Bug 180394 – CountingLock could avoid the isHeldBit check in tryOptimizedRead

• Status: REOPENED
• Component: Web Template Framework

[Filip Pizlo]

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.

[Filip Pizlo]

*** This bug has been marked as a duplicate of bug 180638 ***

[Filip Pizlo]

I shouldn't have duped this.