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 * http://creativecommons.org/publicdomain/zero/1.0/
5 */
6
7package java.util.concurrent;
8import java.util.*;
9
10/**
11 * A {@link Deque} that additionally supports blocking operations that wait
12 * for the deque to become non-empty when retrieving an element, and wait for
13 * space to become available in the deque when storing an element.
14 *
15 * <p>{@code BlockingDeque} methods come in four forms, with different ways
16 * of handling operations that cannot be satisfied immediately, but may be
17 * satisfied at some point in the future:
18 * one throws an exception, the second returns a special value (either
19 * {@code null} or {@code false}, depending on the operation), the third
20 * blocks the current thread indefinitely until the operation can succeed,
21 * and the fourth blocks for only a given maximum time limit before giving
22 * up.  These methods are summarized in the following table:
23 *
24 * <p>
25 * <table BORDER CELLPADDING=3 CELLSPACING=1>
26 *  <tr>
27 *    <td ALIGN=CENTER COLSPAN = 5> <b>First Element (Head)</b></td>
28 *  </tr>
29 *  <tr>
30 *    <td></td>
31 *    <td ALIGN=CENTER><em>Throws exception</em></td>
32 *    <td ALIGN=CENTER><em>Special value</em></td>
33 *    <td ALIGN=CENTER><em>Blocks</em></td>
34 *    <td ALIGN=CENTER><em>Times out</em></td>
35 *  </tr>
36 *  <tr>
37 *    <td><b>Insert</b></td>
38 *    <td>{@link #addFirst addFirst(e)}</td>
39 *    <td>{@link #offerFirst(Object) offerFirst(e)}</td>
40 *    <td>{@link #putFirst putFirst(e)}</td>
41 *    <td>{@link #offerFirst(Object, long, TimeUnit) offerFirst(e, time, unit)}</td>
42 *  </tr>
43 *  <tr>
44 *    <td><b>Remove</b></td>
45 *    <td>{@link #removeFirst removeFirst()}</td>
46 *    <td>{@link #pollFirst pollFirst()}</td>
47 *    <td>{@link #takeFirst takeFirst()}</td>
48 *    <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
49 *  </tr>
50 *  <tr>
51 *    <td><b>Examine</b></td>
52 *    <td>{@link #getFirst getFirst()}</td>
53 *    <td>{@link #peekFirst peekFirst()}</td>
54 *    <td><em>not applicable</em></td>
55 *    <td><em>not applicable</em></td>
56 *  </tr>
57 *  <tr>
58 *    <td ALIGN=CENTER COLSPAN = 5> <b>Last Element (Tail)</b></td>
59 *  </tr>
60 *  <tr>
61 *    <td></td>
62 *    <td ALIGN=CENTER><em>Throws exception</em></td>
63 *    <td ALIGN=CENTER><em>Special value</em></td>
64 *    <td ALIGN=CENTER><em>Blocks</em></td>
65 *    <td ALIGN=CENTER><em>Times out</em></td>
66 *  </tr>
67 *  <tr>
68 *    <td><b>Insert</b></td>
69 *    <td>{@link #addLast addLast(e)}</td>
70 *    <td>{@link #offerLast(Object) offerLast(e)}</td>
71 *    <td>{@link #putLast putLast(e)}</td>
72 *    <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
73 *  </tr>
74 *  <tr>
75 *    <td><b>Remove</b></td>
76 *    <td>{@link #removeLast() removeLast()}</td>
77 *    <td>{@link #pollLast() pollLast()}</td>
78 *    <td>{@link #takeLast takeLast()}</td>
79 *    <td>{@link #pollLast(long, TimeUnit) pollLast(time, unit)}</td>
80 *  </tr>
81 *  <tr>
82 *    <td><b>Examine</b></td>
83 *    <td>{@link #getLast getLast()}</td>
84 *    <td>{@link #peekLast peekLast()}</td>
85 *    <td><em>not applicable</em></td>
86 *    <td><em>not applicable</em></td>
87 *  </tr>
88 * </table>
89 *
90 * <p>Like any {@link BlockingQueue}, a {@code BlockingDeque} is thread safe,
91 * does not permit null elements, and may (or may not) be
92 * capacity-constrained.
93 *
94 * <p>A {@code BlockingDeque} implementation may be used directly as a FIFO
95 * {@code BlockingQueue}. The methods inherited from the
96 * {@code BlockingQueue} interface are precisely equivalent to
97 * {@code BlockingDeque} methods as indicated in the following table:
98 *
99 * <p>
100 * <table BORDER CELLPADDING=3 CELLSPACING=1>
101 *  <tr>
102 *    <td ALIGN=CENTER> <b>{@code BlockingQueue} Method</b></td>
103 *    <td ALIGN=CENTER> <b>Equivalent {@code BlockingDeque} Method</b></td>
104 *  </tr>
105 *  <tr>
106 *    <td ALIGN=CENTER COLSPAN = 2> <b>Insert</b></td>
107 *  </tr>
108 *  <tr>
109 *    <td>{@link #add(Object) add(e)}</td>
110 *    <td>{@link #addLast(Object) addLast(e)}</td>
111 *  </tr>
112 *  <tr>
113 *    <td>{@link #offer(Object) offer(e)}</td>
114 *    <td>{@link #offerLast(Object) offerLast(e)}</td>
115 *  </tr>
116 *  <tr>
117 *    <td>{@link #put(Object) put(e)}</td>
118 *    <td>{@link #putLast(Object) putLast(e)}</td>
119 *  </tr>
120 *  <tr>
121 *    <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
122 *    <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
123 *  </tr>
124 *  <tr>
125 *    <td ALIGN=CENTER COLSPAN = 2> <b>Remove</b></td>
126 *  </tr>
127 *  <tr>
128 *    <td>{@link #remove() remove()}</td>
129 *    <td>{@link #removeFirst() removeFirst()}</td>
130 *  </tr>
131 *  <tr>
132 *    <td>{@link #poll() poll()}</td>
133 *    <td>{@link #pollFirst() pollFirst()}</td>
134 *  </tr>
135 *  <tr>
136 *    <td>{@link #take() take()}</td>
137 *    <td>{@link #takeFirst() takeFirst()}</td>
138 *  </tr>
139 *  <tr>
140 *    <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
141 *    <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
142 *  </tr>
143 *  <tr>
144 *    <td ALIGN=CENTER COLSPAN = 2> <b>Examine</b></td>
145 *  </tr>
146 *  <tr>
147 *    <td>{@link #element() element()}</td>
148 *    <td>{@link #getFirst() getFirst()}</td>
149 *  </tr>
150 *  <tr>
151 *    <td>{@link #peek() peek()}</td>
152 *    <td>{@link #peekFirst() peekFirst()}</td>
153 *  </tr>
154 * </table>
155 *
156 * <p>Memory consistency effects: As with other concurrent
157 * collections, actions in a thread prior to placing an object into a
158 * {@code BlockingDeque}
159 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
160 * actions subsequent to the access or removal of that element from
161 * the {@code BlockingDeque} in another thread.
162 *
163 * <p>This interface is a member of the
164 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
165 * Java Collections Framework</a>.
166 *
167 * @since 1.6
168 * @author Doug Lea
169 * @param <E> the type of elements held in this collection
170 */
171public interface BlockingDeque<E> extends BlockingQueue<E>, Deque<E> {
172    /*
173     * We have "diamond" multiple interface inheritance here, and that
174     * introduces ambiguities.  Methods might end up with different
175     * specs depending on the branch chosen by javadoc.  Thus a lot of
176     * methods specs here are copied from superinterfaces.
177     */
178
179    /**
180     * Inserts the specified element at the front of this deque if it is
181     * possible to do so immediately without violating capacity restrictions,
182     * throwing an {@code IllegalStateException} if no space is currently
183     * available.  When using a capacity-restricted deque, it is generally
184     * preferable to use {@link #offerFirst(Object) offerFirst}.
185     *
186     * @param e the element to add
187     * @throws IllegalStateException {@inheritDoc}
188     * @throws ClassCastException {@inheritDoc}
189     * @throws NullPointerException if the specified element is null
190     * @throws IllegalArgumentException {@inheritDoc}
191     */
192    void addFirst(E e);
193
194    /**
195     * Inserts the specified element at the end of this deque if it is
196     * possible to do so immediately without violating capacity restrictions,
197     * throwing an {@code IllegalStateException} if no space is currently
198     * available.  When using a capacity-restricted deque, it is generally
199     * preferable to use {@link #offerLast(Object) offerLast}.
200     *
201     * @param e the element to add
202     * @throws IllegalStateException {@inheritDoc}
203     * @throws ClassCastException {@inheritDoc}
204     * @throws NullPointerException if the specified element is null
205     * @throws IllegalArgumentException {@inheritDoc}
206     */
207    void addLast(E e);
208
209    /**
210     * Inserts the specified element at the front of this deque if it is
211     * possible to do so immediately without violating capacity restrictions,
212     * returning {@code true} upon success and {@code false} if no space is
213     * currently available.
214     * When using a capacity-restricted deque, this method is generally
215     * preferable to the {@link #addFirst(Object) addFirst} method, which can
216     * fail to insert an element only by throwing an exception.
217     *
218     * @param e the element to add
219     * @throws ClassCastException {@inheritDoc}
220     * @throws NullPointerException if the specified element is null
221     * @throws IllegalArgumentException {@inheritDoc}
222     */
223    boolean offerFirst(E e);
224
225    /**
226     * Inserts the specified element at the end of this deque if it is
227     * possible to do so immediately without violating capacity restrictions,
228     * returning {@code true} upon success and {@code false} if no space is
229     * currently available.
230     * When using a capacity-restricted deque, this method is generally
231     * preferable to the {@link #addLast(Object) addLast} method, which can
232     * fail to insert an element only by throwing an exception.
233     *
234     * @param e the element to add
235     * @throws ClassCastException {@inheritDoc}
236     * @throws NullPointerException if the specified element is null
237     * @throws IllegalArgumentException {@inheritDoc}
238     */
239    boolean offerLast(E e);
240
241    /**
242     * Inserts the specified element at the front of this deque,
243     * waiting if necessary for space to become available.
244     *
245     * @param e the element to add
246     * @throws InterruptedException if interrupted while waiting
247     * @throws ClassCastException if the class of the specified element
248     *         prevents it from being added to this deque
249     * @throws NullPointerException if the specified element is null
250     * @throws IllegalArgumentException if some property of the specified
251     *         element prevents it from being added to this deque
252     */
253    void putFirst(E e) throws InterruptedException;
254
255    /**
256     * Inserts the specified element at the end of this deque,
257     * waiting if necessary for space to become available.
258     *
259     * @param e the element to add
260     * @throws InterruptedException if interrupted while waiting
261     * @throws ClassCastException if the class of the specified element
262     *         prevents it from being added to this deque
263     * @throws NullPointerException if the specified element is null
264     * @throws IllegalArgumentException if some property of the specified
265     *         element prevents it from being added to this deque
266     */
267    void putLast(E e) throws InterruptedException;
268
269    /**
270     * Inserts the specified element at the front of this deque,
271     * waiting up to the specified wait time if necessary for space to
272     * become available.
273     *
274     * @param e the element to add
275     * @param timeout how long to wait before giving up, in units of
276     *        {@code unit}
277     * @param unit a {@code TimeUnit} determining how to interpret the
278     *        {@code timeout} parameter
279     * @return {@code true} if successful, or {@code false} if
280     *         the specified waiting time elapses before space is available
281     * @throws InterruptedException if interrupted while waiting
282     * @throws ClassCastException if the class of the specified element
283     *         prevents it from being added to this deque
284     * @throws NullPointerException if the specified element is null
285     * @throws IllegalArgumentException if some property of the specified
286     *         element prevents it from being added to this deque
287     */
288    boolean offerFirst(E e, long timeout, TimeUnit unit)
289        throws InterruptedException;
290
291    /**
292     * Inserts the specified element at the end of this deque,
293     * waiting up to the specified wait time if necessary for space to
294     * become available.
295     *
296     * @param e the element to add
297     * @param timeout how long to wait before giving up, in units of
298     *        {@code unit}
299     * @param unit a {@code TimeUnit} determining how to interpret the
300     *        {@code timeout} parameter
301     * @return {@code true} if successful, or {@code false} if
302     *         the specified waiting time elapses before space is available
303     * @throws InterruptedException if interrupted while waiting
304     * @throws ClassCastException if the class of the specified element
305     *         prevents it from being added to this deque
306     * @throws NullPointerException if the specified element is null
307     * @throws IllegalArgumentException if some property of the specified
308     *         element prevents it from being added to this deque
309     */
310    boolean offerLast(E e, long timeout, TimeUnit unit)
311        throws InterruptedException;
312
313    /**
314     * Retrieves and removes the first element of this deque, waiting
315     * if necessary until an element becomes available.
316     *
317     * @return the head of this deque
318     * @throws InterruptedException if interrupted while waiting
319     */
320    E takeFirst() throws InterruptedException;
321
322    /**
323     * Retrieves and removes the last element of this deque, waiting
324     * if necessary until an element becomes available.
325     *
326     * @return the tail of this deque
327     * @throws InterruptedException if interrupted while waiting
328     */
329    E takeLast() throws InterruptedException;
330
331    /**
332     * Retrieves and removes the first element of this deque, waiting
333     * up to the specified wait time if necessary for an element to
334     * become available.
335     *
336     * @param timeout how long to wait before giving up, in units of
337     *        {@code unit}
338     * @param unit a {@code TimeUnit} determining how to interpret the
339     *        {@code timeout} parameter
340     * @return the head of this deque, or {@code null} if the specified
341     *         waiting time elapses before an element is available
342     * @throws InterruptedException if interrupted while waiting
343     */
344    E pollFirst(long timeout, TimeUnit unit)
345        throws InterruptedException;
346
347    /**
348     * Retrieves and removes the last element of this deque, waiting
349     * up to the specified wait time if necessary for an element to
350     * become available.
351     *
352     * @param timeout how long to wait before giving up, in units of
353     *        {@code unit}
354     * @param unit a {@code TimeUnit} determining how to interpret the
355     *        {@code timeout} parameter
356     * @return the tail of this deque, or {@code null} if the specified
357     *         waiting time elapses before an element is available
358     * @throws InterruptedException if interrupted while waiting
359     */
360    E pollLast(long timeout, TimeUnit unit)
361        throws InterruptedException;
362
363    /**
364     * Removes the first occurrence of the specified element from this deque.
365     * If the deque does not contain the element, it is unchanged.
366     * More formally, removes the first element {@code e} such that
367     * {@code o.equals(e)} (if such an element exists).
368     * Returns {@code true} if this deque contained the specified element
369     * (or equivalently, if this deque changed as a result of the call).
370     *
371     * @param o element to be removed from this deque, if present
372     * @return {@code true} if an element was removed as a result of this call
373     * @throws ClassCastException if the class of the specified element
374     *         is incompatible with this deque
375     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
376     * @throws NullPointerException if the specified element is null
377     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
378     */
379    boolean removeFirstOccurrence(Object o);
380
381    /**
382     * Removes the last occurrence of the specified element from this deque.
383     * If the deque does not contain the element, it is unchanged.
384     * More formally, removes the last element {@code e} such that
385     * {@code o.equals(e)} (if such an element exists).
386     * Returns {@code true} if this deque contained the specified element
387     * (or equivalently, if this deque changed as a result of the call).
388     *
389     * @param o element to be removed from this deque, if present
390     * @return {@code true} if an element was removed as a result of this call
391     * @throws ClassCastException if the class of the specified element
392     *         is incompatible with this deque
393     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
394     * @throws NullPointerException if the specified element is null
395     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
396     */
397    boolean removeLastOccurrence(Object o);
398
399    // *** BlockingQueue methods ***
400
401    /**
402     * Inserts the specified element into the queue represented by this deque
403     * (in other words, at the tail of this deque) if it is possible to do so
404     * immediately without violating capacity restrictions, returning
405     * {@code true} upon success and throwing an
406     * {@code IllegalStateException} if no space is currently available.
407     * When using a capacity-restricted deque, it is generally preferable to
408     * use {@link #offer(Object) offer}.
409     *
410     * <p>This method is equivalent to {@link #addLast(Object) addLast}.
411     *
412     * @param e the element to add
413     * @throws IllegalStateException {@inheritDoc}
414     * @throws ClassCastException if the class of the specified element
415     *         prevents it from being added to this deque
416     * @throws NullPointerException if the specified element is null
417     * @throws IllegalArgumentException if some property of the specified
418     *         element prevents it from being added to this deque
419     */
420    boolean add(E e);
421
422    /**
423     * Inserts the specified element into the queue represented by this deque
424     * (in other words, at the tail of this deque) if it is possible to do so
425     * immediately without violating capacity restrictions, returning
426     * {@code true} upon success and {@code false} if no space is currently
427     * available.  When using a capacity-restricted deque, this method is
428     * generally preferable to the {@link #add} method, which can fail to
429     * insert an element only by throwing an exception.
430     *
431     * <p>This method is equivalent to {@link #offerLast(Object) offerLast}.
432     *
433     * @param e the element to add
434     * @throws ClassCastException if the class of the specified element
435     *         prevents it from being added to this deque
436     * @throws NullPointerException if the specified element is null
437     * @throws IllegalArgumentException if some property of the specified
438     *         element prevents it from being added to this deque
439     */
440    boolean offer(E e);
441
442    /**
443     * Inserts the specified element into the queue represented by this deque
444     * (in other words, at the tail of this deque), waiting if necessary for
445     * space to become available.
446     *
447     * <p>This method is equivalent to {@link #putLast(Object) putLast}.
448     *
449     * @param e the element to add
450     * @throws InterruptedException {@inheritDoc}
451     * @throws ClassCastException if the class of the specified element
452     *         prevents it from being added to this deque
453     * @throws NullPointerException if the specified element is null
454     * @throws IllegalArgumentException if some property of the specified
455     *         element prevents it from being added to this deque
456     */
457    void put(E e) throws InterruptedException;
458
459    /**
460     * Inserts the specified element into the queue represented by this deque
461     * (in other words, at the tail of this deque), waiting up to the
462     * specified wait time if necessary for space to become available.
463     *
464     * <p>This method is equivalent to
465     * {@link #offerLast(Object,long,TimeUnit) offerLast}.
466     *
467     * @param e the element to add
468     * @return {@code true} if the element was added to this deque, else
469     *         {@code false}
470     * @throws InterruptedException {@inheritDoc}
471     * @throws ClassCastException if the class of the specified element
472     *         prevents it from being added to this deque
473     * @throws NullPointerException if the specified element is null
474     * @throws IllegalArgumentException if some property of the specified
475     *         element prevents it from being added to this deque
476     */
477    boolean offer(E e, long timeout, TimeUnit unit)
478        throws InterruptedException;
479
480    /**
481     * Retrieves and removes the head of the queue represented by this deque
482     * (in other words, the first element of this deque).
483     * This method differs from {@link #poll poll} only in that it
484     * throws an exception if this deque is empty.
485     *
486     * <p>This method is equivalent to {@link #removeFirst() removeFirst}.
487     *
488     * @return the head of the queue represented by this deque
489     * @throws NoSuchElementException if this deque is empty
490     */
491    E remove();
492
493    /**
494     * Retrieves and removes the head of the queue represented by this deque
495     * (in other words, the first element of this deque), or returns
496     * {@code null} if this deque is empty.
497     *
498     * <p>This method is equivalent to {@link #pollFirst()}.
499     *
500     * @return the head of this deque, or {@code null} if this deque is empty
501     */
502    E poll();
503
504    /**
505     * Retrieves and removes the head of the queue represented by this deque
506     * (in other words, the first element of this deque), waiting if
507     * necessary until an element becomes available.
508     *
509     * <p>This method is equivalent to {@link #takeFirst() takeFirst}.
510     *
511     * @return the head of this deque
512     * @throws InterruptedException if interrupted while waiting
513     */
514    E take() throws InterruptedException;
515
516    /**
517     * Retrieves and removes the head of the queue represented by this deque
518     * (in other words, the first element of this deque), waiting up to the
519     * specified wait time if necessary for an element to become available.
520     *
521     * <p>This method is equivalent to
522     * {@link #pollFirst(long,TimeUnit) pollFirst}.
523     *
524     * @return the head of this deque, or {@code null} if the
525     *         specified waiting time elapses before an element is available
526     * @throws InterruptedException if interrupted while waiting
527     */
528    E poll(long timeout, TimeUnit unit)
529        throws InterruptedException;
530
531    /**
532     * Retrieves, but does not remove, the head of the queue represented by
533     * this deque (in other words, the first element of this deque).
534     * This method differs from {@link #peek peek} only in that it throws an
535     * exception if this deque is empty.
536     *
537     * <p>This method is equivalent to {@link #getFirst() getFirst}.
538     *
539     * @return the head of this deque
540     * @throws NoSuchElementException if this deque is empty
541     */
542    E element();
543
544    /**
545     * Retrieves, but does not remove, the head of the queue represented by
546     * this deque (in other words, the first element of this deque), or
547     * returns {@code null} if this deque is empty.
548     *
549     * <p>This method is equivalent to {@link #peekFirst() peekFirst}.
550     *
551     * @return the head of this deque, or {@code null} if this deque is empty
552     */
553    E peek();
554
555    /**
556     * Removes the first occurrence of the specified element from this deque.
557     * If the deque does not contain the element, it is unchanged.
558     * More formally, removes the first element {@code e} such that
559     * {@code o.equals(e)} (if such an element exists).
560     * Returns {@code true} if this deque contained the specified element
561     * (or equivalently, if this deque changed as a result of the call).
562     *
563     * <p>This method is equivalent to
564     * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
565     *
566     * @param o element to be removed from this deque, if present
567     * @return {@code true} if this deque changed as a result of the call
568     * @throws ClassCastException if the class of the specified element
569     *         is incompatible with this deque
570     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
571     * @throws NullPointerException if the specified element is null
572     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
573     */
574    boolean remove(Object o);
575
576    /**
577     * Returns {@code true} if this deque contains the specified element.
578     * More formally, returns {@code true} if and only if this deque contains
579     * at least one element {@code e} such that {@code o.equals(e)}.
580     *
581     * @param o object to be checked for containment in this deque
582     * @return {@code true} if this deque contains the specified element
583     * @throws ClassCastException if the class of the specified element
584     *         is incompatible with this deque
585     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
586     * @throws NullPointerException if the specified element is null
587     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
588     */
589    public boolean contains(Object o);
590
591    /**
592     * Returns the number of elements in this deque.
593     *
594     * @return the number of elements in this deque
595     */
596    public int size();
597
598    /**
599     * Returns an iterator over the elements in this deque in proper sequence.
600     * The elements will be returned in order from first (head) to last (tail).
601     *
602     * @return an iterator over the elements in this deque in proper sequence
603     */
604    Iterator<E> iterator();
605
606    // *** Stack methods ***
607
608    /**
609     * Pushes an element onto the stack represented by this deque.  In other
610     * words, inserts the element at the front of this deque unless it would
611     * violate capacity restrictions.
612     *
613     * <p>This method is equivalent to {@link #addFirst(Object) addFirst}.
614     *
615     * @throws IllegalStateException {@inheritDoc}
616     * @throws ClassCastException {@inheritDoc}
617     * @throws NullPointerException if the specified element is null
618     * @throws IllegalArgumentException {@inheritDoc}
619     */
620    void push(E e);
621}
622