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org.dbunit.util.concurrent
Class BoundedLinkedQueue  

java.lang.Object
  org.dbunit.util.concurrent.BoundedLinkedQueue

All Implemented Interfaces:

BoundedChannel, Channel, Puttable, Takable

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public class BoundedLinkedQueue

extends java.lang.Object

implements BoundedChannel

A bounded variant of LinkedQueue class. This class may be preferable to BoundedBuffer because it allows a bit more concurency among puts and takes, because it does not pre-allocate fixed storage for elements, and allows capacity to be dynamically reset. On the other hand, since it allocates a node object on each put, it can be slow on systems with slow allocation and GC. Also, it may be preferable to LinkedQueue when you need to limit the capacity to prevent resource exhaustion. This protection normally does not hurt much performance-wise: When the queue is not empty or full, most puts and takes are still usually able to execute concurrently.

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Field Summary
protected  int	capacity_           Number of elements allowed
protected  LinkedNode	head_           Dummy header node of list.
protected  LinkedNode	last_           The last node of list.
protected  java.lang.Object	putGuard_           Helper monitor.
protected  int	putSidePutPermits_           One side of a split permit count.
protected  java.lang.Object	takeGuard_           Helper monitor.
protected  int	takeSidePutPermits_           Number of takes since last reconcile

 

Constructor Summary

BoundedLinkedQueue()           Create a queue with the current default capacity

BoundedLinkedQueue(int capacity)           Create a queue with the given capacity

 

Method Summary
protected  void	allowTake()           Notify a waiting take if needed
int	capacity()           Return the current capacity of this queue
protected  java.lang.Object	extract()           Main mechanics for take/poll
protected  void	insert(java.lang.Object x)           Create and insert a node.
boolean	isEmpty()
boolean	offer(java.lang.Object x, long msecs)           Place item in channel only if it can be accepted within msecs milliseconds.
java.lang.Object	peek()           Return, but do not remove object at head of Channel, or null if it is empty.
java.lang.Object	poll(long msecs)           Return and remove an item from channel only if one is available within msecs milliseconds.
void	put(java.lang.Object x)           Place item in the channel, possibly waiting indefinitely until it can be accepted.
protected  int	reconcilePutPermits()           Move put permits from take side to put side; return the number of put side permits that are available.
void	setCapacity(int newCapacity)           Reset the capacity of this queue.
int	size()           Return the number of elements in the queue.
java.lang.Object	take()           Return and remove an item from channel, possibly waiting indefinitely until such an item exists.

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Field Detail

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.

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last_

protected LinkedNode last_

The last node of list. Put() appends to list, so modifies last_

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putGuard_

protected final java.lang.Object putGuard_

Helper monitor. Ensures that only one put at a time executes.

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takeGuard_

protected final java.lang.Object takeGuard_

Helper monitor. Protects and provides wait queue for takes

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capacity_

protected int capacity_

Number of elements allowed

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putSidePutPermits_

protected int putSidePutPermits_

One side of a split permit count. The counts represent permits to do a put. (The queue is full when zero). Invariant: putSidePutPermits_ + takeSidePutPermits_ = capacity_ - length. (The length is never separately recorded, so this cannot be checked explicitly.) To minimize contention between puts and takes, the put side uses up all of its permits before transfering them from the take side. The take side just increments the count upon each take. Thus, most puts and take can run independently of each other unless the queue is empty or full. Initial value is queue capacity.

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takeSidePutPermits_

protected int takeSidePutPermits_

Number of takes since last reconcile

Constructor Detail

BoundedLinkedQueue

public BoundedLinkedQueue(int capacity)

Create a queue with the given capacity

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BoundedLinkedQueue

public BoundedLinkedQueue()

Create a queue with the current default capacity

Method Detail

reconcilePutPermits

protected final int reconcilePutPermits()

Move put permits from take side to put side; return the number of put side permits that are available. Call only under synch on puGuard_ AND this.

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capacity

public int capacity()

Return the current capacity of this queue

Specified by:

capacity in interface BoundedChannel

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size

public int size()

Return the number of elements in the queue. This is only a snapshot value, that may be in the midst of changing. The returned value will be unreliable in the presence of active puts and takes, and should only be used as a heuristic estimate, for example for resource monitoring purposes.

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setCapacity

public void setCapacity(int newCapacity)

Reset the capacity of this queue. If the new capacity is less than the old capacity, existing elements are NOT removed, but incoming puts will not proceed until the number of elements is less than the new capacity.

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extract

protected java.lang.Object extract()

Main mechanics for take/poll

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peek

public java.lang.Object peek()

Description copied from interface: Channel

Return, but do not remove object at head of Channel, or null if it is empty.

Specified by:

peek in interface Channel

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take

public java.lang.Object take()
                      throws java.lang.InterruptedException

Description copied from interface: Channel

Return and remove an item from channel, possibly waiting indefinitely until such an item exists.

Specified by:

take in interface Channel

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poll

public java.lang.Object poll(long msecs)
                      throws java.lang.InterruptedException

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 interface Channel

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allowTake

protected final void allowTake()

Notify a waiting take if needed

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insert

protected void insert(java.lang.Object x)

Create and insert a node. Call only under synch on putGuard_

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put

public void put(java.lang.Object x)
         throws java.lang.InterruptedException

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 interface Channel

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offer

public boolean offer(java.lang.Object x,
                     long msecs)
              throws java.lang.InterruptedException

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 interface Channel

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isEmpty

public boolean isEmpty()

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