// Copyright (c) 2012 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 BASE_THREADING_THREAD_LOCAL_STORAGE_H_
#define BASE_THREADING_THREAD_LOCAL_STORAGE_H_
#include "base/base_export.h"
#include "base/basictypes.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 BASE_EXPORT 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 BASE_EXPORT 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 BASE_EXPORT 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 BASE_EXPORT Slot : public StaticSlot {
public:
// Calls StaticSlot::Initialize().
explicit Slot(TLSDestructorFunc destructor = NULL);
private:
using StaticSlot::initialized_;
using StaticSlot::slot_;
DISALLOW_COPY_AND_ASSIGN(Slot);
};
DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
};
} // namespace base
#endif // BASE_THREADING_THREAD_LOCAL_STORAGE_H_