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       1             : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* vim: set ts=8 sts=2 et sw=2 tw=80: */
       3             : // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
       4             : // Use of this source code is governed by a BSD-style license that can be
       5             : // found in the LICENSE file.
       6             : 
       7             : // WARNING: Thread local storage is a bit tricky to get right.  Please make
       8             : // sure that this is really the proper solution for what you're trying to
       9             : // achieve.  Don't prematurely optimize, most likely you can just use a Lock.
      10             : //
      11             : // These classes implement a warpper around the platform's TLS storage
      12             : // mechanism.  On construction, they will allocate a TLS slot, and free the
      13             : // TLS slot on destruction.  No memory management (creation or destruction) is
      14             : // handled.  This means for uses of ThreadLocalPointer, you must correctly
      15             : // manage the memory yourself, these classes will not destroy the pointer for
      16             : // you.  There are no at-thread-exit actions taken by these classes.
      17             : //
      18             : // ThreadLocalPointer<Type> wraps a Type*.  It performs no creation or
      19             : // destruction, so memory management must be handled elsewhere.  The first call
      20             : // to Get() on a thread will return NULL.  You can update the pointer with a
      21             : // call to Set().
      22             : //
      23             : // ThreadLocalBoolean wraps a bool.  It will default to false if it has never
      24             : // been set otherwise with Set().
      25             : //
      26             : // Thread Safety:  An instance of ThreadLocalStorage is completely thread safe
      27             : // once it has been created.  If you want to dynamically create an instance,
      28             : // you must of course properly deal with safety and race conditions.  This
      29             : // means a function-level static initializer is generally inappropiate.
      30             : //
      31             : // Example usage:
      32             : //   // My class is logically attached to a single thread.  We cache a pointer
      33             : //   // on the thread it was created on, so we can implement current().
      34             : //   MyClass::MyClass() {
      35             : //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);
      36             : //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);
      37             : //   }
      38             : //
      39             : //   MyClass::~MyClass() {
      40             : //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
      41             : //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
      42             : //   }
      43             : //
      44             : //   // Return the current MyClass associated with the calling thread, can be
      45             : //   // NULL if there isn't a MyClass associated.
      46             : //   MyClass* MyClass::current() {
      47             : //     return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();
      48             : //   }
      49             : 
      50             : #ifndef BASE_THREAD_LOCAL_H_
      51             : #define BASE_THREAD_LOCAL_H_
      52             : 
      53             : #include "base/basictypes.h"
      54             : 
      55             : #if defined(OS_POSIX)
      56             : #include <pthread.h>
      57             : #endif
      58             : 
      59             : namespace base {
      60             : 
      61             : // Helper functions that abstract the cross-platform APIs.  Do not use directly.
      62             : struct ThreadLocalPlatform {
      63             : #if defined(OS_WIN)
      64             :   typedef int SlotType;
      65             : #elif defined(OS_POSIX)
      66             :   typedef pthread_key_t SlotType;
      67             : #endif
      68             : 
      69             :   static void AllocateSlot(SlotType& slot);
      70             :   static void FreeSlot(SlotType& slot);
      71             :   static void* GetValueFromSlot(SlotType& slot);
      72             :   static void SetValueInSlot(SlotType& slot, void* value);
      73             : };
      74             : 
      75             : template <typename Type>
      76             : class ThreadLocalPointer {
      77             :  public:
      78           6 :   ThreadLocalPointer() : slot_() {
      79           6 :     ThreadLocalPlatform::AllocateSlot(slot_);
      80           6 :   }
      81             : 
      82           0 :   ~ThreadLocalPointer() {
      83           0 :     ThreadLocalPlatform::FreeSlot(slot_);
      84           0 :   }
      85             : 
      86        1119 :   Type* Get() {
      87        1119 :     return static_cast<Type*>(ThreadLocalPlatform::GetValueFromSlot(slot_));
      88             :   }
      89             : 
      90          76 :   void Set(Type* ptr) {
      91          76 :     ThreadLocalPlatform::SetValueInSlot(slot_, ptr);
      92          76 :   }
      93             : 
      94             :  private:
      95             :   typedef ThreadLocalPlatform::SlotType SlotType;
      96             : 
      97             :   SlotType slot_;
      98             : 
      99             :   DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);
     100             : };
     101             : 
     102             : class ThreadLocalBoolean {
     103             :  public:
     104           3 :   ThreadLocalBoolean() { }
     105           0 :   ~ThreadLocalBoolean() { }
     106             : 
     107           0 :   bool Get() {
     108           0 :     return tlp_.Get() != NULL;
     109             :   }
     110             : 
     111           8 :   void Set(bool val) {
     112           8 :     uintptr_t intVal = val ? 1 : 0;
     113           8 :     tlp_.Set(reinterpret_cast<void*>(intVal));
     114           8 :   }
     115             : 
     116             :  private:
     117             :   ThreadLocalPointer<void> tlp_;
     118             : 
     119             :   DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);
     120             : };
     121             : 
     122             : }  // namespace base
     123             : 
     124             : #endif  // BASE_THREAD_LOCAL_H_