digitalmars.D.bugs - [Issue 3637] New: Array append patch to prevent stomping and to enhance thread-local append performance
- d-bugmail puremagic.com (50/50) Dec 21 2009 http://d.puremagic.com/issues/show_bug.cgi?id=3637
- d-bugmail puremagic.com (14/14) Dec 22 2009 http://d.puremagic.com/issues/show_bug.cgi?id=3637
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- d-bugmail puremagic.com (12/12) Feb 22 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3637
- d-bugmail puremagic.com (12/12) Mar 08 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3637
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[]. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 21 2009
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. -- 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 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. -- 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 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. -- 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 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. -- 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 ---------------------------------------------------------------------------- Status|NEW |ASSIGNED AssignedTo|sean invisibleduck.org |schveiguy yahoo.com 08:37:48 PST --- changeset 252 http://www.dsource.org/projects/druntime/changeset/252 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 08 2010