Improve locking for batched mouse and gamepad sensor events

By unlocking the mutex before we enqueue the new entry, we can avoid the input thread immediately contending on the mutex after the new item wakes it up.

src/InputStream.c

@@ -724,9 +724,14 @@ int LiSendMouseMoveEvent(short deltaX, short deltaY) {
 
     // Queue a packet holder if this is the only pending relative mouse event
     if (!currentRelativeMouseState.dirty) {
+        // Set the dirty flag to claim ownership of inserting the packet holder
+        // and unlock to allow other threads to enqueue or process input.
+        currentRelativeMouseState.dirty = true;
+        PltUnlockMutex(&batchedInputMutex);
+
         holder = allocatePacketHolder(0);
         if (holder == NULL) {
-            PltUnlockMutex(&batchedInputMutex);
+            currentRelativeMouseState.dirty = false;
             return -1;
         }
 
@@ -747,22 +752,21 @@ int LiSendMouseMoveEvent(short deltaX, short deltaY) {
         // Remaining fields are set in the input thread based on the latest currentRelativeMouseState values
 
         err = LbqOfferQueueItem(&packetQueue, holder, &holder->entry);
-        if (err == LBQ_SUCCESS) {
+        if (err != LBQ_SUCCESS) {
-            currentRelativeMouseState.dirty = true;
-        }
-        else {
             LC_ASSERT(err == LBQ_BOUND_EXCEEDED);
             Limelog("Input queue reached maximum size limit\n");
             freePacketHolder(holder);
+
+            // We weren't able to insert the entry, so let the next call try again
+            currentRelativeMouseState.dirty = false;
         }
     }
     else {
         // There's already a packet holder queued to send this event
+        PltUnlockMutex(&batchedInputMutex);
         err = 0;
     }
 
-    PltUnlockMutex(&batchedInputMutex);
-
     return err;
 }
 
@@ -785,9 +789,14 @@ int LiSendMousePositionEvent(short x, short y, short referenceWidth, short refer
 
     // Queue a packet holder if this is the only pending absolute mouse event
     if (!currentAbsoluteMouseState.dirty) {
+        // Set the dirty flag to claim ownership of inserting the packet holder
+        // and unlock to allow other threads to enqueue or process input.
+        currentAbsoluteMouseState.dirty = true;
+        PltUnlockMutex(&batchedInputMutex);
+
         holder = allocatePacketHolder(0);
         if (holder == NULL) {
-            PltUnlockMutex(&batchedInputMutex);
+            currentAbsoluteMouseState.dirty = false;
             return -1;
         }
 
@@ -803,22 +812,21 @@ int LiSendMousePositionEvent(short x, short y, short referenceWidth, short refer
         // Remaining fields are set in the input thread based on the latest currentAbsoluteMouseState values
 
         err = LbqOfferQueueItem(&packetQueue, holder, &holder->entry);
-        if (err == LBQ_SUCCESS) {
+        if (err != LBQ_SUCCESS) {
-            currentAbsoluteMouseState.dirty = true;
-        }
-        else {
             LC_ASSERT(err == LBQ_BOUND_EXCEEDED);
             Limelog("Input queue reached maximum size limit\n");
             freePacketHolder(holder);
+
+            // We weren't able to insert the entry, so let the next call try again
+            currentAbsoluteMouseState.dirty = false;
         }
     }
     else {
         // There's already a packet holder queued to send this event
+        PltUnlockMutex(&batchedInputMutex);
         err = 0;
     }
 
-    PltUnlockMutex(&batchedInputMutex);
-
     // This is not thread safe, but it's not a big deal because callers that want to
     // use LiSendRelativeMotionAsMousePositionEvent() must not mix these function
     // without synchronization (otherwise the state of the cursor on the host is
@@ -1536,9 +1544,14 @@ int LiSendControllerMotionEvent(uint8_t controllerNumber, uint8_t motionType, fl
 
     // Queue a packet holder if this is the only pending sensor event
     if (!currentGamepadSensorState[controllerNumber][motionType - 1].dirty) {
+        // Set the dirty flag to claim ownership of inserting the packet holder
+        // and unlock to allow other threads to enqueue or process input.
+        currentGamepadSensorState[controllerNumber][motionType - 1].dirty = true;
+        PltUnlockMutex(&batchedInputMutex);
+
         holder = allocatePacketHolder(0);
         if (holder == NULL) {
-            PltUnlockMutex(&batchedInputMutex);
+            currentGamepadSensorState[controllerNumber][motionType - 1].dirty = false;
             return -1;
         }
 
@@ -1554,22 +1567,21 @@ int LiSendControllerMotionEvent(uint8_t controllerNumber, uint8_t motionType, fl
         // Remaining fields are set in the input thread based on the latest currentGamepadSensorState values
 
         err = LbqOfferQueueItem(&packetQueue, holder, &holder->entry);
-        if (err == LBQ_SUCCESS) {
+        if (err != LBQ_SUCCESS) {
-            currentGamepadSensorState[controllerNumber][motionType - 1].dirty = true;
-        }
-        else {
             LC_ASSERT(err == LBQ_BOUND_EXCEEDED);
             Limelog("Input queue reached maximum size limit\n");
             freePacketHolder(holder);
+
+            // We weren't able to insert the entry, so let the next call try again
+            currentGamepadSensorState[controllerNumber][motionType - 1].dirty = false;
         }
     }
     else {
         // There's already a packet holder queued to send this event
+        PltUnlockMutex(&batchedInputMutex);
         err = 0;
     }
 
-    PltUnlockMutex(&batchedInputMutex);
-
     return err;
 }