Fix deadlock in resizing from resetting the fence too early

charles-lunarg · charles-lunarg · commit 2c85b7759cfe · 2021-12-29T16:52:29.000-06:00
Because acquiring the swapchain image index may cause drawFrame to return early,
it was possible to cause the next vkWaitForFences to deadlock. By delaying fence
resetting till after acquiring, it prevents the deadlock.
diff --git a/code/17_swap_chain_recreation.cpp b/code/17_swap_chain_recreation.cpp
@@ -671,7 +671,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -683,6 +682,7 @@ class HelloTriangleApplication {
             throw std::runtime_error("failed to acquire swap chain image!");
         }
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/18_vertex_input.cpp b/code/18_vertex_input.cpp
@@ -716,7 +716,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -728,6 +727,7 @@ class HelloTriangleApplication {
             throw std::runtime_error("failed to acquire swap chain image!");
         }
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/19_vertex_buffer.cpp b/code/19_vertex_buffer.cpp
@@ -772,7 +772,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -784,6 +783,7 @@ class HelloTriangleApplication {
             throw std::runtime_error("failed to acquire swap chain image!");
         }
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/20_staging_buffer.cpp b/code/20_staging_buffer.cpp
@@ -820,7 +820,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -832,6 +831,7 @@ class HelloTriangleApplication {
             throw std::runtime_error("failed to acquire swap chain image!");
         }
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/21_index_buffer.cpp b/code/21_index_buffer.cpp
@@ -853,7 +853,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -865,6 +864,7 @@ class HelloTriangleApplication {
             throw std::runtime_error("failed to acquire swap chain image!");
         }
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/22_descriptor_layout.cpp b/code/22_descriptor_layout.cpp
@@ -922,7 +922,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -936,6 +935,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/23_descriptor_sets.cpp b/code/23_descriptor_sets.cpp
@@ -980,7 +980,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -994,6 +993,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/24_texture_image.cpp b/code/24_texture_image.cpp
@@ -1135,7 +1135,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1149,6 +1148,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/25_sampler.cpp b/code/25_sampler.cpp
@@ -1173,7 +1173,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1187,6 +1186,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/26_texture_mapping.cpp b/code/26_texture_mapping.cpp
@@ -1203,7 +1203,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1217,6 +1216,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/27_depth_buffering.cpp b/code/27_depth_buffering.cpp
@@ -1283,7 +1283,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1297,6 +1296,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/28_model_loading.cpp b/code/28_model_loading.cpp
@@ -1329,7 +1329,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1343,6 +1342,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/29_mipmapping.cpp b/code/29_mipmapping.cpp
@@ -1423,7 +1423,6 @@ class HelloTriangleApplication {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1437,6 +1436,7 @@ class HelloTriangleApplication {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/code/30_multisampling.cpp b/code/30_multisampling.cpp
@@ -1473,7 +1473,6 @@ VkSampleCountFlagBits getMaxUsableSampleCount() {
 
     void drawFrame() {
         vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
-        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         uint32_t imageIndex;
         VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
@@ -1487,6 +1486,7 @@ VkSampleCountFlagBits getMaxUsableSampleCount() {
 
         updateUniformBuffer(currentFrame);
 
+        vkResetFences(device, 1, &inFlightFences[currentFrame]);
 
         vkResetCommandBuffer(commandBuffers[currentFrame], /*VkCommandBufferResetFlagBits*/ 0);
         recordCommandBuffer(commandBuffers[currentFrame], imageIndex);
diff --git a/en/03_Drawing_a_triangle/04_Swap_chain_recreation.md b/en/03_Drawing_a_triangle/04_Swap_chain_recreation.md
@@ -165,6 +165,39 @@ The `vkQueuePresentKHR` function returns the same values with the same meaning.
 In this case we will also recreate the swap chain if it is suboptimal, because
 we want the best possible result.
 
+## Fixing a deadlock
+
+If we try to run the code now, it is possible to encounter a deadlock.
+Debugging the code, we find that the application reaches `vkWaitForFences` but
+never continues past it. This is because when `vkAcquireNextImageKHR` returns
+`VK_ERROR_OUT_OF_DATE_KHR`, we recreate the swapchain and then return from
+`drawFrame`. But before that happens, the current frame's fence was waited upon
+and reset. Since we return immediately, no work is submitted for execution and
+the fence will never be signaled, causing `vkWaitForFences` to halt forever.
+
+There is a simple fix thankfully. Delay resetting the fence until after we
+know for sure we will be submitting work with it. Thus, if we return early, the
+fence is still signaled and `vkWaitForFences` wont deadlock the next time we
+use the same fence object.
+
+The beginning of `drawFrame` should now look like this:
+```c++
+vkWaitForFences(device, 1, &inFlightFences[currentFrame], VK_TRUE, UINT64_MAX);
+
+uint32_t imageIndex;
+VkResult result = vkAcquireNextImageKHR(device, swapChain, UINT64_MAX, imageAvailableSemaphores[currentFrame], VK_NULL_HANDLE, &imageIndex);
+
+if (result == VK_ERROR_OUT_OF_DATE_KHR) {
+    recreateSwapChain();
+    return;
+} else if (result != VK_SUCCESS && result != VK_SUBOPTIMAL_KHR) {
+    throw std::runtime_error("failed to acquire swap chain image!");
+}
+
+// Only reset the fence if we are submitting work
+vkResetFences(device, 1, &inFlightFences[currentFrame]);
+```
+
 ## Handling resizes explicitly
 
 Although many drivers and platforms trigger `VK_ERROR_OUT_OF_DATE_KHR` automatically after a window resize, it is not guaranteed to happen. That's why we'll add some extra code to also handle resizes explicitly. First add a new member variable that flags that a resize has happened:
