13 |
|
* have smaller stack space footprints and faster completion mechanics |
14 |
|
* but higher per-task footprints. Compared to LinkedAsyncActions, |
15 |
|
* BinaryAsyncActions are simpler to use and have less overhead in |
16 |
< |
* typical uasges but are restricted to binary computation trees. |
16 |
> |
* typical usages but are restricted to binary computation trees. |
17 |
|
* |
18 |
< |
* <p>Upon construction, an BinaryAsyncAction does not bear any |
18 |
> |
* <p>Upon construction, a BinaryAsyncAction does not bear any |
19 |
|
* linkages. For non-root tasks, links must be established using |
20 |
< |
* method <tt>linkSubtasks</tt> before use. |
20 |
> |
* method {@link #linkSubtasks} before use. |
21 |
|
* |
22 |
|
* <p><b>Sample Usage.</b> A version of Fibonacci: |
23 |
|
* <pre> |
27 |
|
* Fib(int n) { this.n = n; } |
28 |
|
* protected void compute() { |
29 |
|
* if (n > 1) { |
30 |
< |
* linkAndForkSubtasks(new Fib(n-1), new Fib(n-2)); |
30 |
> |
* linkAndForkSubtasks(new Fib(n-1), new Fib(n-2)); |
31 |
|
* else { |
32 |
< |
* result = n; // fib(0)==0; fib(1)==1 |
33 |
< |
* complete(); |
32 |
> |
* result = n; // fib(0)==0; fib(1)==1 |
33 |
> |
* complete(); |
34 |
|
* } |
35 |
|
* } |
36 |
|
* protected void onComplete(BinaryAsyncAction x, BinaryAsyncAction y) { |
37 |
< |
* result = ((Fib)x).result + ((Fib)y).result; |
37 |
> |
* result = ((Fib)x).result + ((Fib)y).result; |
38 |
|
* } |
39 |
|
* } |
40 |
|
* </pre> |
41 |
< |
* An alternative, and usually faster strategy is to instead use a |
41 |
> |
* An alternative, and usually faster, strategy is to instead use a |
42 |
|
* loop to fork subtasks: |
43 |
|
* <pre> |
44 |
|
* protected void compute() { |
45 |
|
* Fib f = this; |
46 |
|
* while (f.n > 1) { |
47 |
< |
* Fib left = new Fib(f.n - 1); |
48 |
< |
* Fib right = new Fib(f.n - 2); |
49 |
< |
* f.linkSubtasks(left, right); |
50 |
< |
* right.fork(); // fork right |
51 |
< |
* f = left; // loop on left |
47 |
> |
* Fib left = new Fib(f.n - 1); |
48 |
> |
* Fib right = new Fib(f.n - 2); |
49 |
> |
* f.linkSubtasks(left, right); |
50 |
> |
* right.fork(); // fork right |
51 |
> |
* f = left; // loop on left |
52 |
|
* } |
53 |
|
* f.result = f.n; |
54 |
|
* f.complete(); |
57 |
|
* </pre> |
58 |
|
*/ |
59 |
|
public abstract class BinaryAsyncAction extends ForkJoinTask<Void> { |
60 |
< |
private volatile int controlState; |
61 |
< |
|
62 |
< |
static final AtomicIntegerFieldUpdater<BinaryAsyncAction> controlStateUpdater = |
60 |
> |
private volatile int controlState; |
61 |
> |
|
62 |
> |
static final AtomicIntegerFieldUpdater<BinaryAsyncAction> controlStateUpdater = |
63 |
|
AtomicIntegerFieldUpdater.newUpdater(BinaryAsyncAction.class, "controlState"); |
64 |
< |
|
64 |
> |
|
65 |
|
/** |
66 |
|
* Parent to propagate completion; nulled after completion to |
67 |
|
* avoid retaining entire tree as garbage |
75 |
|
|
76 |
|
/** |
77 |
|
* Creates a new action. Unless this is a root task, you will need |
78 |
< |
* to link it using method <tt>linkSubtasks</tt> before forking as |
78 |
> |
* to link it using method {@link #linkSubtasks} before forking as |
79 |
|
* a subtask. |
80 |
|
*/ |
81 |
|
protected BinaryAsyncAction() { |
89 |
|
* as parent, and each other as siblings. |
90 |
|
* @param x one subtask |
91 |
|
* @param y the other subtask |
92 |
< |
* @throws NullPointerException if either argument is null. |
92 |
> |
* @throws NullPointerException if either argument is null |
93 |
|
*/ |
94 |
|
public final void linkSubtasks(BinaryAsyncAction x, BinaryAsyncAction y) { |
95 |
|
x.parent = y.parent = this; |
98 |
|
} |
99 |
|
|
100 |
|
/** |
101 |
< |
* Overridable callback action triggered upon <tt>complete</tt> of |
101 |
> |
* Overridable callback action triggered upon {@code complete} of |
102 |
|
* subtasks. Upon invocation, both subtasks have completed. |
103 |
< |
* After return, this task <tt>isDone</tt> and is joinable by |
103 |
> |
* After return, this task {@code isDone} and is joinable by |
104 |
|
* other tasks. The default version of this method does nothing. |
105 |
|
* But it may be overridden in subclasses to perform some action |
106 |
|
* (for example a reduction) when this task is completes. |
112 |
|
|
113 |
|
/** |
114 |
|
* Overridable callback action triggered by |
115 |
< |
* <tt>completeExceptionally</tt>. Upon invocation, this task has |
115 |
> |
* {@code completeExceptionally}. Upon invocation, this task has |
116 |
|
* aborted due to an exception (accessible via |
117 |
< |
* <tt>getException</tt>). If this method returns <tt>true</tt>, |
117 |
> |
* {@code getException}). If this method returns {@code true}, |
118 |
|
* the exception propagates to the current task's |
119 |
|
* parent. Otherwise, normal completion is propagated. The |
120 |
|
* default version of this method does nothing and returns |
121 |
< |
* <tt>true</tt>. |
121 |
> |
* {@code true}. |
122 |
|
* @return true if this task's exception should be propagated to |
123 |
< |
* this tasks parent. |
123 |
> |
* this task's parent |
124 |
|
*/ |
125 |
|
protected boolean onException() { |
126 |
|
return true; |
127 |
|
} |
128 |
|
|
129 |
|
/** |
130 |
< |
* Equivalent in effect to invoking <tt>linkSubtasks</tt> and then |
130 |
> |
* Equivalent in effect to invoking {@link #linkSubtasks} and then |
131 |
|
* forking both tasks. |
132 |
|
* @param x one subtask |
133 |
|
* @param y the other subtask |
156 |
|
|
157 |
|
/** |
158 |
|
* Completes this task, and if this task has a sibling that is |
159 |
< |
* also complete, invokes <tt>onComplete</tt> of parent task, and so |
159 |
> |
* also complete, invokes {@code onComplete} of parent task, and so |
160 |
|
* on. If an exception is encountered, tasks instead |
161 |
< |
* <tt>completeExceptionally</tt>. |
161 |
> |
* {@code completeExceptionally}. |
162 |
|
*/ |
163 |
|
public final void complete() { |
164 |
|
// todo: Use tryUnfork without possibly blowing stack |
169 |
|
a.sibling = null; |
170 |
|
a.parent = null; |
171 |
|
a.completeThis(); |
172 |
< |
if (p == null || p.compareAndSetControlState(0, 1)) |
172 |
> |
if (p == null || p.compareAndSetControlState(0, 1)) |
173 |
|
break; |
174 |
|
try { |
175 |
|
p.onComplete(a, s); |
184 |
|
/** |
185 |
|
* Completes this task abnormally. Unless this task already |
186 |
|
* cancelled or aborted, upon invocation, this method invokes |
187 |
< |
* <tt>onException</tt>, and then, depending on its return value, |
188 |
< |
* completees parent (if one exists) exceptionally or normally. To |
187 |
> |
* {@code onException}, and then, depending on its return value, |
188 |
> |
* completes parent (if one exists) exceptionally or normally. To |
189 |
|
* avoid unbounded exception loops, this method aborts if an |
190 |
< |
* exception is encountered in any <tt>onException</tt> |
190 |
> |
* exception is encountered in any {@code onException} |
191 |
|
* invocation. |
192 |
|
* @param ex the exception to throw when joining this task |
193 |
|
* @throws NullPointerException if ex is null |
194 |
|
* @throws Throwable if any invocation of |
195 |
< |
* <tt>onException</tt> does so. |
195 |
> |
* {@code onException} does so |
196 |
|
*/ |
197 |
|
public final void completeExceptionally(Throwable ex) { |
198 |
|
BinaryAsyncAction a = this; |
209 |
|
/** |
210 |
|
* Returns this task's parent, or null if none or this task |
211 |
|
* is already complete. |
212 |
< |
* @return this task's parent, or null if none. |
212 |
> |
* @return this task's parent, or null if none |
213 |
|
*/ |
214 |
|
public final BinaryAsyncAction getParent() { |
215 |
|
return parent; |
218 |
|
/** |
219 |
|
* Returns this task's sibling, or null if none or this task is |
220 |
|
* already complete. |
221 |
< |
* @return this task's sibling, or null if none. |
221 |
> |
* @return this task's sibling, or null if none |
222 |
|
*/ |
223 |
|
public BinaryAsyncAction getSibling() { |
224 |
|
return sibling; |
267 |
|
} |
268 |
|
|
269 |
|
/** |
270 |
< |
* Sets the control state to the given value, |
270 |
> |
* Increments the control state. |
271 |
|
* @param value the new value |
272 |
|
*/ |
273 |
|
protected final void incrementControlState() { |
275 |
|
} |
276 |
|
|
277 |
|
/** |
278 |
< |
* Decrement the control state |
278 |
> |
* Decrements the control state. |
279 |
|
* @return true if successful |
280 |
|
*/ |
281 |
|
protected final void decrementControlState() { |
282 |
|
controlStateUpdater.decrementAndGet(this); |
283 |
|
} |
284 |
|
|
285 |
+ |
|
286 |
|
} |