Package org.apache.derby.impl.services.locks

Class ActiveLock

  • All Implemented Interfaces:
    Latch, Control
    public final class ActiveLock
extends Lock
    A Lock represents a granted or waiting lock request.
    MT - Mutable - Immutable identity : Thread Aware

    • Field Detail

      • wakeUpNow

        byte wakeUpNow
        Set to true if the object waiting on this thread should wake up, MT - mutable - java synchronized(this)

      • potentiallyGranted

        boolean potentiallyGranted
        Set to true if the Lock potentially could be granted. MT - mutable - single thread required

      • canSkip

        protected boolean canSkip
        If true then this lock can be granted even if it is not the first lock request on the wait queue. This can occur if the compatibility space already holds a lock on the object.

    • Constructor Detail

      • ActiveLock

        protected ActiveLock​(CompatibilitySpace space,
                     Lockable ref,
                     java.lang.Object qualifier)
        Initialize the lock, should be seen as part of the constructor. A future version of this class may become mutable - mutable identity. MT - single thread required

    • Method Detail

      • setPotentiallyGranted

        protected boolean setPotentiallyGranted()
        Set the potentially granted flag, returns true if the flag changed its state. MT - single thread required

      • clearPotentiallyGranted

        protected void clearPotentiallyGranted()
        Clear the potentially granted flag. MT - single thread required

      • waitForGrant

        protected byte waitForGrant​(int timeout)
                     throws StandardException
        Wait for a lock to be granted, returns when the lock is granted.

        The sleep wakeup scheme depends on the two booleans wakeUpNow and potentiallyGranted. MT - Single thread required - and assumed to be the thread requesting the lock.

        Returns:
        true if the wait ended early (ie. someone else woke us up).
        Throws:
        StandardException - timeout, deadlock or thread interrupted

      • wakeUp

        protected void wakeUp​(byte why)
        Wake up anyone sleeping on this lock. MT - Thread Safe