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Fix shared lock file FD leak.

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This fixes behavior in this situation:

	l1 <- lockShared Nothing "lck"
	l2 <- lockShared Nothing "lck"
	dropLock l1
	dropLock l2

Before, the lock was dropped upon the second dropLock call, but the fd
remained open, and would never be closed while the program was running.

Fixed by a rather round-about method, but it should work well enough.

It would have been simpler to open open the shared lock once, and not open
it again in the second call to lockShared. But, that's difficult to do
atomically.

This also affects Windows and PID locks, not just posix locks.

In the case of pid locks, multiple calls to waitLock within the same
process are allowed because the side lock is locked using a posix lock,
and so multiple exclusive locks can be taken in the same process. So,
this change fixes a similar problem with pid locks.

	l1 <- waitLock (Seconds 1) "lck"
	l2 <- waitLock (Seconds 1) "lck"
	dropLock l1
	dropLock l2

Here the l2 side lock fd remained open but not locked,
although the pid lock file was removed. After this change, the second
dropLock will close both fds to the side lock, and delete the pidlock.
This commit is contained in:
Joey Hess 2016-03-01 15:31:39 -04:00
parent 26c499492f
commit 3334130368
Failed to extract signature
7 changed files with 88 additions and 64 deletions
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12
Utility/LockPool/PidLock.hs
View file

@ -32,17 +32,17 @@ import Prelude
-- Takes a pid lock, blocking until the lock is available or the timeout.
waitLock :: Seconds -> LockFile -> IO LockHandle
waitLock timeout file = makeLockHandle
waitLock timeout file = makeLockHandle P.lockPool file
-- LockShared for STM lock, because a pid lock can be the top-level
-- lock with various other STM level locks gated behind it.
(P.waitTakeLock P.lockPool file LockShared)
(mk <$> F.waitLock timeout file)
(\p f -> P.waitTakeLock p f LockShared)
(\f -> mk <$> F.waitLock timeout f)
-- Tries to take a pid lock, but does not block.
tryLock :: LockFile -> IO (Maybe LockHandle)
tryLock file = tryMakeLockHandle
(P.tryTakeLock P.lockPool file LockShared)
(fmap mk <$> F.tryLock file)
tryLock file = tryMakeLockHandle P.lockPool file
(\p f -> P.tryTakeLock p f LockShared)
(\f -> fmap mk <$> F.tryLock f)
checkLocked :: LockFile -> IO (Maybe Bool)
checkLocked file = P.getLockStatus P.lockPool file