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On execution media element load algorithm https://html.spec.whatwg.org/multipage/media.html#media-element-load-algorithm we can observe race condition between parallel running fetch requests: R1: (media element) initial request (see "resource_fetch_algorithm" function) R2: (gstreamer) duration "seek-data" request (see PlayerEvent::SeekData) R3: (gstreamer) continue on last interrupted time "seek-data" request At time there are only one current fetch context for media element but because resource fetch and cancellation are async operations need to identify (by request id) and skip processing outdated fetch request (fetch listener callbacks). Async load in background sequence (stream content length = 2757913): ``` R1 (seek-offset=0): [------------------------------X] R2 (seek-offset=2757866): [---------Y] AS-****-+++-AE R3 (seek-offset=98304): [----------------Z] BS-****-+++BE R1 (seek-offset=0): [------X] R2 (seek-offset=2757866): [--------Y] (discarded data) AS-****---------+++-AE - A*/B* performed seeks (*** seek lock, +++ flush buffer queue + reset EOS) (on Gstreamer streaming thread) - X/Y/Z "end-of-stream" events from fetch requests (on Servo script thread) ``` All incoming input data from different requests are mixed and pushed to active media player, plus abnormal behaviour due to intermixed X/Y/Z "end-of-stream" events. To handle it properly we will unblock seek lock on "seek-data" event (on script thread) as soon as possible (GStreamer will be able to flush buffer queue and reset EOS state) and introduce buffered data source to delay pushing input data/EOS event until media player will be actually ready. Testing: Improvements to the following tests: - /html/canvas/element/manual/imagebitmap/createImageBitmap-origin.sub.html - /html/semantics/embedded-content/the-canvas-element/security.pattern.fillStyle.sub.html Fixes: https://github.com/servo/servo/issues/31931 Fixes: https://github.com/servo/servo/issues/36989 Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com> |
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