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// Copyright 2012 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// emulates google3/base/once.h
//
// This header is intended to be included only by v8's internal code. Users
// should not use this directly.
//
// This is basically a portable version of pthread_once().
//
// This header declares:
// * A type called OnceType.
// * A macro V8_DECLARE_ONCE() which declares a (global) variable of type
// OnceType.
// * A function CallOnce(OnceType* once, void (*init_func)()).
// This function, when invoked multiple times given the same OnceType object,
// will invoke init_func on the first call only, and will make sure none of
// the calls return before that first call to init_func has finished.
//
// Additionally, the following features are supported:
// * A macro V8_ONCE_INIT which is expanded into the expression used to
// initialize a OnceType. This is only useful when clients embed a OnceType
// into a structure of their own and want to initialize it statically.
// * The user can provide a parameter which CallOnce() forwards to the
// user-provided function when it is called. Usage example:
// CallOnce(&my_once, &MyFunctionExpectingIntArgument, 10);
// * This implementation guarantees that OnceType is a POD (i.e. no static
// initializer generated).
//
// This implements a way to perform lazy initialization. It's more efficient
// than using mutexes as no lock is needed if initialization has already
// happened.
//
// Example usage:
// void Init();
// V8_DECLARE_ONCE(once_init);
//
// // Calls Init() exactly once.
// void InitOnce() {
// CallOnce(&once_init, &Init);
// }
//
// Note that if CallOnce() is called before main() has begun, it must
// only be called by the thread that will eventually call main() -- that is,
// the thread that performs dynamic initialization. In general this is a safe
// assumption since people don't usually construct threads before main() starts,
// but it is technically not guaranteed. Unfortunately, Win32 provides no way
// whatsoever to statically-initialize its synchronization primitives, so our
// only choice is to assume that dynamic initialization is single-threaded.
#ifndef V8_ONCE_H_
#define V8_ONCE_H_
#include "atomicops.h"
namespace v8 {
namespace internal {
typedef AtomicWord OnceType;
#define V8_ONCE_INIT 0
#define V8_DECLARE_ONCE(NAME) ::v8::internal::OnceType NAME
enum {
ONCE_STATE_UNINITIALIZED = 0,
ONCE_STATE_EXECUTING_FUNCTION = 1,
ONCE_STATE_DONE = 2
};
typedef void (*NoArgFunction)();
typedef void (*PointerArgFunction)(void* arg);
template <typename T>
struct OneArgFunction {
typedef void (*type)(T);
};
void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg);
inline void CallOnce(OnceType* once, NoArgFunction init_func) {
if (Acquire_Load(once) != ONCE_STATE_DONE) {
CallOnceImpl(once, reinterpret_cast<PointerArgFunction>(init_func), NULL);
}
}
template <typename Arg>
inline void CallOnce(OnceType* once,
typename OneArgFunction<Arg*>::type init_func, Arg* arg) {
if (Acquire_Load(once) != ONCE_STATE_DONE) {
CallOnceImpl(once, reinterpret_cast<PointerArgFunction>(init_func),
static_cast<void*>(arg));
}
}
} } // namespace v8::internal
#endif // V8_ONCE_H_