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, as explained at |
4 |
|
|
* http://creativecommons.org/licenses/publicdomain |
5 |
|
|
*/ |
6 |
|
|
|
7 |
|
|
import java.util.concurrent.*; |
8 |
|
|
import java.util.*; |
9 |
|
|
|
10 |
|
|
/** |
11 |
|
|
* A computation that is broken into a series of task executions, each |
12 |
|
|
* separated by a Phaser arrival. Concrete subclasses must |
13 |
|
|
* define method <tt>compute</tt>, that performs the action occurring |
14 |
|
|
* at each step of the barrier. Upon invocation of this task, the |
15 |
|
|
* <tt>compute</tt> method is repeatedly invoked until the barrier |
16 |
|
|
* <tt>isTerminated</tt> or until its execution throws an exception. |
17 |
|
|
* |
18 |
|
|
* <p> <b>Sample Usage.</b> Here is a sketch of a set of CyclicActions |
19 |
|
|
* that each perform 500 iterations of an imagined image smoothing |
20 |
|
|
* operation. Note that the aggregate ImageSmoother task itself is not |
21 |
|
|
* a CyclicTask. |
22 |
|
|
* |
23 |
|
|
* <pre> |
24 |
|
|
* class ImageSmoother extends RecursiveAction { |
25 |
|
|
* protected void compute() { |
26 |
|
|
* Phaser b = new Phaser() { |
27 |
|
|
* protected boolean onAdvance(int cycle, int registeredParties) { |
28 |
|
|
* return registeredParties <= 0 || cycle >= 500; |
29 |
|
|
* } |
30 |
|
|
* } |
31 |
|
|
* int n = pool.getParallelismLevel(); |
32 |
|
|
* CyclicAction[] actions = new CyclicAction[n]; |
33 |
|
|
* for (int i = 0; i < n; ++i) { |
34 |
|
|
* action[i] = new CyclicAction(b) { |
35 |
|
|
* protected void compute() { |
36 |
|
|
* smoothImagePart(i); |
37 |
|
|
* } |
38 |
|
|
* } |
39 |
|
|
* } |
40 |
|
|
* invokeAll(actions); |
41 |
|
|
* } |
42 |
|
|
* } |
43 |
|
|
* </pre> |
44 |
|
|
*/ |
45 |
|
|
public abstract class CyclicAction extends ForkJoinTask<Void> { |
46 |
|
|
final Phaser barrier; |
47 |
|
|
boolean deregistered; |
48 |
|
|
int lastArrived; |
49 |
|
|
|
50 |
|
|
/** |
51 |
|
|
* Constructs a new CyclicAction using the supplied barrier, |
52 |
|
|
* registering for this barrier upon construction. |
53 |
|
|
* @param barrier the barrier |
54 |
|
|
*/ |
55 |
|
|
public CyclicAction(Phaser barrier) { |
56 |
|
|
this.barrier = barrier; |
57 |
|
|
lastArrived = barrier.register() - 1; |
58 |
|
|
} |
59 |
|
|
|
60 |
|
|
/** |
61 |
|
|
* The computation performed by this task on each cycle of the |
62 |
|
|
* barrier. While you must define this method, you should not in |
63 |
|
|
* general call it directly. |
64 |
|
|
*/ |
65 |
|
|
protected abstract void step(); |
66 |
|
|
|
67 |
|
|
/** |
68 |
|
|
* Returns the barrier |
69 |
|
|
*/ |
70 |
|
|
public final Phaser getBarrier() { |
71 |
|
|
return barrier; |
72 |
|
|
} |
73 |
|
|
|
74 |
|
|
/** |
75 |
|
|
* Returns the current cycle of the barrier |
76 |
|
|
*/ |
77 |
|
|
public final int getCycle() { |
78 |
|
|
return barrier.getPhase(); |
79 |
|
|
} |
80 |
|
|
|
81 |
|
|
public final Void getRawResult() { return null; } |
82 |
|
|
protected final void setRawResult(Void mustBeNull) { } |
83 |
|
|
|
84 |
|
|
private void deregister() { |
85 |
|
|
if (!deregistered) { |
86 |
|
|
deregistered = true; |
87 |
|
|
barrier.arriveAndDeregister(); |
88 |
|
|
} |
89 |
|
|
} |
90 |
|
|
|
91 |
|
|
protected final boolean exec() { |
92 |
|
|
Phaser b = barrier; |
93 |
|
|
if (!isDone()) { |
94 |
|
|
b.awaitAdvance(lastArrived); |
95 |
|
|
if (b.getPhase() >= 0) { |
96 |
|
|
try { |
97 |
|
|
step(); |
98 |
|
|
} catch (Throwable rex) { |
99 |
|
|
deregister(); |
100 |
|
|
completeExceptionally(rex); |
101 |
|
|
return false; |
102 |
|
|
} |
103 |
|
|
if ((lastArrived = b.arrive()) >= 0) { |
104 |
|
|
this.fork(); |
105 |
|
|
return false; |
106 |
|
|
} |
107 |
|
|
} |
108 |
|
|
} |
109 |
|
|
deregister(); |
110 |
|
|
return true; |
111 |
|
|
} |
112 |
|
|
|
113 |
|
|
} |