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.*;

/**
 * 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 = new AtomicReferenceFieldUpdater<CancellableTask, Object>(new CancellableTask[0], new Object[0], "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 &&
            r != Thread.currentThread() &&
            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
     */
    protected Runnable getRunnable() {
        return runnable;
    }

    /**
     * Set the Runnable forming the basis of this task.
     * @param r the runnable action
     */
    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:	1.5
Committed:	Tue Jun 24 14:34:47 2003 UTC (20 years, 11 months ago) by dl
Branch:	MAIN
Changes since 1.4:	+13 -2 lines
Log Message:	Added missing javadoc tags; minor reformatting
#	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
10	/**
11	* Base class for cancellable actions running in the Executor
12	* framework. In addition to serving as a standalone class, this
13	* provides <tt>protected</tt> functionality that may be useful when
14	* creating customized task classes.
15	* @since 1.5
16	* @author Doug Lea
17	*/
18
19	public class CancellableTask implements Cancellable, Runnable {
20	/**
21	* Holds the run-state, taking on values:
22	* null = not yet started,
23	* [some thread ref] = running,
24	* DONE = completed normally,
25	* CANCELLED = cancelled (may or may not have ever run).
26	* Transitions use atomic updates.
27	*/
28	private volatile Object runner;
29
30	/**
31	* Special value for "runner" indicating task is completed
32	*/
33	private static final Object DONE = new Object();
34
35	/**
36	* Special value for "runner" indicating task is cancelled
37	*/
38	private static final Object CANCELLED = new Object();
39
40	private static AtomicReferenceFieldUpdater<CancellableTask, Object>
41	runnerUpdater = new AtomicReferenceFieldUpdater<CancellableTask, Object>(new CancellableTask[0], new Object[0], "runner");
42
43	/**
44	* The runnable underlying this task
45	*/
46	private volatile Runnable runnable;
47
48	/**
49	* Creates a new CancellableTask which invokes the given
50	* <tt>Runnable</tt> when executed.
51	* @param r the runnable action
52	*/
53	public CancellableTask(Runnable r) {
54	this.runnable = r;
55	}
56
57	/**
58	* Creates a new CancellableTask without a runnable action, which
59	* must be set using <tt>setRunnable</tt> before use. This is
60	* intended for use in subclasses that must complete superclass
61	* construction beofre establishing the runnable action.
62	*/
63	protected CancellableTask() {
64	}
65
66
67	public boolean cancel(boolean mayInterruptIfRunning) {
68	Object r = runner;
69	if (r == DONE \|\| r == CANCELLED)
70	return false;
71
72	if (mayInterruptIfRunning &&
73	r != null &&
74	r instanceof Thread &&
75	r != Thread.currentThread() &&
76	runnerUpdater.compareAndSet(this, r, CANCELLED))
77
78	((Thread)r).interrupt();
79	else
80	runnerUpdater.set(this, CANCELLED);
81	return true;
82	}
83
84	public boolean isCancelled() {
85	return runner == CANCELLED;
86	}
87
88	public boolean isDone() {
89	Object r = runner;
90	return r == DONE \|\| r == CANCELLED;
91	}
92
93	/**
94	* Return the Runnable forming the basis of this task.
95	* @return the runnable action
96	*/
97	protected Runnable getRunnable() {
98	return runnable;
99	}
100
101	/**
102	* Set the Runnable forming the basis of this task.
103	* @param r the runnable action
104	*/
105	protected void setRunnable(Runnable r) {
106	runnable = r;
107	}
108
109	/**
110	* Set the state of this task to Cancelled
111	*/
112	protected void setCancelled() {
113	runnerUpdater.set(this, CANCELLED);
114	}
115
116	/**
117	* Set the state of this task to Done, unless already
118	* in a Cancelled state, in which Cancelled status is preserved.
119	*
120	*/
121	protected void setDone() {
122	for (;;) {
123	Object r = runner;
124	if (r == DONE \|\| r == CANCELLED)
125	return;
126	if (runnerUpdater.compareAndSet(this, r, DONE))
127	return;
128	}
129	}
130
131	/**
132	* Attempt to set the state of this task to Running, succeeding
133	* only if the state is currently NOT Done, Running, or Cancelled.
134	* @return true if successful
135	*/
136	protected boolean setRunning() {
137	return runnerUpdater.compareAndSet(this, null, Thread.currentThread());
138	}
139
140	public void run() {
141	if (setRunning()) {
142	try {
143	runnable.run();
144	}
145	finally {
146	setDone();
147	}
148	}
149	}
150
151	/**
152	* Implementation of Future methods under the control of a current
153	* CancellableTask. This is split into an inner class to permit
154	* Future support to be mixed-in with other flavors of tasks.
155	*/
156	protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
157	private final Callable<V> callable;
158	private final ReentrantLock lock = new ReentrantLock();
159	private final Condition accessible = lock.newCondition();
160	private V result;
161	private Throwable exception;
162
163	/**
164	* Create an InnerCancellableFuture that will execute the
165	* given callable.
166	* @param callable the function to execute
167	*/
168	protected InnerCancellableFuture(Callable<V> callable) {
169	this.callable = callable;
170	}
171
172	public boolean isDone() {
173	return CancellableTask.this.isDone();
174	}
175
176	public void run() {
177	try {
178	set(callable.call());
179	}
180	catch(Throwable ex) {
181	setException(ex);
182	}
183	}
184
185	public V get() throws InterruptedException, ExecutionException {
186	lock.lock();
187	try {
188	while (!isDone())
189	accessible.await();
190	if (isCancelled())
191	throw new CancellationException();
192	else if (exception != null)
193	throw new ExecutionException(exception);
194	else
195	return result;
196	}
197	finally {
198	lock.unlock();
199	}
200	}
201
202	public V get(long timeout, TimeUnit unit)
203	throws InterruptedException, ExecutionException, TimeoutException {
204	lock.lock();
205	try {
206	if (!isDone()) {
207	long nanos = unit.toNanos(timeout);
208	do {
209	if (nanos <= 0)
210	throw new TimeoutException();
211	nanos = accessible.awaitNanos(nanos);
212	} while (!isDone());
213	}
214	if (isCancelled())
215	throw new CancellationException();
216	else if (exception != null)
217	throw new ExecutionException(exception);
218	else
219	return result;
220	}
221	finally {
222	lock.unlock();
223	}
224	}
225
226	protected void set(V v) {
227	lock.lock();
228	try {
229	result = v;
230	setDone();
231	accessible.signalAll();
232	}
233	finally {
234	lock.unlock();
235	}
236	}
237
238	protected void setException(Throwable t) {
239	lock.lock();
240	try {
241	exception = t;
242	setDone();
243	accessible.signalAll();
244	}
245	finally {
246	lock.unlock();
247	}
248	}
249	}
250
251	}