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
#	User	Rev	Content
1	dl	1.1	/*
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	dl	1.6	import java.util.concurrent.locks.*;
10	dl	1.1
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	dl	1.5	* @since 1.5
17			* @author Doug Lea
18	dl	1.1	*/
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	dl	1.5	/**
32	dl	1.1	* Special value for "runner" indicating task is completed
33			*/
34			private static final Object DONE = new Object();
35
36	dl	1.5	/**
37	dl	1.1	* 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	dl	1.9	runnerUpdater =
43			AtomicReferenceFieldUpdater.newUpdater
44			(CancellableTask.class, Object.class, "runner");
45	dl	1.1
46			/**
47			* The runnable underlying this task
48			*/
49			private volatile Runnable runnable;
50
51			/**
52	brian	1.4	* Creates a new CancellableTask which invokes the given
53			* <tt>Runnable</tt> when executed.
54	dl	1.5	* @param r the runnable action
55	dl	1.1	*/
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	dl	1.3	runnerUpdater.compareAndSet(this, r, CANCELLED))
79	dl	1.1
80			((Thread)r).interrupt();
81	dl	1.3	else
82	dl	1.1	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	dl	1.5	* @return the runnable action
98	tim	1.10	* @see #setRunnable
99	dl	1.1	*/
100			protected Runnable getRunnable() {
101			return runnable;
102			}
103
104			/**
105			* Set the Runnable forming the basis of this task.
106	dl	1.5	* @param r the runnable action
107	tim	1.10	* @see #getRunnable
108	dl	1.1	*/
109			protected void setRunnable(Runnable r) {
110			runnable = r;
111			}
112
113			/**
114	tim	1.10	* Set the state of this task to Cancelled.
115	dl	1.1	*/
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	dl	1.2	* @return true if successful
139	dl	1.1	*/
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	dl	1.5
167			/**
168			* Create an InnerCancellableFuture that will execute the
169			* given callable.
170			* @param callable the function to execute
171			*/
172	dl	1.1	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			}