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import java.util.*; |
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/** |
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* A {@linkplain BlockingQueue blocking queue} in which each |
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* <tt>put</tt> must wait for a <tt>take</tt>, and vice versa. A |
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* synchronous queue does not have any internal capacity, not even a |
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* capacity of one. You cannot <tt>peek</tt> at a synchronous queue |
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* because an element is only present when you try to take it; you |
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* cannot add an element (using any method) unless another thread is |
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* trying to remove it; you cannot iterate as there is nothing to |
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* iterate. The <em>head</em> of the queue is the element that the |
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* first queued thread is trying to add to the queue; if there are no |
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* queued threads then no element is being added and the head is |
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* <tt>null</tt>. For purposes of other <tt>Collection</tt> methods |
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* (for example <tt>contains</tt>), a <tt>SynchronousQueue</tt> acts |
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* as an empty collection. This queue does not permit <tt>null</tt> |
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* elements. |
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* A {@linkplain BlockingQueue blocking queue} in which each insert |
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* operation must wait for a corresponding remove operation by another |
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* thread, and vice versa. A synchronous queue does not have any |
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* internal capacity, not even a capacity of one. You cannot |
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* <tt>peek</tt> at a synchronous queue because an element is only |
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* present when you try to remove it; you cannot insert an element |
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* (using any method) unless another thread is trying to remove it; |
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* you cannot iterate as there is nothing to iterate. The |
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* <em>head</em> of the queue is the element that the first queued |
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* inserting thread is trying to add to the queue; if there is no such |
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* queued thread then no element is available for removal and |
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* <tt>poll()</tt> will return <tt>null</tt>. For purposes of other |
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* <tt>Collection</tt> methods (for example <tt>contains</tt>), a |
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* <tt>SynchronousQueue</tt> acts as an empty collection. This queue |
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* does not permit <tt>null</tt> elements. |
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* |
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* <p>Synchronous queues are similar to rendezvous channels used in |
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* CSP and Ada. They are well suited for handoff designs, in which an |
