LayerTreeHost construction race condition fix #1517
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This fixes race condition happening during LayerTreeHost construction The problem is seen with Process Swap On Cross-Site Navigation enabled. The race condition happens during LayerTreeHost construction. The scenario is: - on THREAD_A (main thread) LayerTreeHost constructor starts; it first creates AcceleratedSurfaceLibWPE, then ThreadedCompositor - ThreadedCompositor constructor creates run loop (m_compositingRunLoop), executes & synchronously waits for initialization task on the run loop. This task calls m_client.nativeSurfaceHandleForCompositing() on THREAD_B (compositing thread) and this ends up calling AcceleratedSurfaceLibWPE::initialize() Note: at this point, LayerTreeHost constructor hasn't set LayerTreeHost::m_compositor value yet - still on THREAD_B, AcceleratedSurfaceLibWPE::initialize connects backend events (wpe_renderer_backend_egl_target_set_client). And sometimes we get first frame_complete event quickly (I've only seen that with PSON enabled). The handler for frame_complete is already registered, and it calls surface.m_client.frameComplete(). And LayerTreeHost::frameComplete() calls 'm_compositor->frameComplete()', but this requires THREAD_A to already have set m_compositor value in ThreadedCompositor constructor, and some memory barrier between threads A & B. So m_compositor can be null here, which causes SIGSEGV. The proposed fix introduces additional 'LayerTreeHost::initialized' atomic bool which enables to prevent this case and adds memory barrier (via atomic_bool load/store) between threads.
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associated RDK ticket: https://jira.rdkcentral.com/jira/browse/RDKDEV-1128 |
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This fixes race condition happening during LayerTreeHost construction The problem is seen with Process Swap On Cross-Site Navigation enabled.
The race condition happens during LayerTreeHost construction. The scenario is:
on THREAD_A (main thread) LayerTreeHost constructor starts; it first creates AcceleratedSurfaceLibWPE, then ThreadedCompositor
ThreadedCompositor constructor creates run loop (m_compositingRunLoop), executes & synchronously waits for initialization task on the run loop. This task calls m_client.nativeSurfaceHandleForCompositing() on THREAD_B (compositing thread) and this ends up calling AcceleratedSurfaceLibWPE::initialize() Note: at this point, LayerTreeHost constructor hasn't set LayerTreeHost::m_compositor value yet
still on THREAD_B, AcceleratedSurfaceLibWPE::initialize connects backend events (wpe_renderer_backend_egl_target_set_client). And sometimes we get first frame_complete event quickly (I've only seen that with PSON enabled). The handler for frame_complete is already registered, and it calls surface.m_client.frameComplete(). And LayerTreeHost::frameComplete() calls 'm_compositor->frameComplete()', but this requires THREAD_A to already have set m_compositor value in ThreadedCompositor constructor, and some memory barrier between threads A & B. So m_compositor can be null here, which causes SIGSEGV.
The proposed fix introduces additional 'LayerTreeHost::initialized' atomic bool which enables to prevent this case and adds memory barrier (via atomic_bool load/store) between threads.
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