base/threading/thread_local_storage.h

   1 // Copyright (c) 2012 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 #ifndef BASE_THREADING_THREAD_LOCAL_STORAGE_H_
   6 #define BASE_THREADING_THREAD_LOCAL_STORAGE_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/basictypes.h"
  10
  11 #if defined(OS_POSIX)
  12 #include <pthread.h>
  13 #endif
  14
  15 namespace base {
  16
  17 // Wrapper for thread local storage.  This class doesn't do much except provide
  18 // an API for portability.
  19 class BASE_EXPORT ThreadLocalStorage {
  20  public:
  21
  22   // Prototype for the TLS destructor function, which can be optionally used to
  23   // cleanup thread local storage on thread exit.  'value' is the data that is
  24   // stored in thread local storage.
  25   typedef void (*TLSDestructorFunc)(void* value);
  26
  27   // StaticSlot uses its own struct initializer-list style static
  28   // initialization, as base's LINKER_INITIALIZED requires a constructor and on
  29   // some compilers (notably gcc 4.4) this still ends up needing runtime
  30   // initialization.
  31   #define TLS_INITIALIZER {0}
  32
  33   // A key representing one value stored in TLS.
  34   // Initialize like
  35   //   ThreadLocalStorage::StaticSlot my_slot = TLS_INITIALIZER;
  36   // If you're not using a static variable, use the convenience class
  37   // ThreadLocalStorage::Slot (below) instead.
  38   struct BASE_EXPORT StaticSlot {
  39     // Set up the TLS slot.  Called by the constructor.
  40     // 'destructor' is a pointer to a function to perform per-thread cleanup of
  41     // this object.  If set to NULL, no cleanup is done for this TLS slot.
  42     // Returns false on error.
  43     bool Initialize(TLSDestructorFunc destructor);
  44
  45     // Free a previously allocated TLS 'slot'.
  46     // If a destructor was set for this slot, removes
  47     // the destructor so that remaining threads exiting
  48     // will not free data.
  49     void Free();
  50
  51     // Get the thread-local value stored in slot 'slot'.
  52     // Values are guaranteed to initially be zero.
  53     void* Get() const;
  54
  55     // Set the thread-local value stored in slot 'slot' to
  56     // value 'value'.
  57     void Set(void* value);
  58
  59     bool initialized() const { return initialized_; }
  60
  61     // The internals of this struct should be considered private.
  62     bool initialized_;
  63 #if defined(OS_WIN)
  64     int slot_;
  65 #elif defined(OS_POSIX)
  66     pthread_key_t key_;
  67 #endif
  68
  69   };
  70
  71   // A convenience wrapper around StaticSlot with a constructor. Can be used
  72   // as a member variable.
  73   class BASE_EXPORT Slot : public StaticSlot {
  74    public:
  75     // Calls StaticSlot::Initialize().
  76     explicit Slot(TLSDestructorFunc destructor = NULL);
  77
  78    private:
  79     using StaticSlot::initialized_;
  80 #if defined(OS_WIN)
  81     using StaticSlot::slot_;
  82 #elif defined(OS_POSIX)
  83     using StaticSlot::key_;
  84 #endif
  85     DISALLOW_COPY_AND_ASSIGN(Slot);
  86   };
  87
  88   DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
  89 };
  90
  91 }  // namespace base
  92
  93 #endif  // BASE_THREADING_THREAD_LOCAL_STORAGE_H_