org.apache.hadoop.hbase.client.locking

Class EntityLock

java.lang.Object

org.apache.hadoop.hbase.client.locking.EntityLock

@InterfaceAudience.Public
public class EntityLock
extends Object

Lock for HBase Entity either a Table, a Namespace, or Regions. These are remote locks which live on master, and need periodic heartbeats to keep them alive. (Once we request the lock, internally an heartbeat thread will be started on the client). If master does not receive the heartbeat in time, it'll release the lock and make it available to other users.

Use LockServiceClient to build instances. Then call requestLock(). requestLock() will contact master to queue the lock and start the heartbeat thread which will check lock's status periodically and once the lock is acquired, it will send the heartbeats to the master.

Use await(long, java.util.concurrent.TimeUnit) or await(long, TimeUnit) to wait for the lock to be acquired. Always call unlock() irrespective of whether lock was acquired or not. If the lock was acquired, it'll be released. If it was not acquired, it is possible that master grants the lock in future and the heartbeat thread keeps it alive forever by sending heartbeats. Calling unlock() will stop the heartbeat thread and cancel the lock queued on master.

There are 4 ways in which these remote locks may be released/can be lost:

• Call unlock().
• Lock times out on master: Can happen because of network issues, GC pauses, etc. Worker thread will call the given abortable as soon as it detects such a situation.
• Fail to contact master: If worker thread can not contact mater and thus fails to send heartbeat before the timeout expires, it assumes that lock is lost and calls the abortable.
• Worker thread is interrupted.

Use example: EntityLock lock = lockServiceClient.*Lock(...., "exampled lock", abortable); lock.requestLock(); .... ....can do other initializations here since lock is 'asynchronous'... .... if (lock.await(timeout)) { ....logic requiring mutual exclusion } lock.unlock();

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	EntityLock.LockHeartbeatWorker

Field Summary

Fields

Modifier and Type	Field and Description
static String	HEARTBEAT_TIME_BUFFER

Method Summary

Modifier and Type	Method and Description
void	await()
boolean	await(long timeout, TimeUnit timeUnit)
boolean	isLocked()
void	requestLock() Sends rpc to the master to request lock.
String	toString()
void	unlock()

Methods inherited from class java.lang.Object

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

Field Detail

HEARTBEAT_TIME_BUFFER

public static final String HEARTBEAT_TIME_BUFFER

See Also:

Constant Field Values

Method Detail

toString

public String toString()

Overrides:

toString in class Object

isLocked

public boolean isLocked()

requestLock

public void requestLock()
                 throws IOException

Sends rpc to the master to request lock. The lock request is queued with other lock requests. Call await() to wait on lock. Always call unlock() after calling the below, even after error.

Throws:

IOException

await

public boolean await(long timeout,
                     TimeUnit timeUnit)
              throws InterruptedException

Parameters:

timeout - in milliseconds. If set to 0, waits indefinitely.

Returns:

true if lock was acquired; and false if waiting time elapsed before lock could be acquired.

Throws:

InterruptedException

await

public void await()
           throws InterruptedException

Throws:

InterruptedException

unlock

public void unlock()
            throws IOException

Throws:

IOException