util/concurrent/CancellableTask.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;

/**
 * Base class for cancellable actions running in the Executor
 * framework. In addition to serving as a standalone class, this
 * provides <tt>protected</tt> functionality that may be useful when
 * creating customized task classes.
 * @since 1.5
 * @author Doug Lea
 */

public class CancellableTask implements Cancellable, Runnable {
    /** 
     * Holds the run-state, taking on values:
     *   null              = not yet started,
     *   [some thread ref] = running,
     *   DONE              = completed normally,
     *   CANCELLED         = cancelled (may or may not have ever run).
     * Transitions use atomic updates.
     */
    private volatile Object runner;

    /**
     * Special value for "runner" indicating task is completed
     */
    private static final Object DONE = new Object();

    /**
     * Special value for "runner" indicating task is cancelled
     */
    private static final Object CANCELLED = new Object();

    private static AtomicReferenceFieldUpdater<CancellableTask, Object> 
        runnerUpdater = 
        AtomicReferenceFieldUpdater.newUpdater
        (CancellableTask.class, Object.class, "runner");

    /**
     * The runnable underlying this task
     */
    private volatile Runnable runnable;

    /**
     * Creates a new CancellableTask which invokes the given
     * <tt>Runnable</tt> when executed.
     * @param r the runnable action
     */
    public CancellableTask(Runnable r) {
        this.runnable = r;
    }

    /**
     * Creates a new CancellableTask without a runnable action, which
     * must be set using <tt>setRunnable</tt> before use.  This is
     * intended for use in subclasses that must complete superclass
     * construction beofre establishing the runnable action.
     */
    protected CancellableTask() {
    }


    public boolean cancel(boolean mayInterruptIfRunning) {
        Object r = runner;
        if (r == DONE || r == CANCELLED)
            return false;

        if (mayInterruptIfRunning &&
            r != null &&
            r instanceof Thread &&
            runnerUpdater.compareAndSet(this, r, CANCELLED)) 

            ((Thread)r).interrupt();
        else 
            runnerUpdater.set(this, CANCELLED);
        return true;
    }
    
    public boolean isCancelled() {
        return runner == CANCELLED;
    }
    
    public boolean isDone() {
        Object r = runner;
        return r == DONE || r == CANCELLED;
    }

    /**
     * Return the Runnable forming the basis of this task.
     * @return the runnable action
     * @see #setRunnable
     */
    protected Runnable getRunnable() {
        return runnable;
    }

    /**
     * Set the Runnable forming the basis of this task.
     * @param r the runnable action
     * @see #getRunnable
     */
    protected void setRunnable(Runnable r) {
        runnable = r;
    }

    /**
     * Set the state of this task to Cancelled.
     */
    protected void setCancelled() {
        runnerUpdater.set(this, CANCELLED);
    }
    
    /**
     * Set the state of this task to Done, unless already
     * in a Cancelled state, in which Cancelled status is preserved.
     *
     */
    protected void setDone() {
        for (;;) {
            Object r = runner;
            if (r == DONE || r == CANCELLED) 
                return;
            if (runnerUpdater.compareAndSet(this, r, DONE))
                return;
        }
    }

    /**
     * Attempt to set the state of this task to Running, succeeding
     * only if the state is currently NOT Done, Running, or Cancelled.
     * @return true if successful
     */ 
    protected boolean setRunning() {
        return runnerUpdater.compareAndSet(this, null, Thread.currentThread());
    }

    public void run() {
        if (setRunning()) {
            try {
                runnable.run();
            }
            finally {
                setDone();
            }
        }
    }

    /**
     * Implementation of Future methods under the control of a current
     * CancellableTask. This is split into an inner class to permit
     * Future support to be mixed-in with other flavors of tasks.
     */
    protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
        private final Callable<V> callable;
        private final ReentrantLock lock = new ReentrantLock();
        private final Condition accessible = lock.newCondition();
        private V result;
        private Throwable exception;

        /**
         * Create an InnerCancellableFuture that will execute the
         * given callable.
         * @param callable the function to execute
         */
        protected InnerCancellableFuture(Callable<V> callable) {
            this.callable = callable;
        }

        public boolean isDone() {
            return CancellableTask.this.isDone();
        }

        public void run() {
            try {
                set(callable.call());
            }
            catch(Throwable ex) {
                setException(ex);
            }
        }

        public V get() throws InterruptedException, ExecutionException {
            lock.lock();
            try {
                while (!isDone())
                    accessible.await();
                if (isCancelled())
                    throw new CancellationException();
                else if (exception != null)
                    throw new ExecutionException(exception);
                else
                    return result;
            }
            finally {
                lock.unlock();
            }
        }

        public V get(long timeout, TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
            lock.lock();
            try {
                if (!isDone()) {
                    long nanos = unit.toNanos(timeout);
                    do {
                        if (nanos <= 0)
                            throw new TimeoutException();
                        nanos = accessible.awaitNanos(nanos);
                    } while (!isDone());
                }
                if (isCancelled())
                    throw new CancellationException();
                else if (exception != null)
                    throw new ExecutionException(exception);
                else
                    return result;
            }
            finally {
                lock.unlock();
            }
        }

        protected void set(V v) {
            lock.lock();
            try {
                result = v;
                setDone();
                accessible.signalAll();
            }
            finally {
                lock.unlock();
            }
        }

        protected void setException(Throwable t) {
            lock.lock();
            try {
                exception = t;
                setDone();
                accessible.signalAll();
            }
            finally {
                lock.unlock();
            }
        }
    }
   
}
Revision:	1.10
Committed:	Wed Aug 6 18:22:09 2003 UTC (20 years, 10 months ago) by tim
Branch:	MAIN
CVS Tags:	JSR166_CR1
Changes since 1.9:	+3 -1 lines
Log Message:	Fixes to minor errors found by DocCheck
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain. Use, modify, and
4	* redistribute this code in any way without acknowledgement.
5	*/
6
7	package java.util.concurrent;
8	import java.util.concurrent.atomic.*;
9	import java.util.concurrent.locks.*;
10
11	/**
12	* Base class for cancellable actions running in the Executor
13	* framework. In addition to serving as a standalone class, this
14	* provides <tt>protected</tt> functionality that may be useful when
15	* creating customized task classes.
16	* @since 1.5
17	* @author Doug Lea
18	*/
19
20	public class CancellableTask implements Cancellable, Runnable {
21	/**
22	* Holds the run-state, taking on values:
23	* null = not yet started,
24	* [some thread ref] = running,
25	* DONE = completed normally,
26	* CANCELLED = cancelled (may or may not have ever run).
27	* Transitions use atomic updates.
28	*/
29	private volatile Object runner;
30
31	/**
32	* Special value for "runner" indicating task is completed
33	*/
34	private static final Object DONE = new Object();
35
36	/**
37	* Special value for "runner" indicating task is cancelled
38	*/
39	private static final Object CANCELLED = new Object();
40
41	private static AtomicReferenceFieldUpdater<CancellableTask, Object>
42	runnerUpdater =
43	AtomicReferenceFieldUpdater.newUpdater
44	(CancellableTask.class, Object.class, "runner");
45
46	/**
47	* The runnable underlying this task
48	*/
49	private volatile Runnable runnable;
50
51	/**
52	* Creates a new CancellableTask which invokes the given
53	* <tt>Runnable</tt> when executed.
54	* @param r the runnable action
55	*/
56	public CancellableTask(Runnable r) {
57	this.runnable = r;
58	}
59
60	/**
61	* Creates a new CancellableTask without a runnable action, which
62	* must be set using <tt>setRunnable</tt> before use. This is
63	* intended for use in subclasses that must complete superclass
64	* construction beofre establishing the runnable action.
65	*/
66	protected CancellableTask() {
67	}
68
69
70	public boolean cancel(boolean mayInterruptIfRunning) {
71	Object r = runner;
72	if (r == DONE \|\| r == CANCELLED)
73	return false;
74
75	if (mayInterruptIfRunning &&
76	r != null &&
77	r instanceof Thread &&
78	runnerUpdater.compareAndSet(this, r, CANCELLED))
79
80	((Thread)r).interrupt();
81	else
82	runnerUpdater.set(this, CANCELLED);
83	return true;
84	}
85
86	public boolean isCancelled() {
87	return runner == CANCELLED;
88	}
89
90	public boolean isDone() {
91	Object r = runner;
92	return r == DONE \|\| r == CANCELLED;
93	}
94
95	/**
96	* Return the Runnable forming the basis of this task.
97	* @return the runnable action
98	* @see #setRunnable
99	*/
100	protected Runnable getRunnable() {
101	return runnable;
102	}
103
104	/**
105	* Set the Runnable forming the basis of this task.
106	* @param r the runnable action
107	* @see #getRunnable
108	*/
109	protected void setRunnable(Runnable r) {
110	runnable = r;
111	}
112
113	/**
114	* Set the state of this task to Cancelled.
115	*/
116	protected void setCancelled() {
117	runnerUpdater.set(this, CANCELLED);
118	}
119
120	/**
121	* Set the state of this task to Done, unless already
122	* in a Cancelled state, in which Cancelled status is preserved.
123	*
124	*/
125	protected void setDone() {
126	for (;;) {
127	Object r = runner;
128	if (r == DONE \|\| r == CANCELLED)
129	return;
130	if (runnerUpdater.compareAndSet(this, r, DONE))
131	return;
132	}
133	}
134
135	/**
136	* Attempt to set the state of this task to Running, succeeding
137	* only if the state is currently NOT Done, Running, or Cancelled.
138	* @return true if successful
139	*/
140	protected boolean setRunning() {
141	return runnerUpdater.compareAndSet(this, null, Thread.currentThread());
142	}
143
144	public void run() {
145	if (setRunning()) {
146	try {
147	runnable.run();
148	}
149	finally {
150	setDone();
151	}
152	}
153	}
154
155	/**
156	* Implementation of Future methods under the control of a current
157	* CancellableTask. This is split into an inner class to permit
158	* Future support to be mixed-in with other flavors of tasks.
159	*/
160	protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
161	private final Callable<V> callable;
162	private final ReentrantLock lock = new ReentrantLock();
163	private final Condition accessible = lock.newCondition();
164	private V result;
165	private Throwable exception;
166
167	/**
168	* Create an InnerCancellableFuture that will execute the
169	* given callable.
170	* @param callable the function to execute
171	*/
172	protected InnerCancellableFuture(Callable<V> callable) {
173	this.callable = callable;
174	}
175
176	public boolean isDone() {
177	return CancellableTask.this.isDone();
178	}
179
180	public void run() {
181	try {
182	set(callable.call());
183	}
184	catch(Throwable ex) {
185	setException(ex);
186	}
187	}
188
189	public V get() throws InterruptedException, ExecutionException {
190	lock.lock();
191	try {
192	while (!isDone())
193	accessible.await();
194	if (isCancelled())
195	throw new CancellationException();
196	else if (exception != null)
197	throw new ExecutionException(exception);
198	else
199	return result;
200	}
201	finally {
202	lock.unlock();
203	}
204	}
205
206	public V get(long timeout, TimeUnit unit)
207	throws InterruptedException, ExecutionException, TimeoutException {
208	lock.lock();
209	try {
210	if (!isDone()) {
211	long nanos = unit.toNanos(timeout);
212	do {
213	if (nanos <= 0)
214	throw new TimeoutException();
215	nanos = accessible.awaitNanos(nanos);
216	} while (!isDone());
217	}
218	if (isCancelled())
219	throw new CancellationException();
220	else if (exception != null)
221	throw new ExecutionException(exception);
222	else
223	return result;
224	}
225	finally {
226	lock.unlock();
227	}
228	}
229
230	protected void set(V v) {
231	lock.lock();
232	try {
233	result = v;
234	setDone();
235	accessible.signalAll();
236	}
237	finally {
238	lock.unlock();
239	}
240	}
241
242	protected void setException(Throwable t) {
243	lock.lock();
244	try {
245	exception = t;
246	setDone();
247	accessible.signalAll();
248	}
249	finally {
250	lock.unlock();
251	}
252	}
253	}
254
255	}