alluxio.master.file.meta

Class InodeLockManager

java.lang.Object

alluxio.master.file.meta.InodeLockManager

public class InodeLockManager
extends Object

Class for managing inode locking. We manage locks centrally instead of embedded in the inode tree. This allows us to create locks only as needed, and garbage collect locks that aren't in use. As a result, we save memory when the inode tree contains many millions of files. We use WeakSafeReentrantReadWriteLock instead of ReentrantReadWriteLock because the read locks and write locks returned by ReentrantReadWriteLock do not contain a reference to the original ReentrantReadWriteLock, so the original lock can be garbage collected early. WeakSafeReentrantReadWriteLock stores the reference to the original lock to avoid this problem. See https://github.com/google/guava/issues/2477

Field Summary

Fields

Modifier and Type	Field and Description
LockPool<Edge>	mEdgeLocks Cache for supplying edge locks, similar to mInodeLocks.
LockPool<Long>	mInodeLocks Pool for supplying inode locks.

Constructor Summary

Constructors

Constructor and Description
InodeLockManager()

Method Summary

Modifier and Type	Method and Description
void	assertAllLocksReleased() Asserts that all locks have been released, throwing an exception if any locks are still taken.
LockResource	lockEdge(Edge edge, LockMode mode) Acquires an edge lock.
LockResource	lockInode(InodeView inode, LockMode mode) Acquires an inode lock.
LockResource	lockUpdate(long inodeId) Acquires the lock for modifying an inode's last modified time or size.
Optional<Scoped>	tryAcquirePersistingLock(long inodeId) Tries to acquire a lock for persisting the specified inode id.
Optional<LockResource>	tryLockEdge(Edge edge, LockMode mode) Attempts to acquire an edge lock.
Optional<LockResource>	tryLockInode(Long inodeId, LockMode mode) Attempts to acquire an inode lock.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

mInodeLocks

public final LockPool<Long> mInodeLocks

Pool for supplying inode locks. To lock an inode, its inode id must be searched in this pool to get the appropriate read lock. We use weak values so that when nothing holds a reference to a lock, the garbage collector can remove the lock's entry from the pool.

mEdgeLocks

public final LockPool<Edge> mEdgeLocks

Cache for supplying edge locks, similar to mInodeLocks.

Constructor Detail

InodeLockManager

public InodeLockManager()

Method Detail

assertAllLocksReleased

public void assertAllLocksReleased()

Asserts that all locks have been released, throwing an exception if any locks are still taken.

lockInode

public LockResource lockInode(InodeView inode,
                              LockMode mode)

Acquires an inode lock.

Parameters:

inode - the inode to lock

mode - the mode to lock in

Returns:

a lock resource which must be closed to release the lock

tryLockInode

public Optional<LockResource> tryLockInode(Long inodeId,
                                           LockMode mode)

Attempts to acquire an inode lock.

Parameters:

inodeId - the inode id to try locking

mode - the mode to lock in

Returns:

either an empty optional, or a lock resource which must be closed to release the lock

lockEdge

public LockResource lockEdge(Edge edge,
                             LockMode mode)

Acquires an edge lock.

Parameters:

edge - the edge to lock

mode - the mode to lock in

Returns:

a lock resource which must be closed to release the lock

tryLockEdge

public Optional<LockResource> tryLockEdge(Edge edge,
                                          LockMode mode)

Attempts to acquire an edge lock.

Parameters:

edge - the edge to try locking

mode - the mode to lock in

Returns:

either an empty optional, or a lock resource which must be closed to release the lock

tryAcquirePersistingLock

public Optional<Scoped> tryAcquirePersistingLock(long inodeId)

Tries to acquire a lock for persisting the specified inode id.

Parameters:

inodeId - the inode to acquire the lock for

Returns:

an optional wrapping a closure for releasing the lock on success, or Optional.empty if the lock is already taken

lockUpdate

public LockResource lockUpdate(long inodeId)

Acquires the lock for modifying an inode's last modified time or size. As a pre-requisite, the current thread should already hold a read lock on the inode.

Parameters:

inodeId - the id of the inode to lock

Returns:

a lock resource which must be closed to release the lock