com.espertech.esper.epl.variable

Class VersionedValueList<T>

java.lang.Object

com.espertech.esper.epl.variable.VersionedValueList<T>

public class VersionedValueList<T>
extends Object

A self-cleaning list of versioned-values.

The current and prior version are held for lock-less read access in a transient variable.

The list relies on transient as well as a read-lock to guard against concurrent modification. However a read lock is only taken when a list of old versions must be updated.

When a high watermark is reached, the list on write access removes old versions up to the number of milliseconds compared to current write timestamp.

If an older version is requested then held by the list, the list can either throw an exception or return the current value.

Constructor Summary

Constructors

Constructor and Description
VersionedValueList(String name, int initialVersion, T initialValue, long timestamp, long millisecondLifetimeOldVersions, Lock readLock, int highWatermark, boolean errorWhenNotFound) Ctor.

Method Summary

Modifier and Type	Method and Description
Object	addValue(int version, T value, long timestamp) Add a value and version to the list, returning the prior value of the variable.
protected CurrentValue<T>	getCurrentAndPriorValue() Returns the current and prior version.
String	getName() Returns the name of the value stored.
protected ArrayList<VersionedValue<T>>	getOlderVersions() Returns the list of old versions, for testing purposes.
T	getVersion(int versionAndOlder) Retrieve a value for the given version or older then then given version.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

VersionedValueList

public VersionedValueList(String name,
                          int initialVersion,
                          T initialValue,
                          long timestamp,
                          long millisecondLifetimeOldVersions,
                          Lock readLock,
                          int highWatermark,
                          boolean errorWhenNotFound)

Ctor.

Parameters:

name - variable name

initialVersion - first version number

initialValue - first value

timestamp - timestamp of first version

millisecondLifetimeOldVersions - number of milliseconds after which older versions get expired and removed

readLock - for coordinating update to old versions

highWatermark - when the number of old versions reached high watermark, the list inspects size on every write

errorWhenNotFound - true if an exception should be throw if the requested version cannot be found, or false if the engine should log a warning

Method Detail

getName

public String getName()

Returns the name of the value stored.

Returns:

value name

getVersion

public T getVersion(int versionAndOlder)

Retrieve a value for the given version or older then then given version.

The implementaton only locks the read lock if an older version the the prior version is requested.

Parameters:

versionAndOlder - the version we are looking for

Returns:

value for the version or the next older version, ignoring newer versions

addValue

public Object addValue(int version,
                       T value,
                       long timestamp)

Add a value and version to the list, returning the prior value of the variable.

Parameters:

version - for the value to add

value - to add

timestamp - the time associated with the version

Returns:

prior value

getCurrentAndPriorValue

protected CurrentValue<T> getCurrentAndPriorValue()

Returns the current and prior version.

Returns:

value

getOlderVersions

protected ArrayList<VersionedValue<T>> getOlderVersions()

Returns the list of old versions, for testing purposes.

Returns:

list of versions older then current and prior version

toString

public String toString()

Overrides:

toString in class Object