Common: Add dead thread support to WorkSema

MTGS supports having exceptions kill the thread and send their result back to a thread calling WaitGS...

common/Semaphore.cpp

@@ -28,6 +28,7 @@ void Threading::WorkSema::WaitForWork()
 	// RUNNING_0: Change state to SLEEPING, wake up thread if WAITING_EMPTY
 	// RUNNING_N: Change state to RUNNING_0 (and preserve WAITING_EMPTY flag)
 	s32 value = m_state.load(std::memory_order_relaxed);
+	pxAssert(!IsDead(value));
 	while (!m_state.compare_exchange_weak(value, NextStateWaitForWork(value), std::memory_order_acq_rel, std::memory_order_relaxed))
 		;
 	if (IsReadyForSleep(value))
@@ -43,6 +44,7 @@ void Threading::WorkSema::WaitForWork()
 void Threading::WorkSema::WaitForWorkWithSpin()
 {
 	s32 value = m_state.load(std::memory_order_relaxed);
+	pxAssert(!IsDead(value));
 	while (IsReadyForSleep(value))
 	{
 		if (m_state.compare_exchange_weak(value, STATE_SPINNING, std::memory_order_release, std::memory_order_relaxed))
@@ -70,28 +72,29 @@ void Threading::WorkSema::WaitForWorkWithSpin()
 	m_state.fetch_and(STATE_FLAG_WAITING_EMPTY, std::memory_order_acquire);
 }
 
-void Threading::WorkSema::WaitForEmpty()
+bool Threading::WorkSema::WaitForEmpty()
 {
 	s32 value = m_state.load(std::memory_order_acquire);
 	while (true)
 	{
 		if (value < 0)
-			return; // STATE_SLEEPING or STATE_SPINNING, queue is empty!
+			return !IsDead(value); // STATE_SLEEPING or STATE_SPINNING, queue is empty!
 		if (m_state.compare_exchange_weak(value, value | STATE_FLAG_WAITING_EMPTY, std::memory_order_relaxed, std::memory_order_acquire))
 			break;
 	}
 	pxAssertDev(!(value & STATE_FLAG_WAITING_EMPTY), "Multiple threads attempted to wait for empty (not currently supported)");
 	m_empty_sema.WaitWithYield();
+	return !IsDead(m_state.load(std::memory_order_relaxed));
 }
 
-void Threading::WorkSema::WaitForEmptyWithSpin()
+bool Threading::WorkSema::WaitForEmptyWithSpin()
 {
 	s32 value = m_state.load(std::memory_order_acquire);
 	u32 waited = 0;
 	while (true)
 	{
 		if (value < 0)
-			return; // STATE_SLEEPING or STATE_SPINNING, queue is empty!
+			return !IsDead(value); // STATE_SLEEPING or STATE_SPINNING, queue is empty!
 		if (waited > SPIN_TIME_NS && m_state.compare_exchange_weak(value, value | STATE_FLAG_WAITING_EMPTY, std::memory_order_relaxed, std::memory_order_acquire))
 			break;
 		waited += ShortSpin();
@@ -99,6 +102,19 @@ void Threading::WorkSema::WaitForEmptyWithSpin()
 	}
 	pxAssertDev(!(value & STATE_FLAG_WAITING_EMPTY), "Multiple threads attempted to wait for empty (not currently supported)");
 	m_empty_sema.WaitWithYield();
+	return !IsDead(m_state.load(std::memory_order_relaxed));
+}
+
+void Threading::WorkSema::Kill()
+{
+	s32 value = m_state.exchange(std::numeric_limits<s32>::min(), std::memory_order_release);
+	if (value & STATE_FLAG_WAITING_EMPTY)
+		m_empty_sema.Post();
+}
+
+void Threading::WorkSema::Reset()
+{
+	m_state = STATE_RUNNING_0;
 }
 
 #if !defined(__APPLE__) // macOS implementations are in DarwinSemaphore

common/Threading.h

@@ -273,6 +273,7 @@ namespace Threading
 		// So optimize states for fast NotifyOfWork
 		enum
 		{
+			/* Any <-2 state: STATE_DEAD: Thread has crashed and is awaiting revival */
 			STATE_SPINNING = -2, ///< Worker thread is spinning waiting for work
 			STATE_SLEEPING = -1, ///< Worker thread is sleeping on m_sema
 			STATE_RUNNING_0 = 0, ///< Worker thread is processing work, but no work has been added since it last checked for new work
@@ -280,6 +281,11 @@ namespace Threading
 			STATE_FLAG_WAITING_EMPTY = 1 << 30, ///< Flag to indicate that a thread is sleeping on m_empty_sema (can be applied to any STATE_RUNNING)
 		};
 
+		bool IsDead(s32 state)
+		{
+			return state < STATE_SPINNING;
+		}
+
 		bool IsReadyForSleep(s32 state)
 		{
 			s32 waiting_empty_cleared = state & (STATE_FLAG_WAITING_EMPTY - 1);
@@ -297,6 +303,7 @@ namespace Threading
 		void NotifyOfWork()
 		{
 			// State change:
+			// DEAD: Stay in DEAD (starting DEAD state is INT_MIN so we can assume we won't flip over to anything else)
 			// SPINNING: Change state to RUNNING.  Thread will notice and process the new data
 			// SLEEPING: Change state to RUNNING and wake worker.  Thread will wake up and process the new data.
 			// RUNNING_0: Change state to RUNNING_N.
@@ -310,10 +317,18 @@ namespace Threading
 		void WaitForWork();
 		/// Wait for work to be added to the queue, spinning for a bit before sleeping the thread
 		void WaitForWorkWithSpin();
-		/// Wait for the worker thread to finish processing all entries in the queue
-		void WaitForEmpty();
-		/// Wait for the worker thread to finish processing all entries in the queue, spinning a bit before sleeping the thread
-		void WaitForEmptyWithSpin();
+		/// Wait for the worker thread to finish processing all entries in the queue or die
+		/// Returns false if the thread is dead
+		bool WaitForEmpty();
+		/// Wait for the worker thread to finish processing all entries in the queue or die, spinning a bit before sleeping the thread
+		/// Returns false if the thread is dead
+		bool WaitForEmptyWithSpin();
+		/// Called by the worker thread to notify others of its death
+		/// Dead threads don't process work, and WaitForEmpty will return instantly even though there may be work in the queue
+		void Kill();
+		/// Reset the semaphore to the initial state
+		/// Should be called by the worker thread if it restarts after dying
+		void Reset();
 	};
 
 	class Semaphore