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/*
* Copyright (C) 2014, 2015 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. 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.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 APPLE INC. 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.
*/
#ifndef AsyncTask_h
#define AsyncTask_h
#include "BAssert.h"
#include "Inline.h"
#include "Mutex.h"
#include <atomic>
#include <condition_variable>
#include <thread>
namespace bmalloc {
template<typename Object, typename Function>
class AsyncTask {
public:
AsyncTask(Object&, const Function&);
~AsyncTask();
void run();
private:
enum State { Sleeping, Running, RunRequested };
void runSlowCase();
static void threadEntryPoint(AsyncTask*);
void threadRunLoop();
std::atomic<State> m_state;
Mutex m_conditionMutex;
std::condition_variable_any m_condition;
std::thread m_thread;
Object& m_object;
Function m_function;
};
template<typename Object, typename Function>
AsyncTask<Object, Function>::AsyncTask(Object& object, const Function& function)
: m_state(Running)
, m_condition()
, m_thread(std::thread(&AsyncTask::threadEntryPoint, this))
, m_object(object)
, m_function(function)
{
}
template<typename Object, typename Function>
AsyncTask<Object, Function>::~AsyncTask()
{
// We'd like to mark our destructor deleted but C++ won't allow it because
// we are an automatic member of Heap.
RELEASE_BASSERT(0);
}
template<typename Object, typename Function>
inline void AsyncTask<Object, Function>::run()
{
if (m_state == RunRequested)
return;
runSlowCase();
}
template<typename Object, typename Function>
NO_INLINE void AsyncTask<Object, Function>::runSlowCase()
{
State oldState = m_state.exchange(RunRequested);
if (oldState == RunRequested || oldState == Running)
return;
BASSERT(oldState == Sleeping);
std::lock_guard<Mutex> lock(m_conditionMutex);
m_condition.notify_all();
}
template<typename Object, typename Function>
void AsyncTask<Object, Function>::threadEntryPoint(AsyncTask* asyncTask)
{
asyncTask->threadRunLoop();
}
template<typename Object, typename Function>
void AsyncTask<Object, Function>::threadRunLoop()
{
// This loop ratchets downward from most active to least active state. While
// we ratchet downward, any other thread may reset our state.
// We require any state change while we are sleeping to signal to our
// condition variable and wake us up.
while (1) {
State expectedState = RunRequested;
if (m_state.compare_exchange_weak(expectedState, Running))
(m_object.*m_function)();
expectedState = Running;
if (m_state.compare_exchange_weak(expectedState, Sleeping)) {
std::unique_lock<Mutex> lock(m_conditionMutex);
m_condition.wait(lock, [&]() { return m_state != Sleeping; });
}
}
}
} // namespace bmalloc
#endif // AsyncTask_h
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