michael@0: // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: // WARNING: Thread local storage is a bit tricky to get right.  Please make
michael@0: // sure that this is really the proper solution for what you're trying to
michael@0: // achieve.  Don't prematurely optimize, most likely you can just use a Lock.
michael@0: //
michael@0: // These classes implement a warpper around the platform's TLS storage
michael@0: // mechanism.  On construction, they will allocate a TLS slot, and free the
michael@0: // TLS slot on destruction.  No memory management (creation or destruction) is
michael@0: // handled.  This means for uses of ThreadLocalPointer, you must correctly
michael@0: // manage the memory yourself, these classes will not destroy the pointer for
michael@0: // you.  There are no at-thread-exit actions taken by these classes.
michael@0: //
michael@0: // ThreadLocalPointer<Type> wraps a Type*.  It performs no creation or
michael@0: // destruction, so memory management must be handled elsewhere.  The first call
michael@0: // to Get() on a thread will return NULL.  You can update the pointer with a
michael@0: // call to Set().
michael@0: //
michael@0: // ThreadLocalBoolean wraps a bool.  It will default to false if it has never
michael@0: // been set otherwise with Set().
michael@0: //
michael@0: // Thread Safety:  An instance of ThreadLocalStorage is completely thread safe
michael@0: // once it has been created.  If you want to dynamically create an instance,
michael@0: // you must of course properly deal with safety and race conditions.  This
michael@0: // means a function-level static initializer is generally inappropiate.
michael@0: //
michael@0: // Example usage:
michael@0: //   // My class is logically attached to a single thread.  We cache a pointer
michael@0: //   // on the thread it was created on, so we can implement current().
michael@0: //   MyClass::MyClass() {
michael@0: //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);
michael@0: //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);
michael@0: //   }
michael@0: //
michael@0: //   MyClass::~MyClass() {
michael@0: //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
michael@0: //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
michael@0: //   }
michael@0: //
michael@0: //   // Return the current MyClass associated with the calling thread, can be
michael@0: //   // NULL if there isn't a MyClass associated.
michael@0: //   MyClass* MyClass::current() {
michael@0: //     return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();
michael@0: //   }
michael@0: 
michael@0: #ifndef BASE_THREAD_LOCAL_H_
michael@0: #define BASE_THREAD_LOCAL_H_
michael@0: 
michael@0: #include "base/basictypes.h"
michael@0: 
michael@0: #if defined(OS_POSIX)
michael@0: #include <pthread.h>
michael@0: #endif
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: // Helper functions that abstract the cross-platform APIs.  Do not use directly.
michael@0: struct ThreadLocalPlatform {
michael@0: #if defined(OS_WIN)
michael@0:   typedef int SlotType;
michael@0: #elif defined(OS_POSIX)
michael@0:   typedef pthread_key_t SlotType;
michael@0: #endif
michael@0: 
michael@0:   static void AllocateSlot(SlotType& slot);
michael@0:   static void FreeSlot(SlotType& slot);
michael@0:   static void* GetValueFromSlot(SlotType& slot);
michael@0:   static void SetValueInSlot(SlotType& slot, void* value);
michael@0: };
michael@0: 
michael@0: template <typename Type>
michael@0: class ThreadLocalPointer {
michael@0:  public:
michael@0:   ThreadLocalPointer() : slot_() {
michael@0:     ThreadLocalPlatform::AllocateSlot(slot_);
michael@0:   }
michael@0: 
michael@0:   ~ThreadLocalPointer() {
michael@0:     ThreadLocalPlatform::FreeSlot(slot_);
michael@0:   }
michael@0: 
michael@0:   Type* Get() {
michael@0:     return static_cast<Type*>(ThreadLocalPlatform::GetValueFromSlot(slot_));
michael@0:   }
michael@0: 
michael@0:   void Set(Type* ptr) {
michael@0:     ThreadLocalPlatform::SetValueInSlot(slot_, ptr);
michael@0:   }
michael@0: 
michael@0:  private:
michael@0:   typedef ThreadLocalPlatform::SlotType SlotType;
michael@0: 
michael@0:   SlotType slot_;
michael@0: 
michael@0:   DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);
michael@0: };
michael@0: 
michael@0: class ThreadLocalBoolean {
michael@0:  public:
michael@0:   ThreadLocalBoolean() { }
michael@0:   ~ThreadLocalBoolean() { }
michael@0: 
michael@0:   bool Get() {
michael@0:     return tlp_.Get() != NULL;
michael@0:   }
michael@0: 
michael@0:   void Set(bool val) {
michael@0:     tlp_.Set(reinterpret_cast<void*>(val ? 1 : 0));
michael@0:   }
michael@0: 
michael@0:  private:
michael@0:   ThreadLocalPointer<void> tlp_;
michael@0: 
michael@0:   DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);
michael@0: };
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: #endif  // BASE_THREAD_LOCAL_H_