org.hawkular.metrics.client.common

Class MetricBuffer

java.lang.Object

org.hawkular.metrics.client.common.MetricBuffer

public final class MetricBuffer
extends Object

A FIFO buffer with fixed capacity. When capacity is reached, older elements are discarded. Metric buffers are not thread-safe. Insertion of null elements is silently ignored.

This class is particularly useful when you want to:

• buffer metrics collected before sending to the backend
• retrieve metrics from the buffer in batches for sending
• re-insert batches in the buffer if sending failed (as much as capacity permits)

Author:

Thomas Segismont

Constructor Summary

Constructors

Constructor and Description
MetricBuffer(int capacity) Creates a new buffer with fixed capacity.

Method Summary

Modifier and Type	Method and Description
void	insert(SingleMetric metric) Inserts a new element in this buffer.
void	reInsert(List<SingleMetric> metrics) Re-inserts a batch previously removed with remove(int).
int	remainingCapacity()
List<SingleMetric>	remove(int batchSize) Retrieves and removes the oldest elements in this buffer.
int	size()

Methods inherited from class java.lang.Object

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

Constructor Detail

MetricBuffer

public MetricBuffer(int capacity)

Creates a new buffer with fixed capacity.

Parameters:

capacity - the maximum number of elements in the buffer

Method Detail

size

public int size()

Returns:

the number of elements in this buffer

remainingCapacity

public int remainingCapacity()

Returns:

the number of elements which can be inserted without discarding older elements

insert

public void insert(SingleMetric metric)

Inserts a new element in this buffer. If remainingCapacity() is zero, the oldest element is discarded.

Parameters:

metric - silently ignored if null

remove

public List<SingleMetric> remove(int batchSize)

Retrieves and removes the oldest elements in this buffer.

Parameters:

batchSize - the desired number of elements to return

Returns:

a list of N elements, in insertion order, where N is the minimum of batchSize and buffer size

Throws:

IllegalArgumentException - if batchSize < 0

reInsert

public void reInsert(List<SingleMetric> metrics)

Re-inserts a batch previously removed with remove(int). Elements are re-inserted as much as capacity permits. The elements are expected to be sorted in their order of insertion in the buffer before they were removed.

Example

Consider a buffer with a capacity of 5 elements. The buffer is filled with five elements:

buffer.insert(metric1); ... ; buffer.insert(metric5);

The buffer looks like:

metric5 >> metric4 >> metric3 >> metric2 >> metric1

A batch of two elements is removed:

List batch = buffer.remove(2);

The buffer looks like:

metric5 >> metric4 >> metric3

And the batch list:

metric1 << metric2

Now a new element is inserted:

buffer.insert(metric6);

The buffers looks like:

metric6 >> metric5 >> metric4 >> metric3

But the batch previously removed needs to be re-inserted, because sending failed.

buffer.reInsert(batch);

As there's room for a single element, after re-insertion the buffer will look like:

metric6 >> metric5 >> metric4 >> metric3 >> metric2

Parameters:

metrics - silently ignored if null or empty; null elements in the list are also silently ignored