org.rrd4j.core
Class RrdDbPool

java.lang.Object
  org.rrd4j.core.RrdDbPool

public abstract class RrdDbPool
extends Object

This class should be used to synchronize access to RRD files in a multithreaded environment. This class should be also used to prevent opening of too many RRD files at the same time (thus avoiding operating system limits).

The abstract wrapper for different implementations of the pools.

Field Summary

static int

INITIAL_CAPACITY Initial capacity of the pool i.e. maximum number of simultaneously open RRD files.

Constructor Summary

RrdDbPool()

Method Summary

abstract int	getCapacity() Returns the maximum number of simultaneously open RRD files.
static RrdDbPool	getInstance() Creates a single instance of the class on the first call, or returns already existing one.
abstract int	getOpenCount(RrdDb rrdDb) Returns the number of usage for a RRD.
abstract int	getOpenCount(String path) Returns the number of usage for a RRD.
abstract int	getOpenFileCount() Returns the number of open RRD files.
abstract String[]	getOpenFiles() Returns an array of open file names.
abstract void	release(RrdDb rrdDb) Releases RrdDb reference previously obtained from the pool.
abstract RrdDb	requestRrdDb(RrdDef rrdDef) Requests a RrdDb reference for the given RRD file definition object.
abstract RrdDb	requestRrdDb(String path) Requests a RrdDb reference for the given RRD file path.
abstract RrdDb	requestRrdDb(String path, String sourcePath) Requests a RrdDb reference for the given path.
abstract void	setCapacity(int capacity) Sets the maximum number of simultaneously open RRD files.

Methods inherited from class java.lang.Object

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

Field Detail

INITIAL_CAPACITY

public static final int INITIAL_CAPACITY

Initial capacity of the pool i.e. maximum number of simultaneously open RRD files. The pool will never open too many RRD files at the same time.

See Also:

Constant Field Values

Constructor Detail

RrdDbPool

public RrdDbPool()

Method Detail

getInstance

public static RrdDbPool getInstance()

Creates a single instance of the class on the first call, or returns already existing one. Uses Initialization On Demand Holder idiom.

Returns:

Single instance of this class

Throws:

RuntimeException - Thrown if the default RRD backend is not derived from the RrdFileBackendFactory

requestRrdDb

public abstract RrdDb requestRrdDb(String path)
                            throws IOException

Requests a RrdDb reference for the given RRD file path.

• If the file is already open, previously returned RrdDb reference will be returned. Its usage count will be incremented by one.
• If the file is not already open and the number of already open RRD files is less than INITIAL_CAPACITY, the file will be open and a new RrdDb reference will be returned. If the file is not already open and the number of already open RRD files is equal to INITIAL_CAPACITY, the method blocks until some RRD file is closed.

Parameters:

path - Path to existing RRD file

Returns:

reference for the give RRD file

Throws:

IOException - Thrown in case of I/O error

requestRrdDb

public abstract RrdDb requestRrdDb(RrdDef rrdDef)
                            throws IOException

Requests a RrdDb reference for the given RRD file definition object.

• If the file with the path specified in the RrdDef object is already open, the method blocks until the file is closed.
• If the file is not already open and the number of already open RRD files is less than INITIAL_CAPACITY, a new RRD file will be created and a its RrdDb reference will be returned. If the file is not already open and the number of already open RRD files is equal to INITIAL_CAPACITY, the method blocks until some RRD file is closed.

Parameters:

rrdDef - Definition of the RRD file to be created

Returns:

Reference to the newly created RRD file

Throws:

IOException - Thrown in case of I/O error

requestRrdDb

public abstract RrdDb requestRrdDb(String path,
                                   String sourcePath)
                            throws IOException

Requests a RrdDb reference for the given path. The file will be created from external data (from XML dump, RRD file or RRDTool's binary RRD file).

• If the file with the path specified is already open, the method blocks until the file is closed.
• If the file is not already open and the number of already open RRD files is less than INITIAL_CAPACITY, a new RRD file will be created and a its RrdDb reference will be returned. If the file is not already open and the number of already open RRD files is equal to INITIAL_CAPACITY, the method blocks until some RRD file is closed.

Parameters:

path - Path to RRD file which should be created

sourcePath - Path to external data which is to be converted to Rrd4j's native RRD file format

Returns:

Reference to the newly created RRD file

Throws:

IOException - Thrown in case of I/O error

release

public abstract void release(RrdDb rrdDb)
                      throws IOException

Releases RrdDb reference previously obtained from the pool. When a reference is released, its usage count is decremented by one. If usage count drops to zero, the underlying RRD file will be closed.

Parameters:

rrdDb - RrdDb reference to be returned to the pool

Throws:

IOException - Thrown in case of I/O error

getCapacity

public abstract int getCapacity()

Returns the maximum number of simultaneously open RRD files.

Returns:

maximum number of simultaneously open RRD files

setCapacity

public abstract void setCapacity(int capacity)

Sets the maximum number of simultaneously open RRD files.

Parameters:

capacity - Maximum number of simultaneously open RRD files.

getOpenFiles

public abstract String[] getOpenFiles()

Returns an array of open file names.

Returns:

Array with canonical paths to open RRD files held in the pool.

getOpenFileCount

public abstract int getOpenFileCount()

Returns the number of open RRD files.

Returns:

Number of currently open RRD files held in the pool.

getOpenCount

public abstract int getOpenCount(RrdDb rrdDb)
                          throws IOException

Returns the number of usage for a RRD.

Parameters:

rrdDb - RrdDb reference for which informations is needed.

Returns:

the number of request for this rrd

Throws:

IOException

getOpenCount

public abstract int getOpenCount(String path)
                          throws IOException

Returns the number of usage for a RRD.

Parameters:

path - RRD file for which informations is needed.

Returns:

the number of request for this file

Throws:

IOException