Package me.ahoo.cosid.machine.lease

Class MachineLeaseManager

java.lang.Object

me.ahoo.cosid.machine.lease.MachineLeaseManager

public class MachineLeaseManager
extends Object

The single machine id allocation algorithm, on top of any MachineLeaseStore.

Order: take back this instance's own lease, then a released machine id, then a never-used one, and only then an expired one. A stable instance never takes over another instance's expired lease, and with MachineIdDistributor.FOREVER_SAFE_GUARD_DURATION no lease ever expires.

Every time comes from MachineLeaseStore.serverTime(), except the watermark written on release, which is the generator's last timestamp from this host's clock. Hosts' clocks must therefore be kept in sync: a host running ahead only delays the next owner of a released machine id (it waits until its clock passes the watermark), which is safe but slow.

Since:

3.4.0

Constructor Summary

Constructors

Constructor	Description
MachineLeaseManager(MachineLeaseStore store)

Method Summary

Modifier and Type	Method	Description
Lease	acquire(String namespace, InstanceId instanceId, int machineBit, Duration safeGuardDuration)	Take a machine id for the instance.
MachineLeaseStore	getStore()
Optional<Lease>	reclaim(String namespace, InstanceId instanceId)	Take back the lease this instance holds, for instance after a restart without a lease in memory.
boolean	release(Lease lease, long watermark)	Release a lease on shutdown.
Optional<Lease>	renew(Lease lease)	Renew a lease.

Methods inherited from class java.lang.Object

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

Constructor Details

MachineLeaseManager

public MachineLeaseManager(MachineLeaseStore store)

Method Details

getStore

public MachineLeaseStore getStore()

acquire

public Lease acquire(String namespace,
 InstanceId instanceId,
 int machineBit,
 Duration safeGuardDuration)
              throws MachineIdOverflowException

Take a machine id for the instance.

Throws:

MachineIdOverflowException - if every machine id is held by a live (or stable) owner

reclaim

public Optional<Lease> reclaim(String namespace,
 InstanceId instanceId)

Take back the lease this instance holds, for instance after a restart without a lease in memory.

Returns:

empty if the instance holds none: it was released or taken over

renew

public Optional<Lease> renew(Lease lease)

Renew a lease.

Returns:

the renewed lease, or empty if it was taken over in the meantime

release

public boolean release(Lease lease,
 long watermark)

Release a lease on shutdown.

Parameters:

watermark - the generator's last timestamp (host clock), the next owner's clock-backwards watermark

Returns:

false if the lease was taken over in the meantime