[Webkit-unassigned] [Bug 137162] New: Web Replay: Playback position updates should be sent before the next event loop input is dispatched

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=137162

           Summary: Web Replay: Playback position updates should be sent
                    before the next event loop input is dispatched
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Web Inspector
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: burg at cs.washington.edu
                CC: timothy at apple.com, joepeck at webkit.org,
                    webkit-bug-importer at group.apple.com,
                    graouts at webkit.org
            Blocks: 136292


To drive updates to playback position in the UI we send ReplayPosition coordinates as the backend dispatches inputs.
However, right now the semantics of being at a ReplayPosition is currently muddy. The update is currently sent *after*
the input at the offset is dispatched. This leads to unexpected results if the debugger pauses while the input is dispatched,
and the frontend has a stale playback position when the debugger pauses.

What it should mean is that for ReplayPosition(segmentOffset=n, inputOffset=m), the backend is about to dispatch input m,
but has not yet begun to do so. Thus, any subsequent page execution events (profiling, debugger pauses, etc) are caused by
m being dispatched.

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