1 Notes about the Chrome memory allocator. 2 3 Background 4 ---------- 5 We use this library as a generic way to fork into any of several allocators. 6 Currently we can, at runtime, switch between: 7 the default windows allocator 8 the windows low-fragmentation-heap 9 tcmalloc 10 11 The mechanism for hooking LIBCMT in windows is rather tricky. The core 12 problem is that by default, the windows library does not declare malloc and 13 free as weak symbols. Because of this, they cannot be overriden. To work 14 around this, we start with the LIBCMT.LIB, and manually remove all allocator 15 related functions from it using the visual studio library tool. Once removed, 16 we can now link against the library and provide custom versions of the 17 allocator related functionality. 18 19 20 Source code 21 ----------- 22 This directory contains just the allocator (i.e. shim) layer that switches 23 between the different underlying memory allocation implementations. 24 25 The tcmalloc library originates outside of Chromium and exists in 26 ../../third_party/tcmalloc (currently, the actual location is defined in the 27 allocator.gyp file). The third party sources use a vendor-branch SCM pattern to 28 track Chromium-specific changes independently from upstream changes. 29 30 The general intent is to push local changes upstream so that over 31 time we no longer need any forked files. 32 33 34 Adding a new allocator 35 ---------------------- 36 Adding a new allocator requires definition of the following five functions: 37 38 extern "C" { 39 bool init(); 40 void* malloc(size_t s); 41 void* realloc(void* p, size_t s); 42 void free(void* s); 43 size_t msize(void* p); 44 } 45 46 All other allocation related functions (new/delete/calloc/etc) have been 47 implemented generically to work across all allocators. 48 49 50 Usage 51 ----- 52 You can use the different allocators by setting the environment variable 53 CHROME_ALLOCATOR to: 54 "tcmalloc" - TC Malloc (default) 55 "winheap" - Windows default heap 56 "winlfh" - Windows Low-Fragmentation heap 57
