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Fix race condition when notifying workers of new tasks #6

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Fix race condition when notifying workers of new tasks #6

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77 changes: 43 additions & 34 deletions src/ThreadWorker.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -41,8 +41,8 @@ namespace execq
void shutdown();

private:
std::atomic_bool m_shouldQuit { false };
std::atomic_bool m_checkNextTask { false };
bool m_shouldQuit = false;
bool m_checkNextTask = false;
std::condition_variable m_condition;
std::mutex m_mutex;
std::unique_ptr<std::thread> m_thread;
Expand Down Expand Up @@ -82,58 +82,67 @@ execq::impl::ThreadWorker::~ThreadWorker()

bool execq::impl::ThreadWorker::notifyWorker()
{
std::lock_guard<std::mutex> lock(m_mutex);
if (m_checkNextTask)
{
return false;
}

m_checkNextTask = true;
if (!m_thread)
{
m_thread.reset(new std::thread(&ThreadWorker::threadMain, this));
std::lock_guard<std::mutex> lock(m_mutex);
if (m_checkNextTask)
{
return false;
}

m_checkNextTask = true;
if (!m_thread)
{
m_thread.reset(new std::thread(&ThreadWorker::threadMain, this));
}
}

m_condition.notify_one();

return true;
}

void execq::impl::ThreadWorker::shutdown()
{
std::lock_guard<std::mutex> lock(m_mutex);
m_shouldQuit = true;
{
std::lock_guard<std::mutex> lock(m_mutex);
m_shouldQuit = true;
}
m_condition.notify_one();
}

void execq::impl::ThreadWorker::threadMain()
{
while (true)
{
if (m_shouldQuit)
{
break;
}

m_checkNextTask = false;
Task task = m_provider.nextTask();
if (task.valid())
{
task();
continue;
std::unique_lock<std::mutex> lock(m_mutex);
while (!m_checkNextTask && !m_shouldQuit)
{
m_condition.wait(lock);
}

if (m_shouldQuit)
{
break;
}
}

std::unique_lock<std::mutex> lock(m_mutex);
if (m_checkNextTask)

while (true)
{
continue;
Task task = m_provider.nextTask();
if (task.valid())
{
task();
}
else
{
break;
}
}

if (m_shouldQuit)

{
break;
std::lock_guard<std::mutex> lock(m_mutex);
m_checkNextTask = false;
}

m_condition.wait(lock);
}
}