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// Copyright 2013 the V8 project 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 V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
#define V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
#include "src/base/base-export.h"
#include "src/base/lazy-instance.h"
#include "src/base/platform/mutex.h"
namespace v8 {
namespace base {
// Forward declarations.
class ConditionVariableEvent;
class TimeDelta;
// -----------------------------------------------------------------------------
// ConditionVariable
//
// This class is a synchronization primitive that can be used to block a thread,
// or multiple threads at the same time, until:
// - a notification is received from another thread,
// - a timeout expires, or
// - a spurious wakeup occurs
// Any thread that intends to wait on a ConditionVariable has to acquire a lock
// on a Mutex first. The |Wait()| and |WaitFor()| operations atomically release
// the mutex and suspend the execution of the calling thread. When the condition
// variable is notified, the thread is awakened, and the mutex is reacquired.
class V8_BASE_EXPORT ConditionVariable final {
public:
ConditionVariable();
~ConditionVariable();
// If any threads are waiting on this condition variable, calling
// |NotifyOne()| unblocks one of the waiting threads.
void NotifyOne();
// Unblocks all threads currently waiting for this condition variable.
void NotifyAll();
// |Wait()| causes the calling thread to block until the condition variable is
// notified or a spurious wakeup occurs. Atomically releases the mutex, blocks
// the current executing thread, and adds it to the list of threads waiting on
// this condition variable. The thread will be unblocked when |NotifyAll()| or
// |NotifyOne()| is executed. It may also be unblocked spuriously. When
// unblocked, regardless of the reason, the lock on the mutex is reacquired
// and |Wait()| exits.
void Wait(Mutex* mutex);
// Atomically releases the mutex, blocks the current executing thread, and
// adds it to the list of threads waiting on this condition variable. The
// thread will be unblocked when |NotifyAll()| or |NotifyOne()| is executed,
// or when the relative timeout |rel_time| expires. It may also be unblocked
// spuriously. When unblocked, regardless of the reason, the lock on the mutex
// is reacquired and |WaitFor()| exits. Returns true if the condition variable
// was notified prior to the timeout.
bool WaitFor(Mutex* mutex, const TimeDelta& rel_time) V8_WARN_UNUSED_RESULT;
// The implementation-defined native handle type.
#if V8_OS_POSIX
using NativeHandle = pthread_cond_t;
#elif V8_OS_WIN
using NativeHandle = CONDITION_VARIABLE;
#endif
NativeHandle& native_handle() {
return native_handle_;
}
const NativeHandle& native_handle() const {
return native_handle_;
}
private:
NativeHandle native_handle_;
DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
};
// POD ConditionVariable initialized lazily (i.e. the first time Pointer() is
// called).
// Usage:
// static LazyConditionVariable my_condvar =
// LAZY_CONDITION_VARIABLE_INITIALIZER;
//
// void my_function() {
// MutexGuard lock_guard(&my_mutex);
// my_condvar.Pointer()->Wait(&my_mutex);
// }
using LazyConditionVariable =
LazyStaticInstance<ConditionVariable,
DefaultConstructTrait<ConditionVariable>,
ThreadSafeInitOnceTrait>::type;
#define LAZY_CONDITION_VARIABLE_INITIALIZER LAZY_STATIC_INSTANCE_INITIALIZER
} // namespace base
} // namespace v8
#endif // V8_BASE_PLATFORM_CONDITION_VARIABLE_H_
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