EDU.oswego.cs.dl.util.concurrent
Class LinkedQueue
- Channel, Puttable, Takable
A linked list based channel implementation.
The algorithm avoids contention between puts
and takes when the queue is not empty.
Normally a put and a take can proceed simultaneously.
(Although it does not allow multiple concurrent puts or takes.)
This class tends to perform more efficently than
other Channel implementations in producer/consumer
applications.
[
Introduction to this package. ]
protected Object | extract() - Main mechanics for take/poll *
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protected void | insert(Object x) - Main mechanics for put/offer *
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boolean | isEmpty()
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boolean | offer(Object x, long msecs) - Place item in channel only if it can be accepted within
msecs milliseconds.
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Object | peek() - Return, but do not remove object at head of Channel,
or null if it is empty.
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Object | poll(long msecs) - Return and remove an item from channel only if one is available within
msecs milliseconds.
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void | put(Object x) - Place item in the channel, possibly waiting indefinitely until
it can be accepted.
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Object | take() - Return and remove an item from channel,
possibly waiting indefinitely until
such an item exists.
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head_
protected LinkedNode head_
Dummy header node of list. The first actual node, if it exists, is always
at head_.next. After each take, the old first node becomes the head.
last_
protected LinkedNode last_
The last node of list. Put() appends to list, so modifies last_
putLock_
protected final Object putLock_
Helper monitor for managing access to last node.
waitingForTake_
protected int waitingForTake_
The number of threads waiting for a take.
Notifications are provided in put only if greater than zero.
The bookkeeping is worth it here since in reasonably balanced
usages, the notifications will hardly ever be necessary, so
the call overhead to notify can be eliminated.
LinkedQueue
public LinkedQueue()
extract
protected Object extract()
Main mechanics for take/poll *
insert
protected void insert(Object x)
Main mechanics for put/offer *
isEmpty
public boolean isEmpty()
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.
- offer in interface Channel
- offer in interface Puttable
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.
- true if accepted, else false
peek
public Object peek()
Return, but do not remove object at head of Channel,
or null if it is empty.
- peek in interface Channel
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.
- poll in interface Channel
- poll in interface Takable
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.
- 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.
- put in interface Channel
- put in interface Puttable
take
public Object take()
throws InterruptedException
Return and remove an item from channel,
possibly waiting indefinitely until
such an item exists.
- take in interface Channel
- take in interface Takable
- some item from the channel. Different implementations
may guarantee various properties (such as FIFO) about that item