EDU.oswego.cs.dl.util.concurrent

Class SynchronousChannel

Implemented Interfaces:
BoundedChannel, Channel, Puttable, Takable

public class SynchronousChannel
extends Object
implements BoundedChannel

A rendezvous channel, similar to those used in CSP and Ada. Each put must wait for a take, and vice versa. Synchronous channels are well suited for handoff designs, in which an object running in one thread must synch up with an object running in another thread in order to hand it some information, event, or task.

If you only need threads to synch up without exchanging information, consider using a Barrier. If you need bidirectional exchanges, consider using a Rendezvous.

[ Introduction to this package. ]

See Also:
CyclicBarrier, Rendezvous

Nested Class Summary

protected static class
SynchronousChannel.Queue
Simple FIFO queue class to hold waiting puts/takes.

Field Summary

protected static Object
CANCELLED
Special marker used in queue nodes to indicate that the thread waiting for a change in the node has timed out or been interrupted.
protected SynchronousChannel.Queue
waitingPuts
protected SynchronousChannel.Queue
waitingTakes

Method Summary

int
capacity()
boolean
offer(Object x, long msecs)
Place item in channel only if it can be accepted within msecs milliseconds.
Object
peek()
Object
poll(long msecs)
Return and remove an item from channel only if one is available within msecs milliseconds.
void
put(Object x)
Place item in the channel, possibly waiting indefinitely until it can be accepted.
Object
take()
Return and remove an item from channel, possibly waiting indefinitely until such an item exists.

Field Details

CANCELLED

protected static final Object CANCELLED
Special marker used in queue nodes to indicate that the thread waiting for a change in the node has timed out or been interrupted.

waitingPuts

protected final SynchronousChannel.Queue waitingPuts

waitingTakes

protected final SynchronousChannel.Queue waitingTakes

Method Details

capacity

public int capacity()
Specified by:
capacity in interface BoundedChannel
Returns:
zero -- Synchronous channels have no internal capacity.

offer

public boolean offer(Object x,
                     long msecs)
            throws InterruptedException
Place item in channel only if it can be accepted within msecs milliseconds. The time bound is interpreted in a coarse-grained, best-effort fashion.
Specified by:
offer in interface Channel
offer in interface Puttable
Parameters:
msecs - the number of milliseconds to wait. If less than or equal to zero, the method does not perform any timed waits, but might still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention for the channel.
Returns:
true if accepted, else false

peek

public Object peek()
Specified by:
peek in interface Channel
Returns:
null -- Synchronous channels do not hold contents unless actively taken

poll

public Object poll(long msecs)
            throws InterruptedException
Return and remove an item from channel only if one is available within msecs milliseconds. The time bound is interpreted in a coarse grained, best-effort fashion.
Specified by:
poll in interface Channel
poll in interface Takable
Parameters:
msecs - the number of milliseconds to wait. If less than or equal to zero, the operation does not perform any timed waits, but might still require access to a synchronization lock, which can impose unbounded delay if there is a lot of contention for the channel.
Returns:
some item, or null if the channel is empty.

put

public void put(Object x)
            throws InterruptedException
Place item in the channel, possibly waiting indefinitely until it can be accepted. Channels implementing the BoundedChannel subinterface are generally guaranteed to block on puts upon reaching capacity, but other implementations may or may not block.
Specified by:
put in interface Channel
put in interface Puttable
Parameters:

take

public Object take()
            throws InterruptedException
Return and remove an item from channel, possibly waiting indefinitely until such an item exists.
Specified by:
take in interface Channel
take in interface Takable
Returns:
some item from the channel. Different implementations may guarantee various properties (such as FIFO) about that item