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java.lang.Object | +--java.util.AbstractCollection | +--edu.emory.mathcs.util.AbstractQueue | +--edu.emory.mathcs.util.concurrent.SynchronousQueue
A blocking queue in which each put must wait for a take, 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 take it; you cannot add 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 thread is trying to add to the queue; if there are no queued threads then no element is being added and the head is 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. Fairness generally decreases throughput but reduces variability and avoids starvation.
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.
Constructor Summary | |
SynchronousQueue()
Creates a SynchronousQueue with nonfair access policy. |
|
SynchronousQueue(boolean fair)
Creates a SynchronousQueue with specified fairness policy. |
Method Summary | |
void |
clear()
Does nothing. |
boolean |
contains(java.lang.Object o)
Always returns false. |
boolean |
containsAll(java.util.Collection c)
Returns false unless given collection is empty. |
int |
drainTo(java.util.Collection c)
Removes all available elements from this queue and adds them into the given collection. |
int |
drainTo(java.util.Collection c,
int maxElements)
Removes at most the given number of available elements from this queue and adds them into the given collection. |
boolean |
isEmpty()
Always returns true. |
java.util.Iterator |
iterator()
Returns an empty iterator in which hasNext always returns false. |
boolean |
offer(java.lang.Object o)
Inserts the specified element into this queue, if another thread is waiting to receive it. |
boolean |
offer(java.lang.Object o,
long timeout,
TimeUnit unit)
Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it. |
java.lang.Object |
peek()
Always returns null. |
java.lang.Object |
poll()
Retrieves and removes the head of this queue, if another thread is currently making an element available. |
java.lang.Object |
poll(long timeout,
TimeUnit unit)
Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it. |
void |
put(java.lang.Object o)
Adds the specified element to this queue, waiting if necessary for another thread to receive it. |
int |
remainingCapacity()
Always returns zero. |
boolean |
remove(java.lang.Object o)
Always returns false. |
boolean |
removeAll(java.util.Collection c)
Always returns false. |
boolean |
retainAll(java.util.Collection c)
Always returns false. |
int |
size()
Always returns zero. |
java.lang.Object |
take()
Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it. |
java.lang.Object[] |
toArray()
Returns a zero-length array. |
java.lang.Object[] |
toArray(java.lang.Object[] a)
Sets the zeroeth element of the specified array to null (if the array has non-zero length) and returns it. |
Methods inherited from class edu.emory.mathcs.util.AbstractQueue |
add, addAll, element, remove |
Methods inherited from class java.util.AbstractCollection |
toString |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Methods inherited from interface edu.emory.mathcs.util.concurrent.BlockingQueue |
add |
Methods inherited from interface edu.emory.mathcs.util.Queue |
element, remove |
Methods inherited from interface java.util.Collection |
addAll, equals, hashCode |
Constructor Detail |
public SynchronousQueue()
public SynchronousQueue(boolean fair)
fair
- if true, threads contend in FIFO order for access;
otherwise the order is unspecified.Method Detail |
public void put(java.lang.Object o) throws java.lang.InterruptedException
put
in interface BlockingQueue
o
- the element to add
java.lang.InterruptedException
- if interrupted while waiting.
java.lang.NullPointerException
- if the specified element is null.public boolean offer(java.lang.Object o, long timeout, TimeUnit unit) throws java.lang.InterruptedException
offer
in interface BlockingQueue
o
- the element to addtimeout
- how long to wait before giving up, in units of
unitunit
- a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException
- if interrupted while waiting.
java.lang.NullPointerException
- if the specified element is null.public java.lang.Object take() throws java.lang.InterruptedException
take
in interface BlockingQueue
java.lang.InterruptedException
- if interrupted while waiting.public java.lang.Object poll(long timeout, TimeUnit unit) throws java.lang.InterruptedException
poll
in interface BlockingQueue
timeout
- how long to wait before giving up, in units of
unitunit
- a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException
- if interrupted while waiting.public boolean offer(java.lang.Object o)
offer
in interface BlockingQueue
o
- the element to add.
java.lang.NullPointerException
- if the specified element is nullpublic java.lang.Object poll()
poll
in interface Queue
public boolean isEmpty()
isEmpty
in interface java.util.Collection
isEmpty
in class java.util.AbstractCollection
public int size()
size
in interface java.util.Collection
size
in class java.util.AbstractCollection
public int remainingCapacity()
remainingCapacity
in interface BlockingQueue
public void clear()
clear
in interface java.util.Collection
clear
in class AbstractQueue
public boolean contains(java.lang.Object o)
contains
in interface java.util.Collection
contains
in class java.util.AbstractCollection
o
- the element
public boolean remove(java.lang.Object o)
remove
in interface java.util.Collection
remove
in class java.util.AbstractCollection
o
- the element to remove
public boolean containsAll(java.util.Collection c)
containsAll
in interface java.util.Collection
containsAll
in class java.util.AbstractCollection
c
- the collection
public boolean removeAll(java.util.Collection c)
removeAll
in interface java.util.Collection
removeAll
in class java.util.AbstractCollection
c
- the collection
public boolean retainAll(java.util.Collection c)
retainAll
in interface java.util.Collection
retainAll
in class java.util.AbstractCollection
c
- the collection
public java.lang.Object peek()
peek
in interface Queue
public java.util.Iterator iterator()
iterator
in interface java.util.Collection
iterator
in class java.util.AbstractCollection
public java.lang.Object[] toArray()
toArray
in interface java.util.Collection
toArray
in class java.util.AbstractCollection
public java.lang.Object[] toArray(java.lang.Object[] a)
toArray
in interface java.util.Collection
toArray
in class java.util.AbstractCollection
a
- the array
public int drainTo(java.util.Collection c)
BlockingQueue
drainTo
in interface BlockingQueue
c
- the collection to transfer elements into
public int drainTo(java.util.Collection c, int maxElements)
BlockingQueue
drainTo
in interface BlockingQueue
c
- the collection to transfer elements intomaxElements
- the maximum number of elements to transfer
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