[Webkit-unassigned] [Bug 149509] New: Parallel copy phase synchronization should be simplified

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=149509

            Bug ID: 149509
           Summary: Parallel copy phase synchronization should be
                    simplified
    Classification: Unclassified
           Product: WebKit
           Version: Other
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: fpizlo at apple.com

Currently, we don't wait for the copy phase to finish after we have already finished it and the copied space is unable to handle any more copy tasks joining.  This means that we have weird hacks to ensure that things don't go to badly when a copy thread starts copying after we already finished copying.  It also meant two separate mechanisms for waiting for copying threads to finish - one mechanism in the Heap phase logic and another in the CopiedSpace::doneCopying() method.

We can get rid of a lot of the weirdness by just having a sound shutdown sequence:

1) Threads concur on when there is no more work. We already have this; once Heap::getNextBlocksToCopy() returns no work in any thread, it will also return no work in any other thread that asks for work.
2) Main thread waits for the threads to not be copying anymore.
3) Do whatever we need to do after copying finishes.

Currently, we do (3) before (2) and so we have weird problems.

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