test/loops/LinkedAsyncAction.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;

/**
 * AsyncActions that may be linked in parent-child relationships.
 *
 * <p>Upon construction, a LinkedAsyncAction may register as a
 * subtask of a given parent task. In this case, completion of this
 * task will propagate to its parent. If the parent's pending subtask
 * completion count becomes zero, it too will complete.
 * LinkedAsyncActions rarely use methods {@code join} or
 * {@code invoke} but instead propagate completion to parents
 * implicitly via {@code complete}.  While typical, it is not necessary
 * for each task to {@code complete} itself. For example, it is
 * possible to treat one subtask as a continuation of the current task
 * by not registering it on construction.  In this case, a
 * {@code complete} of the subtask will trigger {@code complete} of the
 * parent without the parent explicitly doing so.
 *
 * <p>In addition to supporting these different computation styles
 * compared to Recursive tasks, LinkedAsyncActions may have smaller
 * stack space footprints while executing, but may have greater
 * per-task overhead.
 *
 * <p><b>Sample Usage.</b> Here is a sketch of a LinkedAsyncAction
 * that visits all of the nodes of a graph. The details of the graph's
 * Node and Edge classes are omitted, but we assume each node contains
 * an {@code AtomicBoolean} mark that starts out false. To execute
 * this, you would create a GraphVisitor for the root node with null
 * parent, and {@code invoke} in a ForkJoinPool. Upon return, all
 * reachable nodes will have been visited.
 *
 * <pre>
 * class GraphVisitor extends LinkedAsyncAction {
 *   final Node node;
 *   GraphVisitor(GraphVistor parent, Node node) {
 *     super(parent); this.node = node;
 *   }
 *   protected void compute() {
 *     if (node.mark.compareAndSet(false, true)) {
 *       for (Edge e : node.edges()) {
 *         Node dest = e.getDestination();
 *         if (!dest.mark.get())
 *           new GraphVisitor(this, dest).fork();
 *       }
 *       visit(node);
 *     }
 *     complete();
 *   }
 * }
 * </pre>
 */
public abstract class LinkedAsyncAction extends ForkJoinTask<Void> {

    /**
     * The maximum number of pending children
     */
    private static int maxPending = 0xffff;

    private volatile int controlState;

    static final AtomicIntegerFieldUpdater<LinkedAsyncAction> controlStateUpdater =
        AtomicIntegerFieldUpdater.newUpdater(LinkedAsyncAction.class, "controlState");


    /**
     * Parent to notify on completion
     */
    private LinkedAsyncAction parent;

    /**
     * Creates a new action with no parent. (You can add a parent
     * later (but before forking) via {@code reinitialize}).
     */
    protected LinkedAsyncAction() {
    }

    /**
     * Creates a new action with the given parent. If the parent is
     * non-null, this task registers with the parent, in which case,
     * the parent task cannot complete until this task completes.
     * @param parent the parent task, or null if none
     */
    protected LinkedAsyncAction(LinkedAsyncAction parent) {
        this.parent = parent;
        if (parent != null)
            parent.incrementControlState();
    }

    /**
     * Creates a new action with the given parent, optionally
     * registering with the parent. If the parent is non-null and
     * {@code register} is true, this task registers with the
     * parent, in which case, the parent task cannot complete until
     * this task completes.
     * @param parent the parent task, or null if none
     * @param register true if parent must wait for this task
     * to complete before it completes
     */
    protected LinkedAsyncAction(LinkedAsyncAction parent, boolean register) {
        this.parent = parent;
        if (parent != null && register)
            parent.incrementControlState();
    }

    /**
     * Creates a new action with the given parent, optionally
     * registering with the parent, and setting the pending join count
     * to the given value. If the parent is non-null and
     * {@code register} is true, this task registers with the
     * parent, in which case, the parent task cannot complete until
     * this task completes. Setting the pending join count requires
     * care -- it is correct only if child tasks do not themselves
     * register.
     * @param parent the parent task, or null if none
     * @param register true if parent must wait for this task
     * to complete before it completes
     * @param pending the pending join count
     */
    protected LinkedAsyncAction(LinkedAsyncAction parent,
                          boolean register,
                          int pending) {
        this.parent = parent;
        setControlState(pending);
        if (parent != null && register)
            parent.incrementControlState();
    }

    public final Void getRawResult() { return null; }
    protected final void setRawResult(Void mustBeNull) { }

    /**
     * Overridable callback action triggered by {@code complete}.  Upon
     * invocation, all subtasks have completed.  After return, this
     * task {@code isDone} and is joinable by other tasks. The
     * default version of this method does nothing. But it may be
     * overridden in subclasses to perform some action when this task
     * is about to complete.
     */
    protected void onCompletion() {
    }

    /**
     * Overridable callback action triggered by
     * {@code completeExceptionally}.  Upon invocation, this task has
     * aborted due to an exception (accessible via
     * {@code getException}). If this method returns {@code true},
     * the exception propagates to the current task's
     * parent. Otherwise, normal completion is propagated.  The
     * default version of this method does nothing and returns
     * {@code true}.
     * @return true if this task's exception should be propagated to
     * this task's parent.
     */
    protected boolean onException() {
        return true;
    }

    /** Basic per-task complete */
    private void completeThis() {
        complete(null);
    }

    /** Basic per-task completeExceptionally */
    private void completeThisExceptionally(Throwable ex) {
        super.completeExceptionally(ex);
    }

    /**
     * Completes this task. If the pending subtask completion count is
     * zero, invokes {@code onCompletion}, then causes this task to
     * be joinable ({@code isDone} becomes true), and then
     * recursively applies to this task's parent, if it exists. If an
     * exception is encountered in any {@code onCompletion}
     * invocation, that task and its ancestors
     * {@code completeExceptionally}.
     */
    public final void complete() {
        LinkedAsyncAction a = this;
        while (a != null && !a.isDone()) {
            int c = a.getControlState();
            if (c <= 0) {
                try {
                    a.onCompletion();
                    a.completeThis();
                } catch (Throwable rex) {
                    a.completeExceptionally(rex);
                    return;
                }
                a = a.parent;
            }
            else if (a.compareAndSetControlState(c, c-1))
                return;
        }
    }

    /**
     * Completes this task abnormally. Unless this task already
     * cancelled or aborted, upon invocation, this method invokes
     * {@code onException}, and then, depending on its return value,
     * completes parent (if one exists) exceptionally or normally.  To
     * avoid unbounded exception loops, this method aborts if an
     * exception is encountered in any {@code onException}
     * invocation.
     * @param ex the exception to throw when joining this task
     * @throws NullPointerException if ex is null
     * @throws Throwable if any invocation of
     * {@code onException} does so
     */
    public final void completeExceptionally(Throwable ex) {
        LinkedAsyncAction a = this;
        while (!a.isCompletedAbnormally()) {
            a.completeThisExceptionally(ex);
            boolean up = a.onException(); // abort if this throws
            a = a.parent;
            if (a == null)
                break;
            if (!up) {
                a.complete();
                break;
            }
        }
    }

    /**
     * Returns this task's parent, or null if none.
     * @return this task's parent, or null if none
     */
    public final LinkedAsyncAction getParent() {
        return parent;
    }

    /**
     * Returns the number of subtasks that have not yet completed.
     * @return the number of subtasks that have not yet completed
     */
    public final int getPendingSubtaskCount() {
        return getControlState();
    }

    /**
     * Resets the internal bookkeeping state of this task, maintaining
     * the current parent but clearing pending joins.
     */
    public void reinitialize() {
        super.reinitialize();
    }

    /**
     * Resets the internal bookkeeping state of this task, maintaining
     * the current parent and setting pending joins to the given value.
     * @param pending the number of pending joins
     */
    public void reinitialize(int pending) {
        super.reinitialize();
        setControlState(pending);
    }

    /**
     * Reinitialize with the given parent, optionally registering.
     * @param parent the parent task, or null if none
     * @param register true if parent must wait for this task
     * to complete before it completes
     */
    public void reinitialize(LinkedAsyncAction parent, boolean register) {
        this.parent = parent;
        super.reinitialize();
        if (parent != null && register)
            parent.incrementControlState();
    }

    /**
     * Reinitialize with the given parent, optionally registering
     * and setting pending join count.
     * @param parent the parent task, or null if none
     * @param register true if parent must wait for this task
     * to complete before it completes
     * @param pending the pending join count
     */
    public void reinitialize(LinkedAsyncAction parent,
                             boolean register,
                             int pending) {
        this.parent = parent;
        super.reinitialize();
        setControlState(pending);
        if (parent != null && register)
            parent.incrementControlState();
    }

    /**
     * Gets the control state, which is initially zero, or negative if
     * this task has completed or cancelled. Once negative, the value
     * cannot be changed.
     * @return control state
     */
    protected final int getControlState() {
        return controlState;
    }

    /**
     * Atomically sets the control state to the given updated value if
     * the current value is and equal to the expected value.
     * @param expect the expected value
     * @param update the new value
     * @return true if successful
     */
    protected final boolean compareAndSetControlState(int expect,
                                                      int update) {
        return controlStateUpdater.compareAndSet(this, expect, update);
    }

    /**
     * Sets the control state to the given value.
     * @param value the new value
     */
    protected final void setControlState(int value) {
        controlState = value;
    }

    /**
     * Increments the control state.
     * @return true if successful
     */
    protected final void incrementControlState() {
        controlStateUpdater.incrementAndGet(this);
    }

    /**
     * Decrements the control state.
     * @return true if successful
     */
    protected final void decrementControlState() {
        controlStateUpdater.decrementAndGet(this);
    }

}
Revision:	1.12
Committed:	Mon Nov 26 11:47:41 2012 UTC (11 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.11:	+3 -4 lines
Log Message:	javadoc style
#	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, as explained at
4	jsr166	1.5	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7			import java.util.*;
8			import java.util.concurrent.*;
9			import java.util.concurrent.atomic.*;
10
11			/**
12			* AsyncActions that may be linked in parent-child relationships.
13			*
14	jsr166	1.9	* <p>Upon construction, a LinkedAsyncAction may register as a
15	dl	1.1	* subtask of a given parent task. In this case, completion of this
16			* task will propagate to its parent. If the parent's pending subtask
17			* completion count becomes zero, it too will complete.
18	jsr166	1.10	* LinkedAsyncActions rarely use methods {@code join} or
19			* {@code invoke} but instead propagate completion to parents
20			* implicitly via {@code complete}. While typical, it is not necessary
21			* for each task to {@code complete} itself. For example, it is
22	dl	1.1	* possible to treat one subtask as a continuation of the current task
23			* by not registering it on construction. In this case, a
24	jsr166	1.10	* {@code complete} of the subtask will trigger {@code complete} of the
25	dl	1.1	* parent without the parent explicitly doing so.
26			*
27	jsr166	1.6	* <p>In addition to supporting these different computation styles
28	dl	1.1	* compared to Recursive tasks, LinkedAsyncActions may have smaller
29			* stack space footprints while executing, but may have greater
30			* per-task overhead.
31			*
32	jsr166	1.9	* <p><b>Sample Usage.</b> Here is a sketch of a LinkedAsyncAction
33	dl	1.1	* that visits all of the nodes of a graph. The details of the graph's
34			* Node and Edge classes are omitted, but we assume each node contains
35	jsr166	1.10	* an {@code AtomicBoolean} mark that starts out false. To execute
36	dl	1.1	* this, you would create a GraphVisitor for the root node with null
37	jsr166	1.10	* parent, and {@code invoke} in a ForkJoinPool. Upon return, all
38	dl	1.1	* reachable nodes will have been visited.
39			*
40			* <pre>
41			* class GraphVisitor extends LinkedAsyncAction {
42	jsr166	1.7	* final Node node;
43			* GraphVisitor(GraphVistor parent, Node node) {
44			* super(parent); this.node = node;
45			* }
46			* protected void compute() {
47			* if (node.mark.compareAndSet(false, true)) {
48			* for (Edge e : node.edges()) {
49			* Node dest = e.getDestination();
50			* if (!dest.mark.get())
51			* new GraphVisitor(this, dest).fork();
52			* }
53			* visit(node);
54			* }
55			* complete();
56	dl	1.1	* }
57			* }
58			* </pre>
59			*/
60			public abstract class LinkedAsyncAction extends ForkJoinTask<Void> {
61
62			/**
63			* The maximum number of pending children
64			*/
65			private static int maxPending = 0xffff;
66
67			private volatile int controlState;
68
69			static final AtomicIntegerFieldUpdater<LinkedAsyncAction> controlStateUpdater =
70			AtomicIntegerFieldUpdater.newUpdater(LinkedAsyncAction.class, "controlState");
71
72
73			/**
74			* Parent to notify on completion
75			*/
76			private LinkedAsyncAction parent;
77
78			/**
79			* Creates a new action with no parent. (You can add a parent
80	jsr166	1.10	* later (but before forking) via {@code reinitialize}).
81	dl	1.1	*/
82			protected LinkedAsyncAction() {
83			}
84
85			/**
86			* Creates a new action with the given parent. If the parent is
87	jsr166	1.8	* non-null, this task registers with the parent, in which case,
88	dl	1.1	* the parent task cannot complete until this task completes.
89			* @param parent the parent task, or null if none
90			*/
91			protected LinkedAsyncAction(LinkedAsyncAction parent) {
92			this.parent = parent;
93			if (parent != null)
94			parent.incrementControlState();
95			}
96
97			/**
98			* Creates a new action with the given parent, optionally
99			* registering with the parent. If the parent is non-null and
100	jsr166	1.10	* {@code register} is true, this task registers with the
101	dl	1.1	* parent, in which case, the parent task cannot complete until
102			* this task completes.
103			* @param parent the parent task, or null if none
104			* @param register true if parent must wait for this task
105			* to complete before it completes
106			*/
107			protected LinkedAsyncAction(LinkedAsyncAction parent, boolean register) {
108			this.parent = parent;
109			if (parent != null && register)
110			parent.incrementControlState();
111			}
112
113			/**
114			* Creates a new action with the given parent, optionally
115			* registering with the parent, and setting the pending join count
116			* to the given value. If the parent is non-null and
117	jsr166	1.10	* {@code register} is true, this task registers with the
118	dl	1.1	* parent, in which case, the parent task cannot complete until
119			* this task completes. Setting the pending join count requires
120			* care -- it is correct only if child tasks do not themselves
121			* register.
122			* @param parent the parent task, or null if none
123			* @param register true if parent must wait for this task
124			* to complete before it completes
125			* @param pending the pending join count
126			*/
127			protected LinkedAsyncAction(LinkedAsyncAction parent,
128			boolean register,
129			int pending) {
130			this.parent = parent;
131			setControlState(pending);
132			if (parent != null && register)
133			parent.incrementControlState();
134			}
135
136			public final Void getRawResult() { return null; }
137			protected final void setRawResult(Void mustBeNull) { }
138
139			/**
140	jsr166	1.10	* Overridable callback action triggered by {@code complete}. Upon
141	dl	1.1	* invocation, all subtasks have completed. After return, this
142	jsr166	1.10	* task {@code isDone} and is joinable by other tasks. The
143	jsr166	1.4	* default version of this method does nothing. But it may be
144	dl	1.1	* overridden in subclasses to perform some action when this task
145			* is about to complete.
146			*/
147			protected void onCompletion() {
148			}
149
150			/**
151			* Overridable callback action triggered by
152	jsr166	1.10	* {@code completeExceptionally}. Upon invocation, this task has
153	dl	1.1	* aborted due to an exception (accessible via
154	jsr166	1.10	* {@code getException}). If this method returns {@code true},
155	dl	1.1	* the exception propagates to the current task's
156			* parent. Otherwise, normal completion is propagated. The
157			* default version of this method does nothing and returns
158	jsr166	1.10	* {@code true}.
159	dl	1.1	* @return true if this task's exception should be propagated to
160	jsr166	1.8	* this task's parent.
161	dl	1.1	*/
162			protected boolean onException() {
163			return true;
164			}
165
166			/** Basic per-task complete */
167			private void completeThis() {
168			complete(null);
169			}
170
171			/** Basic per-task completeExceptionally */
172			private void completeThisExceptionally(Throwable ex) {
173			super.completeExceptionally(ex);
174			}
175
176			/**
177			* Completes this task. If the pending subtask completion count is
178	jsr166	1.10	* zero, invokes {@code onCompletion}, then causes this task to
179			* be joinable ({@code isDone} becomes true), and then
180	jsr166	1.8	* recursively applies to this task's parent, if it exists. If an
181	jsr166	1.10	* exception is encountered in any {@code onCompletion}
182	dl	1.1	* invocation, that task and its ancestors
183	jsr166	1.10	* {@code completeExceptionally}.
184	dl	1.1	*/
185			public final void complete() {
186			LinkedAsyncAction a = this;
187			while (a != null && !a.isDone()) {
188			int c = a.getControlState();
189			if (c <= 0) {
190			try {
191			a.onCompletion();
192			a.completeThis();
193			} catch (Throwable rex) {
194			a.completeExceptionally(rex);
195			return;
196			}
197			a = a.parent;
198			}
199			else if (a.compareAndSetControlState(c, c-1))
200			return;
201			}
202			}
203
204			/**
205			* Completes this task abnormally. Unless this task already
206			* cancelled or aborted, upon invocation, this method invokes
207	jsr166	1.10	* {@code onException}, and then, depending on its return value,
208	jsr166	1.11	* completes parent (if one exists) exceptionally or normally. To
209	dl	1.1	* avoid unbounded exception loops, this method aborts if an
210	jsr166	1.10	* exception is encountered in any {@code onException}
211	dl	1.1	* invocation.
212			* @param ex the exception to throw when joining this task
213			* @throws NullPointerException if ex is null
214			* @throws Throwable if any invocation of
215	jsr166	1.12	* {@code onException} does so
216	dl	1.1	*/
217			public final void completeExceptionally(Throwable ex) {
218			LinkedAsyncAction a = this;
219			while (!a.isCompletedAbnormally()) {
220			a.completeThisExceptionally(ex);
221			boolean up = a.onException(); // abort if this throws
222			a = a.parent;
223			if (a == null)
224			break;
225			if (!up) {
226			a.complete();
227			break;
228			}
229			}
230			}
231
232			/**
233			* Returns this task's parent, or null if none.
234	jsr166	1.12	* @return this task's parent, or null if none
235	dl	1.1	*/
236			public final LinkedAsyncAction getParent() {
237			return parent;
238			}
239
240			/**
241			* Returns the number of subtasks that have not yet completed.
242	jsr166	1.12	* @return the number of subtasks that have not yet completed
243	dl	1.1	*/
244			public final int getPendingSubtaskCount() {
245			return getControlState();
246			}
247
248			/**
249			* Resets the internal bookkeeping state of this task, maintaining
250			* the current parent but clearing pending joins.
251			*/
252			public void reinitialize() {
253			super.reinitialize();
254			}
255
256			/**
257			* Resets the internal bookkeeping state of this task, maintaining
258			* the current parent and setting pending joins to the given value.
259			* @param pending the number of pending joins
260			*/
261			public void reinitialize(int pending) {
262			super.reinitialize();
263			setControlState(pending);
264			}
265
266			/**
267			* Reinitialize with the given parent, optionally registering.
268			* @param parent the parent task, or null if none
269			* @param register true if parent must wait for this task
270			* to complete before it completes
271			*/
272			public void reinitialize(LinkedAsyncAction parent, boolean register) {
273			this.parent = parent;
274			super.reinitialize();
275			if (parent != null && register)
276			parent.incrementControlState();
277			}
278
279			/**
280			* Reinitialize with the given parent, optionally registering
281			* and setting pending join count.
282			* @param parent the parent task, or null if none
283			* @param register true if parent must wait for this task
284			* to complete before it completes
285			* @param pending the pending join count
286			*/
287			public void reinitialize(LinkedAsyncAction parent,
288			boolean register,
289			int pending) {
290			this.parent = parent;
291			super.reinitialize();
292			setControlState(pending);
293			if (parent != null && register)
294			parent.incrementControlState();
295			}
296
297			/**
298			* Gets the control state, which is initially zero, or negative if
299			* this task has completed or cancelled. Once negative, the value
300			* cannot be changed.
301			* @return control state
302			*/
303			protected final int getControlState() {
304			return controlState;
305			}
306
307			/**
308			* Atomically sets the control state to the given updated value if
309			* the current value is and equal to the expected value.
310			* @param expect the expected value
311			* @param update the new value
312			* @return true if successful
313			*/
314	jsr166	1.2	protected final boolean compareAndSetControlState(int expect,
315	dl	1.1	int update) {
316			return controlStateUpdater.compareAndSet(this, expect, update);
317			}
318
319			/**
320	jsr166	1.3	* Sets the control state to the given value.
321	dl	1.1	* @param value the new value
322			*/
323			protected final void setControlState(int value) {
324			controlState = value;
325			}
326
327			/**
328	jsr166	1.3	* Increments the control state.
329	dl	1.1	* @return true if successful
330			*/
331			protected final void incrementControlState() {
332			controlStateUpdater.incrementAndGet(this);
333			}
334
335			/**
336	jsr166	1.3	* Decrements the control state.
337	dl	1.1	* @return true if successful
338			*/
339			protected final void decrementControlState() {
340			controlStateUpdater.decrementAndGet(this);
341			}
342
343			}