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