base/thread_local_storage.h

// Copyright 2008, Google Inc.
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#ifndef BASE_THREAD_LOCAL_STORAGE_H_
#define BASE_THREAD_LOCAL_STORAGE_H_

#include "base/basictypes.h"

#if defined(OS_WIN)
typedef int TLSSlot;
#elif defined(OS_POSIX)
#include <pthread.h>
typedef pthread_key_t TLSSlot;
#endif  // OS_*

// Wrapper for thread local storage.  This class doesn't
// do much except provide an API for portability later.
class ThreadLocalStorage {
 public:
  // Prototype for the TLS destructor function, which can be
  // optionally used to cleanup thread local storage on
  // thread exit.  'value' is the data that is stored
  // in thread local storage.
  typedef void (*TLSDestructorFunc)(void* value);

  // Allocate a TLS 'slot'.
  // 'destructor' is a pointer to a function to perform
  // per-thread cleanup of this object.  If set to NULL,
  // no cleanup is done for this TLS slot.
  // Returns an index > 0 on success, or -1 on failure.
  static TLSSlot Alloc(TLSDestructorFunc destructor = NULL);

  // Free a previously allocated TLS 'slot'.
  // If a destructor was set for this slot, removes
  // the destructor so that remaining threads exiting
  // will not free data.
  static void Free(TLSSlot slot);

  // Get the thread-local value stored in slot 'slot'.
  // Values are guaranteed to initially be zero.
  static void* Get(TLSSlot slot);

  // Set the thread-local value stored in slot 'slot' to
  // value 'value'.
  static void Set(TLSSlot slot, void* value);

#if defined(OS_WIN)
  // Function called when on thread exit to call TLS
  // destructor functions.  This function is used internally.
  static void ThreadExit();

 private:
  // Function to lazily initialize our thread local storage.
  static void **Initialize();

 private:
  // The maximum number of 'slots' in our thread local storage stack.
  // For now, this is fixed.  We could either increase statically, or
  // we could make it dynamic in the future.
  static const int kThreadLocalStorageSize = 64;

  static long tls_key_;
  static long tls_max_;
  static TLSDestructorFunc tls_destructors_[kThreadLocalStorageSize];
#endif  // OS_WIN

  DISALLOW_EVIL_CONSTRUCTORS(ThreadLocalStorage);
};

#endif  // BASE_THREAD_LOCAL_STORAGE_H_