MessageQueue (Log-Writers and Shared Components 3.1.2 API)

java.lang.Object
- com.kdgregory.logging.common.util.MessageQueue

```
public class MessageQueue
extends Object
```
A thread-safe message queue that keeps track of the current number of entries and optionally discards messages after its size reaches a given threshold.
Implementation note: all operations are coded as update queue followed by update count. This means that it is possible that size() may not reflect the actual size of the queue at any given point in time (but usually will).

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class MessageQueue.DiscardAction
Controls how messages are discarded once the threshold is reached.

Nested Classes
Modifier and Type	Class and Description
`static class`	`MessageQueue.DiscardAction` Controls how messages are discarded once the threshold is reached.

Constructor Summary

Constructors
Constructor and Description

MessageQueue(int discardThreshold, MessageQueue.DiscardAction discardAction)

Constructors
Constructor and Description
`MessageQueue(int discardThreshold, MessageQueue.DiscardAction discardAction)`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`LogMessage`	`dequeue()` Removes a message from the front of the queue.
`LogMessage`	`dequeue(long waitTime)` Removes a message from the front of the queue, waiting for a specified number of milliseconds if the queue is empty.
`void`	`enqueue(LogMessage message)` Adds a message to the end of the queue.
`MessageQueue.DiscardAction`	`getDiscardAction()` Returns the current discard action; this is intended for testing.
`int`	`getDiscardThreshold()` Returns the current discard threshold; this is intended for testing.
`int`	`getDroppedMessageCount()` Returns the number of messages that have been dropped.
`boolean`	`isEmpty()` Determines whether the queue is empty.
`int`	`queueSize()` Returns the current number of elements in the queue, as recorded by the queue itself.
`void`	`requeue(LogMessage message)` Adds a message to the start of the queue.
`void`	`setDiscardAction(MessageQueue.DiscardAction value)` Changes the discard action
`void`	`setDiscardThreshold(int value)` Changes the discard threshold.
`int`	`size()` Returns the current number of elements in the queue, as recorded by the atomic counter.
`List<LogMessage>`	`toList()` Copies the current queue contents into a List.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - MessageQueue
```
public MessageQueue(int discardThreshold,
                    MessageQueue.DiscardAction discardAction)
```
- Method Detail
  - setDiscardThreshold
```
public void setDiscardThreshold(int value)
```
    Changes the discard threshold.
  - getDiscardThreshold
```
public int getDiscardThreshold()
```
    Returns the current discard threshold; this is intended for testing.
  - setDiscardAction
```
public void setDiscardAction(MessageQueue.DiscardAction value)
```
    Changes the discard action
  - getDiscardAction
```
public MessageQueue.DiscardAction getDiscardAction()
```
    Returns the current discard action; this is intended for testing.
  - getDroppedMessageCount
```
public int getDroppedMessageCount()
```
    Returns the number of messages that have been dropped.
  - isEmpty
```
public boolean isEmpty()
```
    Determines whether the queue is empty. Beware that the queue could be empty when checked, but another thread could concurrently add a message.
  - enqueue
```
public void enqueue(LogMessage message)
```
    Adds a message to the end of the queue.
    Note: discard policy is checked after adding the message. If the policy is "newest", then this message will be removed.
  - requeue
```
public void requeue(LogMessage message)
```
    Adds a message to the start of the queue.
    Note: discard policy is checked after adding the message. If the policy is "oldest", then this message will be removed (assuming that someone else has not dequeued it).
  - dequeue
```
public LogMessage dequeue()
```
    Removes a message from the front of the queue. Returns null if there are no messages.
  - dequeue
```
public LogMessage dequeue(long waitTime)
```
    Removes a message from the front of the queue, waiting for a specified number of milliseconds if the queue is empty. Returns null if there are no messages in the desired time, or if the thread is interrupted.
  - size
```
public int size()
```
    Returns the current number of elements in the queue, as recorded by the atomic counter. This is an O(1) operation, but might not be exact.
  - queueSize
```
public int queueSize()
```
    Returns the current number of elements in the queue, as recorded by the queue itself. This is an O(N) operation. This is intended for testing.
  - toList
```
public List<LogMessage> toList()
```
    Copies the current queue contents into a List. This is intended for testing.

Class MessageQueue

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

MessageQueue

Method Detail

setDiscardThreshold

getDiscardThreshold

setDiscardAction

getDiscardAction

getDroppedMessageCount

isEmpty

enqueue

requeue

dequeue

dequeue

size

queueSize

toList