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 {@link Cancellable} {@link java.lang.Runnable} 
 * actions within the {@link 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 before 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
     * <tt>CancellableTask</tt>, which it relies on for methods
     * <tt>isDone</tt>, <tt>isCancelled</tt> and <tt>cancel</tt>. This
     * class is split into an inner class to permit Future support to
     * be mixed-in with other flavors of tasks.  Normally, such a
     * class will delegate <tt>Future</tt> <tt>get</tt> methods to the
     * <tt>InnerCancellableFuture</tt>, and internally arrange that
     * <tt>set</tt> methods be invoked when computations are ready.
     *
     * <p><b>Sample Usage</b>. Here are fragments of an example subclass.
     * <pre>
     *  class MyFutureTask&lt;V&gt; extends CancellableTask implements Future&lt;
V&gt; {
     *                
     *    MyFutureTask(Callable&lt;V&gt; callable) {
     *      setRunnable(new InnerCancellableFuture&lt;V&gt;(callable));
     *    }
     *
     *    public V get() throws InterruptedException, ExecutionException {
     *      return ((InnerCancellableFuture&lt;V&gt;)getRunnable()).get();
     *    }
     *    // (And similarly for timeout version.)
     *
     *    void action() { // whatever action causes execution
     *      try {
     *        ((InnerCancellableFuture&lt;V&gt;)getRunnable()).set(compute());
     *      } catch (Exception ex) {
     *        ((InnerCancellableFuture&lt;V&gt;)getRunnable()).setException(ex);
     *      }
     *   }
     * }
     *</pre>
     */
    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 cancel(boolean mayInterruptIfRunning) {
            return CancellableTask.this.cancel(mayInterruptIfRunning);
        }
        
        public boolean isCancelled() {
            return CancellableTask.this.isCancelled();
        }


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


        /**
         * Sets this Future to the results of <tt>callable.call</tt>
         */
        public void run() {
            try {
                set(callable.call());
            } catch(Throwable ex) {
                setException(ex);
            }
        }

        /**
         * Waits if necessary for the call to <tt>callable.call</tt> to
         * complete, and then retrieves its result.
         *
         * @return computed result
         * @throws CancellationException here???
         * @throws ExecutionException if underlying computation threw an
         * exception
         * @throws InterruptedException if current thread was interrupted
         * while waiting
         */
        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();
            }
        }

        /**
         * Waits if necessary for at most the given time for the call to
         * <tt>callable.call</tt> to complete, and then retrieves its
         * result.
         *
         * @param timeout the maximum time to wait
         * @param unit the time unit of the timeout argument
         * @return computed result
         * @throws ExecutionException if underlying computation threw an
         * exception
         * @throws InterruptedException if current thread was interrupted
         * while waiting
         * @throws TimeoutException if the wait timed out
         */
        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();
            }
        }

        /**
         * Sets the result of this Future to the given value.
         * @param v the value
         */ 
        protected void set(V v) {
            lock.lock();
            try {
                result = v;
                setDone();
                accessible.signalAll();
            } finally {
                lock.unlock();
            }
        }

        /**
         * Causes this futue to report an <tt>ExecutionException</tt>
         * with the given throwable as its cause.
         * @param t the cause of failure.
         */ 
        protected void setException(Throwable t) {
            lock.lock();
            try {
                exception = t;
                setDone();
                accessible.signalAll();
            } finally {
                lock.unlock();
            }
        }
    }
   
}
Revision:	1.14
Committed:	Sun Aug 31 13:33:13 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.13:	+7 -6 lines
Log Message:	Removed non-standard tags and misc javadoc cleanup
#	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 {@link Cancellable} {@link java.lang.Runnable}
13	* actions within the {@link Executor} framework. In addition to
14	* serving as a standalone class, this provides <tt>protected</tt>
15	* functionality that may be useful when creating customized task
16	* classes.
17	* @since 1.5
18	* @author Doug Lea
19	*/
20
21	public class CancellableTask implements Cancellable, Runnable {
22	/**
23	* Holds the run-state, taking on values:
24	* null = not yet started,
25	* [some thread ref] = running,
26	* DONE = completed normally,
27	* CANCELLED = cancelled (may or may not have ever run).
28	* Transitions use atomic updates.
29	*/
30	private volatile Object runner;
31
32	/**
33	* Special value for "runner" indicating task is completed
34	*/
35	private static final Object DONE = new Object();
36
37	/**
38	* Special value for "runner" indicating task is cancelled
39	*/
40	private static final Object CANCELLED = new Object();
41
42	private static AtomicReferenceFieldUpdater<CancellableTask, Object>
43	runnerUpdater =
44	AtomicReferenceFieldUpdater.newUpdater
45	(CancellableTask.class, Object.class, "runner");
46
47	/**
48	* The runnable underlying this task
49	*/
50	private volatile Runnable runnable;
51
52	/**
53	* Creates a new CancellableTask which invokes the given
54	* <tt>Runnable</tt> when executed.
55	* @param r the runnable action
56	*/
57	public CancellableTask(Runnable r) {
58	this.runnable = r;
59	}
60
61	/**
62	* Creates a new CancellableTask without a runnable action, which
63	* must be set using <tt>setRunnable</tt> before use. This is
64	* intended for use in subclasses that must complete superclass
65	* construction before establishing the runnable action.
66	*/
67	protected CancellableTask() {
68	}
69
70
71	public boolean cancel(boolean mayInterruptIfRunning) {
72	Object r = runner;
73	if (r == DONE \|\| r == CANCELLED)
74	return false;
75
76	if (mayInterruptIfRunning &&
77	r != null &&
78	r instanceof Thread &&
79	runnerUpdater.compareAndSet(this, r, CANCELLED))
80
81	((Thread)r).interrupt();
82	else
83	runnerUpdater.set(this, CANCELLED);
84	return true;
85	}
86
87	public boolean isCancelled() {
88	return runner == CANCELLED;
89	}
90
91	public boolean isDone() {
92	Object r = runner;
93	return r == DONE \|\| r == CANCELLED;
94	}
95
96	/**
97	* Return the Runnable forming the basis of this task.
98	* @return the runnable action
99	* @see #setRunnable
100	*/
101	protected Runnable getRunnable() {
102	return runnable;
103	}
104
105	/**
106	* Set the Runnable forming the basis of this task.
107	* @param r the runnable action
108	* @see #getRunnable
109	*/
110	protected void setRunnable(Runnable r) {
111	runnable = r;
112	}
113
114	/**
115	* Set the state of this task to Cancelled.
116	*/
117	protected void setCancelled() {
118	runnerUpdater.set(this, CANCELLED);
119	}
120
121	/**
122	* Set the state of this task to Done, unless already
123	* in a Cancelled state, in which Cancelled status is preserved.
124	*
125	*/
126	protected void setDone() {
127	for (;;) {
128	Object r = runner;
129	if (r == DONE \|\| r == CANCELLED)
130	return;
131	if (runnerUpdater.compareAndSet(this, r, DONE))
132	return;
133	}
134	}
135
136	/**
137	* Attempt to set the state of this task to Running, succeeding
138	* only if the state is currently NOT Done, Running, or Cancelled.
139	* @return true if successful
140	*/
141	protected boolean setRunning() {
142	return runnerUpdater.compareAndSet(this, null, Thread.currentThread());
143	}
144
145	public void run() {
146	if (setRunning()) {
147	try {
148	runnable.run();
149	} finally {
150	setDone();
151	}
152	}
153	}
154
155	/**
156	* Implementation of Future methods under the control of a current
157	* <tt>CancellableTask</tt>, which it relies on for methods
158	* <tt>isDone</tt>, <tt>isCancelled</tt> and <tt>cancel</tt>. This
159	* class is split into an inner class to permit Future support to
160	* be mixed-in with other flavors of tasks. Normally, such a
161	* class will delegate <tt>Future</tt> <tt>get</tt> methods to the
162	* <tt>InnerCancellableFuture</tt>, and internally arrange that
163	* <tt>set</tt> methods be invoked when computations are ready.
164	*
165	* <p><b>Sample Usage</b>. Here are fragments of an example subclass.
166	* <pre>
167	* class MyFutureTask<V> extends CancellableTask implements Future<
168	V> {
169	*
170	* MyFutureTask(Callable<V> callable) {
171	* setRunnable(new InnerCancellableFuture<V>(callable));
172	* }
173	*
174	* public V get() throws InterruptedException, ExecutionException {
175	* return ((InnerCancellableFuture<V>)getRunnable()).get();
176	* }
177	* // (And similarly for timeout version.)
178	*
179	* void action() { // whatever action causes execution
180	* try {
181	* ((InnerCancellableFuture<V>)getRunnable()).set(compute());
182	* } catch (Exception ex) {
183	* ((InnerCancellableFuture<V>)getRunnable()).setException(ex);
184	* }
185	* }
186	* }
187	*</pre>
188	*/
189	protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
190	private final Callable<V> callable;
191	private final ReentrantLock lock = new ReentrantLock();
192	private final Condition accessible = lock.newCondition();
193	private V result;
194	private Throwable exception;
195
196	/**
197	* Create an InnerCancellableFuture that will execute the
198	* given callable.
199	* @param callable the function to execute
200	*/
201	protected InnerCancellableFuture(Callable<V> callable) {
202	this.callable = callable;
203	}
204
205	public boolean cancel(boolean mayInterruptIfRunning) {
206	return CancellableTask.this.cancel(mayInterruptIfRunning);
207	}
208
209	public boolean isCancelled() {
210	return CancellableTask.this.isCancelled();
211	}
212
213
214	public boolean isDone() {
215	return CancellableTask.this.isDone();
216	}
217
218
219	/**
220	* Sets this Future to the results of <tt>callable.call</tt>
221	*/
222	public void run() {
223	try {
224	set(callable.call());
225	} catch(Throwable ex) {
226	setException(ex);
227	}
228	}
229
230	/**
231	* Waits if necessary for the call to <tt>callable.call</tt> to
232	* complete, and then retrieves its result.
233	*
234	* @return computed result
235	* @throws CancellationException here???
236	* @throws ExecutionException if underlying computation threw an
237	* exception
238	* @throws InterruptedException if current thread was interrupted
239	* while waiting
240	*/
241	public V get() throws InterruptedException, ExecutionException {
242	lock.lock();
243	try {
244	while (!isDone())
245	accessible.await();
246	if (isCancelled())
247	throw new CancellationException();
248	else if (exception != null)
249	throw new ExecutionException(exception);
250	else
251	return result;
252	} finally {
253	lock.unlock();
254	}
255	}
256
257	/**
258	* Waits if necessary for at most the given time for the call to
259	* <tt>callable.call</tt> to complete, and then retrieves its
260	* result.
261	*
262	* @param timeout the maximum time to wait
263	* @param unit the time unit of the timeout argument
264	* @return computed result
265	* @throws ExecutionException if underlying computation threw an
266	* exception
267	* @throws InterruptedException if current thread was interrupted
268	* while waiting
269	* @throws TimeoutException if the wait timed out
270	*/
271	public V get(long timeout, TimeUnit unit)
272	throws InterruptedException, ExecutionException, TimeoutException {
273	lock.lock();
274	try {
275	if (!isDone()) {
276	long nanos = unit.toNanos(timeout);
277	do {
278	if (nanos <= 0)
279	throw new TimeoutException();
280	nanos = accessible.awaitNanos(nanos);
281	} while (!isDone());
282	}
283	if (isCancelled())
284	throw new CancellationException();
285	else if (exception != null)
286	throw new ExecutionException(exception);
287	else
288	return result;
289	} finally {
290	lock.unlock();
291	}
292	}
293
294	/**
295	* Sets the result of this Future to the given value.
296	* @param v the value
297	*/
298	protected void set(V v) {
299	lock.lock();
300	try {
301	result = v;
302	setDone();
303	accessible.signalAll();
304	} finally {
305	lock.unlock();
306	}
307	}
308
309	/**
310	* Causes this futue to report an <tt>ExecutionException</tt>
311	* with the given throwable as its cause.
312	* @param t the cause of failure.
313	*/
314	protected void setException(Throwable t) {
315	lock.lock();
316	try {
317	exception = t;
318	setDone();
319	accessible.signalAll();
320	} finally {
321	lock.unlock();
322	}
323	}
324	}
325
326	}