fine-grained locking when annex.pidlock is enabled
This locking has been missing from the beginning of annex.pidlock. It used to be possble, when two threads are doing conflicting things, for both to run at the same time despite using locking. Seems likely that nothing actually had a problem, but it was possible, and this eliminates that possible source of failure. Sponsored-by: Dartmouth College's Datalad project
This commit is contained in:
Joey Hess
parent
a5fcc03595
commit
e5ca67ea1c
6 changed files with 121 additions and 61 deletions
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@ -1,7 +1,7 @@
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{- Wraps Utility.LockPool, making pid locks be used when git-annex is so
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- configured.
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-
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- Copyright 2015-2020 Joey Hess <id@joeyh.name>
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- Copyright 2015-2021 Joey Hess <id@joeyh.name>
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-
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- Licensed under the GNU AGPL version 3 or higher.
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-}
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@ -28,7 +28,7 @@ import qualified Utility.LockPool.PidLock as Pid
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import qualified Utility.LockPool.LockHandle as H
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import Utility.LockPool.LockHandle (LockHandle, dropLock)
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import Utility.LockFile.Posix (openLockFile)
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import Utility.LockPool.STM (LockFile)
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import Utility.LockPool.STM (LockFile, LockMode(..))
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import Utility.LockFile.LockStatus
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import Config (pidLockFile)
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import Messages (warning)
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@ -36,16 +36,16 @@ import Messages (warning)
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import System.Posix
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lockShared :: Maybe FileMode -> LockFile -> Annex LockHandle
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lockShared m f = pidLock m f $ Posix.lockShared m f
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lockShared m f = pidLock m f LockShared $ Posix.lockShared m f
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lockExclusive :: Maybe FileMode -> LockFile -> Annex LockHandle
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lockExclusive m f = pidLock m f $ Posix.lockExclusive m f
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lockExclusive m f = pidLock m f LockExclusive $ Posix.lockExclusive m f
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tryLockShared :: Maybe FileMode -> LockFile -> Annex (Maybe LockHandle)
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tryLockShared m f = tryPidLock m f $ Posix.tryLockShared m f
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tryLockShared m f = tryPidLock m f LockShared $ Posix.tryLockShared m f
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tryLockExclusive :: Maybe FileMode -> LockFile -> Annex (Maybe LockHandle)
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tryLockExclusive m f = tryPidLock m f $ Posix.tryLockExclusive m f
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tryLockExclusive m f = tryPidLock m f LockExclusive $ Posix.tryLockExclusive m f
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checkLocked :: LockFile -> Annex (Maybe Bool)
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checkLocked f = Posix.checkLocked f `pidLockCheck` checkpid
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@ -67,22 +67,22 @@ pidLockCheck :: IO a -> (LockFile -> IO a) -> Annex a
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pidLockCheck posixcheck pidcheck = debugLocks $
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liftIO . maybe posixcheck pidcheck =<< pidLockFile
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pidLock :: Maybe FileMode -> LockFile -> IO LockHandle -> Annex LockHandle
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pidLock m f posixlock = debugLocks $ go =<< pidLockFile
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pidLock :: Maybe FileMode -> LockFile -> LockMode -> IO LockHandle -> Annex LockHandle
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pidLock m f lockmode posixlock = debugLocks $ go =<< pidLockFile
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where
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go Nothing = liftIO posixlock
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go (Just pidlock) = do
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timeout <- annexPidLockTimeout <$> Annex.getGitConfig
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liftIO $ dummyPosixLock m f
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Pid.waitLock timeout pidlock warning
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Pid.waitLock f lockmode timeout pidlock warning
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tryPidLock :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle) -> Annex (Maybe LockHandle)
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tryPidLock m f posixlock = debugLocks $ liftIO . go =<< pidLockFile
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tryPidLock :: Maybe FileMode -> LockFile -> LockMode -> IO (Maybe LockHandle) -> Annex (Maybe LockHandle)
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tryPidLock m f lockmode posixlock = debugLocks $ liftIO . go =<< pidLockFile
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where
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go Nothing = posixlock
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go (Just pidlock) = do
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dummyPosixLock m f
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Pid.tryLock pidlock
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Pid.tryLock f lockmode pidlock
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-- The posix lock file is created even when using pid locks, in order to
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-- avoid complicating any code that might expect to be able to see that
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@ -1,6 +1,6 @@
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{- Pid locking support.
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-
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- Copyright 2014-2020 Joey Hess <id@joeyh.name>
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- Copyright 2014-2021 Joey Hess <id@joeyh.name>
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-
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- Licensed under the GNU AGPL version 3 or higher.
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-}
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@ -53,7 +53,7 @@ pidLockChildProcess cmd ps f a = do
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cleanup
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(go gonopidlock p pidlock)
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where
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setup pidlock = PidP.tryLock pidlock
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setup pidlock = PidP.tryLock' pidlock
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cleanup (Just h) = dropLock h
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cleanup Nothing = return ()
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@ -83,7 +83,7 @@ runsGitAnnexChildProcessViaGit a = pidLockFile >>= \case
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Nothing -> a
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Just pidlock -> bracket (setup pidlock) cleanup (go pidlock)
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where
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setup pidlock = liftIO $ PidP.tryLock pidlock
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setup pidlock = liftIO $ PidP.tryLock' pidlock
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cleanup (Just h) = liftIO $ dropLock h
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cleanup Nothing = return ()
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@ -112,7 +112,7 @@ runsGitAnnexChildProcessViaGit' r a = pidLockFile >>= \case
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Nothing -> liftIO $ a r
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Just pidlock -> liftIO $ bracket (setup pidlock) cleanup (go pidlock)
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where
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setup pidlock = PidP.tryLock pidlock
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setup pidlock = PidP.tryLock' pidlock
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cleanup (Just h) = dropLock h
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cleanup Nothing = return ()
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@ -8,6 +8,7 @@
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{-# LANGUAGE OverloadedStrings #-}
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module Utility.LockFile.PidLock (
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PidLockFile,
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LockHandle,
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tryLock,
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waitLock,
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@ -53,13 +54,13 @@ import System.FilePath
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import Control.Applicative
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import Prelude
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type LockFile = RawFilePath
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type PidLockFile = RawFilePath
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data LockHandle
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= LockHandle LockFile FileStatus SideLockHandle
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= LockHandle PidLockFile FileStatus SideLockHandle
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| ParentLocked
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type SideLockHandle = Maybe (LockFile, Posix.LockHandle)
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type SideLockHandle = Maybe (RawFilePath, Posix.LockHandle)
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data PidLock = PidLock
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{ lockingPid :: ProcessID
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@ -72,13 +73,13 @@ mkPidLock = PidLock
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<$> getProcessID
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<*> getHostName
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readPidLock :: LockFile -> IO (Maybe PidLock)
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readPidLock :: PidLockFile -> IO (Maybe PidLock)
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readPidLock lockfile = (readish =<<)
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<$> catchMaybeIO (readFile (fromRawFilePath lockfile))
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-- To avoid races when taking over a stale pid lock, a side lock is used.
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-- This is a regular posix exclusive lock.
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trySideLock :: LockFile -> (SideLockHandle -> IO a) -> IO a
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trySideLock :: PidLockFile -> (SideLockHandle -> IO a) -> IO a
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trySideLock lockfile a = do
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sidelock <- sideLockFile lockfile
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mlck <- catchDefaultIO Nothing $
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@ -113,7 +114,7 @@ dropSideLock (Just (f, h)) = do
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-- The side lock is put in /dev/shm. This will work on most any
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-- Linux system, even if its whole root filesystem doesn't support posix
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-- locks. /tmp is used as a fallback.
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sideLockFile :: LockFile -> IO LockFile
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sideLockFile :: PidLockFile -> IO RawFilePath
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sideLockFile lockfile = do
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f <- fromRawFilePath <$> absPath lockfile
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let base = intercalate "_" (splitDirectories (makeRelative "/" f))
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@ -136,7 +137,7 @@ sideLockFile lockfile = do
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--
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-- If a parent process is holding the lock, determined by a
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-- "PIDLOCK_lockfile" environment variable, does not block either.
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tryLock :: LockFile -> IO (Maybe LockHandle)
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tryLock :: PidLockFile -> IO (Maybe LockHandle)
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tryLock lockfile = do
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abslockfile <- absPath lockfile
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lockenv <- pidLockEnv abslockfile
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@ -256,7 +257,7 @@ checkInsaneLustre dest = do
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--
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-- After the first second waiting, runs the callback to display a message,
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-- so the user knows why it's stalled.
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waitLock :: MonadIO m => Seconds -> LockFile -> (String -> m ()) -> (Bool -> IO ()) -> m LockHandle
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waitLock :: MonadIO m => Seconds -> PidLockFile -> (String -> m ()) -> (Bool -> IO ()) -> m LockHandle
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waitLock (Seconds timeout) lockfile displaymessage sem = go timeout
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where
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go n
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@ -273,14 +274,14 @@ waitLock (Seconds timeout) lockfile displaymessage sem = go timeout
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liftIO $ sem False
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waitedLock (Seconds timeout) lockfile displaymessage
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waitedLock :: MonadIO m => Seconds -> LockFile -> (String -> m ()) -> m LockHandle
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waitedLock :: MonadIO m => Seconds -> PidLockFile -> (String -> m ()) -> m LockHandle
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waitedLock (Seconds timeout) lockfile displaymessage = do
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displaymessage $ show timeout ++ " second timeout exceeded while waiting for pid lock file " ++ fromRawFilePath lockfile
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giveup $ "Gave up waiting for pid lock file " ++ fromRawFilePath lockfile
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-- | Use when the pid lock has already been taken by another thread of the
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-- same process, or perhaps is in the process of being taken.
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alreadyLocked :: MonadIO m => LockFile -> m LockHandle
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alreadyLocked :: MonadIO m => PidLockFile -> m LockHandle
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alreadyLocked lockfile = liftIO $ do
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abslockfile <- absPath lockfile
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st <- getFileStatus abslockfile
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@ -294,10 +295,10 @@ dropLock (LockHandle lockfile _ sidelock) = do
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removeWhenExistsWith removeLink lockfile
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dropLock ParentLocked = return ()
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getLockStatus :: LockFile -> IO LockStatus
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getLockStatus :: PidLockFile -> IO LockStatus
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getLockStatus = maybe StatusUnLocked (StatusLockedBy . lockingPid) <$$> readPidLock
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checkLocked :: LockFile -> IO (Maybe Bool)
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checkLocked :: PidLockFile -> IO (Maybe Bool)
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checkLocked lockfile = conv <$> getLockStatus lockfile
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where
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conv (StatusLockedBy _) = Just True
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@ -305,7 +306,7 @@ checkLocked lockfile = conv <$> getLockStatus lockfile
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-- Checks that the lock file still exists, and is the same file that was
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-- locked to get the LockHandle.
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checkSaneLock :: LockFile -> LockHandle -> IO Bool
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checkSaneLock :: PidLockFile -> LockHandle -> IO Bool
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checkSaneLock lockfile (LockHandle _ st _) =
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go =<< catchMaybeIO (getFileStatus lockfile)
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where
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@ -8,7 +8,7 @@
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{-# LANGUAGE CPP #-}
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module Utility.LockPool.LockHandle (
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LockHandle,
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LockHandle(..),
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FileLockOps(..),
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dropLock,
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#ifndef mingw32_HOST_OS
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@ -86,4 +86,3 @@ mkLockHandle :: P.LockHandle -> FileLockOps -> IO LockHandle
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mkLockHandle ph fo = do
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atomically $ P.registerCloseLockFile ph (fDropLock fo)
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return $ LockHandle ph fo
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@ -10,6 +10,7 @@ module Utility.LockPool.PidLock (
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LockHandle,
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waitLock,
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tryLock,
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tryLock',
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checkLocked,
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getLockStatus,
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LockStatus(..),
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@ -34,34 +35,72 @@ import Control.Monad.IO.Class
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import Control.Applicative
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import Prelude
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-- Takes a pid lock, blocking until the lock is available or the timeout.
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-- Does locking using a pid lock, blocking until the lock is available
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-- or the timeout.
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--
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-- There are two levels of locks. A STM lock is used to handle
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-- fine-grained locking amoung threads, locking a specific lockfile,
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-- but only in memory. The pid lock handles locking between processes.
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--
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-- The Seconds is how long to delay if the pid lock is held by another
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-- process.
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waitLock
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:: (MonadIO m, MonadMask m)
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=> Seconds
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-> LockFile
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=> LockFile
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-> LockMode
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-> Seconds
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-> F.PidLockFile
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-> (String -> m ())
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-> m LockHandle
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waitLock timeout file displaymessage = makeLockHandle P.lockPool file
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-- LockShared for STM lock, because a pid lock can be the top-level
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-- lock with various other STM level locks gated behind it.
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(\p f -> P.waitTakeLock p f LockShared)
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(\f (P.FirstLock firstlock firstlocksem) -> mk
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<$> if firstlock
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then F.waitLock timeout f displaymessage $
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void . atomically . tryPutTMVar firstlocksem . P.FirstLockSemWaited
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else liftIO (atomically $ readTMVar firstlocksem) >>= \case
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P.FirstLockSemWaited True -> F.alreadyLocked f
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P.FirstLockSemTried True -> F.alreadyLocked f
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P.FirstLockSemWaited False -> F.waitedLock timeout f displaymessage
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P.FirstLockSemTried False -> F.waitLock timeout f displaymessage $
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waitLock stmlockfile lockmode timeout pidlockfile displaymessage = do
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sl@(LockHandle ph _) <- takestmlock
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pl <- takepidlock
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-- When the STM lock gets dropped, also drop the pid lock.
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liftIO $ atomically $
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P.registerPostReleaseLock ph (dropLock pl)
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return sl
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where
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takestmlock = makeLockHandle P.lockPool stmlockfile
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(\p f -> P.waitTakeLock p f lockmode)
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(\_ _ -> pure stmonlyflo)
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takepidlock = makeLockHandle P.lockPool pidlockfile
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-- LockShared because multiple threads can share the pid lock;
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-- it remains locked until all threads using it drop
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-- their locks.
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(\p f -> P.waitTakeLock p f LockShared)
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(\f (P.FirstLock firstlock firstlocksem) -> mkflo
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<$> if firstlock
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then F.waitLock timeout f displaymessage $
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void . atomically . tryPutTMVar firstlocksem . P.FirstLockSemWaited
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)
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else liftIO (atomically $ readTMVar firstlocksem) >>= \case
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P.FirstLockSemWaited True -> F.alreadyLocked f
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P.FirstLockSemTried True -> F.alreadyLocked f
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P.FirstLockSemWaited False -> F.waitedLock timeout f displaymessage
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P.FirstLockSemTried False -> F.waitLock timeout f displaymessage $
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void . atomically . tryPutTMVar firstlocksem . P.FirstLockSemWaited
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)
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-- Tries to take a pid lock, but does not block.
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tryLock :: LockFile -> IO (Maybe LockHandle)
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tryLock file = tryMakeLockHandle P.lockPool file
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tryLock :: LockFile -> LockMode -> F.PidLockFile -> IO (Maybe LockHandle)
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tryLock stmlockfile lockmode pidlockfile = takestmlock >>= \case
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Just (sl@(LockHandle ph _)) -> tryLock' pidlockfile >>= \case
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Just pl -> do
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liftIO $ atomically $
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P.registerPostReleaseLock ph (dropLock pl)
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return (Just sl)
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Nothing -> do
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dropLock sl
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return Nothing
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Nothing -> return Nothing
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where
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takestmlock = tryMakeLockHandle P.lockPool stmlockfile
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(\p f -> P.tryTakeLock p f lockmode)
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(\_ _ -> pure (Just stmonlyflo))
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tryLock' :: F.PidLockFile -> IO (Maybe LockHandle)
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tryLock' pidlockfile = tryMakeLockHandle P.lockPool pidlockfile
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(\p f -> P.tryTakeLock p f LockShared)
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(\f (P.FirstLock firstlock firstlocksem) -> fmap mk
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(\f (P.FirstLock firstlock firstlocksem) -> fmap mkflo
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<$> if firstlock
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then do
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lh <- F.tryLock f
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@ -85,8 +124,14 @@ getLockStatus file = P.getLockStatus P.lockPool file
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(StatusLockedBy <$> getProcessID)
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(F.getLockStatus file)
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mk :: F.LockHandle -> FileLockOps
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mk h = FileLockOps
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mkflo :: F.LockHandle -> FileLockOps
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mkflo h = FileLockOps
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{ fDropLock = F.dropLock h
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, fCheckSaneLock = \f -> F.checkSaneLock f h
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}
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stmonlyflo :: FileLockOps
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stmonlyflo = FileLockOps
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{ fDropLock = return ()
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, fCheckSaneLock = const (return True)
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}
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@ -19,6 +19,7 @@ module Utility.LockPool.STM (
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releaseLock,
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CloseLockFile,
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registerCloseLockFile,
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registerPostReleaseLock,
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) where
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import Utility.Monad
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@ -37,7 +38,7 @@ data LockMode = LockExclusive | LockShared
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-- This TMVar is full when the handle is open, and is emptied when it's
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-- closed.
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type LockHandle = TMVar (LockPool, LockFile, CloseLockFile)
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type LockHandle = TMVar (LockPool, LockFile, CloseLockFile, PostReleaseLock)
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-- When a shared lock is taken, this will only be true for the first
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-- process, not subsequent processes. The first process should
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@ -54,8 +55,12 @@ type LockCount = Integer
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data LockStatus = LockStatus LockMode LockCount FirstLockSem
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-- Action that closes the underlying lock file.
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type CloseLockFile = IO ()
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-- Action that is run after the LockHandle is released.
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type PostReleaseLock = IO ()
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-- This TMVar is normally kept full.
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type LockPool = TMVar (M.Map LockFile LockStatus)
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@ -82,7 +87,7 @@ tryTakeLock pool file mode = do
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m <- takeTMVar pool
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let success firstlock v = do
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putTMVar pool (M.insert file v m)
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tmv <- newTMVar (pool, file, noop)
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tmv <- newTMVar (pool, file, noop, noop)
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return (Just (tmv, firstlock))
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case M.lookup file m of
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Just (LockStatus mode' n firstlocksem)
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@ -96,14 +101,22 @@ tryTakeLock pool file mode = do
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return Nothing
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_ -> do
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firstlocksem <- newEmptyTMVar
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success (FirstLock True firstlocksem) $ LockStatus mode 1 firstlocksem
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success (FirstLock True firstlocksem) $
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LockStatus mode 1 firstlocksem
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-- Call after waitTakeLock or tryTakeLock, to register a CloseLockFile
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-- action to run when releasing the lock.
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registerCloseLockFile :: LockHandle -> CloseLockFile -> STM ()
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registerCloseLockFile h closelockfile = do
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(p, f, c) <- takeTMVar h
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putTMVar h (p, f, c >> closelockfile)
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(p, f, c, r) <- takeTMVar h
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putTMVar h (p, f, c >> closelockfile, r)
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-- Call after waitTakeLock or tryTakeLock, to register a PostReleaseLock
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-- action to run after releasing the lock.
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registerPostReleaseLock :: LockHandle -> PostReleaseLock -> STM ()
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registerPostReleaseLock h postreleaselock = do
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(p, f, c, r) <- takeTMVar h
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putTMVar h (p, f, c, r >> postreleaselock)
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-- Checks if a lock is being held. If it's held by the current process,
|
||||
-- runs the getdefault action; otherwise runs the checker action.
|
||||
|
|
@ -134,11 +147,12 @@ getLockStatus pool file getdefault checker = do
|
|||
--
|
||||
-- Note that the lock pool is left empty while the CloseLockFile action
|
||||
-- is run, to avoid race with another thread trying to open the same lock
|
||||
-- file.
|
||||
-- file. However, the pool is full again when the PostReleaseLock action
|
||||
-- runs.
|
||||
releaseLock :: LockHandle -> IO ()
|
||||
releaseLock h = go =<< atomically (tryTakeTMVar h)
|
||||
where
|
||||
go (Just (pool, file, closelockfile)) = do
|
||||
go (Just (pool, file, closelockfile, postreleaselock)) = do
|
||||
(m, lastuser) <- atomically $ do
|
||||
m <- takeTMVar pool
|
||||
return $ case M.lookup file m of
|
||||
|
|
@ -147,7 +161,8 @@ releaseLock h = go =<< atomically (tryTakeTMVar h)
|
|||
| otherwise ->
|
||||
(M.insert file (LockStatus mode (pred n) firstlocksem) m, False)
|
||||
Nothing -> (m, True)
|
||||
() <- when lastuser closelockfile
|
||||
when lastuser closelockfile
|
||||
atomically $ putTMVar pool m
|
||||
when lastuser postreleaselock
|
||||
-- The LockHandle was already closed.
|
||||
go Nothing = return ()
|
||||
|
|
|
|||
Loading…
Add table
Reference in a new issue