Package org.camunda.bpm.engine.impl.cmd

Class AcquireJobsCmd

java.lang.Object

org.camunda.bpm.engine.impl.cmd.AcquireJobsCmd

All Implemented Interfaces:

OptimisticLockingListener, Command<AcquiredJobs>

public class AcquireJobsCmd
extends java.lang.Object
implements Command<AcquiredJobs>, OptimisticLockingListener

Author:

Nick Burch, Daniel Meyer

Field Summary

Fields

Modifier and Type	Field	Description
protected AcquiredJobs	acquiredJobs
protected int	numJobsToAcquire

Constructor Summary

Constructors

Constructor	Description
AcquireJobsCmd(JobExecutor jobExecutor)
AcquireJobsCmd(JobExecutor jobExecutor, int numJobsToAcquire)

Method Summary

Modifier and Type	Method	Description
AcquiredJobs	execute(CommandContext commandContext)
OptimisticLockingResult	failedOperation(DbOperation operation)	Signifies that an operation failed due to optimistic locking.
java.lang.Class<? extends DbEntity>	getEntityType()	The type of the entity for which this listener should be notified.
boolean	isRetryable()	When CockroachDB is used, this command may be retried multiple times until it is successful, or the retries are exhausted.
protected void	lockJob(AcquirableJobEntity job)

Methods inherited from class java.lang.Object

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

Field Detail

acquiredJobs

protected AcquiredJobs acquiredJobs

numJobsToAcquire

protected int numJobsToAcquire

Constructor Detail

AcquireJobsCmd

public AcquireJobsCmd(JobExecutor jobExecutor)

AcquireJobsCmd

public AcquireJobsCmd(JobExecutor jobExecutor,
                      int numJobsToAcquire)

Method Detail

execute

public AcquiredJobs execute(CommandContext commandContext)

Specified by:

execute in interface Command<AcquiredJobs>

isRetryable

public boolean isRetryable()

When CockroachDB is used, this command may be retried multiple times until it is successful, or the retries are exhausted. CockroachDB uses a stricter, SERIALIZABLE transaction isolation which ensures a serialized manner of transaction execution. A concurrent transaction that attempts to modify the same data as another transaction is required to abort, rollback and retry. This also makes our use-case of pessimistic locks redundant since we only use them as synchronization barriers, and not to lock actual data which would protect it from concurrent modifications. The AcquireJobs command only executes internal code, so we are certain that a retry of failed job locks will not impact user data, and may be performed multiple times.

Specified by:

isRetryable in interface Command<AcquiredJobs>

Returns:

true if the CrdbTransactionRetryInterceptor can make a transparent retry of this command upon failure with a CrdbTransactionRetryException (only used when running on CockroachDB).

lockJob

protected void lockJob(AcquirableJobEntity job)

getEntityType

public java.lang.Class<? extends DbEntity> getEntityType()

Description copied from interface: OptimisticLockingListener

The type of the entity for which this listener should be notified. If the implementation returns 'null', the listener is notified for all entity types.

Specified by:

getEntityType in interface OptimisticLockingListener

Returns:

the entity type for which the listener should be notified.

failedOperation

public OptimisticLockingResult failedOperation(DbOperation operation)

Description copied from interface: OptimisticLockingListener

Signifies that an operation failed due to optimistic locking.

Specified by:

failedOperation in interface OptimisticLockingListener

Parameters:

operation - the failed operation.

Returns:

OptimisticLockingResult that instructs the caller how to handle the result of the failed operation.