digitalmars.D.bugs - [Issue 3637] New: Array append patch to prevent stomping and to enhance thread-local append performance
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http://d.puremagic.com/issues/show_bug.cgi?id=3637
Summary: Array append patch to prevent stomping and to enhance
thread-local append performance
Product: D
Version: future
Platform: x86
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: druntime
AssignedTo: sean invisibleduck.org
ReportedBy: schveiguy yahoo.com
12:10:42 PST ---
Created an attachment (id=528)
Patch to prevent array stomping and increase append performance
The attached patch fixes 2 problems:
1. Array stomping. A slice of an array can stomp on another array if the slice
starts at the beginning of the other array. This patch prevents such problems
by storing the "allocated length" or the length of valid data at the end of the
array.
2. Array append previously required acquiring the GC lock, even when the array
can be extended in-place. The patch makes use of an 8-element MRU (most
recently used) cache in thread-local storage that allows the runtime to avoid
taking the global lock to look up an array's allocated length. This allows one
to append to up to 8 arrays per thread without taking the global lock unless an
actual re-allocation is required. Shared array appending still requires a
global lock for appending, and does not have a cache associated with it.
However, shared appending is still safe as far as stomping goes.
Note that with this patch, the following trick *no longer works*:
int[] bigarray = new int[10000];
bigarray.length = 0;
foreach(i; 0..10000)
bigarray ~= i;
Because truncating the array this way can cause stomping, the first append will
reallocate bigarray and you will lose the benefit of preallocating the original
array.
A (yet unwritten) library function is required to preallocate an array.
To apply the patch, download the 2.037 distribution (this code was only tested
against the distribution), and apply the patch from the src/druntime directory:
cd dmd2/src/druntime
patch -p0 < append.patch
then build and re-install druntime and phobos libraries.
The patch was tested on Linux dmd version 2.037. An earlier version of the
patch which was mostly the same was tested on Windows dmd 2.036 and Mac OSX
10.6 dmd 2.037. The difference between the earlier and this version of the
patch is the handling of appending dchar to char[] and wchar[].
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Dec 21 2009
d-bugmail puremagic.com
http://d.puremagic.com/issues/show_bug.cgi?id=3637
Leandro Lucarella <llucax gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
mime type| |
patch| |
PST ---
(From update of attachment 528)
Fix the MIME type and mark the attachment as a patch.
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Dec 22 2009
http://d.puremagic.com/issues/show_bug.cgi?id=3637
Leandro Lucarella <llucax gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |llucax gmail.com
PST ---
It is really necessary change the GC API to fix this? I think it's a really bad
idea to modify the GC API (add a function) just because dynamic arrays have
problems (I don't want to start over the discussion about dynamic arrays being
broken :).
If you absolutely need this new function: BlkInfo gc_malloc_bi(size_t sz, uint
ba = 0); then maybe it's better to change the existing regular gc_malloc() to:
void* gc_malloc(size_t sz, uint ba = 0, BlkInfo bi = null);
The advantage is that it's API-backward compatible and doesn't introduce a new
function to the GC API and the downside is it's not binary-backward compatible,
but I don't think people care much about this in D.
The inability to pre-allocate can be a little bad too, but it was awkward
anyway, so providing a better way to do so can be a good thing after all.
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Dec 22 2009
http://d.puremagic.com/issues/show_bug.cgi?id=3637 20:19:09 PST --- It's not *necessary* to change the API to fix this, but it is hugely advantageous. If you want to know the block size of the chunk you just allocated, the current API requires *another* lock of the GC, and a search through the pools. All the info is there in malloc, it's just not returned. BTW, just an additional size parameter would suffice (this is how gcx handles the allocation). Having it return a BlkInfo struct is convenient because that is the data type I'm working with when setting allocated length. And introducing a new function is just as backwards compatible as adding a new optional parameter to a current function. Preallocation needs to be a runtime function that is yet to be written which allocates a large block but sets the "allocated" size to 0. It can also avoid pre-initializing the block if the block has no pointers (something that the old trick didn't do). -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 22 2009
http://d.puremagic.com/issues/show_bug.cgi?id=3637 PST ---It's not *necessary* to change the API to fix this, but it is hugely advantageous. If you want to know the block size of the chunk you just allocated, the current API requires *another* lock of the GC, and a search through the pools. All the info is there in malloc, it's just not returned. BTW, just an additional size parameter would suffice (this is how gcx handles the allocation). Having it return a BlkInfo struct is convenient because that is the data type I'm working with when setting allocated length.Yes, that seems reasonable since BlkInfo is already part of the API.And introducing a new function is just as backwards compatible as adding a new optional parameter to a current function.I know that, but it adds complexity to the API, and seems a little weird since gc_malloc() and gc_malloc_bi() are basically the same. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 23 2009
http://d.puremagic.com/issues/show_bug.cgi?id=3637
Steven Schveighoffer <schveiguy yahoo.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
obsolete| |
06:28:15 PST ---
Created an attachment (id=569)
Patch to druntime revision 245 to implement array appending
generated with svn diff.
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Feb 18 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3637 06:29:32 PST --- Note that shared data isn't properly synchronized when being copied, but this also happens in all the other array functions (not just appending). I will file a separate bug on this. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 18 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3637
Steven Schveighoffer <schveiguy yahoo.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
obsolete| |
06:34:43 PST ---
Created an attachment (id=570)
Patch to druntime revision 245 to implement array appending
The only addition to this patch is I added comments identifying where the
compiler fails to deliver the proper typeinfo for shared appending.
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Feb 18 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3637
Steven Schveighoffer <schveiguy yahoo.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
AssignedTo|sean invisibleduck.org |schveiguy yahoo.com
08:37:48 PST ---
changeset 252
http://www.dsource.org/projects/druntime/changeset/252
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Feb 22 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3637
Walter Bright <bugzilla digitalmars.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
CC| |bugzilla digitalmars.com
Resolution| |FIXED
22:26:33 PST ---
Fixed dmd 2.041
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Mar 08 2010