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 |
dl |
1.14 |
* 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 |
dl |
1.5 |
* @since 1.5 |
18 |
|
|
* @author Doug Lea |
19 |
dl |
1.1 |
*/ |
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 |
dl |
1.5 |
/** |
33 |
dl |
1.1 |
* Special value for "runner" indicating task is completed |
34 |
|
|
*/ |
35 |
|
|
private static final Object DONE = new Object(); |
36 |
|
|
|
37 |
dl |
1.5 |
/** |
38 |
dl |
1.1 |
* 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 |
dl |
1.9 |
runnerUpdater = |
44 |
|
|
AtomicReferenceFieldUpdater.newUpdater |
45 |
|
|
(CancellableTask.class, Object.class, "runner"); |
46 |
dl |
1.1 |
|
47 |
|
|
/** |
48 |
|
|
* The runnable underlying this task |
49 |
|
|
*/ |
50 |
|
|
private volatile Runnable runnable; |
51 |
|
|
|
52 |
|
|
/** |
53 |
brian |
1.4 |
* Creates a new CancellableTask which invokes the given |
54 |
|
|
* <tt>Runnable</tt> when executed. |
55 |
dl |
1.5 |
* @param r the runnable action |
56 |
dl |
1.16 |
* @throws NullPointerException if runnable is null |
57 |
dl |
1.1 |
*/ |
58 |
|
|
public CancellableTask(Runnable r) { |
59 |
dl |
1.16 |
if (r == null) |
60 |
|
|
throw new NullPointerException(); |
61 |
dl |
1.1 |
this.runnable = r; |
62 |
|
|
} |
63 |
|
|
|
64 |
|
|
/** |
65 |
|
|
* Creates a new CancellableTask without a runnable action, which |
66 |
|
|
* must be set using <tt>setRunnable</tt> before use. This is |
67 |
|
|
* intended for use in subclasses that must complete superclass |
68 |
dl |
1.14 |
* construction before establishing the runnable action. |
69 |
dl |
1.1 |
*/ |
70 |
|
|
protected CancellableTask() { |
71 |
|
|
} |
72 |
|
|
|
73 |
|
|
|
74 |
|
|
public boolean cancel(boolean mayInterruptIfRunning) { |
75 |
|
|
Object r = runner; |
76 |
|
|
if (r == DONE || r == CANCELLED) |
77 |
|
|
return false; |
78 |
|
|
|
79 |
|
|
if (mayInterruptIfRunning && |
80 |
|
|
r != null && |
81 |
|
|
r instanceof Thread && |
82 |
dl |
1.3 |
runnerUpdater.compareAndSet(this, r, CANCELLED)) |
83 |
dl |
1.1 |
|
84 |
|
|
((Thread)r).interrupt(); |
85 |
dl |
1.3 |
else |
86 |
dl |
1.1 |
runnerUpdater.set(this, CANCELLED); |
87 |
|
|
return true; |
88 |
|
|
} |
89 |
|
|
|
90 |
|
|
public boolean isCancelled() { |
91 |
|
|
return runner == CANCELLED; |
92 |
|
|
} |
93 |
|
|
|
94 |
|
|
public boolean isDone() { |
95 |
|
|
Object r = runner; |
96 |
|
|
return r == DONE || r == CANCELLED; |
97 |
|
|
} |
98 |
|
|
|
99 |
|
|
/** |
100 |
|
|
* Return the Runnable forming the basis of this task. |
101 |
dl |
1.5 |
* @return the runnable action |
102 |
tim |
1.10 |
* @see #setRunnable |
103 |
dl |
1.1 |
*/ |
104 |
|
|
protected Runnable getRunnable() { |
105 |
|
|
return runnable; |
106 |
|
|
} |
107 |
|
|
|
108 |
|
|
/** |
109 |
|
|
* Set the Runnable forming the basis of this task. |
110 |
dl |
1.5 |
* @param r the runnable action |
111 |
tim |
1.10 |
* @see #getRunnable |
112 |
dl |
1.1 |
*/ |
113 |
|
|
protected void setRunnable(Runnable r) { |
114 |
|
|
runnable = r; |
115 |
|
|
} |
116 |
|
|
|
117 |
|
|
/** |
118 |
tim |
1.10 |
* Set the state of this task to Cancelled. |
119 |
dl |
1.1 |
*/ |
120 |
|
|
protected void setCancelled() { |
121 |
|
|
runnerUpdater.set(this, CANCELLED); |
122 |
|
|
} |
123 |
|
|
|
124 |
|
|
/** |
125 |
|
|
* Set the state of this task to Done, unless already |
126 |
|
|
* in a Cancelled state, in which Cancelled status is preserved. |
127 |
|
|
* |
128 |
|
|
*/ |
129 |
|
|
protected void setDone() { |
130 |
|
|
for (;;) { |
131 |
|
|
Object r = runner; |
132 |
|
|
if (r == DONE || r == CANCELLED) |
133 |
|
|
return; |
134 |
|
|
if (runnerUpdater.compareAndSet(this, r, DONE)) |
135 |
|
|
return; |
136 |
|
|
} |
137 |
|
|
} |
138 |
|
|
|
139 |
|
|
/** |
140 |
|
|
* Attempt to set the state of this task to Running, succeeding |
141 |
|
|
* only if the state is currently NOT Done, Running, or Cancelled. |
142 |
dl |
1.2 |
* @return true if successful |
143 |
dl |
1.1 |
*/ |
144 |
|
|
protected boolean setRunning() { |
145 |
|
|
return runnerUpdater.compareAndSet(this, null, Thread.currentThread()); |
146 |
|
|
} |
147 |
|
|
|
148 |
dl |
1.17 |
/** |
149 |
|
|
* Runs the runnable if not cancelled, maintaining run status. |
150 |
|
|
*/ |
151 |
dl |
1.1 |
public void run() { |
152 |
|
|
if (setRunning()) { |
153 |
|
|
try { |
154 |
|
|
runnable.run(); |
155 |
tim |
1.11 |
} finally { |
156 |
dl |
1.1 |
setDone(); |
157 |
|
|
} |
158 |
|
|
} |
159 |
|
|
} |
160 |
|
|
|
161 |
|
|
/** |
162 |
dl |
1.16 |
* Reset the run state of this task to its initial state unless |
163 |
|
|
* it has been cancelled. (Note that a cancelled task cannot be |
164 |
|
|
* reset.) |
165 |
|
|
* @return true if successful |
166 |
dl |
1.15 |
*/ |
167 |
dl |
1.16 |
protected boolean reset() { |
168 |
|
|
for (;;) { |
169 |
|
|
Object r = runner; |
170 |
|
|
if (r == CANCELLED) |
171 |
|
|
return false; |
172 |
|
|
if (runnerUpdater.compareAndSet(this, r, null)) |
173 |
|
|
return true; |
174 |
|
|
} |
175 |
dl |
1.15 |
} |
176 |
|
|
|
177 |
|
|
/** |
178 |
dl |
1.1 |
* Implementation of Future methods under the control of a current |
179 |
dl |
1.13 |
* <tt>CancellableTask</tt>, which it relies on for methods |
180 |
|
|
* <tt>isDone</tt>, <tt>isCancelled</tt> and <tt>cancel</tt>. This |
181 |
|
|
* class is split into an inner class to permit Future support to |
182 |
|
|
* be mixed-in with other flavors of tasks. Normally, such a |
183 |
|
|
* class will delegate <tt>Future</tt> <tt>get</tt> methods to the |
184 |
|
|
* <tt>InnerCancellableFuture</tt>, and internally arrange that |
185 |
|
|
* <tt>set</tt> methods be invoked when computations are ready. |
186 |
|
|
* |
187 |
|
|
* <p><b>Sample Usage</b>. Here are fragments of an example subclass. |
188 |
|
|
* <pre> |
189 |
dl |
1.19 |
* class MyFutureTask<V> extends CancellableTask implements Future<V> { |
190 |
dl |
1.13 |
* |
191 |
|
|
* MyFutureTask(Callable<V> callable) { |
192 |
|
|
* setRunnable(new InnerCancellableFuture<V>(callable)); |
193 |
|
|
* } |
194 |
|
|
* |
195 |
|
|
* public V get() throws InterruptedException, ExecutionException { |
196 |
|
|
* return ((InnerCancellableFuture<V>)getRunnable()).get(); |
197 |
|
|
* } |
198 |
|
|
* // (And similarly for timeout version.) |
199 |
|
|
* |
200 |
|
|
* void action() { // whatever action causes execution |
201 |
|
|
* try { |
202 |
|
|
* ((InnerCancellableFuture<V>)getRunnable()).set(compute()); |
203 |
|
|
* } catch (Exception ex) { |
204 |
|
|
* ((InnerCancellableFuture<V>)getRunnable()).setException(ex); |
205 |
|
|
* } |
206 |
|
|
* } |
207 |
|
|
* } |
208 |
|
|
*</pre> |
209 |
dl |
1.1 |
*/ |
210 |
|
|
protected class InnerCancellableFuture<V> implements Future<V>, Runnable { |
211 |
|
|
private final Callable<V> callable; |
212 |
|
|
private final ReentrantLock lock = new ReentrantLock(); |
213 |
|
|
private final Condition accessible = lock.newCondition(); |
214 |
|
|
private V result; |
215 |
|
|
private Throwable exception; |
216 |
dl |
1.5 |
|
217 |
|
|
/** |
218 |
|
|
* Create an InnerCancellableFuture that will execute the |
219 |
|
|
* given callable. |
220 |
|
|
* @param callable the function to execute |
221 |
|
|
*/ |
222 |
dl |
1.1 |
protected InnerCancellableFuture(Callable<V> callable) { |
223 |
|
|
this.callable = callable; |
224 |
|
|
} |
225 |
tim |
1.12 |
|
226 |
|
|
public boolean cancel(boolean mayInterruptIfRunning) { |
227 |
|
|
return CancellableTask.this.cancel(mayInterruptIfRunning); |
228 |
|
|
} |
229 |
|
|
|
230 |
|
|
public boolean isCancelled() { |
231 |
|
|
return CancellableTask.this.isCancelled(); |
232 |
|
|
} |
233 |
|
|
|
234 |
dl |
1.1 |
|
235 |
|
|
public boolean isDone() { |
236 |
|
|
return CancellableTask.this.isDone(); |
237 |
|
|
} |
238 |
|
|
|
239 |
dl |
1.13 |
|
240 |
|
|
/** |
241 |
|
|
* Sets this Future to the results of <tt>callable.call</tt> |
242 |
|
|
*/ |
243 |
dl |
1.1 |
public void run() { |
244 |
|
|
try { |
245 |
|
|
set(callable.call()); |
246 |
tim |
1.11 |
} catch(Throwable ex) { |
247 |
dl |
1.1 |
setException(ex); |
248 |
|
|
} |
249 |
|
|
} |
250 |
|
|
|
251 |
dl |
1.13 |
/** |
252 |
|
|
* Waits if necessary for the call to <tt>callable.call</tt> to |
253 |
|
|
* complete, and then retrieves its result. |
254 |
|
|
* |
255 |
|
|
* @return computed result |
256 |
|
|
* @throws CancellationException here??? |
257 |
|
|
* @throws ExecutionException if underlying computation threw an |
258 |
|
|
* exception |
259 |
|
|
* @throws InterruptedException if current thread was interrupted |
260 |
|
|
* while waiting |
261 |
|
|
*/ |
262 |
dl |
1.1 |
public V get() throws InterruptedException, ExecutionException { |
263 |
|
|
lock.lock(); |
264 |
|
|
try { |
265 |
|
|
while (!isDone()) |
266 |
|
|
accessible.await(); |
267 |
|
|
if (isCancelled()) |
268 |
|
|
throw new CancellationException(); |
269 |
|
|
else if (exception != null) |
270 |
|
|
throw new ExecutionException(exception); |
271 |
|
|
else |
272 |
|
|
return result; |
273 |
tim |
1.11 |
} finally { |
274 |
dl |
1.1 |
lock.unlock(); |
275 |
|
|
} |
276 |
|
|
} |
277 |
|
|
|
278 |
dl |
1.13 |
/** |
279 |
|
|
* Waits if necessary for at most the given time for the call to |
280 |
|
|
* <tt>callable.call</tt> to complete, and then retrieves its |
281 |
|
|
* result. |
282 |
|
|
* |
283 |
|
|
* @param timeout the maximum time to wait |
284 |
dl |
1.14 |
* @param unit the time unit of the timeout argument |
285 |
dl |
1.13 |
* @return computed result |
286 |
|
|
* @throws ExecutionException if underlying computation threw an |
287 |
|
|
* exception |
288 |
|
|
* @throws InterruptedException if current thread was interrupted |
289 |
|
|
* while waiting |
290 |
|
|
* @throws TimeoutException if the wait timed out |
291 |
|
|
*/ |
292 |
dl |
1.1 |
public V get(long timeout, TimeUnit unit) |
293 |
|
|
throws InterruptedException, ExecutionException, TimeoutException { |
294 |
|
|
lock.lock(); |
295 |
|
|
try { |
296 |
|
|
if (!isDone()) { |
297 |
|
|
long nanos = unit.toNanos(timeout); |
298 |
|
|
do { |
299 |
|
|
if (nanos <= 0) |
300 |
|
|
throw new TimeoutException(); |
301 |
|
|
nanos = accessible.awaitNanos(nanos); |
302 |
|
|
} while (!isDone()); |
303 |
|
|
} |
304 |
|
|
if (isCancelled()) |
305 |
|
|
throw new CancellationException(); |
306 |
|
|
else if (exception != null) |
307 |
|
|
throw new ExecutionException(exception); |
308 |
|
|
else |
309 |
|
|
return result; |
310 |
tim |
1.11 |
} finally { |
311 |
dl |
1.1 |
lock.unlock(); |
312 |
|
|
} |
313 |
|
|
} |
314 |
|
|
|
315 |
dl |
1.13 |
/** |
316 |
|
|
* Sets the result of this Future to the given value. |
317 |
|
|
* @param v the value |
318 |
|
|
*/ |
319 |
dl |
1.1 |
protected void set(V v) { |
320 |
|
|
lock.lock(); |
321 |
|
|
try { |
322 |
|
|
result = v; |
323 |
|
|
setDone(); |
324 |
|
|
accessible.signalAll(); |
325 |
tim |
1.11 |
} finally { |
326 |
dl |
1.1 |
lock.unlock(); |
327 |
|
|
} |
328 |
|
|
} |
329 |
|
|
|
330 |
dl |
1.13 |
/** |
331 |
dl |
1.18 |
* Causes this future to report an <tt>ExecutionException</tt> |
332 |
dl |
1.13 |
* with the given throwable as its cause. |
333 |
|
|
* @param t the cause of failure. |
334 |
|
|
*/ |
335 |
dl |
1.1 |
protected void setException(Throwable t) { |
336 |
|
|
lock.lock(); |
337 |
|
|
try { |
338 |
|
|
exception = t; |
339 |
|
|
setDone(); |
340 |
|
|
accessible.signalAll(); |
341 |
tim |
1.11 |
} finally { |
342 |
dl |
1.1 |
lock.unlock(); |
343 |
|
|
} |
344 |
|
|
} |
345 |
|
|
} |
346 |
|
|
|
347 |
|
|
} |