SynchronousQueue
open class SynchronousQueue<E : Any!> : AbstractQueue<E>, BlockingQueue<E>, Serializable
A blocking queue in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa. A synchronous queue does not have any internal capacity, not even a capacity of one. You cannot peek at a synchronous queue because an element is only present when you try to remove it; you cannot insert an element (using any method) unless another thread is trying to remove it; you cannot iterate as there is nothing to iterate. The head of the queue is the element that the first queued inserting thread is trying to add to the queue; if there is no such queued thread then no element is available for removal and poll() will return null. For purposes of other Collection methods (for example contains), a SynchronousQueue acts as an empty collection. This queue does not permit null elements.
Synchronous queues are similar to rendezvous channels used in CSP and Ada. They are well suited for handoff designs, in which an object running in one thread must sync up with an object running in another thread in order to hand it some information, event, or task.
This class supports an optional fairness policy for ordering waiting producer and consumer threads. By default, this ordering is not guaranteed. However, a queue constructed with fairness set to true grants threads access in FIFO order.
This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.
This class is a member of the Java Collections Framework.
Summary
| Public constructors |
|
Creates a SynchronousQueue with nonfair access policy.
|
|
Creates a SynchronousQueue with the specified fairness policy.
|
| Public methods |
| open Unit |
Does nothing.
|
| open Boolean |
Always returns false.
|
| open Boolean |
Returns false unless the given collection is empty.
|
| open Int |
|
| open Int |
|
| open Boolean |
Always returns true.
|
| open MutableIterator<E> |
Returns an empty iterator in which hasNext always returns false.
|
| open Boolean |
Inserts the specified element into this queue, if another thread is waiting to receive it.
|
| open Boolean |
Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.
|
| open E? |
Always returns null.
|
| open E? |
Retrieves and removes the head of this queue, if another thread is currently making an element available.
|
| open E |
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.
|
| open Unit |
Adds the specified element to this queue, waiting if necessary for another thread to receive it.
|
| open Int |
Always returns zero.
|
| open Boolean |
Always returns false.
|
| open Boolean |
Always returns false.
|
| open Boolean |
Always returns false.
|
| open Spliterator<E> |
Returns an empty spliterator in which calls to trySplit always return null.
|
| open E |
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.
|
| open Array<Any!> |
Returns a zero-length array.
|
| open Array<T> |
Sets the zeroth element of the specified array to null (if the array has non-zero length) and returns it.
|
| open String |
Always returns "[]".
|
| Inherited functions |
From class AbstractQueue
Boolean |
add(element: E)
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.
This implementation returns true if offer succeeds, else throws an IllegalStateException.
|
Boolean |
addAll(elements: Collection<E>)
Adds all of the elements in the specified collection to this queue. Attempts to addAll of a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.
This implementation iterates over the specified collection, and adds each element returned by the iterator to this queue, in turn. A runtime exception encountered while trying to add an element (including, in particular, a null element) may result in only some of the elements having been successfully added when the associated exception is thrown.
|
E |
element()
Retrieves, but does not remove, the head of this queue. This method differs from peek only in that it throws an exception if this queue is empty.
This implementation returns the result of peek unless the queue is empty.
|
E |
remove()
Retrieves and removes the head of this queue. This method differs from poll only in that it throws an exception if this queue is empty.
This implementation returns the result of poll unless the queue is empty.
|
|
From class AbstractCollection
Boolean |
contains(element: E?)
Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that Objects.equals(o, e).
|
Boolean |
containsAll(elements: Collection<E>)
Returns true if this collection contains all of the elements in the specified collection.
|
Boolean |
isEmpty()
Returns true if this collection contains no elements.
|
MutableIterator<E> |
iterator()
Returns an iterator over the elements contained in this collection.
|
Boolean |
remove(element: E?)
Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that Objects.equals(o, e), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).
|
Boolean |
removeAll(elements: Collection<E>)
Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.
|
Boolean |
retainAll(elements: Collection<E>)
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
|
Array<Any!> |
toArray()
Returns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's runtime component type is Object.
The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.
|
Array<T> |
toArray(a: Array<T>)
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.
If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)
If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
|
String |
toString()
Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).
|
|
From class Queue
Boolean |
offer(e: E)
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions. When using a capacity-restricted queue, this method is generally preferable to add, which can fail to insert an element only by throwing an exception.
|
E? |
peek()
Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
|
E? |
poll()
Retrieves and removes the head of this queue, or returns null if this queue is empty.
|
|
| Properties |
| open Int |
Always returns zero.
|
Public constructors
SynchronousQueue
SynchronousQueue()
Creates a SynchronousQueue with nonfair access policy.
SynchronousQueue
SynchronousQueue(fair: Boolean)
Creates a SynchronousQueue with the specified fairness policy.
| Parameters |
fair |
Boolean: if true, waiting threads contend in FIFO order for access; otherwise the order is unspecified. |
Public methods
clear
open fun clear(): Unit
Does nothing. A SynchronousQueue has no internal capacity.
| Exceptions |
java.lang.UnsupportedOperationException |
if the clear operation is not supported by this collection |
contains
open fun contains(element: E?): Boolean
Always returns false. A SynchronousQueue has no internal capacity.
| Exceptions |
java.lang.ClassCastException |
if the class of the specified element is incompatible with this queue (optional) |
java.lang.NullPointerException |
if the specified element is null (optional) |
containsAll
open fun containsAll(elements: Collection<E>): Boolean
Returns false unless the given collection is empty. A SynchronousQueue has no internal capacity.
| Parameters |
c |
the collection |
| Return |
Boolean |
false unless given collection is empty |
| Exceptions |
java.lang.ClassCastException |
if the types of one or more elements in the specified collection are incompatible with this collection (java.util.Collection#) |
java.lang.NullPointerException |
if the specified collection contains one or more null elements and this collection does not permit null elements (java.util.Collection#) or if the specified collection is null. |
drainTo
open fun drainTo(c: MutableCollection<in E>!): Int
| Return |
Int |
the number of elements transferred |
| Exceptions |
java.lang.UnsupportedOperationException |
if addition of elements is not supported by the specified collection |
java.lang.ClassCastException |
if the class of an element of this queue prevents it from being added to the specified collection |
java.lang.NullPointerException |
if the specified collection is null |
java.lang.IllegalArgumentException |
if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection |
drainTo
open fun drainTo(
c: MutableCollection<in E>!,
maxElements: Int
): Int
| Parameters |
c |
MutableCollection<in E>!: the collection to transfer elements into |
maxElements |
Int: the maximum number of elements to transfer |
| Return |
Int |
the number of elements transferred |
| Exceptions |
java.lang.UnsupportedOperationException |
if addition of elements is not supported by the specified collection |
java.lang.ClassCastException |
if the class of an element of this queue prevents it from being added to the specified collection |
java.lang.NullPointerException |
if the specified collection is null |
java.lang.IllegalArgumentException |
if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection |
isEmpty
open fun isEmpty(): Boolean
Always returns true. A SynchronousQueue has no internal capacity.
iterator
open fun iterator(): MutableIterator<E>
Returns an empty iterator in which hasNext always returns false.
offer
open fun offer(e: E): Boolean
Inserts the specified element into this queue, if another thread is waiting to receive it.
| Parameters |
e |
E: the element to add |
| Return |
Boolean |
true if the element was added to this queue, else false |
| Exceptions |
java.lang.ClassCastException |
if the class of the specified element prevents it from being added to this queue |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
offer
open fun offer(
e: E,
timeout: Long,
unit: TimeUnit!
): Boolean
Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.
| Parameters |
e |
E: the element to add |
timeout |
Long: how long to wait before giving up, in units of unit |
unit |
TimeUnit!: a TimeUnit determining how to interpret the timeout parameter |
| Return |
Boolean |
true if successful, or false if the specified waiting time elapses before a consumer appears |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
java.lang.ClassCastException |
if the class of the specified element prevents it from being added to this queue |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
peek
open fun peek(): E?
Always returns null. A SynchronousQueue does not return elements unless actively waited on.
poll
open fun poll(): E?
Retrieves and removes the head of this queue, if another thread is currently making an element available.
| Return |
E? |
the head of this queue, or null if no element is available |
poll
open fun poll(
timeout: Long,
unit: TimeUnit!
): E
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.
| Parameters |
timeout |
Long: how long to wait before giving up, in units of unit |
unit |
TimeUnit!: a TimeUnit determining how to interpret the timeout parameter |
| Return |
E |
the head of this queue, or null if the specified waiting time elapses before an element is present |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
put
open fun put(e: E): Unit
Adds the specified element to this queue, waiting if necessary for another thread to receive it.
| Parameters |
e |
E: the element to add |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
java.lang.ClassCastException |
if the class of the specified element prevents it from being added to this queue |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
remainingCapacity
open fun remainingCapacity(): Int
Always returns zero. A SynchronousQueue has no internal capacity.
remove
open fun remove(element: E?): Boolean
Always returns false. A SynchronousQueue has no internal capacity.
| Parameters |
o |
the element to remove |
| Exceptions |
java.lang.ClassCastException |
if the class of the specified element is incompatible with this queue (optional) |
java.lang.NullPointerException |
if the specified element is null (optional) |
java.lang.UnsupportedOperationException |
if the remove operation is not supported by this collection |
removeAll
open fun removeAll(elements: Collection<E>): Boolean
Always returns false. A SynchronousQueue has no internal capacity.
| Parameters |
c |
the collection |
| Exceptions |
java.lang.UnsupportedOperationException |
if the removeAll method is not supported by this collection |
java.lang.ClassCastException |
if the types of one or more elements in this collection are incompatible with the specified collection (java.util.Collection#) |
java.lang.NullPointerException |
if this collection contains one or more null elements and the specified collection does not support null elements (java.util.Collection#) or if the specified collection is null |
retainAll
open fun retainAll(elements: Collection<E>): Boolean
Always returns false. A SynchronousQueue has no internal capacity.
| Parameters |
c |
the collection |
| Exceptions |
java.lang.UnsupportedOperationException |
if the retainAll operation is not supported by this collection |
java.lang.ClassCastException |
if the types of one or more elements in this collection are incompatible with the specified collection (java.util.Collection#) |
java.lang.NullPointerException |
if this collection contains one or more null elements and the specified collection does not permit null elements (java.util.Collection#) or if the specified collection is null |
spliterator
open fun spliterator(): Spliterator<E>
Returns an empty spliterator in which calls to trySplit always return null.
take
open fun take(): E
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.
| Return |
E |
the head of this queue |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
toArray
open fun toArray(): Array<Any!>
Returns a zero-length array.
toArray
open fun <T : Any!> toArray(a: Array<T>): Array<T>
Sets the zeroth element of the specified array to null (if the array has non-zero length) and returns it.
| Parameters |
<T> |
the component type of the array to contain the collection |
a |
Array<T>: the array |
| Return |
Array<T> |
the specified array |
| Exceptions |
java.lang.ArrayStoreException |
if the runtime type of any element in this collection is not assignable to the runtime component type of the specified array |
java.lang.NullPointerException |
if the specified array is null |
toString
open fun toString(): String
Always returns "[]".
Properties
size
open val size: Int
Always returns zero. A SynchronousQueue has no internal capacity.
