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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_SEMAPHORE_H_
#define V8_BASE_PLATFORM_SEMAPHORE_H_
#include "src/base/base-export.h"
#include "src/base/lazy-instance.h"
#if V8_OS_WIN
#include "src/base/win32-headers.h"
#endif
#if V8_OS_MACOSX
#include <dispatch/dispatch.h>
#elif V8_OS_POSIX
#include <semaphore.h>
#endif
#if V8_OS_STARBOARD
#include "starboard/common/semaphore.h"
#endif
namespace v8 {
namespace base {
// Forward declarations.
class TimeDelta;
// ----------------------------------------------------------------------------
// Semaphore
//
// A semaphore object is a synchronization object that maintains a count. The
// count is decremented each time a thread completes a wait for the semaphore
// object and incremented each time a thread signals the semaphore. When the
// count reaches zero, threads waiting for the semaphore blocks until the
// count becomes non-zero.
class V8_BASE_EXPORT Semaphore final {
public:
explicit Semaphore(int count);
Semaphore(const Semaphore&) = delete;
Semaphore& operator=(const Semaphore&) = delete;
~Semaphore();
// Increments the semaphore counter.
void Signal();
// Decrements the semaphore counter if it is positive, or blocks until it
// becomes positive and then decrements the counter.
void Wait();
// Like Wait() but returns after rel_time time has passed. If the timeout
// happens the return value is false and the counter is unchanged. Otherwise
// the semaphore counter is decremented and true is returned.
bool WaitFor(const TimeDelta& rel_time) V8_WARN_UNUSED_RESULT;
#if V8_OS_MACOSX
using NativeHandle = dispatch_semaphore_t;
#elif V8_OS_POSIX
using NativeHandle = sem_t;
#elif V8_OS_WIN
using NativeHandle = HANDLE;
#elif V8_OS_STARBOARD
using NativeHandle = starboard::Semaphore;
#endif
NativeHandle& native_handle() {
return native_handle_;
}
const NativeHandle& native_handle() const {
return native_handle_;
}
private:
NativeHandle native_handle_;
};
// POD Semaphore initialized lazily (i.e. the first time Pointer() is called).
// Usage:
// // The following semaphore starts at 0.
// static LazySemaphore<0>::type my_semaphore = LAZY_SEMAPHORE_INITIALIZER;
//
// void my_function() {
// // Do something with my_semaphore.Pointer().
// }
//
template <int N>
struct CreateSemaphoreTrait {
static Semaphore* Create() {
return new Semaphore(N);
}
};
template <int N>
struct LazySemaphore {
using typename LazyDynamicInstance<Semaphore, CreateSemaphoreTrait<N>,
ThreadSafeInitOnceTrait>::type;
};
#define LAZY_SEMAPHORE_INITIALIZER LAZY_DYNAMIC_INSTANCE_INITIALIZER
} // namespace base
} // namespace v8
#endif // V8_BASE_PLATFORM_SEMAPHORE_H_
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