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
     */
    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:	1.9
Committed:	Tue Aug 5 00:37:41 2003 UTC (20 years, 10 months ago) by dl
Branch:	MAIN
Changes since 1.8:	+3 -1 lines
Log Message:	Kill old JSR166Support
#	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	*/
99	protected Runnable getRunnable() {
100	return runnable;
101	}
102
103	/**
104	* Set the Runnable forming the basis of this task.
105	* @param r the runnable action
106	*/
107	protected void setRunnable(Runnable r) {
108	runnable = r;
109	}
110
111	/**
112	* Set the state of this task to Cancelled
113	*/
114	protected void setCancelled() {
115	runnerUpdater.set(this, CANCELLED);
116	}
117
118	/**
119	* Set the state of this task to Done, unless already
120	* in a Cancelled state, in which Cancelled status is preserved.
121	*
122	*/
123	protected void setDone() {
124	for (;;) {
125	Object r = runner;
126	if (r == DONE \|\| r == CANCELLED)
127	return;
128	if (runnerUpdater.compareAndSet(this, r, DONE))
129	return;
130	}
131	}
132
133	/**
134	* Attempt to set the state of this task to Running, succeeding
135	* only if the state is currently NOT Done, Running, or Cancelled.
136	* @return true if successful
137	*/
138	protected boolean setRunning() {
139	return runnerUpdater.compareAndSet(this, null, Thread.currentThread());
140	}
141
142	public void run() {
143	if (setRunning()) {
144	try {
145	runnable.run();
146	}
147	finally {
148	setDone();
149	}
150	}
151	}
152
153	/**
154	* Implementation of Future methods under the control of a current
155	* CancellableTask. This is split into an inner class to permit
156	* Future support to be mixed-in with other flavors of tasks.
157	*/
158	protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
159	private final Callable<V> callable;
160	private final ReentrantLock lock = new ReentrantLock();
161	private final Condition accessible = lock.newCondition();
162	private V result;
163	private Throwable exception;
164
165	/**
166	* Create an InnerCancellableFuture that will execute the
167	* given callable.
168	* @param callable the function to execute
169	*/
170	protected InnerCancellableFuture(Callable<V> callable) {
171	this.callable = callable;
172	}
173
174	public boolean isDone() {
175	return CancellableTask.this.isDone();
176	}
177
178	public void run() {
179	try {
180	set(callable.call());
181	}
182	catch(Throwable ex) {
183	setException(ex);
184	}
185	}
186
187	public V get() throws InterruptedException, ExecutionException {
188	lock.lock();
189	try {
190	while (!isDone())
191	accessible.await();
192	if (isCancelled())
193	throw new CancellationException();
194	else if (exception != null)
195	throw new ExecutionException(exception);
196	else
197	return result;
198	}
199	finally {
200	lock.unlock();
201	}
202	}
203
204	public V get(long timeout, TimeUnit unit)
205	throws InterruptedException, ExecutionException, TimeoutException {
206	lock.lock();
207	try {
208	if (!isDone()) {
209	long nanos = unit.toNanos(timeout);
210	do {
211	if (nanos <= 0)
212	throw new TimeoutException();
213	nanos = accessible.awaitNanos(nanos);
214	} while (!isDone());
215	}
216	if (isCancelled())
217	throw new CancellationException();
218	else if (exception != null)
219	throw new ExecutionException(exception);
220	else
221	return result;
222	}
223	finally {
224	lock.unlock();
225	}
226	}
227
228	protected void set(V v) {
229	lock.lock();
230	try {
231	result = v;
232	setDone();
233	accessible.signalAll();
234	}
235	finally {
236	lock.unlock();
237	}
238	}
239
240	protected void setException(Throwable t) {
241	lock.lock();
242	try {
243	exception = t;
244	setDone();
245	accessible.signalAll();
246	}
247	finally {
248	lock.unlock();
249	}
250	}
251	}
252
253	}