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