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.
 */

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 invoking the given
     * runnable when executed.
     */
    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.
     */
    protected Runnable getRunnable() {
        return runnable;
    }

    /**
     * Set the Runnable forming the basis of this task.
     */
    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;
        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:	1.2
Committed:	Fri Jun 6 16:53:04 2003 UTC (21 years ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PRELIMINARY_TEST_RELEASE_1
Changes since 1.1:	+1 -1 lines
Log Message:	Minor doc updates; FairReentrantLock serialize now
#	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
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			*/
16
17			public class CancellableTask implements Cancellable, Runnable {
18			/**
19			* Holds the run-state, taking on values:
20			* null = not yet started,
21			* [some thread ref] = running,
22			* DONE = completed normally,
23			* CANCELLED = cancelled (may or may not have ever run).
24			* Transitions use atomic updates.
25			*/
26			private volatile Object runner;
27
28			/*
29			* Special value for "runner" indicating task is completed
30			*/
31			private static final Object DONE = new Object();
32
33			/*
34			* Special value for "runner" indicating task is cancelled
35			*/
36			private static final Object CANCELLED = new Object();
37
38			private static AtomicReferenceFieldUpdater<CancellableTask, Object>
39			runnerUpdater = new AtomicReferenceFieldUpdater<CancellableTask, Object>(new CancellableTask[0], new Object[0], "runner");
40
41			/**
42			* The runnable underlying this task
43			*/
44			private volatile Runnable runnable;
45
46			/**
47			* Creates a new CancellableTask invoking the given
48			* runnable when executed.
49			*/
50			public CancellableTask(Runnable r) {
51			this.runnable = r;
52			}
53
54			/**
55			* Creates a new CancellableTask without a runnable action, which
56			* must be set using <tt>setRunnable</tt> before use. This is
57			* intended for use in subclasses that must complete superclass
58			* construction beofre establishing the runnable action.
59			*/
60			protected CancellableTask() {
61			}
62
63
64			public boolean cancel(boolean mayInterruptIfRunning) {
65			Object r = runner;
66			if (r == DONE \|\| r == CANCELLED)
67			return false;
68
69			if (mayInterruptIfRunning &&
70			r != null &&
71			r instanceof Thread &&
72			r != Thread.currentThread() &&
73			runnerUpdater.compareAndSet(this, r, CANCELLED)) {
74
75			((Thread)r).interrupt();
76			}
77			else {
78			runnerUpdater.set(this, CANCELLED);
79			}
80			return true;
81			}
82
83			public boolean isCancelled() {
84			return runner == CANCELLED;
85			}
86
87			public boolean isDone() {
88			Object r = runner;
89			return r == DONE \|\| r == CANCELLED;
90			}
91
92			/**
93			* Return the Runnable forming the basis of this task.
94			*/
95			protected Runnable getRunnable() {
96			return runnable;
97			}
98
99			/**
100			* Set the Runnable forming the basis of this task.
101			*/
102			protected void setRunnable(Runnable r) {
103			runnable = r;
104			}
105
106			/**
107			* Set the state of this task to Cancelled
108			*/
109			protected void setCancelled() {
110			runnerUpdater.set(this, CANCELLED);
111			}
112
113			/**
114			* Set the state of this task to Done, unless already
115			* in a Cancelled state, in which Cancelled status is preserved.
116			*
117			*/
118			protected void setDone() {
119			for (;;) {
120			Object r = runner;
121			if (r == DONE \|\| r == CANCELLED)
122			return;
123			if (runnerUpdater.compareAndSet(this, r, DONE))
124			return;
125			}
126			}
127
128			/**
129			* Attempt to set the state of this task to Running, succeeding
130			* only if the state is currently NOT Done, Running, or Cancelled.
131	dl	1.2	* @return true if successful
132	dl	1.1	*/
133			protected boolean setRunning() {
134			return runnerUpdater.compareAndSet(this, null, Thread.currentThread());
135			}
136
137			public void run() {
138			if (setRunning()) {
139			try {
140			runnable.run();
141			}
142			finally {
143			setDone();
144			}
145			}
146			}
147
148			/**
149			* Implementation of Future methods under the control of a current
150			* CancellableTask. This is split into an inner class to permit
151			* Future support to be mixed-in with other flavors of tasks.
152			*/
153			protected class InnerCancellableFuture<V> implements Future<V>, Runnable {
154			private final Callable<V> callable;
155			private final ReentrantLock lock = new ReentrantLock();
156			private final Condition accessible = lock.newCondition();
157			private V result;
158			private Throwable exception;
159			protected InnerCancellableFuture(Callable<V> callable) {
160			this.callable = callable;
161			}
162
163			public boolean isDone() {
164			return CancellableTask.this.isDone();
165			}
166
167			public void run() {
168			try {
169			set(callable.call());
170			}
171			catch(Throwable ex) {
172			setException(ex);
173			}
174			}
175
176			public V get() throws InterruptedException, ExecutionException {
177			lock.lock();
178			try {
179			while (!isDone())
180			accessible.await();
181			if (isCancelled())
182			throw new CancellationException();
183			else if (exception != null)
184			throw new ExecutionException(exception);
185			else
186			return result;
187			}
188			finally {
189			lock.unlock();
190			}
191			}
192
193			public V get(long timeout, TimeUnit unit)
194			throws InterruptedException, ExecutionException, TimeoutException {
195			lock.lock();
196			try {
197			if (!isDone()) {
198			long nanos = unit.toNanos(timeout);
199			do {
200			if (nanos <= 0)
201			throw new TimeoutException();
202			nanos = accessible.awaitNanos(nanos);
203			} while (!isDone());
204			}
205			if (isCancelled())
206			throw new CancellationException();
207			else if (exception != null)
208			throw new ExecutionException(exception);
209			else
210			return result;
211			}
212			finally {
213			lock.unlock();
214			}
215			}
216
217			protected void set(V v) {
218			lock.lock();
219			try {
220			result = v;
221			setDone();
222			accessible.signalAll();
223			}
224			finally {
225			lock.unlock();
226			}
227			}
228
229			protected void setException(Throwable t) {
230			lock.lock();
231			try {
232			exception = t;
233			setDone();
234			accessible.signalAll();
235			}
236			finally {
237			lock.unlock();
238			}
239			}
240			}
241
242			}