Parallel copy phase synchronization should be simplified
https://bugs.webkit.org/show_bug.cgi?id=149509
Reviewed by Mark Lam.
Before this change, we didn't wait for the copy phase to finish before starting to do things to
copied space that presumed that copying was done. Copied space would "detect" that nobody was
copying anymore by waiting for all loaned blocks to be returned. But that would succeed if some
thread had not yet started copying. So, we had weird hacks to ensure that a block was loaned
before any threads started. It also meant that we had 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. This just changes the code to do
(3) after (2), and so we can get rid of the synchronization in doneCopying() and we can safely
call startCopying() inside GCThread. This also means that we don't need to make CopyVisitor a
property of GCThread. Instead, GCThread just instantiates its own CopyVisitor when it needs to.
* heap/CopiedSpace.cpp:
(JSC::CopiedSpace::doneCopying):
* heap/GCThread.cpp:
(JSC::GCThread::GCThread):
(JSC::GCThread::slotVisitor):
(JSC::GCThread::waitForNextPhase):
(JSC::GCThread::gcThreadMain):
(JSC::GCThread::copyVisitor): Deleted.
* heap/GCThread.h:
* heap/Heap.cpp:
(JSC::Heap::Heap):
(JSC::Heap::copyBackingStores):
(JSC::Heap::gatherStackRoots):
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@190185 268f45cc-cd09-0410-ab3c-d52691b4dbfc
7 files changed
