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Interface FencedLock

A linearizable, distributed lock.

FencedLock is CP with respect to the CAP principle. It works on top of the Raft consensus algorithm. It offers linearizability during crash-stop failures and network partitions. If a network partition occurs, it remains available on at most one side of the partition.

FencedLock works on top of CP sessions. Please refer to CP Session IMDG documentation section for more information.

Important note: FencedLock is non-reentrant. Once a caller acquires the lock, it can not acquire the lock reentrantly. So, the next acquire attempt made within the same chain of async calls will lead to a dead lock.

Hierarchy

Index

Methods

destroy

  • destroy(): Promise<void>
  • Destroys this object cluster-wide. Clears all resources taken for this object.

    Returns Promise<void>

getName

  • getName(): string
  • Returns the unique name of this object.

    Returns string

getPartitionKey

  • getPartitionKey(): string
  • Returns the key of the partition that this DistributedObject is assigned to. For a partitioned data structure, the returned value will not be null, but otherwise undefined.

    Returns string

getServiceName

  • getServiceName(): string

isLocked

  • isLocked(): Promise<boolean>
  • Returns whether this lock is locked or not.

    throws

    LockOwnershipLostError if the underlying CP session was closed before the client releases the lock

    Returns Promise<boolean>

    true if this lock is locked by any caller in the cluster, false otherwise.

lock

  • lock(): Promise<Long>
  • Acquires the lock and returns the fencing token assigned to the current lock acquire.

    If the lock is not available, then the returned Promise is resolved only when the lock has been acquired.

    Fencing tokens are monotonic 64-bit integers that are incremented each time the lock switches from the free state to the acquired state. They are simply used for ordering lock holders. A lock holder can pass its fencing to the shared resource to fence off previous lock holders. When this resource receives an operation, it can validate the fencing token in the operation.

    You can read more about the fencing token idea in Martin Kleppmann's "How to do distributed locking" blog post and Google's Chubby paper.

    throws

    LockOwnershipLostError if the underlying CP session was closed before the client releases the lock

    Returns Promise<Long>

    fencing token

tryLock

  • tryLock(timeout?: number): Promise<Long | undefined>
  • Acquires the lock only if it is free and returns the fencing token assigned to the current lock acquire.

    If the lock is already held by another caller, then this method immediately returns undefined, which means a failed lock attempt.

    throws

    LockOwnershipLostError if the underlying CP session was closed before the client releases the lock

    Parameters

    • Optional timeout: number

      optional timeout in milliseconds to acquire the lock before giving up; when it's not specified the operation will return immediately after the acquire attempt

    Returns Promise<Long | undefined>

    fencing token (see {@link FencedLock#lock} for more information on fencing tokens) when lock is acquired; or undefined when attempt failed

unlock

  • unlock(fence: Long): Promise<void>
  • Releases the lock if the lock is currently held by the client.

    throws

    IllegalMonitorStateError if the client does not hold the lock

    throws

    LockOwnershipLostError if the underlying CP session was closed before the client releases the lock

    Parameters

    • fence: Long

      fencing token returned from lock/tryLock method.

    Returns Promise<void>

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