ch.rgw.io
Class LockFile

java.lang.Object
  ch.rgw.io.LockFile

public class LockFile
extends java.lang.Object

A class that creates and detects lockfile to provide cooperative detection od running instances of an applicatiion (or for other purposes)

Author:

gerry

Constructor Summary

LockFile(java.io.File dir, java.lang.String basename, int maxNum, int timeoutSeconds)
Create an instance of a LockFile class.

Method Summary

boolean	existsLock() Check if at least one lockfile with the given pattern exists
int	lock() create a lockfile with the parameters as given to the constructor.
boolean	updateLock(int n) Refresh the lock i.e. extend its validity time by the original timeout once again.

Methods inherited from class java.lang.Object

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

Constructor Detail

LockFile

public LockFile(java.io.File dir,
                java.lang.String basename,
                int maxNum,
                int timeoutSeconds)

Create an instance of a LockFile class. This will not yet create an actual file. A call to LockFile#lock() will create a file in the given dir and with the given name and a suffix ranging from 1 to maxNum.

Parameters:

dir - the dir where the lockfile(s) should be created

basename - the basename for the files

maxNum - maximum number of instances of this lock that may be aquired simultaneously

timeoutSeconds - after what time will a lock treaded as invalid

Method Detail

lock

public int lock()
         throws java.io.IOException

create a lockfile with the parameters as given to the constructor. There will be created at most maxNUm lockfiles. Each of them will expire after timeoutSeconds, or after the application exits. If the application does not exist normally, the lockfile might not be deleted. It will the be considered valid until the expire time is reached.

Returns:

lock number on success, 0 if there are already maxNum lockfiles and the lock could not be aquired

Throws:

java.io.IOException - id something went wrong

updateLock

public boolean updateLock(int n)

Refresh the lock i.e. extend its validity time by the original timeout once again. An application should prefer this update mechanism over a too long timeout, because in case of abnormal termination, the lock does not stay too long active.

Parameters:

n - number of the lockfile (as received by the lock() call)

Returns:

true on success

existsLock

public boolean existsLock()
                   throws java.io.IOException

Check if at least one lockfile with the given pattern exists

Returns:

true if one ore more lockfiles exist

Throws:

java.io.IOException