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[Impeller] Fix a race between SwapchainImplVK::Present and WaitForFence #49777

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Jan 16, 2024
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[Impeller] Fix a race between SwapchainImplVK::Present and WaitForFence #49777

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23 changes: 15 additions & 8 deletions impeller/renderer/backend/vulkan/swapchain_impl_vk.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@

#include "impeller/renderer/backend/vulkan/swapchain_impl_vk.h"

#include "fml/synchronization/count_down_latch.h"
#include "fml/synchronization/semaphore.h"
#include "impeller/base/validation.h"
#include "impeller/renderer/backend/vulkan/command_buffer_vk.h"
#include "impeller/renderer/backend/vulkan/command_encoder_vk.h"
Expand Down Expand Up @@ -32,12 +32,11 @@ struct FrameSynchronizer {
std::shared_ptr<CommandBuffer> final_cmd_buffer;
/// @brief A latch that is signaled _after_ a given swapchain image is
/// presented.
std::shared_ptr<fml::CountDownLatch> present_latch;
std::shared_ptr<fml::Semaphore> present_semaphore;
bool is_valid = false;

explicit FrameSynchronizer(const vk::Device& device) {
auto acquire_res = device.createFenceUnique(
vk::FenceCreateInfo{vk::FenceCreateFlagBits::eSignaled});
auto acquire_res = device.createFenceUnique({});
auto render_res = device.createSemaphoreUnique({});
auto present_res = device.createSemaphoreUnique({});
if (acquire_res.result != vk::Result::eSuccess ||
Expand All @@ -49,14 +48,21 @@ struct FrameSynchronizer {
acquire = std::move(acquire_res.value);
render_ready = std::move(render_res.value);
present_ready = std::move(present_res.value);
present_latch = std::make_shared<fml::CountDownLatch>(0u);
is_valid = true;
}

~FrameSynchronizer() = default;

bool WaitForFence(const vk::Device& device) {
present_latch->Wait();
if (!present_semaphore) {
return true;
}

if (!present_semaphore->Wait()) {
VALIDATION_LOG << "Present semaphore wait failed";
return false;
}
present_semaphore.reset();
if (auto result = device.waitForFences(
*acquire, // fence
true, // wait all
Expand All @@ -71,7 +77,6 @@ struct FrameSynchronizer {
VALIDATION_LOG << "Could not reset fence: " << vk::to_string(result);
return false;
}
present_latch = std::make_shared<fml::CountDownLatch>(1u);
return true;
}
};
Expand Down Expand Up @@ -505,7 +510,7 @@ bool SwapchainImplVK::Present(const std::shared_ptr<SwapchainImageVK>& image,
present_info.setWaitSemaphores(*sync->present_ready);

auto result = present_queue_.presentKHR(present_info);
sync->present_latch->CountDown();
sync->present_semaphore->Signal();

switch (result) {
case vk::Result::eErrorOutOfDateKHR:
Expand All @@ -529,6 +534,8 @@ bool SwapchainImplVK::Present(const std::shared_ptr<SwapchainImageVK>& image,
}
FML_UNREACHABLE();
};

sync->present_semaphore = std::make_shared<fml::Semaphore>(0u);
if (context.GetSyncPresentation()) {
task();
} else {
Expand Down