68  * of elements requires a traversal of the elements, and so may report
  69  * inaccurate results if this collection is modified during traversal.
  70  *
  71  * <p>Bulk operations that add, remove, or examine multiple elements,
  72  * such as {@link #addAll}, {@link #removeIf} or {@link #forEach},
  73  * are <em>not</em> guaranteed to be performed atomically.
  74  * For example, a {@code forEach} traversal concurrent with an {@code
  75  * addAll} operation might observe only some of the added elements.
  76  *
  77  * <p>This class and its iterator implement all of the <em>optional</em>
  78  * methods of the {@link Deque} and {@link Iterator} interfaces.
  79  *
  80  * <p>Memory consistency effects: As with other concurrent collections,
  81  * actions in a thread prior to placing an object into a
  82  * {@code ConcurrentLinkedDeque}
  83  * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
  84  * actions subsequent to the access or removal of that element from
  85  * the {@code ConcurrentLinkedDeque} in another thread.
  86  *
  87  * <p>This class is a member of the
  88  * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
  89  * Java Collections Framework</a>.
  90  *
  91  * @since 1.7
  92  * @author Doug Lea
  93  * @author Martin Buchholz
  94  * @param <E> the type of elements held in this deque
  95  */
  96 public class ConcurrentLinkedDeque<E>
  97     extends AbstractCollection<E>
  98     implements Deque<E>, java.io.Serializable {
  99 
 100     /*
 101      * This is an implementation of a concurrent lock-free deque
 102      * supporting interior removes but not interior insertions, as
 103      * required to support the entire Deque interface.
 104      *
 105      * We extend the techniques developed for ConcurrentLinkedQueue and
 106      * LinkedTransferQueue (see the internal docs for those classes).
 107      * Understanding the ConcurrentLinkedQueue implementation is a
 108      * prerequisite for understanding the implementation of this class.

  68  * of elements requires a traversal of the elements, and so may report
  69  * inaccurate results if this collection is modified during traversal.
  70  *
  71  * <p>Bulk operations that add, remove, or examine multiple elements,
  72  * such as {@link #addAll}, {@link #removeIf} or {@link #forEach},
  73  * are <em>not</em> guaranteed to be performed atomically.
  74  * For example, a {@code forEach} traversal concurrent with an {@code
  75  * addAll} operation might observe only some of the added elements.
  76  *
  77  * <p>This class and its iterator implement all of the <em>optional</em>
  78  * methods of the {@link Deque} and {@link Iterator} interfaces.
  79  *
  80  * <p>Memory consistency effects: As with other concurrent collections,
  81  * actions in a thread prior to placing an object into a
  82  * {@code ConcurrentLinkedDeque}
  83  * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
  84  * actions subsequent to the access or removal of that element from
  85  * the {@code ConcurrentLinkedDeque} in another thread.
  86  *
  87  * <p>This class is a member of the
  88  * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
  89  * Java Collections Framework</a>.
  90  *
  91  * @since 1.7
  92  * @author Doug Lea
  93  * @author Martin Buchholz
  94  * @param <E> the type of elements held in this deque
  95  */
  96 public class ConcurrentLinkedDeque<E>
  97     extends AbstractCollection<E>
  98     implements Deque<E>, java.io.Serializable {
  99 
 100     /*
 101      * This is an implementation of a concurrent lock-free deque
 102      * supporting interior removes but not interior insertions, as
 103      * required to support the entire Deque interface.
 104      *
 105      * We extend the techniques developed for ConcurrentLinkedQueue and
 106      * LinkedTransferQueue (see the internal docs for those classes).
 107      * Understanding the ConcurrentLinkedQueue implementation is a
 108      * prerequisite for understanding the implementation of this class.