weblogic.cluster.singleton
Interface LeasingBasis

All Known Subinterfaces:

RemoteLeasingBasis

All Known Implementing Classes:

DatabaseLeasingBasis, RemoteLeasingBasisImpl, ReplicatedLeasingBasis, SimpleLeasingBasis

public interface LeasingBasis

A LeasingBasis provides the underpinnings for implementing the LeaseManager. Different LeasingBasis-es with different characteristics can be plugged in. For example, a LeasingBasis might be implemented against a backing database, against a uniquely-chosen file store, or from first principles using a distributed agreement algorithm.

Method Summary

boolean	acquire(String leaseName, String owner, int leaseTimeout) Attempts to claim immediate ownership of a lease for this server.
String[]	findExpiredLeases(int gracePeriod) Returns a list of the servers that have consistently missed sending heartbeats in a timely manner, and failed to do so for longer than their grace period.
String	findOwner(String leaseName) Returns the identity of the server that currently owns the lease.
String	findPreviousOwner(String leaseName)
void	release(String leaseName, String owner) If the lease is owned by this server, attempts to give up ownership.
int	renewAllLeases(int healthCheckPeriod, String owner) Attempts to send a heartbeat to prove the health of the server.

Method Detail

acquire

boolean acquire(String leaseName,
                String owner,
                int leaseTimeout)
                throws IOException,
                       LeasingException

Attempts to claim immediate ownership of a lease for this server. Returns true if the lease was successfully claimed or if it is already owned by the server. Returns false if the lease is owned by another server. Throws a LeasingException if there were infrastructure problems trying to get ownership. The leaseTimeout specifies how long the lease will last.

Parameters:

leaseName -

owner -

leaseTimeout - in milliseconds

Returns:

true if the lease was aquired

Throws:

IOException

LeasingException

release

void release(String leaseName,
             String owner)
             throws IOException

If the lease is owned by this server, attempts to give up ownership. Otherwise does nothing. Throws a LeasingException if infrastructure problems make it impossible to access the lease.

Parameters:

leaseName -

owner -

Throws:

IOException

findOwner

String findOwner(String leaseName)
                 throws IOException

Returns the identity of the server that currently owns the lease. Returns null if the lease is not owned. The lease is not considered to be owned if it has been claimed by a server that has missed heartbeats. This is a best-effort result in that the answer may change after the value is returned. Throws a LeasingException if infrastructure problems make it impossible to determine who owns the lease.

Parameters:

leaseName -

Returns:

name of the owner

Throws:

IOException

findPreviousOwner

String findPreviousOwner(String leaseName)
                         throws IOException

Throws:

IOException

renewAllLeases

int renewAllLeases(int healthCheckPeriod,
                   String owner)
                   throws IOException,
                          MissedHeartbeatException

Attempts to send a heartbeat to prove the health of the server. Determines whether or not the heartbeat was sent in a timely manner. This determination should ideally be precise. If it is not, then it has to err on the safe side, i.e., it is better to falsely indicate that a Heartbeat was missed than to fail to indicate that a Heartbeat was missed. The heartbeat is sent for the next period even if the last one was missed. This minimizes the chances of damage while the system is signaling for corrective action. This is semantically equivalent to renewing all of the outstanding leases.

Parameters:

healthCheckPeriod - in milliseconds

owner -

Returns:

number of owned leases

Throws:

IOException

MissedHeartbeatException

findExpiredLeases

String[] findExpiredLeases(int gracePeriod)
                           throws IOException

Returns a list of the servers that have consistently missed sending heartbeats in a timely manner, and failed to do so for longer than their grace period. INVARIANT: If a server stops heartbeating PERMANENTLY, then it will EVENTUALLY be returned in this list, although there is no guarantee as to how long that will take.

Parameters:

gracePeriod - in milliseconds

Throws:

IOException