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: s...@invisibleduck.org ReportedBy: schvei...@yahoo.com --- Comment #0 from Steven Schveighoffer <schvei...@yahoo.com> 2009-12-21 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: -------