Add base::ThreadLocalStorage

base/threading/thread_local_storage.h

Index: base/threading/thread_local_storage.h
diff --git a/base/threading/thread_local_storage.h b/base/threading/thread_local_storage.h
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+++ b/base/threading/thread_local_storage.h
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+// Copyright 2007 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MINI_CHROMIUM_BASE_THREADING_THREAD_LOCAL_STORAGE_H_
+#define MINI_CHROMIUM_BASE_THREADING_THREAD_LOCAL_STORAGE_H_
+
+#include "base/basictypes.h"
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <windows.h>
+#elif defined(OS_POSIX)
+#include <pthread.h>
+#endif
+
+namespace base {
+
+namespace internal {
+
+// WARNING: You should *NOT* be using this class directly.
+// PlatformThreadLocalStorage is low-level abstraction to the OS's TLS
+// interface, you should instead be using ThreadLocalStorage::StaticSlot/Slot.
+class PlatformThreadLocalStorage {
+ public:
+
+#if defined(OS_WIN)
+  typedef unsigned long TLSKey;
+  enum { TLS_KEY_OUT_OF_INDEXES = TLS_OUT_OF_INDEXES };
+#elif defined(OS_POSIX)
+  typedef pthread_key_t TLSKey;
+  // The following is a "reserved key" which is used in our generic Chromium
+  // ThreadLocalStorage implementation.  We expect that an OS will not return
+  // such a key, but if it is returned (i.e., the OS tries to allocate it) we
+  // will just request another key.
+  enum { TLS_KEY_OUT_OF_INDEXES = 0x7FFFFFFF };
+#endif
+
+  // The following methods need to be supported on each OS platform, so that
+  // the Chromium ThreadLocalStore functionality can be constructed.
+  // Chromium will use these methods to acquire a single OS slot, and then use
+  // that to support a much larger number of Chromium slots (independent of the
+  // OS restrictions).
+  // The following returns true if it successfully is able to return an OS
+  // key in |key|.
+  static bool AllocTLS(TLSKey* key);
+  // Note: FreeTLS() doesn't have to be called, it is fine with this leak, OS
+  // might not reuse released slot, you might just reset the TLS value with
+  // SetTLSValue().
+  static void FreeTLS(TLSKey key);
+  static void SetTLSValue(TLSKey key, void* value);
+  static void* GetTLSValue(TLSKey key);
+
+  // Each platform (OS implementation) is required to call this method on each
+  // terminating thread when the thread is about to terminate.  This method
+  // will then call all registered destructors for slots in Chromium
+  // ThreadLocalStorage, until there are no slot values remaining as having
+  // been set on this thread.
+  // Destructors may end up being called multiple times on a terminating
+  // thread, as other destructors may re-set slots that were previously
+  // destroyed.
+#if defined(OS_WIN)
+  // Since Windows which doesn't support TLS destructor, the implementation
+  // should use GetTLSValue() to retrieve the value of TLS slot.
+  static void OnThreadExit();
+#elif defined(OS_POSIX)
+  // |Value| is the data stored in TLS slot, The implementation can't use
+  // GetTLSValue() to retrieve the value of slot as it has already been reset
+  // in Posix.
+  static void OnThreadExit(void* value);
+#endif
+};
+
+}  // namespace internal
+
+// Wrapper for thread local storage.  This class doesn't do much except provide
+// an API for portability.
+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);
+
+  // StaticSlot uses its own struct initializer-list style static
+  // initialization, as base's LINKER_INITIALIZED requires a constructor and on
+  // some compilers (notably gcc 4.4) this still ends up needing runtime
+  // initialization.
+  #define TLS_INITIALIZER {0}
+
+  // A key representing one value stored in TLS.
+  // Initialize like
+  //   ThreadLocalStorage::StaticSlot my_slot = TLS_INITIALIZER;
+  // If you're not using a static variable, use the convenience class
+  // ThreadLocalStorage::Slot (below) instead.
+  struct StaticSlot {
+    // Set up the TLS slot.  Called by the constructor.
+    // '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 false on error.
+    bool Initialize(TLSDestructorFunc destructor);
+
+    // 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.
+    void Free();
+
+    // Get the thread-local value stored in slot 'slot'.
+    // Values are guaranteed to initially be zero.
+    void* Get() const;
+
+    // Set the thread-local value stored in slot 'slot' to
+    // value 'value'.
+    void Set(void* value);
+
+    bool initialized() const { return initialized_; }
+
+    // The internals of this struct should be considered private.
+    bool initialized_;
+    int slot_;
+  };
+
+  // A convenience wrapper around StaticSlot with a constructor. Can be used
+  // as a member variable.
+  class Slot : public StaticSlot {
+   public:
+    // Calls StaticSlot::Initialize().
+    explicit Slot(TLSDestructorFunc destructor = NULL);
+
+   private:
+    using StaticSlot::initialized_;
+    using StaticSlot::slot_;
+
+    DISALLOW_COPY_AND_ASSIGN(Slot);
+  };
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
+};
+
+}  // namespace base
+
+#endif  // MINI_CHROMIUM_BASE_THREADING_THREAD_LOCAL_STORAGE_H_