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-/*************************************************
- *
- * = PACKAGE
- * JACE.Concurrency
- *
- * = FILENAME
- * Lock.java
- *
- *@author Everett Anderson
- *
- *************************************************/
-package JACE.Concurrency;
-
-import JACE.ASX.*;
-
-/**
- * Abstract adapter class which provides useful default implementations
- * for several methods in the AbstractLock interface, as well as
- * protected helper functions for making sure only the owner
- * can perform certain operations.
- *
- *@see JACE.Concurrency.AbstractLock
- */
-public abstract class LockAdapter implements AbstractLock
-{
- /**
- * Default implementation that calls acquire (TimeValue) with a null
- * timeout.
- *
- *@see AbstractLock#acquire
- */
- public int acquire () throws InterruptedException
- {
- try {
- return acquire (null);
- } catch (TimeoutException e) {
- // This should never happen
- return AbstractLock.FAILURE;
- }
- }
-
- /**
- * Acquire ownership of the lock by the given absolute time time-out.
- * A value of null for the timeout parameter results in a blocking
- * acquire.
- * A value of TimeValue.zero throws a TimeoutException if the
- * acquire would block.
- * <P>
- *@param timeout absolute time by which the lock must be acquired
- *@return appropriate Lock return value (AbstractLock.FAILURE,
- * AbstractLock.SUCCESS or AbstractLock.SLEEPHOOK)
- *@exception JACE.ASX.TimeoutException thrown when the lock is not
- * obtained by the desired time
- *@exception InterruptedException indicates another thread has
- * interrupted this one during wait
- *@see AbstractLock#tryAcquire
- */
- public abstract int acquire (TimeValue timeout)
- throws TimeoutException, InterruptedException;
-
- /**
- * Default implementation that calls acquireRead (TimeValue) with a
- * null timeout.
- *
- *@see AbstractLock#acquireRead
- */
- public int acquireRead () throws InterruptedException
- {
- try {
- return acquireRead (null);
- } catch (TimeoutException e) {
- // This should never happen
- }
-
- return AbstractLock.FAILURE;
- }
-
- /**
- * Default implementation that calls acquire (TimeValue).
- *
- *@see AbstractLock#acquireRead(TimeValue)
- */
- public int acquireRead (TimeValue timeout)
- throws TimeoutException, InterruptedException
- {
- return acquire (timeout);
- }
-
- /**
- * Default implementation that calls acquire with a null
- * timeout.
- *
- *@see AbstractLock#acquireWrite
- */
- public int acquireWrite () throws InterruptedException
- {
- try {
- return acquire (null);
- } catch (TimeoutException e) {
- // This should never happen
- }
-
- return AbstractLock.FAILURE;
- }
-
- /**
- * Default implementation that calls acquire (TimeValue).
- *
- *@see AbstractLock#acquireWrite(TimeValue)
- */
- public int acquireWrite (TimeValue timeout)
- throws TimeoutException, InterruptedException
- {
- return acquire (timeout);
- }
-
- /**
- * Default implementation that calls renew (int, TimeValue) with
- * a null timeout.
- *
- *@see AbstractLock#renew(int)
- */
- public int renew (int requeuePosition) throws InterruptedException
- {
- try
- {
- return renew (requeuePosition, null);
- } catch (TimeoutException e) {
- // Note that this should never happen since we requested a
- // blocking acquire.
- return AbstractLock.FAILURE;
- }
- }
-
- /**
- * Give up the lock to some waiting threads (if any), then reacquire
- * by the given absolute time time-out.
- * <P>
- * An optimized method that efficiently reacquires the token if no
- * other threads are waiting. This is useful for situations where
- * you don't want to degrade the quality of service if there are
- * other threads waiting to get the token.
- * <P>
- * A value of null for the timeout should indicate a blocking renew.
- * <P>
- *@param requeuePosition position in the waiters queue to insert
- * this thread. If this value is -1 and there are other
- * threads waiting to obtain the token, this thread is queued
- * at the end. If this value is greater than -1, then it
- * indicates how many entries to skip over before inserting
- * our thread into the queue. (For example, if it is 0,
- * this thread is put at the front of the queue.) If this
- * value is greater than the number of waiters, this thread is
- * simply put at the end of the current waiters queue.
- *
- *@param timeout absolute time by which the lock must be reacquired
- *
- *@return appropriate AbstractLock return value
- * (AbstractLock.FAILURE or AbstractLock.SUCCESS)
- *@exception JACE.ASX.TimeoutException thrown when the lock is not
- * obtained by the desired time
- *@exception InterruptedException indicates another thread has
- * interrupted this one during wait
- */
- public abstract int renew (int requeuePosition,
- TimeValue timeout)
- throws TimeoutException,
- InterruptedException;
-
- /**
- * Default implementation that calls tryAcquire ().
- *
- *@see AbstractLock#tryAcquireRead
- */
- public int tryAcquireRead ()
- {
- return tryAcquire ();
- }
-
- /**
- * Default implementation that calls tryAcquire ().
- *
- *@see AbstractLock#tryAcquireWrite
- */
- public int tryAcquireWrite ()
- {
- return tryAcquire ();
- }
- /**
- * Try to acquire the lock without blocking.
- * <P>
- *@return appropriate AbstractLock return value
- * (AbstractLock.FAILURE or AbstractLock.SUCCESS)
- */
- public abstract int tryAcquire ();
-
- /**
- * Default implementation as a no-op.
- *
- *@see AbstractLock#sleepHook
- */
- public void sleepHook ()
- {
- }
-
- /**
- * Release ownership of this lock.
- * <P>
- *@return appropriate AbstractLock return value
- * (AbstractLock.FAILURE or AbstractLock.SUCCESS)
- */
- public abstract int release ();
-
- /**
- * Obtains an Object which uniquely identifies the current accessor
- * (usually a thread). This is used to make sure only an owner can
- * perform certain operations like release. Subclasses can redefine
- * the behavior as necessary, such as in the Token service where it is
- * defined to be the client ID sent by the proxy.
- * <P>
- * When using Java 1.2 or later, it might be more efficient to use
- * ThreadLocal and an Integer for the ID. The current default
- * implementation returns the Thread.currentThread () reference.
- *
- *@return Object representing a unique ID for this accessor
- */
- protected Object accessorID ()
- {
- return Thread.currentThread();
- }
-
- /**
- * Check to see if the current accessor is the (or a) owner of this
- * lock.
- */
- protected boolean isOwner()
- {
- return accessorID().equals(this.owner_);
- }
-
- /**
- * Set the current accessor to be the (or a) owner of this lock.
- */
- protected void setOwner()
- {
- this.owner_ = accessorID();
- }
-
- /**
- * Make sure that this accessor is no longer the (or a) owner of this
- * lock.
- */
- protected void clearOwner()
- {
- this.owner_ = null;
- }
-
- /**
- * Reference to the accessorID of the owner.
- */
- private Object owner_;
-}