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package java.util.concurrent; |
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/** |
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* A <tt>Future</tt> represents the result of an asynchronous |
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* A {@code Future} represents the result of an asynchronous |
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* computation. Methods are provided to check if the computation is |
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* complete, to wait for its completion, and to retrieve the result of |
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* the computation. The result can only be retrieved using method |
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* <tt>get</tt> when the computation has completed, blocking if |
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* {@code get} when the computation has completed, blocking if |
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* necessary until it is ready. Cancellation is performed by the |
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* <tt>cancel</tt> method. Additional methods are provided to |
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* {@code cancel} method. Additional methods are provided to |
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* determine if the task completed normally or was cancelled. Once a |
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* computation has completed, the computation cannot be cancelled. |
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* If you would like to use a <tt>Future</tt> for the sake |
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* If you would like to use a {@code Future} for the sake |
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* of cancellability but not provide a usable result, you can |
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* declare types of the form {@code Future<?>} and |
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* return <tt>null</tt> as a result of the underlying task. |
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* return {@code null} as a result of the underlying task. |
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* |
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* <p> |
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* <b>Sample Usage</b> (Note that the following classes are all |
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* } |
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* }}</pre> |
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* |
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* The {@link FutureTask} class is an implementation of <tt>Future</tt> that |
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* implements <tt>Runnable</tt>, and so may be executed by an <tt>Executor</tt>. |
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< |
* For example, the above construction with <tt>submit</tt> could be replaced by: |
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> |
* The {@link FutureTask} class is an implementation of {@code Future} that |
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* implements {@code Runnable}, and so may be executed by an {@code Executor}. |
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> |
* For example, the above construction with {@code submit} could be replaced by: |
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* <pre> {@code |
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* FutureTask<String> future = |
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* new FutureTask<String>(new Callable<String>() { |
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* @see Executor |
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* @since 1.5 |
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* @author Doug Lea |
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< |
* @param <V> The result type returned by this Future's <tt>get</tt> method |
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> |
* @param <V> The result type returned by this Future's {@code get} method |
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*/ |
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public interface Future<V> { |
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|
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* Attempts to cancel execution of this task. This attempt will |
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* fail if the task has already completed, has already been cancelled, |
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* or could not be cancelled for some other reason. If successful, |
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< |
* and this task has not started when <tt>cancel</tt> is called, |
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* and this task has not started when {@code cancel} is called, |
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* this task should never run. If the task has already started, |
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* then the <tt>mayInterruptIfRunning</tt> parameter determines |
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> |
* then the {@code mayInterruptIfRunning} parameter determines |
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* whether the thread executing this task should be interrupted in |
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* an attempt to stop the task. |
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* |
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* <p>After this method returns, subsequent calls to {@link #isDone} will |
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* always return <tt>true</tt>. Subsequent calls to {@link #isCancelled} |
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< |
* will always return <tt>true</tt> if this method returned <tt>true</tt>. |
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* always return {@code true}. Subsequent calls to {@link #isCancelled} |
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* will always return {@code true} if this method returned {@code true}. |
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* |
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< |
* @param mayInterruptIfRunning <tt>true</tt> if the thread executing this |
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* @param mayInterruptIfRunning {@code true} if the thread executing this |
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* task should be interrupted; otherwise, in-progress tasks are allowed |
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* to complete |
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< |
* @return <tt>false</tt> if the task could not be cancelled, |
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> |
* @return {@code false} if the task could not be cancelled, |
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* typically because it has already completed normally; |
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* <tt>true</tt> otherwise |
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* {@code true} otherwise |
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*/ |
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boolean cancel(boolean mayInterruptIfRunning); |
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|
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/** |
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< |
* Returns <tt>true</tt> if this task was cancelled before it completed |
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> |
* Returns {@code true} if this task was cancelled before it completed |
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* normally. |
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* |
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< |
* @return <tt>true</tt> if this task was cancelled before it completed |
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> |
* @return {@code true} if this task was cancelled before it completed |
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*/ |
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boolean isCancelled(); |
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|
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/** |
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< |
* Returns <tt>true</tt> if this task completed. |
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> |
* Returns {@code true} if this task completed. |
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* |
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* Completion may be due to normal termination, an exception, or |
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* cancellation -- in all of these cases, this method will return |
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< |
* <tt>true</tt>. |
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> |
* {@code true}. |
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* |
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< |
* @return <tt>true</tt> if this task completed |
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> |
* @return {@code true} if this task completed |
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*/ |
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boolean isDone(); |
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|
