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Prevent WaitForCompletion shutdown deadlock. 

Adjust shutdown order to prevent potential deadlocks
when one thread calls Shutdown, and another calls WaitForCompletion.
This commit is contained in:
Scott Mansell 2023-02-05 17:17:16 +13:00
parent 9c012b09b3
commit 271ffde71d
1 changed files with 10 additions and 7 deletions
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17
Source/Core/Common/WorkQueueThread.h
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@ -93,6 +93,7 @@ public:
// Tells the worker to shut down when it's queue is empty // Tells the worker to shut down when it's queue is empty
// Blocks until the worker thread exits. // Blocks until the worker thread exits.
// If cancel is true, will Cancel before before telling the worker to exit // If cancel is true, will Cancel before before telling the worker to exit
// Otherwise, all currently queued items will complete before the worker exits
void Shutdown(bool cancel = false) void Shutdown(bool cancel = false)
{ {
{ {
@ -117,10 +118,13 @@ public:
void WaitForCompletion() void WaitForCompletion()
{ {
std::unique_lock lg(m_lock); std::unique_lock lg(m_lock);
if (m_idle) // Only check m_idle, we want this to work even another thread called Shutdown // don't check m_shutdown, because it gets set to request a shutdown, and we want to wait until
// after the shutdown completes.
// We also check m_cancelling, because we want to ensure the worker acknowledges our cancel.
if (m_idle && !m_cancelling.load())
return; return;
m_wait_cond_var.wait(lg, [&] { return m_idle; }); m_wait_cond_var.wait(lg, [&] { return m_idle && m_cancelling.load(); });
} }
// If the worker polls IsCanceling(), it can abort its work when Cancelling // If the worker polls IsCanceling(), it can abort its work when Cancelling
@ -134,17 +138,16 @@ private:
while (true) while (true)
{ {
std::unique_lock lg(m_lock); std::unique_lock lg(m_lock);
if (m_items.empty()) while (m_items.empty())
{ {
m_idle = true; m_idle = true;
m_cancelling = false; m_cancelling = false;
m_wait_cond_var.notify_all(); m_wait_cond_var.notify_all();
if (m_shutdown)
return;
m_worker_cond_var.wait( m_worker_cond_var.wait(
lg, [&] { return m_shutdown || m_cancelling.load() || !m_items.empty(); }); lg, [&] { return m_shutdown || m_cancelling.load() || !m_items.empty(); });
if (m_shutdown)
break;
continue;
} }
T item{std::move(m_items.front())}; T item{std::move(m_items.front())};
m_items.pop(); m_items.pop();