org.mbari.siam.distributed.leasing
Class LeaseManager

java.lang.Object
  org.mbari.siam.distributed.leasing.LeaseManager

public class LeaseManager
extends java.lang.Object

LeaseManager was written to manage an intermittent communication link, though it could be used to manage other resources that fit the paradigm. The paradigm consists of two types of "clients". Lessees are clients who want to keep the resource (link) open, and do so by calling establish(), renew() and terminate(). LeaseManager can manage multiple such clients simultaneously, and keeps them in a vector. LeaseListeners are clients who actually perform the resource management based on whether there are any outstanding lessees. In the current implementation, there is just one LeaseListener, who simply turns on/off the RF power to the link. But in principle there can also be multiple listeners, who presumably perform different functions based on the lease state. NOTE: It is important that the callbacks implemented by LeaseListeners execute in a timely manner, so that the remote client is not blocked for an excessive amount of time.

Author:

Tom O'Reilly Modified by Bob Herlien

Nested Class Summary

class

LeaseManager.Lessee A Lessee is constructed and put on the _lessees list for every LeaseManager.establish().

Field Summary

static long

UNKNOWN_TIME Constant which indicates an indeterminate time.

Constructor Summary

LeaseManager()
Constructor.

Method Summary

void	addListener(LeaseListener listener) Add a lease listener.
protected void	debugPrint(java.lang.String message) Print debug message.
int	establish(long leaseMillisec, long nextEstablishTime, java.lang.String clientNote) Called to establish the communications link.
int	establish(long leaseMillisec, java.lang.String clientNote) Called to establish the communications link.
LeaseManager.Lessee	getLessee(int leaseID) Get the Lessee that has a given LeaseID
java.util.Vector	getLessees() Return vector of lessess.
int	nLessees() Return number of lessees
void	renew(int leaseID, long leaseDurationMsec) Called when lease is being renewed.
void	terminate(int leaseID, long nextConnectTime) Called when communications link is being disconnected.

Methods inherited from class java.lang.Object

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

Field Detail

UNKNOWN_TIME

public static final long UNKNOWN_TIME

Constant which indicates an indeterminate time.

See Also:

Constant Field Values

Constructor Detail

LeaseManager

public LeaseManager()

Constructor. connect/disconnect occurs.

Method Detail

addListener

public void addListener(LeaseListener listener)

Add a lease listener.

establish

public int establish(long leaseMillisec,
                     long nextEstablishTime,
                     java.lang.String clientNote)
              throws LeaseRefused

Called to establish the communications link.

Parameters:

leaseMillisec - lease period in milliseconds

nextEstablishTime - Estimated time that this task expects to call establish() again.

clientNote - note about connection

Returns:

leaseID to use with renew(), terminate(). Will be >= 1.

Throws:

LeaseRefused

establish

public int establish(long leaseMillisec,
                     java.lang.String clientNote)
              throws LeaseRefused

Called to establish the communications link.

Parameters:

leaseMillisec - lease period in milliseconds

Returns:

leaseID to use with renew(), terminate(). Will be >= 1.

Throws:

LeaseRefused

getLessee

public LeaseManager.Lessee getLessee(int leaseID)

Get the Lessee that has a given LeaseID

nLessees

public int nLessees()

Return number of lessees

getLessees

public java.util.Vector getLessees()

Return vector of lessess.

renew

public void renew(int leaseID,
                  long leaseDurationMsec)
           throws LeaseRefused

Called when lease is being renewed.

Parameters:

leaseID - lease identifier

leaseDurationMsec - lease period in milliseconds

Throws:

LeaseRefused

terminate

public void terminate(int leaseID,
                      long nextConnectTime)
               throws LeaseRefused

Called when communications link is being disconnected.

Parameters:

nextConnectTime - next scheduled connection time (millisec from epoch)

Throws:

LeaseRefused

debugPrint

protected void debugPrint(java.lang.String message)

Print debug message.