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The Tor Browser
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thread_local.h (4074B)

      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(XP_WIN)
     56 #  include <windows.h>
     57 #else
     58 #  include <pthread.h>
     59 #endif
     60 
     61 namespace base {
     62 
     63 // Helper functions that abstract the cross-platform APIs.  Do not use directly.
     64 struct ThreadLocalPlatform {
     65 #if defined(XP_WIN)
     66  typedef DWORD SlotType;
     67 #else
     68  typedef pthread_key_t SlotType;
     69 #endif
     70 
     71  static void AllocateSlot(SlotType& slot);
     72  static void FreeSlot(SlotType& slot);
     73  static void* GetValueFromSlot(SlotType& slot);
     74  static void SetValueInSlot(SlotType& slot, void* value);
     75 };
     76 
     77 template <typename Type>
     78 class ThreadLocalPointer {
     79 public:
     80  ThreadLocalPointer() : slot_() { ThreadLocalPlatform::AllocateSlot(slot_); }
     81 
     82  ThreadLocalPointer(const ThreadLocalPointer&) = delete;
     83  ThreadLocalPointer& operator=(const ThreadLocalPointer&) = delete;
     84 
     85  ~ThreadLocalPointer() { ThreadLocalPlatform::FreeSlot(slot_); }
     86 
     87  Type* Get() {
     88    return static_cast<Type*>(ThreadLocalPlatform::GetValueFromSlot(slot_));
     89  }
     90 
     91  void Set(Type* ptr) { ThreadLocalPlatform::SetValueInSlot(slot_, ptr); }
     92 
     93 private:
     94  typedef ThreadLocalPlatform::SlotType SlotType;
     95 
     96  SlotType slot_;
     97 };
     98 
     99 class ThreadLocalBoolean {
    100 public:
    101  ThreadLocalBoolean() {}
    102 
    103  ThreadLocalBoolean(const ThreadLocalBoolean&) = delete;
    104  ThreadLocalBoolean& operator=(const ThreadLocalBoolean&) = delete;
    105 
    106  ~ThreadLocalBoolean() {}
    107 
    108  bool Get() { return tlp_.Get() != NULL; }
    109 
    110  void Set(bool val) {
    111    uintptr_t intVal = val ? 1 : 0;
    112    tlp_.Set(reinterpret_cast<void*>(intVal));
    113  }
    114 
    115 private:
    116  ThreadLocalPointer<void> tlp_;
    117 };
    118 
    119 }  // namespace base
    120 
    121 #endif  // BASE_THREAD_LOCAL_H_