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();
            }
        }
    }

    /**
     * Reset the run state of this task to its initial state.
     */
    protected void reset() {
        runnerUpdater.set(this, null);
    }

    /**
     * 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:	1.15
Committed:	Sun Sep 7 23:28:21 2003 UTC (20 years, 8 months ago) by dl
Branch:	MAIN
Changes since 1.14:	+7 -0 lines
Log Message:	Allow resets
#	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	* Reset the run state of this task to its initial state.
157	*/
158	protected void reset() {
159	runnerUpdater.set(this, null);
160	}
161
162	/**
163	* Implementation of Future methods under the control of a current
164	* <tt>CancellableTask</tt>, which it relies on for methods
165	* <tt>isDone</tt>, <tt>isCancelled</tt> and <tt>cancel</tt>. This
166	* class is split into an inner class to permit Future support to
167	* be mixed-in with other flavors of tasks. Normally, such a
168	* class will delegate <tt>Future</tt> <tt>get</tt> methods to the
169	* <tt>InnerCancellableFuture</tt>, and internally arrange that
170	* <tt>set</tt> methods be invoked when computations are ready.
171	*
172	* <p><b>Sample Usage</b>. Here are fragments of an example subclass.
173	* <pre>
174	* class MyFutureTask<V> extends CancellableTask implements Future<
175	V> {
176	*
177	* MyFutureTask(Callable<V> callable) {
178	* setRunnable(new InnerCancellableFuture<V>(callable));
179	* }
180	*
181	* public V get() throws InterruptedException, ExecutionException {
182	* return ((InnerCancellableFuture<V>)getRunnable()).get();
183	* }
184	* // (And similarly for timeout version.)
185	*
186	* void action() { // whatever action causes execution
187	* try {
188	* ((InnerCancellableFuture<V>)getRunnable()).set(compute());
189	* } catch (Exception ex) {
190	* ((InnerCancellableFuture<V>)getRunnable()).setException(ex);
191	* }
192	* }
193	* }
194	*</pre>
195	*/
196	protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
197	private final Callable<V> callable;
198	private final ReentrantLock lock = new ReentrantLock();
199	private final Condition accessible = lock.newCondition();
200	private V result;
201	private Throwable exception;
202
203	/**
204	* Create an InnerCancellableFuture that will execute the
205	* given callable.
206	* @param callable the function to execute
207	*/
208	protected InnerCancellableFuture(Callable<V> callable) {
209	this.callable = callable;
210	}
211
212	public boolean cancel(boolean mayInterruptIfRunning) {
213	return CancellableTask.this.cancel(mayInterruptIfRunning);
214	}
215
216	public boolean isCancelled() {
217	return CancellableTask.this.isCancelled();
218	}
219
220
221	public boolean isDone() {
222	return CancellableTask.this.isDone();
223	}
224
225
226	/**
227	* Sets this Future to the results of <tt>callable.call</tt>
228	*/
229	public void run() {
230	try {
231	set(callable.call());
232	} catch(Throwable ex) {
233	setException(ex);
234	}
235	}
236
237	/**
238	* Waits if necessary for the call to <tt>callable.call</tt> to
239	* complete, and then retrieves its result.
240	*
241	* @return computed result
242	* @throws CancellationException here???
243	* @throws ExecutionException if underlying computation threw an
244	* exception
245	* @throws InterruptedException if current thread was interrupted
246	* while waiting
247	*/
248	public V get() throws InterruptedException, ExecutionException {
249	lock.lock();
250	try {
251	while (!isDone())
252	accessible.await();
253	if (isCancelled())
254	throw new CancellationException();
255	else if (exception != null)
256	throw new ExecutionException(exception);
257	else
258	return result;
259	} finally {
260	lock.unlock();
261	}
262	}
263
264	/**
265	* Waits if necessary for at most the given time for the call to
266	* <tt>callable.call</tt> to complete, and then retrieves its
267	* result.
268	*
269	* @param timeout the maximum time to wait
270	* @param unit the time unit of the timeout argument
271	* @return computed result
272	* @throws ExecutionException if underlying computation threw an
273	* exception
274	* @throws InterruptedException if current thread was interrupted
275	* while waiting
276	* @throws TimeoutException if the wait timed out
277	*/
278	public V get(long timeout, TimeUnit unit)
279	throws InterruptedException, ExecutionException, TimeoutException {
280	lock.lock();
281	try {
282	if (!isDone()) {
283	long nanos = unit.toNanos(timeout);
284	do {
285	if (nanos <= 0)
286	throw new TimeoutException();
287	nanos = accessible.awaitNanos(nanos);
288	} while (!isDone());
289	}
290	if (isCancelled())
291	throw new CancellationException();
292	else if (exception != null)
293	throw new ExecutionException(exception);
294	else
295	return result;
296	} finally {
297	lock.unlock();
298	}
299	}
300
301	/**
302	* Sets the result of this Future to the given value.
303	* @param v the value
304	*/
305	protected void set(V v) {
306	lock.lock();
307	try {
308	result = v;
309	setDone();
310	accessible.signalAll();
311	} finally {
312	lock.unlock();
313	}
314	}
315
316	/**
317	* Causes this futue to report an <tt>ExecutionException</tt>
318	* with the given throwable as its cause.
319	* @param t the cause of failure.
320	*/
321	protected void setException(Throwable t) {
322	lock.lock();
323	try {
324	exception = t;
325	setDone();
326	accessible.signalAll();
327	} finally {
328	lock.unlock();
329	}
330	}
331	}
332
333	}