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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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import java.util.*; |
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/** |
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* AsyncActions that may be linked in parent-child relationships. |
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* |
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* <p> Upon construction, an LinkedAsyncAction may register as a |
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* <p>Upon construction, a LinkedAsyncAction may register as a |
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* subtask of a given parent task. In this case, completion of this |
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* task will propagate to its parent. If the parent's pending subtask |
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* completion count becomes zero, it too will complete. |
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* <tt>complete</tt> of the subtask will trigger <tt>complete</tt> of the |
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* parent without the parent explicitly doing so. |
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* |
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* <p> In addition to supporting these different computation styles |
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* <p>In addition to supporting these different computation styles |
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* compared to Recursive tasks, LinkedAsyncActions may have smaller |
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* stack space footprints while executing, but may have greater |
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* per-task overhead. |
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* |
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* <p> <b>Sample Usage.</b> Here is a sketch of an LinkedAsyncAction |
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* <p><b>Sample Usage.</b> Here is a sketch of a LinkedAsyncAction |
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* that visits all of the nodes of a graph. The details of the graph's |
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* Node and Edge classes are omitted, but we assume each node contains |
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* an <tt>AtomicBoolean</tt> mark that starts out false. To execute |
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* |
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* <pre> |
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* class GraphVisitor extends LinkedAsyncAction { |
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* final Node node; |
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* GraphVisitor(GraphVistor parent, Node node) { |
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* super(parent); this.node = node; |
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* } |
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* protected void compute() { |
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* if (node.mark.compareAndSet(false, true)) { |
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* for (Edge e : node.edges()) { |
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* Node dest = e.getDestination(); |
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* if (!dest.mark.get()) |
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* new GraphVisitor(this, dest).fork(); |
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* } |
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* visit(node); |
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* } |
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* complete(); |
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* final Node node; |
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* GraphVisitor(GraphVistor parent, Node node) { |
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* super(parent); this.node = node; |
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* } |
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* protected void compute() { |
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* if (node.mark.compareAndSet(false, true)) { |
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* for (Edge e : node.edges()) { |
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* Node dest = e.getDestination(); |
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* if (!dest.mark.get()) |
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* new GraphVisitor(this, dest).fork(); |
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* } |
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* visit(node); |
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* } |
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* complete(); |
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* } |
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* } |
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* </pre> |
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– |
* |
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*/ |
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public abstract class LinkedAsyncAction extends ForkJoinTask<Void> { |
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/** |
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* Creates a new action with the given parent. If the parent is |
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* non-null, this tasks registers with the parent, in which case, |
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* non-null, this task registers with the parent, in which case, |
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* the parent task cannot complete until this task completes. |
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* @param parent the parent task, or null if none |
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*/ |
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/** |
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* Creates a new action with the given parent, optionally |
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* registering with the parent. If the parent is non-null and |
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* <tt>register</tt> is true, this tasks registers with the |
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* <tt>register</tt> is true, this task registers with the |
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* parent, in which case, the parent task cannot complete until |
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* this task completes. |
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* @param parent the parent task, or null if none |
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* Creates a new action with the given parent, optionally |
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* registering with the parent, and setting the pending join count |
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* to the given value. If the parent is non-null and |
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* <tt>register</tt> is true, this tasks registers with the |
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* <tt>register</tt> is true, this task registers with the |
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* parent, in which case, the parent task cannot complete until |
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* this task completes. Setting the pending join count requires |
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* care -- it is correct only if child tasks do not themselves |
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* default version of this method does nothing and returns |
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* <tt>true</tt>. |
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* @return true if this task's exception should be propagated to |
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* this tasks parent. |
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* this task's parent. |
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*/ |
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protected boolean onException() { |
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return true; |
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* Completes this task. If the pending subtask completion count is |
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* zero, invokes <tt>onCompletion</tt>, then causes this task to |
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* be joinable (<tt>isDone</tt> becomes true), and then |
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* recursively applies to this tasks's parent, if it exists. If an |
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* recursively applies to this task's parent, if it exists. If an |
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* exception is encountered in any <tt>onCompletion</tt> |
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* invocation, that task and its ancestors |
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* <tt>completeExceptionally</tt>. |