() {
 globalFromD = 100;
 writefln("%d", globalFromD);

 functionFromC(500);
 writefln("%d", globalFromD);

 return 0;
 }
 // end dfile.d

 I compile with:
 dmc -c cfile.c
 And I get an cfile.obj, which is the object code (.o in gcc).
 Then I compile the D code
 dmd dfile.d cfile.obj
 and I get no errors, so I run it, the result:
 // start result
 C:\DCode\libtest>dfile.exe
 100
 100

 C:\DCode\libtest>
 // end result

 Why is it still 100? It should be 500. I don't think functionFromC(
 int ) is being called, and I can't really find any other sources that
 clearly explain how to do this simple stuff, so can anyone explain how
 to fix it?


 I'm guessing that this is a later D2 compiler? If so, then the default
 storage for globals is in Thread Local Storage (local to each thread).
 This could explain why it doesn't work, because globalFromD is in TLS in
 D-land, but in the normal global space in C-land. But there is no
 declaration of the global-space version then, so I'm surprised it would
 compile then.

 I'm really curious why this doesn't work but does compile.

 What version of D compiler are you using?

 When using dmd 2.050 on linux I get this error when compiling:

 steves steve-laptop:~/testd$ gcc -c testc.c
 steves steve-laptop:~/testd$ ~/dmd-2.050/linux/bin/dmd testcallc.d
 testc.o
 /usr/bin/ld: globalFromD: TLS definition in testcallc.o section .tbss
 mismatches non-TLS reference in testc.o
 testc.o: could not read symbols: Bad value
 collect2: ld returned 1 exit status
 --- errorlevel 1

 Maybe it's a bug in Windows dmd?

 -Steve


 Yeah I am using D2

 dmc version: 8.42n
 dmd version: 2.050

 Windows XP. But yeah, it compiles

 here is a screenshot:
 http://img813.imageshack.us/img813/8230/testu.gif

 So I gotta read more about threads eh? But that's all the way at the end
 of the book :-(


 No, not really.  TLS is related to threads, but you don't really have to
 understand how threads work to understand where things are stored.

 I don't know where it is in the book, but try looking for Thread Local
 Storage in the index?


 But anyway, it should not compile right?

 Should I submit a bug report or something?


 Yes please, and be sure to specify that it correctly does not compile on
 linux. http://d.puremagic.com/issues/enter_bug.cgi


 And how I supposed to call the c function?


 Mark the extern(C) integer as __gshared in D.  That will put it in the
 global namespace instead of TLS.

 e.g.:

 extern(C) { // this is needed to make it available from C
    __gshared int globalFromD;
 }

 -Steve
Dec 09 2010
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 09 Dec 2010 11:38:00 -0500, Andrej Mitrovic  
<andrej.mitrovich gmail.com> wrote:


 I know I prefer using shared() when interfacing with C.

 I've tried using __gshared once when interfacing with C code. But I
 had crashes all the time, using shared instead made my app stable
 again. It might be related to the way the C code worked, since
 multiple threads were involved. Anyway.. that's my experience with
 gshared..


__gshared is the equivalent of what normal globals used to be (in D1 and  
earlier versions of D2).  It's the same as a global variable in C.

shared is exactly the same as __gshared except the compiler inserts memory  
barriers around reads/writes (the C compiler does not), and shared is a  
type modifier, so it's available in the TypeInfo of the variable.  Some  
parts of the runtime use that to determine certain behaviors, and I am  
aware of one problem with __gshared that needs to be documented -- array  
appending.

__gshared is unprotected sharing, and the type system is not aware that it  
is shared.  Can you remember what specifically you were doing with the  
variable?

BTW, __gshared should have no problems in a single-threadded app.

-Steve


 On 12/9/10, Steven Schveighoffer <schveiguy yahoo.com> wrote:

 On Thu, 09 Dec 2010 10:15:59 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:

 And how I supposed to call the c function?


 Mark the extern(C) integer as __gshared in D.  That will put it in the
 global namespace instead of TLS.

 e.g.:

 extern(C) { // this is needed to make it available from C
    __gshared int globalFromD;
 }
Dec 09 2010
parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 12/9/10, Steven Schveighoffer <schveiguy yahoo.com> wrote:

 __gshared is unprotected sharing, and the type system is not aware that it
 is shared.  Can you remember what specifically you were doing with the
 variable?


My dev PC is in repairs right now so I don't have the code atm. It's a
project that works with audio devices and does some basic processing
on audio data.

But from what I can recall I would pass my D callback function to C,
which would call the callback with an interrupt or very-high level
priority thread (it depends on the device driver implementation) at
many intervals per second. The D callback would do some processing,
update one structure variable (e.g. struct "status"), and return.
Inside main() I had an infinite loop which would wait for the device
driver to stop calling the callback. One way of knowing if the device
driver stopped is to check a flag inside the struct, e.g. a boolean
status.done.

The problem I was having at first was that the status struct inside
the callback was a new TLS variable, and the one main() was seeing was
a distinct variable. So main() would never see the updated struct.
I've tried marking the struct with __gshared, but this would
immediately crash my application. Using shared() instead fixed this
problem. This was using DMD 2.048 and I haven't tried newer versions
yet.

Of course, there are much better ways of notifying when the device
driver is done instead of polling the status.done flag all the time.
For example, with PortAudio (an audio library) I can use message
passing to notify my foreground thread that the background (working)
thread is done, or that the device driver has suddenly stopped
working. I could do the same with my first project, but PortAudio is a
mature and stable library so I've decided not to deal with device
drivers directly in my D code (otherwise I would have to write code
for all the audio device driver standards -- ASIO, WDM, CoreAudio, etc
etc..).
Dec 09 2010
parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 09 Dec 2010 12:24:05 -0500, Andrej Mitrovic  
<andrej.mitrovich gmail.com> wrote:


 On 12/9/10, Steven Schveighoffer <schveiguy yahoo.com> wrote:

 __gshared is unprotected sharing, and the type system is not aware that  
 it
 is shared.  Can you remember what specifically you were doing with the
 variable?


 My dev PC is in repairs right now so I don't have the code atm. It's a
 project that works with audio devices and does some basic processing
 on audio data.

 But from what I can recall I would pass my D callback function to C,
 which would call the callback with an interrupt or very-high level
 priority thread (it depends on the device driver implementation) at
 many intervals per second. The D callback would do some processing,
 update one structure variable (e.g. struct "status"), and return.
 Inside main() I had an infinite loop which would wait for the device
 driver to stop calling the callback. One way of knowing if the device
 driver stopped is to check a flag inside the struct, e.g. a boolean
 status.done.


Multi-threadded code must do it's own handling of shared reads/writes to  
__gshared data, such as protecting it with a mutex.  Even with shared, it  
does not guarantee multiple operations are atomic (for example reading two  
members of a shared struct).

-Steve
Dec 09 2010
prev sibling next sibling parent reply CrypticMetaphor <CrypticMetaphor88 gmail.com> writes:
On 12/9/2010 5:28 PM, Steven Schveighoffer wrote:

 On Thu, 09 Dec 2010 10:15:59 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:


 On 12/9/2010 3:57 PM, Steven Schveighoffer wrote:

 On Thu, 09 Dec 2010 09:37:03 -0500, CrypticMetaphor
 <CrypticMetaphor88 gmail.com> wrote:


 I found this page that describes how to call c functions from D.

 I found this page that describes how:
 http://arsdnet.net/dtips/#cfunc

 on that page he uses gcc, and I use dmc, but I get different results.
 This is what I did

 // cfile.c file
 extern int globalFromD;

 void functionFromC(int a) {
 globalFromD = a;
 }
 // end cfile.c

 // dfile.d
 extern(C) { // this is needed to make it available from C
 int globalFromD;
 }
 extern(C) { // also needed when listing the prototypes for your C
 functions
 void functionFromC(int);
 }

 import std.stdio; // for writefln

 int main() {
 globalFromD = 100;
 writefln("%d", globalFromD);

 functionFromC(500);
 writefln("%d", globalFromD);

 return 0;
 }
 // end dfile.d

 I compile with:
 dmc -c cfile.c
 And I get an cfile.obj, which is the object code (.o in gcc).
 Then I compile the D code
 dmd dfile.d cfile.obj
 and I get no errors, so I run it, the result:
 // start result
 C:\DCode\libtest>dfile.exe
 100
 100

 C:\DCode\libtest>
 // end result

 Why is it still 100? It should be 500. I don't think functionFromC(
 int ) is being called, and I can't really find any other sources that
 clearly explain how to do this simple stuff, so can anyone explain how
 to fix it?


 I'm guessing that this is a later D2 compiler? If so, then the default
 storage for globals is in Thread Local Storage (local to each thread).
 This could explain why it doesn't work, because globalFromD is in TLS in
 D-land, but in the normal global space in C-land. But there is no
 declaration of the global-space version then, so I'm surprised it would
 compile then.

 I'm really curious why this doesn't work but does compile.

 What version of D compiler are you using?

 When using dmd 2.050 on linux I get this error when compiling:

 steves steve-laptop:~/testd$ gcc -c testc.c
 steves steve-laptop:~/testd$ ~/dmd-2.050/linux/bin/dmd testcallc.d
 testc.o
 /usr/bin/ld: globalFromD: TLS definition in testcallc.o section .tbss
 mismatches non-TLS reference in testc.o
 testc.o: could not read symbols: Bad value
 collect2: ld returned 1 exit status
 --- errorlevel 1

 Maybe it's a bug in Windows dmd?

 -Steve


 Yeah I am using D2

 dmc version: 8.42n
 dmd version: 2.050

 Windows XP. But yeah, it compiles

 here is a screenshot:
 http://img813.imageshack.us/img813/8230/testu.gif

 So I gotta read more about threads eh? But that's all the way at the
 end of the book :-(


 No, not really. TLS is related to threads, but you don't really have to
 understand how threads work to understand where things are stored.

 I don't know where it is in the book, but try looking for Thread Local
 Storage in the index?


 But anyway, it should not compile right?

 Should I submit a bug report or something?


 Yes please, and be sure to specify that it correctly does not compile on
 linux. http://d.puremagic.com/issues/enter_bug.cgi


 And how I supposed to call the c function?


 Mark the extern(C) integer as __gshared in D. That will put it in the
 global namespace instead of TLS.

 e.g.:

 extern(C) { // this is needed to make it available from C
 __gshared int globalFromD;
 }

 -Steve


Alright then!

I submitted a my first bug report and added __gshared in front of 
globalFromD and the output was:

100
500

So it worked. thanks!
Dec 09 2010
parent reply Jesse Phillips <jessekphillips+D gmail.com> writes:
CrypticMetaphor Wrote:


 On 12/9/2010 5:28 PM, Steven Schveighoffer wrote:


 Yes please, and be sure to specify that it correctly does not compile on
 linux. http://d.puremagic.com/issues/enter_bug.cgi



 -Steve


 
 Alright then!
 
 I submitted a my first bug report and added __gshared in front of 
 globalFromD and the output was:
 
 100
 500
 
 So it worked. thanks!


It is a linker bug, so Oplink is at fault. What is the bug number you submitted?
Dec 09 2010
parent CrypticMetaphor <CrypticMetaphor88 gmail.com> writes:
On 12/9/2010 10:04 PM, Jesse Phillips wrote:

 CrypticMetaphor Wrote:
 It is a linker bug, so Oplink is at fault. What is the bug number you
submitted?


bug number: 5337

http://d.puremagic.com/issues/show_bug.cgi?id=5337
Dec 09 2010
prev sibling parent Adam Ruppe <destructionator gmail.com> writes:
I almost forgot I wrote that dtips page! Thanks for bringing it up.

I just updated it to include a brief note on __gshared. The rest of it should
still work, though. Calling C functions is pretty easy.
Dec 09 2010