com.microsoft.azure.eventprocessorhost.Lease Maven / Gradle / Ivy
/*
* Copyright (c) Microsoft. All rights reserved.
* Licensed under the MIT license. See LICENSE file in the project root for full license information.
*/
package com.microsoft.azure.eventprocessorhost;
/**
* Lease class is public so that advanced users can implement an ILeaseManager.
* Unless you are implementing ILeaseManager you should not have to deal with objects
* of this class or derived classes directly.
*
* When implementing an ILeaseManager it may be necessary to derive from this class to
* carry around more information and override isExpired. The data fields have been left
* private instead of protected because they have a full set of getters and setters
* (except partitionId, which is immutable) which provide equivalent access. When
* implementing AzureBlobLease, for example, there was no need for more access than
* the getters and setters provide.
*
* Note that a Lease object just carries information about a partition lease. The functionality
* to acquire/renew/release a lease is all on the ILeaseManager.
*/
public class Lease
{
private final String partitionId;
private long epoch;
private String owner;
private String token;
/**
* Create a Lease for the given partition.
*
* @param partitionId
*/
public Lease(String partitionId)
{
this.partitionId = partitionId;
this.epoch = 0;
this.owner = "";
this.token = "";
}
/**
* Create a Lease by duplicating the given Lease.
*
* @param source
*/
public Lease(Lease source)
{
this.partitionId = source.partitionId;
this.epoch = source.epoch;
this.owner = source.owner;
this.token = source.token;
}
/**
* Epoch is a concept used by Event Hub receivers. Basically, if a receiver is created on a partition
* with a higher epoch than the existing receiver, the previous receiver is forcibly disconnected.
* Attempting to create a receiver with a lower epoch that the existing receiver will fail. The Lease
* carries the epoch around so that when a host steals a lease, it can create a receiver with a higher epoch.
*
* @return
*/
public long getEpoch()
{
return this.epoch;
}
/**
* Set the epoch value.
*
* @param epoch
*/
public void setEpoch(long epoch)
{
this.epoch = epoch;
}
/**
* The most common operation on the epoch value is incrementing it after stealing a lease. This
* convenience function replaces the get-increment-set that would otherwise be required.
*
* @return The new value of the epoch.
*/
public long incrementEpoch()
{
this.epoch++;
return this.epoch;
}
/**
* The owner of a lease is the name of the EventProcessorHost which currently holds the lease.
*
* @return
*/
public String getOwner()
{
return this.owner;
}
/**
* Set the owner string. Used when a host steals a lease.
*
* @param owner
*/
public void setOwner(String owner)
{
this.owner = owner;
}
/**
* Returns the id of the partition that this Lease is for. Immutable so there is no corresponding setter.
*
* @return
*/
public String getPartitionId()
{
return this.partitionId;
}
/**
* The Lease carries an arbitrary string called the "token". AzureStorageCheckpointLeaseManager uses this to
* store the blob lease ID used by the Azure Storage API. Other implementations of ILeaseManager may use it
* for anything.
*
* @return
*/
public String getToken()
{
return this.token;
}
/**
* Set the token value.
*
* @param token
*/
public void setToken(String token)
{
this.token = token;
}
/**
* If an implementation of ILeaseManager supports the concept of lease expiration, then a class derived from Lease
* may override this function to inspect the lease and return whether it has expired.
*
* @return true if the lease is expired, false if it is still valid
* @throws Exception An override which does significant work may need to throw exceptions.
*/
public boolean isExpired() throws Exception
{
// this function is meaningless in the base class
return false;
}
String getStateDebug()
{
return "N/A";
}
}