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// 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
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