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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.concurrent.*; |
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* have smaller stack space footprints and faster completion mechanics |
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* but higher per-task footprints. Compared to LinkedAsyncActions, |
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* BinaryAsyncActions are simpler to use and have less overhead in |
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* typical uasges but are restricted to binary computation trees. |
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* typical usages but are restricted to binary computation trees. |
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* |
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* <p> Upon construction, an BinaryAsyncAction does not bear any |
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* <p>Upon construction, a BinaryAsyncAction does not bear any |
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* linkages. For non-root tasks, links must be established using |
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* method <tt>linkSubtasks</tt> before use. |
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* method {@link #linkSubtasks} before use. |
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* |
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* <p> <b>Sample Usage.</b> A version of Fibonacci: |
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* <p><b>Sample Usage.</b> A version of Fibonacci: |
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* <pre> |
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* class Fib extends BinaryAsyncAction { |
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* final int n; |
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* Fib(int n) { this.n = n; } |
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* protected void compute() { |
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* if (n > 1) { |
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* linkAndForkSubtasks(new Fib(n-1), new Fib(n-2)); |
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* linkAndForkSubtasks(new Fib(n-1), new Fib(n-2)); |
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* else { |
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* result = n; // fib(0)==0; fib(1)==1 |
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* complete(); |
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* result = n; // fib(0)==0; fib(1)==1 |
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* complete(); |
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* } |
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* } |
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* protected void onComplete(BinaryAsyncAction x, BinaryAsyncAction y) { |
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* result = ((Fib)x).result + ((Fib)y).result; |
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* result = ((Fib)x).result + ((Fib)y).result; |
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* } |
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* } |
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* </pre> |
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* An alternative, and usually faster strategy is to instead use a |
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* An alternative, and usually faster, strategy is to instead use a |
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* loop to fork subtasks: |
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* <pre> |
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* protected void compute() { |
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* Fib f = this; |
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* while (f.n > 1) { |
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* Fib left = new Fib(f.n - 1); |
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* Fib right = new Fib(f.n - 2); |
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* f.linkSubtasks(left, right); |
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* right.fork(); // fork right |
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* f = left; // loop on left |
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* Fib left = new Fib(f.n - 1); |
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* Fib right = new Fib(f.n - 2); |
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* f.linkSubtasks(left, right); |
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* right.fork(); // fork right |
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* f = left; // loop on left |
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* } |
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* f.result = f.n; |
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* f.complete(); |
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* </pre> |
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*/ |
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public abstract class BinaryAsyncAction extends ForkJoinTask<Void> { |
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private volatile int controlState; |
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static final AtomicIntegerFieldUpdater<BinaryAsyncAction> controlStateUpdater = |
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AtomicIntegerFieldUpdater.newUpdater(BinaryAsyncAction.class, "controlState"); |
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/** |
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* Parent to propagate completion; nulled after completion to |
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/** |
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* Creates a new action. Unless this is a root task, you will need |
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* to link it using method <tt>linkSubtasks</tt> before forking as |
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* to link it using method {@link #linkSubtasks} before forking as |
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* a subtask. |
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*/ |
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protected BinaryAsyncAction() { |
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* as parent, and each other as siblings. |
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* @param x one subtask |
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* @param y the other subtask |
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* @throws NullPointerException if either argument is null. |
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* @throws NullPointerException if either argument is null |
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*/ |
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public final void linkSubtasks(BinaryAsyncAction x, BinaryAsyncAction y) { |
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x.parent = y.parent = this; |
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} |
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/** |
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* Overridable callback action triggered upon <tt>complete</tt> of |
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* Overridable callback action triggered upon {@code complete} of |
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* subtasks. Upon invocation, both subtasks have completed. |
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* After return, this task <tt>isDone</tt> and is joinable by |
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* After return, this task {@code isDone} and is joinable by |
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* other tasks. The default version of this method does nothing. |
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* But it may be overridden in subclasses to perform some action |
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* (for example a reduction) when this task is completes. |
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/** |
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* Overridable callback action triggered by |
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* <tt>completeExceptionally</tt>. Upon invocation, this task has |
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* {@code completeExceptionally}. Upon invocation, this task has |
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* aborted due to an exception (accessible via |
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* <tt>getException</tt>). If this method returns <tt>true</tt>, |
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* {@code getException}). If this method returns {@code true}, |
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* the exception propagates to the current task's |
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* parent. Otherwise, normal completion is propagated. The |
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* default version of this method does nothing and returns |
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* <tt>true</tt>. |
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* {@code true}. |
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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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} |
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/** |
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* Equivalent in effect to invoking <tt>linkSubtasks</tt> and then |
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* Equivalent in effect to invoking {@link #linkSubtasks} and then |
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* forking both tasks. |
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* @param x one subtask |
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* @param y the other subtask |
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/** |
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* Completes this task, and if this task has a sibling that is |
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* also complete, invokes <tt>onComplete</tt> of parent task, and so |
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* also complete, invokes {@code onComplete} of parent task, and so |
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* on. If an exception is encountered, tasks instead |
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* <tt>completeExceptionally</tt>. |
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* {@code completeExceptionally}. |
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*/ |
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public final void complete() { |
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// todo: Use tryUnfork without possibly blowing stack |
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a.sibling = null; |
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a.parent = null; |
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a.completeThis(); |
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if (p == null || p.compareAndSetControlState(0, 1)) |
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if (p == null || p.markForkJoinTask()) |
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break; |
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try { |
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p.onComplete(a, s); |
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/** |
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* Completes this task abnormally. Unless this task already |
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* cancelled or aborted, upon invocation, this method invokes |
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* <tt>onException</tt>, and then, depending on its return value, |
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* completees parent (if one exists) exceptionally or normally. To |
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* {@code onException}, and then, depending on its return value, |
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* completes parent (if one exists) exceptionally or normally. To |
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* avoid unbounded exception loops, this method aborts if an |
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* exception is encountered in any <tt>onException</tt> |
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* exception is encountered in any {@code onException} |
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* invocation. |
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* @param ex the exception to throw when joining this task |
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* @throws NullPointerException if ex is null |
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* @throws Throwable if any invocation of |
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* <tt>onException</tt> does so. |
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* {@code onException} does so |
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*/ |
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public final void completeExceptionally(Throwable ex) { |
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BinaryAsyncAction a = this; |
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/** |
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* Returns this task's parent, or null if none or this task |
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* is already complete. |
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* @return this task's parent, or null if none. |
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* @return this task's parent, or null if none |
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*/ |
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public final BinaryAsyncAction getParent() { |
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return parent; |
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/** |
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* Returns this task's sibling, or null if none or this task is |
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* already complete. |
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* @return this task's sibling, or null if none. |
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* @return this task's sibling, or null if none |
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*/ |
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public BinaryAsyncAction getSibling() { |
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return sibling; |
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super.reinitialize(); |
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} |
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<<<<<<< BinaryAsyncAction.java |
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======= |
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/** |
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* Gets the control state, which is initially zero, or negative if |
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* this task has completed or cancelled. Once negative, the value |
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} |
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/** |
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* Sets the control state to the given value, |
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* Increments the control state. |
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* @param value the new value |
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*/ |
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protected final void incrementControlState() { |
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} |
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/** |
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* Decrement the control state |
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* Decrements the control state. |
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* @return true if successful |
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*/ |
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protected final void decrementControlState() { |
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controlStateUpdater.decrementAndGet(this); |
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} |
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>>>>>>> 1.14 |
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} |
