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Java Source Code / Java Documentation » 6.0 JDK Core » Collections Jar Zip Logging regex » java.util.concurrent 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001        /*
002         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
003         *
004         * This code is free software; you can redistribute it and/or modify it
005         * under the terms of the GNU General Public License version 2 only, as
006         * published by the Free Software Foundation.  Sun designates this
007         * particular file as subject to the "Classpath" exception as provided
008         * by Sun in the LICENSE file that accompanied this code.
009         *
010         * This code is distributed in the hope that it will be useful, but WITHOUT
011         * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
012         * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
013         * version 2 for more details (a copy is included in the LICENSE file that
014         * accompanied this code).
015         *
016         * You should have received a copy of the GNU General Public License version
017         * 2 along with this work; if not, write to the Free Software Foundation,
018         * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
019         *
020         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
021         * CA 95054 USA or visit www.sun.com if you need additional information or
022         * have any questions.
023         */
024
025        /*
026         * This file is available under and governed by the GNU General Public
027         * License version 2 only, as published by the Free Software Foundation.
028         * However, the following notice accompanied the original version of this
029         * file:
030         *
031         * Written by Doug Lea with assistance from members of JCP JSR-166
032         * Expert Group and released to the public domain, as explained at
033         * http://creativecommons.org/licenses/publicdomain
034         */
035
036        package java.util.concurrent;
037
038        import java.util.concurrent.locks.*;
039        import java.util.*;
040
041        /**
042         * A bounded {@linkplain BlockingQueue blocking queue} backed by an
043         * array.  This queue orders elements FIFO (first-in-first-out).  The
044         * <em>head</em> of the queue is that element that has been on the
045         * queue the longest time.  The <em>tail</em> of the queue is that
046         * element that has been on the queue the shortest time. New elements
047         * are inserted at the tail of the queue, and the queue retrieval
048         * operations obtain elements at the head of the queue.
049         *
050         * <p>This is a classic &quot;bounded buffer&quot;, in which a
051         * fixed-sized array holds elements inserted by producers and
052         * extracted by consumers.  Once created, the capacity cannot be
053         * increased.  Attempts to <tt>put</tt> an element into a full queue
054         * will result in the operation blocking; attempts to <tt>take</tt> an
055         * element from an empty queue will similarly block.
056         *
057         * <p> This class supports an optional fairness policy for ordering
058         * waiting producer and consumer threads.  By default, this ordering
059         * is not guaranteed. However, a queue constructed with fairness set
060         * to <tt>true</tt> grants threads access in FIFO order. Fairness
061         * generally decreases throughput but reduces variability and avoids
062         * starvation.
063         *
064         * <p>This class and its iterator implement all of the
065         * <em>optional</em> methods of the {@link Collection} and {@link
066         * Iterator} interfaces.
067         *
068         * <p>This class is a member of the
069         * <a href="{@docRoot}/../technotes/guides/collections/index.html">
070         * Java Collections Framework</a>.
071         *
072         * @since 1.5
073         * @author Doug Lea
074         * @param <E> the type of elements held in this collection
075         */
076        public class ArrayBlockingQueue<E> extends AbstractQueue<E> implements 
077                BlockingQueue<E>, java.io.Serializable {
078
079            /**
080             * Serialization ID. This class relies on default serialization
081             * even for the items array, which is default-serialized, even if
082             * it is empty. Otherwise it could not be declared final, which is
083             * necessary here.
084             */
085            private static final long serialVersionUID = -817911632652898426L;
086
087            /** The queued items  */
088            private final E[] items;
089            /** items index for next take, poll or remove */
090            private int takeIndex;
091            /** items index for next put, offer, or add. */
092            private int putIndex;
093            /** Number of items in the queue */
094            private int count;
095
096            /*
097             * Concurrency control uses the classic two-condition algorithm
098             * found in any textbook.
099             */
100
101            /** Main lock guarding all access */
102            private final ReentrantLock lock;
103            /** Condition for waiting takes */
104            private final Condition notEmpty;
105            /** Condition for waiting puts */
106            private final Condition notFull;
107
108            // Internal helper methods
109
110            /**
111             * Circularly increment i.
112             */
113            final int inc(int i) {
114                return (++i == items.length) ? 0 : i;
115            }
116
117            /**
118             * Inserts element at current put position, advances, and signals.
119             * Call only when holding lock.
120             */
121            private void insert(E x) {
122                items[putIndex] = x;
123                putIndex = inc(putIndex);
124                ++count;
125                notEmpty.signal();
126            }
127
128            /**
129             * Extracts element at current take position, advances, and signals.
130             * Call only when holding lock.
131             */
132            private E extract() {
133                final E[] items = this .items;
134                E x = items[takeIndex];
135                items[takeIndex] = null;
136                takeIndex = inc(takeIndex);
137                --count;
138                notFull.signal();
139                return x;
140            }
141
142            /**
143             * Utility for remove and iterator.remove: Delete item at position i.
144             * Call only when holding lock.
145             */
146            void removeAt(int i) {
147                final E[] items = this .items;
148                // if removing front item, just advance
149                if (i == takeIndex) {
150                    items[takeIndex] = null;
151                    takeIndex = inc(takeIndex);
152                } else {
153                    // slide over all others up through putIndex.
154                    for (;;) {
155                        int nexti = inc(i);
156                        if (nexti != putIndex) {
157                            items[i] = items[nexti];
158                            i = nexti;
159                        } else {
160                            items[i] = null;
161                            putIndex = i;
162                            break;
163                        }
164                    }
165                }
166                --count;
167                notFull.signal();
168            }
169
170            /**
171             * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
172             * capacity and default access policy.
173             *
174             * @param capacity the capacity of this queue
175             * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
176             */
177            public ArrayBlockingQueue(int capacity) {
178                this (capacity, false);
179            }
180
181            /**
182             * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
183             * capacity and the specified access policy.
184             *
185             * @param capacity the capacity of this queue
186             * @param fair if <tt>true</tt> then queue accesses for threads blocked
187             *        on insertion or removal, are processed in FIFO order;
188             *        if <tt>false</tt> the access order is unspecified.
189             * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
190             */
191            public ArrayBlockingQueue(int capacity, boolean fair) {
192                if (capacity <= 0)
193                    throw new IllegalArgumentException();
194                this .items = (E[]) new Object[capacity];
195                lock = new ReentrantLock(fair);
196                notEmpty = lock.newCondition();
197                notFull = lock.newCondition();
198            }
199
200            /**
201             * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
202             * capacity, the specified access policy and initially containing the
203             * elements of the given collection,
204             * added in traversal order of the collection's iterator.
205             *
206             * @param capacity the capacity of this queue
207             * @param fair if <tt>true</tt> then queue accesses for threads blocked
208             *        on insertion or removal, are processed in FIFO order;
209             *        if <tt>false</tt> the access order is unspecified.
210             * @param c the collection of elements to initially contain
211             * @throws IllegalArgumentException if <tt>capacity</tt> is less than
212             *         <tt>c.size()</tt>, or less than 1.
213             * @throws NullPointerException if the specified collection or any
214             *         of its elements are null
215             */
216            public ArrayBlockingQueue(int capacity, boolean fair,
217                    Collection<? extends E> c) {
218                this (capacity, fair);
219                if (capacity < c.size())
220                    throw new IllegalArgumentException();
221
222                for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
223                    add(it.next());
224            }
225
226            /**
227             * Inserts the specified element at the tail of this queue if it is
228             * possible to do so immediately without exceeding the queue's capacity,
229             * returning <tt>true</tt> upon success and throwing an
230             * <tt>IllegalStateException</tt> if this queue is full.
231             *
232             * @param e the element to add
233             * @return <tt>true</tt> (as specified by {@link Collection#add})
234             * @throws IllegalStateException if this queue is full
235             * @throws NullPointerException if the specified element is null
236             */
237            public boolean add(E e) {
238                return super .add(e);
239            }
240
241            /**
242             * Inserts the specified element at the tail of this queue if it is
243             * possible to do so immediately without exceeding the queue's capacity,
244             * returning <tt>true</tt> upon success and <tt>false</tt> if this queue
245             * is full.  This method is generally preferable to method {@link #add},
246             * which can fail to insert an element only by throwing an exception.
247             *
248             * @throws NullPointerException if the specified element is null
249             */
250            public boolean offer(E e) {
251                if (e == null)
252                    throw new NullPointerException();
253                final ReentrantLock lock = this .lock;
254                lock.lock();
255                try {
256                    if (count == items.length)
257                        return false;
258                    else {
259                        insert(e);
260                        return true;
261                    }
262                } finally {
263                    lock.unlock();
264                }
265            }
266
267            /**
268             * Inserts the specified element at the tail of this queue, waiting
269             * for space to become available if the queue is full.
270             *
271             * @throws InterruptedException {@inheritDoc}
272             * @throws NullPointerException {@inheritDoc}
273             */
274            public void put(E e) throws InterruptedException {
275                if (e == null)
276                    throw new NullPointerException();
277                final E[] items = this .items;
278                final ReentrantLock lock = this .lock;
279                lock.lockInterruptibly();
280                try {
281                    try {
282                        while (count == items.length)
283                            notFull.await();
284                    } catch (InterruptedException ie) {
285                        notFull.signal(); // propagate to non-interrupted thread
286                        throw ie;
287                    }
288                    insert(e);
289                } finally {
290                    lock.unlock();
291                }
292            }
293
294            /**
295             * Inserts the specified element at the tail of this queue, waiting
296             * up to the specified wait time for space to become available if
297             * the queue is full.
298             *
299             * @throws InterruptedException {@inheritDoc}
300             * @throws NullPointerException {@inheritDoc}
301             */
302            public boolean offer(E e, long timeout, TimeUnit unit)
303                    throws InterruptedException {
304
305                if (e == null)
306                    throw new NullPointerException();
307                long nanos = unit.toNanos(timeout);
308                final ReentrantLock lock = this .lock;
309                lock.lockInterruptibly();
310                try {
311                    for (;;) {
312                        if (count != items.length) {
313                            insert(e);
314                            return true;
315                        }
316                        if (nanos <= 0)
317                            return false;
318                        try {
319                            nanos = notFull.awaitNanos(nanos);
320                        } catch (InterruptedException ie) {
321                            notFull.signal(); // propagate to non-interrupted thread
322                            throw ie;
323                        }
324                    }
325                } finally {
326                    lock.unlock();
327                }
328            }
329
330            public E poll() {
331                final ReentrantLock lock = this .lock;
332                lock.lock();
333                try {
334                    if (count == 0)
335                        return null;
336                    E x = extract();
337                    return x;
338                } finally {
339                    lock.unlock();
340                }
341            }
342
343            public E take() throws InterruptedException {
344                final ReentrantLock lock = this .lock;
345                lock.lockInterruptibly();
346                try {
347                    try {
348                        while (count == 0)
349                            notEmpty.await();
350                    } catch (InterruptedException ie) {
351                        notEmpty.signal(); // propagate to non-interrupted thread
352                        throw ie;
353                    }
354                    E x = extract();
355                    return x;
356                } finally {
357                    lock.unlock();
358                }
359            }
360
361            public E poll(long timeout, TimeUnit unit)
362                    throws InterruptedException {
363                long nanos = unit.toNanos(timeout);
364                final ReentrantLock lock = this .lock;
365                lock.lockInterruptibly();
366                try {
367                    for (;;) {
368                        if (count != 0) {
369                            E x = extract();
370                            return x;
371                        }
372                        if (nanos <= 0)
373                            return null;
374                        try {
375                            nanos = notEmpty.awaitNanos(nanos);
376                        } catch (InterruptedException ie) {
377                            notEmpty.signal(); // propagate to non-interrupted thread
378                            throw ie;
379                        }
380
381                    }
382                } finally {
383                    lock.unlock();
384                }
385            }
386
387            public E peek() {
388                final ReentrantLock lock = this .lock;
389                lock.lock();
390                try {
391                    return (count == 0) ? null : items[takeIndex];
392                } finally {
393                    lock.unlock();
394                }
395            }
396
397            // this doc comment is overridden to remove the reference to collections
398            // greater in size than Integer.MAX_VALUE
399            /**
400             * Returns the number of elements in this queue.
401             *
402             * @return the number of elements in this queue
403             */
404            public int size() {
405                final ReentrantLock lock = this .lock;
406                lock.lock();
407                try {
408                    return count;
409                } finally {
410                    lock.unlock();
411                }
412            }
413
414            // this doc comment is a modified copy of the inherited doc comment,
415            // without the reference to unlimited queues.
416            /**
417             * Returns the number of additional elements that this queue can ideally
418             * (in the absence of memory or resource constraints) accept without
419             * blocking. This is always equal to the initial capacity of this queue
420             * less the current <tt>size</tt> of this queue.
421             *
422             * <p>Note that you <em>cannot</em> always tell if an attempt to insert
423             * an element will succeed by inspecting <tt>remainingCapacity</tt>
424             * because it may be the case that another thread is about to
425             * insert or remove an element.
426             */
427            public int remainingCapacity() {
428                final ReentrantLock lock = this .lock;
429                lock.lock();
430                try {
431                    return items.length - count;
432                } finally {
433                    lock.unlock();
434                }
435            }
436
437            /**
438             * Removes a single instance of the specified element from this queue,
439             * if it is present.  More formally, removes an element <tt>e</tt> such
440             * that <tt>o.equals(e)</tt>, if this queue contains one or more such
441             * elements.
442             * Returns <tt>true</tt> if this queue contained the specified element
443             * (or equivalently, if this queue changed as a result of the call).
444             *
445             * @param o element to be removed from this queue, if present
446             * @return <tt>true</tt> if this queue changed as a result of the call
447             */
448            public boolean remove(Object o) {
449                if (o == null)
450                    return false;
451                final E[] items = this .items;
452                final ReentrantLock lock = this .lock;
453                lock.lock();
454                try {
455                    int i = takeIndex;
456                    int k = 0;
457                    for (;;) {
458                        if (k++ >= count)
459                            return false;
460                        if (o.equals(items[i])) {
461                            removeAt(i);
462                            return true;
463                        }
464                        i = inc(i);
465                    }
466
467                } finally {
468                    lock.unlock();
469                }
470            }
471
472            /**
473             * Returns <tt>true</tt> if this queue contains the specified element.
474             * More formally, returns <tt>true</tt> if and only if this queue contains
475             * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
476             *
477             * @param o object to be checked for containment in this queue
478             * @return <tt>true</tt> if this queue contains the specified element
479             */
480            public boolean contains(Object o) {
481                if (o == null)
482                    return false;
483                final E[] items = this .items;
484                final ReentrantLock lock = this .lock;
485                lock.lock();
486                try {
487                    int i = takeIndex;
488                    int k = 0;
489                    while (k++ < count) {
490                        if (o.equals(items[i]))
491                            return true;
492                        i = inc(i);
493                    }
494                    return false;
495                } finally {
496                    lock.unlock();
497                }
498            }
499
500            /**
501             * Returns an array containing all of the elements in this queue, in
502             * proper sequence.
503             *
504             * <p>The returned array will be "safe" in that no references to it are
505             * maintained by this queue.  (In other words, this method must allocate
506             * a new array).  The caller is thus free to modify the returned array.
507             *
508             * <p>This method acts as bridge between array-based and collection-based
509             * APIs.
510             *
511             * @return an array containing all of the elements in this queue
512             */
513            public Object[] toArray() {
514                final E[] items = this .items;
515                final ReentrantLock lock = this .lock;
516                lock.lock();
517                try {
518                    Object[] a = new Object[count];
519                    int k = 0;
520                    int i = takeIndex;
521                    while (k < count) {
522                        a[k++] = items[i];
523                        i = inc(i);
524                    }
525                    return a;
526                } finally {
527                    lock.unlock();
528                }
529            }
530
531            /**
532             * Returns an array containing all of the elements in this queue, in
533             * proper sequence; the runtime type of the returned array is that of
534             * the specified array.  If the queue fits in the specified array, it
535             * is returned therein.  Otherwise, a new array is allocated with the
536             * runtime type of the specified array and the size of this queue.
537             *
538             * <p>If this queue fits in the specified array with room to spare
539             * (i.e., the array has more elements than this queue), the element in
540             * the array immediately following the end of the queue is set to
541             * <tt>null</tt>.
542             *
543             * <p>Like the {@link #toArray()} method, this method acts as bridge between
544             * array-based and collection-based APIs.  Further, this method allows
545             * precise control over the runtime type of the output array, and may,
546             * under certain circumstances, be used to save allocation costs.
547             *
548             * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
549             * The following code can be used to dump the queue into a newly
550             * allocated array of <tt>String</tt>:
551             *
552             * <pre>
553             *     String[] y = x.toArray(new String[0]);</pre>
554             *
555             * Note that <tt>toArray(new Object[0])</tt> is identical in function to
556             * <tt>toArray()</tt>.
557             *
558             * @param a the array into which the elements of the queue are to
559             *          be stored, if it is big enough; otherwise, a new array of the
560             *          same runtime type is allocated for this purpose
561             * @return an array containing all of the elements in this queue
562             * @throws ArrayStoreException if the runtime type of the specified array
563             *         is not a supertype of the runtime type of every element in
564             *         this queue
565             * @throws NullPointerException if the specified array is null
566             */
567            public <T> T[] toArray(T[] a) {
568                final E[] items = this .items;
569                final ReentrantLock lock = this .lock;
570                lock.lock();
571                try {
572                    if (a.length < count)
573                        a = (T[]) java.lang.reflect.Array.newInstance(a
574                                .getClass().getComponentType(), count);
575
576                    int k = 0;
577                    int i = takeIndex;
578                    while (k < count) {
579                        a[k++] = (T) items[i];
580                        i = inc(i);
581                    }
582                    if (a.length > count)
583                        a[count] = null;
584                    return a;
585                } finally {
586                    lock.unlock();
587                }
588            }
589
590            public String toString() {
591                final ReentrantLock lock = this .lock;
592                lock.lock();
593                try {
594                    return super .toString();
595                } finally {
596                    lock.unlock();
597                }
598            }
599
600            /**
601             * Atomically removes all of the elements from this queue.
602             * The queue will be empty after this call returns.
603             */
604            public void clear() {
605                final E[] items = this .items;
606                final ReentrantLock lock = this .lock;
607                lock.lock();
608                try {
609                    int i = takeIndex;
610                    int k = count;
611                    while (k-- > 0) {
612                        items[i] = null;
613                        i = inc(i);
614                    }
615                    count = 0;
616                    putIndex = 0;
617                    takeIndex = 0;
618                    notFull.signalAll();
619                } finally {
620                    lock.unlock();
621                }
622            }
623
624            /**
625             * @throws UnsupportedOperationException {@inheritDoc}
626             * @throws ClassCastException            {@inheritDoc}
627             * @throws NullPointerException          {@inheritDoc}
628             * @throws IllegalArgumentException      {@inheritDoc}
629             */
630            public int drainTo(Collection<? super  E> c) {
631                if (c == null)
632                    throw new NullPointerException();
633                if (c == this )
634                    throw new IllegalArgumentException();
635                final E[] items = this .items;
636                final ReentrantLock lock = this .lock;
637                lock.lock();
638                try {
639                    int i = takeIndex;
640                    int n = 0;
641                    int max = count;
642                    while (n < max) {
643                        c.add(items[i]);
644                        items[i] = null;
645                        i = inc(i);
646                        ++n;
647                    }
648                    if (n > 0) {
649                        count = 0;
650                        putIndex = 0;
651                        takeIndex = 0;
652                        notFull.signalAll();
653                    }
654                    return n;
655                } finally {
656                    lock.unlock();
657                }
658            }
659
660            /**
661             * @throws UnsupportedOperationException {@inheritDoc}
662             * @throws ClassCastException            {@inheritDoc}
663             * @throws NullPointerException          {@inheritDoc}
664             * @throws IllegalArgumentException      {@inheritDoc}
665             */
666            public int drainTo(Collection<? super  E> c, int maxElements) {
667                if (c == null)
668                    throw new NullPointerException();
669                if (c == this )
670                    throw new IllegalArgumentException();
671                if (maxElements <= 0)
672                    return 0;
673                final E[] items = this .items;
674                final ReentrantLock lock = this .lock;
675                lock.lock();
676                try {
677                    int i = takeIndex;
678                    int n = 0;
679                    int sz = count;
680                    int max = (maxElements < count) ? maxElements : count;
681                    while (n < max) {
682                        c.add(items[i]);
683                        items[i] = null;
684                        i = inc(i);
685                        ++n;
686                    }
687                    if (n > 0) {
688                        count -= n;
689                        takeIndex = i;
690                        notFull.signalAll();
691                    }
692                    return n;
693                } finally {
694                    lock.unlock();
695                }
696            }
697
698            /**
699             * Returns an iterator over the elements in this queue in proper sequence.
700             * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
701             * will never throw {@link ConcurrentModificationException},
702             * and guarantees to traverse elements as they existed upon
703             * construction of the iterator, and may (but is not guaranteed to)
704             * reflect any modifications subsequent to construction.
705             *
706             * @return an iterator over the elements in this queue in proper sequence
707             */
708            public Iterator<E> iterator() {
709                final ReentrantLock lock = this .lock;
710                lock.lock();
711                try {
712                    return new Itr();
713                } finally {
714                    lock.unlock();
715                }
716            }
717
718            /**
719             * Iterator for ArrayBlockingQueue
720             */
721            private class Itr implements  Iterator<E> {
722                /**
723                 * Index of element to be returned by next,
724                 * or a negative number if no such.
725                 */
726                private int nextIndex;
727
728                /**
729                 * nextItem holds on to item fields because once we claim
730                 * that an element exists in hasNext(), we must return it in
731                 * the following next() call even if it was in the process of
732                 * being removed when hasNext() was called.
733                 */
734                private E nextItem;
735
736                /**
737                 * Index of element returned by most recent call to next.
738                 * Reset to -1 if this element is deleted by a call to remove.
739                 */
740                private int lastRet;
741
742                Itr() {
743                    lastRet = -1;
744                    if (count == 0)
745                        nextIndex = -1;
746                    else {
747                        nextIndex = takeIndex;
748                        nextItem = items[takeIndex];
749                    }
750                }
751
752                public boolean hasNext() {
753                    /*
754                     * No sync. We can return true by mistake here
755                     * only if this iterator passed across threads,
756                     * which we don't support anyway.
757                     */
758                    return nextIndex >= 0;
759                }
760
761                /**
762                 * Checks whether nextIndex is valid; if so setting nextItem.
763                 * Stops iterator when either hits putIndex or sees null item.
764                 */
765                private void checkNext() {
766                    if (nextIndex == putIndex) {
767                        nextIndex = -1;
768                        nextItem = null;
769                    } else {
770                        nextItem = items[nextIndex];
771                        if (nextItem == null)
772                            nextIndex = -1;
773                    }
774                }
775
776                public E next() {
777                    final ReentrantLock lock = ArrayBlockingQueue.this .lock;
778                    lock.lock();
779                    try {
780                        if (nextIndex < 0)
781                            throw new NoSuchElementException();
782                        lastRet = nextIndex;
783                        E x = nextItem;
784                        nextIndex = inc(nextIndex);
785                        checkNext();
786                        return x;
787                    } finally {
788                        lock.unlock();
789                    }
790                }
791
792                public void remove() {
793                    final ReentrantLock lock = ArrayBlockingQueue.this .lock;
794                    lock.lock();
795                    try {
796                        int i = lastRet;
797                        if (i == -1)
798                            throw new IllegalStateException();
799                        lastRet = -1;
800
801                        int ti = takeIndex;
802                        removeAt(i);
803                        // back up cursor (reset to front if was first element)
804                        nextIndex = (i == ti) ? takeIndex : i;
805                        checkNext();
806                    } finally {
807                        lock.unlock();
808                    }
809                }
810            }
811        }
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