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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_THREADING_THREAD_LOCAL_STORAGE_H_
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#define BASE_THREADING_THREAD_LOCAL_STORAGE_H_
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#include "base/base_export.h"
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#include "base/basictypes.h"
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#elif defined(OS_POSIX)
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// WARNING: You should *NOT* be using this class directly.
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// PlatformThreadLocalStorage is low-level abstraction to the OS's TLS
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// interface, you should instead be using ThreadLocalStorage::StaticSlot/Slot.
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class BASE_EXPORT PlatformThreadLocalStorage {
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typedef unsigned long TLSKey;
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enum { TLS_KEY_OUT_OF_INDEXES = TLS_OUT_OF_INDEXES };
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#elif defined(OS_POSIX)
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typedef pthread_key_t TLSKey;
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// The following is a "reserved key" which is used in our generic Chromium
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// ThreadLocalStorage implementation. We expect that an OS will not return
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// such a key, but if it is returned (i.e., the OS tries to allocate it) we
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// will just request another key.
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enum { TLS_KEY_OUT_OF_INDEXES = 0x7FFFFFFF };
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// The following methods need to be supported on each OS platform, so that
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// the Chromium ThreadLocalStore functionality can be constructed.
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// Chromium will use these methods to acquire a single OS slot, and then use
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// that to support a much larger number of Chromium slots (independent of the
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// The following returns true if it successfully is able to return an OS
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static bool AllocTLS(TLSKey* key);
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// Note: FreeTLS() doesn't have to be called, it is fine with this leak, OS
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// might not reuse released slot, you might just reset the TLS value with
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static void FreeTLS(TLSKey key);
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static void SetTLSValue(TLSKey key, void* value);
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static void* GetTLSValue(TLSKey key);
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// Each platform (OS implementation) is required to call this method on each
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// terminating thread when the thread is about to terminate. This method
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// will then call all registered destructors for slots in Chromium
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// ThreadLocalStorage, until there are no slot values remaining as having
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// been set on this thread.
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// Destructors may end up being called multiple times on a terminating
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// thread, as other destructors may re-set slots that were previously
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// Since Windows which doesn't support TLS destructor, the implementation
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// should use GetTLSValue() to retrieve the value of TLS slot.
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static void OnThreadExit();
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#elif defined(OS_POSIX)
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// |Value| is the data stored in TLS slot, The implementation can't use
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// GetTLSValue() to retrieve the value of slot as it has already been reset
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static void OnThreadExit(void* value);
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} // namespace internal
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// Wrapper for thread local storage. This class doesn't do much except provide
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// an API for portability.
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class BASE_EXPORT ThreadLocalStorage {
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// Prototype for the TLS destructor function, which can be optionally used to
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// cleanup thread local storage on thread exit. 'value' is the data that is
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// stored in thread local storage.
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typedef void (*TLSDestructorFunc)(void* value);
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// StaticSlot uses its own struct initializer-list style static
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// initialization, as base's LINKER_INITIALIZED requires a constructor and on
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// some compilers (notably gcc 4.4) this still ends up needing runtime
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#define TLS_INITIALIZER {0}
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// A key representing one value stored in TLS.
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// ThreadLocalStorage::StaticSlot my_slot = TLS_INITIALIZER;
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// If you're not using a static variable, use the convenience class
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// ThreadLocalStorage::Slot (below) instead.
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struct BASE_EXPORT StaticSlot {
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// Set up the TLS slot. Called by the constructor.
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// 'destructor' is a pointer to a function to perform per-thread cleanup of
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// this object. If set to NULL, no cleanup is done for this TLS slot.
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// Returns false on error.
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bool Initialize(TLSDestructorFunc destructor);
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// Free a previously allocated TLS 'slot'.
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// If a destructor was set for this slot, removes
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// the destructor so that remaining threads exiting
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// will not free data.
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// Get the thread-local value stored in slot 'slot'.
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// Values are guaranteed to initially be zero.
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// Set the thread-local value stored in slot 'slot' to
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void Set(void* value);
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bool initialized() const { return initialized_; }
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// The internals of this struct should be considered private.
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// A convenience wrapper around StaticSlot with a constructor. Can be used
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// as a member variable.
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class BASE_EXPORT Slot : public StaticSlot {
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// Calls StaticSlot::Initialize().
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explicit Slot(TLSDestructorFunc destructor = NULL);
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using StaticSlot::initialized_;
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using StaticSlot::slot_;
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DISALLOW_COPY_AND_ASSIGN(Slot);
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DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
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#endif // BASE_THREADING_THREAD_LOCAL_STORAGE_H_