The Tor Browser / file revision

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 #include "base/thread_local_storage.h"

 #include <windows.h>

 #include "base/logging.h"

 // In order to make TLS destructors work, we need to keep function

 // pointers to the destructor for each TLS that we allocate.

 // We make this work by allocating a single OS-level TLS, which

 // contains an array of slots for the application to use.  In

 // parallel, we also allocate an array of destructors, which we

 // keep track of and call when threads terminate.

 // tls_key_ is the one native TLS that we use.  It stores our

 // table.

 long ThreadLocalStorage::tls_key_ = TLS_OUT_OF_INDEXES;

 // tls_max_ is the high-water-mark of allocated thread local storage.

 // We intentionally skip 0 so that it is not confused with an

 // unallocated TLS slot.

 long ThreadLocalStorage::tls_max_ = 1;

 // An array of destructor function pointers for the slots.  If

 // a slot has a destructor, it will be stored in its corresponding

 // entry in this array.

 ThreadLocalStorage::TLSDestructorFunc

   ThreadLocalStorage::tls_destructors_[kThreadLocalStorageSize];

 void** ThreadLocalStorage::Initialize() {

   if (tls_key_ == TLS_OUT_OF_INDEXES) {

     long value = TlsAlloc();

     DCHECK(value != TLS_OUT_OF_INDEXES);

     // Atomically test-and-set the tls_key.  If the key is TLS_OUT_OF_INDEXES,

     // go ahead and set it.  Otherwise, do nothing, as another

     // thread already did our dirty work.

     if (InterlockedCompareExchange(&tls_key_, value, TLS_OUT_OF_INDEXES) !=

             TLS_OUT_OF_INDEXES) {

       // We've been shortcut. Another thread replaced tls_key_ first so we need

       // to destroy our index and use the one the other thread got first.

       TlsFree(value);

     }

   }

   DCHECK(TlsGetValue(tls_key_) == NULL);

   // Create an array to store our data.

   void** tls_data = new void*[kThreadLocalStorageSize];

   memset(tls_data, 0, sizeof(void*[kThreadLocalStorageSize]));

   TlsSetValue(tls_key_, tls_data);

   return tls_data;

 }

 ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor)

     : initialized_(false) {

   Initialize(destructor);

 }

 bool ThreadLocalStorage::Slot::Initialize(TLSDestructorFunc destructor) {

   if (tls_key_ == TLS_OUT_OF_INDEXES || !TlsGetValue(tls_key_))

     ThreadLocalStorage::Initialize();

   // Grab a new slot.

   slot_ = InterlockedIncrement(&tls_max_) - 1;

   if (slot_ >= kThreadLocalStorageSize) {

     NOTREACHED();

     return false;

   }

   // Setup our destructor.

   tls_destructors_[slot_] = destructor;

   initialized_ = true;

   return true;

 }

 void ThreadLocalStorage::Slot::Free() {

   // At this time, we don't reclaim old indices for TLS slots.

   // So all we need to do is wipe the destructor.

   tls_destructors_[slot_] = NULL;

   initialized_ = false;

 }

 void* ThreadLocalStorage::Slot::Get() const {

   void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));

   if (!tls_data)

     tls_data = ThreadLocalStorage::Initialize();

   DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize);

   return tls_data[slot_];

 }

 void ThreadLocalStorage::Slot::Set(void* value) {

   void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));

   if (!tls_data)

     tls_data = ThreadLocalStorage::Initialize();

   DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize);

   tls_data[slot_] = value;

 }

 void ThreadLocalStorage::ThreadExit() {

   if (tls_key_ == TLS_OUT_OF_INDEXES)

     return;

   void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));

   // Maybe we have never initialized TLS for this thread.

   if (!tls_data)

     return;

   for (int slot = 0; slot < tls_max_; slot++) {

     if (tls_destructors_[slot] != NULL) {

       void* value = tls_data[slot];

       tls_destructors_[slot](value);

     }

   }

   delete[] tls_data;

   // In case there are other "onexit" handlers...

   TlsSetValue(tls_key_, NULL);

 }

 // Thread Termination Callbacks.

 // Windows doesn't support a per-thread destructor with its

 // TLS primitives.  So, we build it manually by inserting a

 // function to be called on each thread's exit.

 // This magic is from http://www.codeproject.com/threads/tls.asp

 // and it works for VC++ 7.0 and later.

 #ifdef _WIN64

 // This makes the linker create the TLS directory if it's not already

 // there.  (e.g. if __declspec(thread) is not used).

 #pragma comment(linker, "/INCLUDE:_tls_used")

 #else  // _WIN64

 // This makes the linker create the TLS directory if it's not already

 // there.  (e.g. if __declspec(thread) is not used).

 #pragma comment(linker, "/INCLUDE:__tls_used")

 #endif  // _WIN64

 // Static callback function to call with each thread termination.

 void NTAPI OnThreadExit(PVOID module, DWORD reason, PVOID reserved)

 {

   // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+

   // and on W2K and W2K3. So don't assume it is sent.

   if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason)

     ThreadLocalStorage::ThreadExit();

 }

 // .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are

 // called automatically by the OS loader code (not the CRT) when the module is

 // loaded and on thread creation. They are NOT called if the module has been

 // loaded by a LoadLibrary() call. It must have implicitly been loaded at

 // process startup.

 // By implicitly loaded, I mean that it is directly referenced by the main EXE

 // or by one of its dependent DLLs. Delay-loaded DLL doesn't count as being

 // implicitly loaded.

 //

 // See VC\crt\src\tlssup.c for reference.

 #ifdef _WIN64

 // .CRT section is merged with .rdata on x64 so it must be constant data.

 #pragma const_seg(".CRT$XLB")

 // When defining a const variable, it must have external linkage to be sure the

 // linker doesn't discard it. If this value is discarded, the OnThreadExit

 // function will never be called.

 extern const PIMAGE_TLS_CALLBACK p_thread_callback;

 const PIMAGE_TLS_CALLBACK p_thread_callback = OnThreadExit;

 // Reset the default section.

 #pragma const_seg()

 #else  // _WIN64

 #pragma data_seg(".CRT$XLB")

 PIMAGE_TLS_CALLBACK p_thread_callback = OnThreadExit;

 // Reset the default section.

 #pragma data_seg()

 #endif  // _WIN64