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Fix potential deadlock in timeline_semaphore sample #1531

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Fix potential deadlock in timeline_semaphore sample #1531

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16 changes: 12 additions & 4 deletions samples/extensions/timeline_semaphore/timeline_semaphore.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -262,10 +262,10 @@ void TimelineSemaphore::signal_next_frame()
}

// Waits for the timeline to reach MAX_STAGES for the current frame
void TimelineSemaphore::wait_for_next_frame()
void TimelineSemaphore::wait_for_next_frame(const uint64_t nextFrame)
{
// MAX_STAGES is used as it provides a boundary value between the stages of this frame and the next
const uint64_t waitValue = (timeline.frame + 1) * Timeline::MAX_STAGES;
const uint64_t waitValue = nextFrame * Timeline::MAX_STAGES;

VkSemaphoreWaitInfo waitInfo;
waitInfo.sType = VK_STRUCTURE_TYPE_SEMAPHORE_WAIT_INFO;
Expand Down Expand Up @@ -307,13 +307,17 @@ void TimelineSemaphore::do_compute_work()
submit_info.signalSemaphoreCount = 1;
submit_info.pSignalSemaphores = &timeline.semaphore;

// Define next frame prior to queue submit to prevent potential deadlock in wait_for_next_frame(). This can happen due to incorrect
// waitValue caused by signalling the main thread to advance the frame before completion of wait_for_next_frame() in worker threads
uint64_t nextFrame = timeline.frame + 1;

// If the threads are being killed, we need to skip the queue submission to allow the program to exit gracefully
if (compute_worker.alive)
{
VK_CHECK(vkQueueSubmit(compute.queue, 1, &submit_info, VK_NULL_HANDLE));
}

wait_for_next_frame();
wait_for_next_frame(nextFrame);
}
}

Expand Down Expand Up @@ -485,13 +489,17 @@ void TimelineSemaphore::do_graphics_work()
wait_on_timeline(Timeline::draw);
}

// Define next frame prior to queue submit to prevent potential deadlock in wait_for_next_frame(). This can happen due to incorrect
// waitValue caused by signalling the main thread to advance the frame before completion of wait_for_next_frame() in worker threads
uint64_t nextFrame = timeline.frame + 1;

// If the threads are being killed, we need to skip the queue submission to allow the program to exit gracefully
if (graphics_worker.alive)
{
VK_CHECK(vkQueueSubmit(graphics.queue, 1, &submit_info, VK_NULL_HANDLE));
}

wait_for_next_frame();
wait_for_next_frame(nextFrame);
}
}

Expand Down
4 changes: 2 additions & 2 deletions samples/extensions/timeline_semaphore/timeline_semaphore.h
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
/* Copyright (c) 2021-2025, Arm Limited and Contributors
/* Copyright (c) 2021-2026, Arm Limited and Contributors
*
* SPDX-License-Identifier: Apache-2.0
*
Expand Down Expand Up @@ -104,7 +104,7 @@ class TimelineSemaphore : public ApiVulkanSample
void signal_timeline(const Timeline::Stages stage);
void wait_on_timeline(const Timeline::Stages stage);
void signal_next_frame();
void wait_for_next_frame();
void wait_for_next_frame(const uint64_t nextFrame);
uint64_t get_timeline_stage_value(const Timeline::Stages stage);

// Compute Work
Expand Down
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