1 // Copyright (c) 2006-2008 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/thread_local_storage.h" 6 7 #include <windows.h> 8 9 #include "base/logging.h" 10 11 // In order to make TLS destructors work, we need to keep function 12 // pointers to the destructor for each TLS that we allocate. 13 // We make this work by allocating a single OS-level TLS, which 14 // contains an array of slots for the application to use. In 15 // parallel, we also allocate an array of destructors, which we 16 // keep track of and call when threads terminate. 17 18 // tls_key_ is the one native TLS that we use. It stores our 19 // table. 20 long ThreadLocalStorage::tls_key_ = TLS_OUT_OF_INDEXES; 21 22 // tls_max_ is the high-water-mark of allocated thread local storage. 23 // We intentionally skip 0 so that it is not confused with an 24 // unallocated TLS slot. 25 long ThreadLocalStorage::tls_max_ = 1; 26 27 // An array of destructor function pointers for the slots. If 28 // a slot has a destructor, it will be stored in its corresponding 29 // entry in this array. 30 ThreadLocalStorage::TLSDestructorFunc 31 ThreadLocalStorage::tls_destructors_[kThreadLocalStorageSize]; 32 33 void** ThreadLocalStorage::Initialize() { 34 if (tls_key_ == TLS_OUT_OF_INDEXES) { 35 long value = TlsAlloc(); 36 DCHECK(value != TLS_OUT_OF_INDEXES); 37 38 // Atomically test-and-set the tls_key. If the key is TLS_OUT_OF_INDEXES, 39 // go ahead and set it. Otherwise, do nothing, as another 40 // thread already did our dirty work. 41 if (InterlockedCompareExchange(&tls_key_, value, TLS_OUT_OF_INDEXES) != 42 TLS_OUT_OF_INDEXES) { 43 // We've been shortcut. Another thread replaced tls_key_ first so we need 44 // to destroy our index and use the one the other thread got first. 45 TlsFree(value); 46 } 47 } 48 DCHECK(TlsGetValue(tls_key_) == NULL); 49 50 // Create an array to store our data. 51 void** tls_data = new void*[kThreadLocalStorageSize]; 52 memset(tls_data, 0, sizeof(void*[kThreadLocalStorageSize])); 53 TlsSetValue(tls_key_, tls_data); 54 return tls_data; 55 } 56 57 ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) 58 : initialized_(false) { 59 Initialize(destructor); 60 } 61 62 bool ThreadLocalStorage::Slot::Initialize(TLSDestructorFunc destructor) { 63 if (tls_key_ == TLS_OUT_OF_INDEXES || !TlsGetValue(tls_key_)) 64 ThreadLocalStorage::Initialize(); 65 66 // Grab a new slot. 67 slot_ = InterlockedIncrement(&tls_max_) - 1; 68 if (slot_ >= kThreadLocalStorageSize) { 69 NOTREACHED(); 70 return false; 71 } 72 73 // Setup our destructor. 74 tls_destructors_[slot_] = destructor; 75 initialized_ = true; 76 return true; 77 } 78 79 void ThreadLocalStorage::Slot::Free() { 80 // At this time, we don't reclaim old indices for TLS slots. 81 // So all we need to do is wipe the destructor. 82 tls_destructors_[slot_] = NULL; 83 initialized_ = false; 84 } 85 86 void* ThreadLocalStorage::Slot::Get() const { 87 void** tls_data = static_cast<void**>(TlsGetValue(tls_key_)); 88 if (!tls_data) 89 tls_data = ThreadLocalStorage::Initialize(); 90 DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize); 91 return tls_data[slot_]; 92 } 93 94 void ThreadLocalStorage::Slot::Set(void* value) { 95 void** tls_data = static_cast<void**>(TlsGetValue(tls_key_)); 96 if (!tls_data) 97 tls_data = ThreadLocalStorage::Initialize(); 98 DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize); 99 tls_data[slot_] = value; 100 } 101 102 void ThreadLocalStorage::ThreadExit() { 103 if (tls_key_ == TLS_OUT_OF_INDEXES) 104 return; 105 106 void** tls_data = static_cast<void**>(TlsGetValue(tls_key_)); 107 108 // Maybe we have never initialized TLS for this thread. 109 if (!tls_data) 110 return; 111 112 for (int slot = 0; slot < tls_max_; slot++) { 113 if (tls_destructors_[slot] != NULL) { 114 void* value = tls_data[slot]; 115 tls_destructors_[slot](value); 116 } 117 } 118 119 delete[] tls_data; 120 121 // In case there are other "onexit" handlers... 122 TlsSetValue(tls_key_, NULL); 123 } 124 125 // Thread Termination Callbacks. 126 // Windows doesn't support a per-thread destructor with its 127 // TLS primitives. So, we build it manually by inserting a 128 // function to be called on each thread's exit. 129 // This magic is from http://www.codeproject.com/threads/tls.asp 130 // and it works for VC++ 7.0 and later. 131 132 #ifdef _WIN64 133 134 // This makes the linker create the TLS directory if it's not already 135 // there. (e.g. if __declspec(thread) is not used). 136 #pragma comment(linker, "/INCLUDE:_tls_used") 137 138 #else // _WIN64 139 140 // This makes the linker create the TLS directory if it's not already 141 // there. (e.g. if __declspec(thread) is not used). 142 #pragma comment(linker, "/INCLUDE:__tls_used") 143 144 #endif // _WIN64 145 146 // Static callback function to call with each thread termination. 147 void NTAPI OnThreadExit(PVOID module, DWORD reason, PVOID reserved) 148 { 149 // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+ 150 // and on W2K and W2K3. So don't assume it is sent. 151 if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason) 152 ThreadLocalStorage::ThreadExit(); 153 } 154 155 // .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are 156 // called automatically by the OS loader code (not the CRT) when the module is 157 // loaded and on thread creation. They are NOT called if the module has been 158 // loaded by a LoadLibrary() call. It must have implicitly been loaded at 159 // process startup. 160 // By implicitly loaded, I mean that it is directly referenced by the main EXE 161 // or by one of its dependent DLLs. Delay-loaded DLL doesn't count as being 162 // implicitly loaded. 163 // 164 // See VC\crt\src\tlssup.c for reference. 165 #ifdef _WIN64 166 167 // .CRT section is merged with .rdata on x64 so it must be constant data. 168 #pragma const_seg(".CRT$XLB") 169 // When defining a const variable, it must have external linkage to be sure the 170 // linker doesn't discard it. If this value is discarded, the OnThreadExit 171 // function will never be called. 172 extern const PIMAGE_TLS_CALLBACK p_thread_callback; 173 const PIMAGE_TLS_CALLBACK p_thread_callback = OnThreadExit; 174 175 // Reset the default section. 176 #pragma const_seg() 177 178 #else // _WIN64 179 180 #pragma data_seg(".CRT$XLB") 181 PIMAGE_TLS_CALLBACK p_thread_callback = OnThreadExit; 182 183 // Reset the default section. 184 #pragma data_seg() 185 186 #endif // _WIN64 187