[Webkit-unassigned] [Bug 85191] New: MediaStream should not be an ActiveDOMObject

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=85191

           Summary: MediaStream should not be an ActiveDOMObject
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: adam.bergkvist at ericsson.com
                CC: abarth at webkit.org, per-erik.brodin at ericsson.com,
                    tommyw at google.com


The model with MediaStreamDescriptor and MediaStream (and LocalMediaStream) allows the JavaScript objects (MediaStream and LocalMediaStream) to be cleaned up while the MediaStreamDescriptor lives on to manage the stream in the platform. This happens for example when a URL is created to represent a MediaStream (using createObjectURL). The MediaStreamDescriptor is put into the MediaStreamRegistry and even though the MediaStream object is lost, the URL still works since the descriptor is kept in the registry.

The changes introduced in r113460 turned MediaStream and LocalMediaStream into ActiveDOMObjects. On page reload, LocalMediaStream calls MediaStreamCenter::didStopLocalMediaStream() via its ActiveDOMObject::stop() method. However, when a page reload occurs, the LocalMediaStream object may have been cleaned up already. As a result, the behavior is different since MediaStreamCenter::didStopLocalMediaStream() is called when the LocalMediaStream object exists, but not if only the MediaStreamDescriptor is left. One way to make the behavior consistent would be to call MediaStreamCenter::didStopLocalMediaStream() when the descriptor is cleaned up, cause then we wouldn't be dependent on the LocalMediaStream object being alive. However, calling MediaStreamCenter::didStopLocalMediaStream() might not be the correct thing to do when all references to the descriptor are lost since there can be MediaStream objects constructed from the tracks of the LocalMediaStream that should continue to w
 ork. MediaStreamCenter::didStopLocalMediaStream() was intended for LocalMediaStream.stop() which is used to revoke access to devices; that should not necessarily happen when the descriptor of a LocalMediaStream is cleaned up. If it's necessary for some ports to signal to the platform that a MediaStreamDescriptor is cleaned up, then I would suggest adding a new function, willDestroyMediaStreamDescriptor(), to the MediaStreamCenter interface.

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