Package EDU.oswego.cs.dl.util.concurrent
Class LinkedQueue
java.lang.Object
EDU.oswego.cs.dl.util.concurrent.LinkedQueue
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.
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected LinkedNode
Dummy header node of list.protected LinkedNode
The last node of list.protected final Object
Helper monitor for managing access to last node.protected int
The number of threads waiting for a take. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprotected Object
extract()
Main mechanics for take/pollprotected void
Main mechanics for put/offerboolean
isEmpty()
boolean
Place item in channel only if it can be accepted within msecs milliseconds.peek()
Return, but do not remove object at head of Channel, or null if it is empty.poll
(long msecs) Return and remove an item from channel only if one is available within msecs milliseconds.void
Place item in the channel, possibly waiting indefinitely until it can be accepted.take()
Return and remove an item from channel, possibly waiting indefinitely until such an item exists.
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Field Details
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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. -
putLock_
Helper monitor for managing access to last node. -
last_
The last node of list. Put() appends to list, so modifies last_ -
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.
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Constructor Details
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LinkedQueue
public LinkedQueue()
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Method Details
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insert
Main mechanics for put/offer -
extract
Main mechanics for take/poll -
put
Description copied from interface:Channel
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 interfaceChannel
- Specified by:
put
in interfacePuttable
- Parameters:
x
- the element to be inserted. Should be non-null.- Throws:
InterruptedException
- if the current thread has been interrupted at a point at which interruption is detected, in which case the element is guaranteed not to be inserted. Otherwise, on normal return, the element is guaranteed to have been inserted.
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offer
Description copied from interface:Channel
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 interfaceChannel
- Specified by:
offer
in interfacePuttable
- Parameters:
x
- the element to be inserted. Should be non-null.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
- Throws:
InterruptedException
- if the current thread has been interrupted at a point at which interruption is detected, in which case the element is guaranteed not to be inserted (i.e., is equivalent to a false return).
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take
Description copied from interface:Channel
Return and remove an item from channel, possibly waiting indefinitely until such an item exists.- Specified by:
take
in interfaceChannel
- Specified by:
take
in interfaceTakable
- Returns:
- some item from the channel. Different implementations may guarantee various properties (such as FIFO) about that item
- Throws:
InterruptedException
- if the current thread has been interrupted at a point at which interruption is detected, in which case state of the channel is unchanged.
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peek
Description copied from interface:Channel
Return, but do not remove object at head of Channel, or null if it is empty. -
isEmpty
public boolean isEmpty() -
poll
Description copied from interface:Channel
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 interfaceChannel
- Specified by:
poll
in interfaceTakable
- 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.
- Throws:
InterruptedException
- if the current thread has been interrupted at a point at which interruption is detected, in which case state of the channel is unchanged (i.e., equivalent to a null return).
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