[Webkit-unassigned] [Bug 180394] New: CountingLock could avoid the isHeldBit check in tryOptimizedRead
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Mon Dec 4 21:41:38 PST 2017
https://bugs.webkit.org/show_bug.cgi?id=180394
Bug ID: 180394
Summary: CountingLock could avoid the isHeldBit check in
tryOptimizedRead
Product: WebKit
Version: WebKit Nightly Build
Hardware: All
OS: All
Status: NEW
Severity: Normal
Priority: P2
Component: Web Template Framework
Assignee: webkit-unassigned at lists.webkit.org
Reporter: fpizlo at apple.com
As the comment in CountingLock.h says:
// FIXME: We could eliminate this check, if we think it's OK to proceed with the optimistic read
// path even after knowing that it must fail. That's probably good for perf since we expect
// failure to be super rare. We would get rid of this check and instead of calling getCount below,
// we would return currentValue ^ mask. If the lock state was empty to begin with, the result
// would be a properly blessed count (both low bits set). If the lock state was anything else, we
// would get an improperly blessed count that would not possibly succeed in validate. We could
// actually do something like "return (currentValue | hasParkedBit) ^ isHeldBit", which would mean
// that we allow parked-but-not-held-locks through.
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