base/threading/thread_local_storage_win.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/threading/thread_local_storage.h"
   6
   7 #include <windows.h>
   8
   9 #include "base/logging.h"
  10
  11 namespace base {
  12
  13 namespace internal {
  14
  15 bool PlatformThreadLocalStorage::AllocTLS(TLSKey* key) {
  16   TLSKey value = TlsAlloc();
  17   if (value != TLS_OUT_OF_INDEXES) {
  18     *key = value;
  19     return true;
  20   }
  21   return false;
  22 }
  23
  24 void PlatformThreadLocalStorage::FreeTLS(TLSKey key) {
  25   BOOL ret = TlsFree(key);
  26   DCHECK(ret);
  27 }
  28
  29 void* PlatformThreadLocalStorage::GetTLSValue(TLSKey key) {
  30   return TlsGetValue(key);
  31 }
  32
  33 void PlatformThreadLocalStorage::SetTLSValue(TLSKey key, void* value) {
  34   BOOL ret = TlsSetValue(key, value);
  35   DCHECK(ret);
  36 }
  37
  38 }  // namespace internal
  39
  40 }  // namespace base
  41
  42 // Thread Termination Callbacks.
  43 // Windows doesn't support a per-thread destructor with its
  44 // TLS primitives.  So, we build it manually by inserting a
  45 // function to be called on each thread's exit.
  46 // This magic is from http://www.codeproject.com/threads/tls.asp
  47 // and it works for VC++ 7.0 and later.
  48
  49 // Force a reference to _tls_used to make the linker create the TLS directory
  50 // if it's not already there.  (e.g. if __declspec(thread) is not used).
  51 // Force a reference to p_thread_callback_base to prevent whole program
  52 // optimization from discarding the variable.
  53 #ifdef _WIN64
  54
  55 #pragma comment(linker, "/INCLUDE:_tls_used")
  56 #pragma comment(linker, "/INCLUDE:p_thread_callback_base")
  57
  58 #else  // _WIN64
  59
  60 #pragma comment(linker, "/INCLUDE:__tls_used")
  61 #pragma comment(linker, "/INCLUDE:_p_thread_callback_base")
  62
  63 #endif  // _WIN64
  64
  65 // Static callback function to call with each thread termination.
  66 void NTAPI OnThreadExit(PVOID module, DWORD reason, PVOID reserved) {
  67   // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+
  68   // and on W2K and W2K3. So don't assume it is sent.
  69   if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason)
  70     base::internal::PlatformThreadLocalStorage::OnThreadExit();
  71 }
  72
  73 // .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are
  74 // called automatically by the OS loader code (not the CRT) when the module is
  75 // loaded and on thread creation. They are NOT called if the module has been
  76 // loaded by a LoadLibrary() call. It must have implicitly been loaded at
  77 // process startup.
  78 // By implicitly loaded, I mean that it is directly referenced by the main EXE
  79 // or by one of its dependent DLLs. Delay-loaded DLL doesn't count as being
  80 // implicitly loaded.
  81 //
  82 // See VC\crt\src\tlssup.c for reference.
  83
  84 // extern "C" suppresses C++ name mangling so we know the symbol name for the
  85 // linker /INCLUDE:symbol pragma above.
  86 extern "C" {
  87 // The linker must not discard p_thread_callback_base.  (We force a reference
  88 // to this variable with a linker /INCLUDE:symbol pragma to ensure that.) If
  89 // this variable is discarded, the OnThreadExit function will never be called.
  90 #ifdef _WIN64
  91
  92 // .CRT section is merged with .rdata on x64 so it must be constant data.
  93 #pragma const_seg(".CRT$XLB")
  94 // When defining a const variable, it must have external linkage to be sure the
  95 // linker doesn't discard it.
  96 extern const PIMAGE_TLS_CALLBACK p_thread_callback_base;
  97 const PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
  98
  99 // Reset the default section.
 100 #pragma const_seg()
 101
 102 #else  // _WIN64
 103
 104 #pragma data_seg(".CRT$XLB")
 105 PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
 106
 107 // Reset the default section.
 108 #pragma data_seg()
 109
 110 #endif  // _WIN64
 111 }  // extern "C"