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Commit fb3beed5 authored by Dominik Laskowski's avatar Dominik Laskowski
Browse files

SF: Do not block the main thread on screenshots 

The destructor of the future returned by std::async blocks until the
async operation completes, which defeats the purpose of spinning up
a thread to wait on the RenderEngine future. Instead, defer the wait
back to the Binder thread.

Bug: 232436803
Test: Perfetto
Change-Id: I7260002741a0174d8960894d490079757dc4bb5b
parent bd55592a

services/surfaceflinger/SurfaceFlinger.cpp

+11 −14
Original line number Diff line number Diff line
@@ -6624,24 +6624,21 @@ ftl::SharedFuture<FenceResult> SurfaceFlinger::captureScreenCommon( 
        });



        if (captureListener) {

            // TODO: The future returned by std::async blocks the main thread. Return a chain of

            // futures to the Binder thread instead.

            std::async([=]() mutable {

                ATRACE_NAME("captureListener is nonnull!");

                auto fenceResult = renderFuture.get();

            // Defer blocking on renderFuture back to the Binder thread.

            return ftl::Future(std::move(renderFuture))

                    .then([captureListener, captureResults = std::move(captureResults)](

                                  FenceResult fenceResult) mutable -> FenceResult {

                        // TODO(b/232535621): Change ScreenCaptureResults to store a FenceResult.

                        captureResults.result = fenceStatus(fenceResult);

                        captureResults.fence = std::move(fenceResult).value_or(Fence::NO_FENCE);

                        captureListener->onScreenCaptureCompleted(captureResults);

            });

                        return base::unexpected(NO_ERROR);

                    })

                    .share();

        }

        return renderFuture;

    });



    if (captureListener) {

        return ftl::yield<FenceResult>(base::unexpected(NO_ERROR)).share();

    }



    // Flatten nested futures.

    auto chain = ftl::Future(std::move(future)).then([](ftl::SharedFuture<FenceResult> future) {

        return future;