129 lines
3.9 KiB
C++
129 lines
3.9 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// WARNING: Thread local storage is a bit tricky to get right. Please make
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// sure that this is really the proper solution for what you're trying to
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// achieve. Don't prematurely optimize, most likely you can just use a Lock.
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//
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// These classes implement a wrapper around the platform's TLS storage
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// mechanism. On construction, they will allocate a TLS slot, and free the
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// TLS slot on destruction. No memory management (creation or destruction) is
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// handled. This means for uses of ThreadLocalPointer, you must correctly
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// manage the memory yourself, these classes will not destroy the pointer for
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// you. There are no at-thread-exit actions taken by these classes.
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//
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// ThreadLocalPointer<Type> wraps a Type*. It performs no creation or
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// destruction, so memory management must be handled elsewhere. The first call
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// to Get() on a thread will return NULL. You can update the pointer with a
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// call to Set().
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//
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// ThreadLocalBoolean wraps a bool. It will default to false if it has never
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// been set otherwise with Set().
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//
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// Thread Safety: An instance of ThreadLocalStorage is completely thread safe
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// once it has been created. If you want to dynamically create an instance,
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// you must of course properly deal with safety and race conditions. This
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// means a function-level static initializer is generally inappropiate.
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//
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// Example usage:
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// // My class is logically attached to a single thread. We cache a pointer
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// // on the thread it was created on, so we can implement current().
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// MyClass::MyClass() {
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// DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);
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// Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);
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// }
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//
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// MyClass::~MyClass() {
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// DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
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// Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
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// }
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//
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// // Return the current MyClass associated with the calling thread, can be
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// // NULL if there isn't a MyClass associated.
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// MyClass* MyClass::current() {
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// return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();
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// }
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#ifndef BASE_THREADING_THREAD_LOCAL_H_
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#define BASE_THREADING_THREAD_LOCAL_H_
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#include "base/base_export.h"
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#include "base/basictypes.h"
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#if defined(OS_POSIX)
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#include <pthread.h>
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#endif
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namespace base {
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namespace internal {
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// Helper functions that abstract the cross-platform APIs. Do not use directly.
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struct BASE_EXPORT ThreadLocalPlatform {
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#if defined(OS_WIN)
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typedef unsigned long SlotType;
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#elif defined(OS_POSIX)
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typedef pthread_key_t SlotType;
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#endif
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static void AllocateSlot(SlotType& slot);
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static void FreeSlot(SlotType& slot);
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static void* GetValueFromSlot(SlotType& slot);
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static void SetValueInSlot(SlotType& slot, void* value);
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};
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} // namespace internal
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template <typename Type>
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class ThreadLocalPointer {
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public:
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ThreadLocalPointer() : slot_() {
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internal::ThreadLocalPlatform::AllocateSlot(slot_);
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}
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~ThreadLocalPointer() {
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internal::ThreadLocalPlatform::FreeSlot(slot_);
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}
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Type* Get() {
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return static_cast<Type*>(
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internal::ThreadLocalPlatform::GetValueFromSlot(slot_));
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}
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void Set(Type* ptr) {
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internal::ThreadLocalPlatform::SetValueInSlot(
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slot_, const_cast<void*>(static_cast<const void*>(ptr)));
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}
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private:
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typedef internal::ThreadLocalPlatform::SlotType SlotType;
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SlotType slot_;
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DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);
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};
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class ThreadLocalBoolean {
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public:
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ThreadLocalBoolean() { }
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~ThreadLocalBoolean() { }
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bool Get() {
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return tlp_.Get() != NULL;
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}
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void Set(bool val) {
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tlp_.Set(val ? this : NULL);
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}
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private:
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ThreadLocalPointer<void> tlp_;
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DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);
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};
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} // namespace base
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#endif // BASE_THREADING_THREAD_LOCAL_H_
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