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

Class FetchExternalTasksCmd

java.lang.Object

org.camunda.bpm.engine.impl.cmd.FetchExternalTasksCmd

All Implemented Interfaces:

Command<List<LockedExternalTask>>

public class FetchExternalTasksCmd
extends Object
implements Command<List<LockedExternalTask>>

Author:

Thorben Lindhauer, Christopher Zell

Field Summary

Fields

Modifier and Type	Field	Description
protected Map<String,TopicFetchInstruction>	fetchInstructions
protected static final EnginePersistenceLogger	LOG
protected int	maxResults
protected List<QueryOrderingProperty>	orderingProperties
protected String	workerId

Constructor Summary

Constructors

Constructor	Description
FetchExternalTasksCmd(String workerId, int maxResults, Map<String,TopicFetchInstruction> instructions)
FetchExternalTasksCmd(String workerId, int maxResults, Map<String,TopicFetchInstruction> instructions, boolean usePriority, List<QueryOrderingProperty> orderingProperties)

Method Summary

Modifier and Type	Method	Description
List<LockedExternalTask>	execute(CommandContext commandContext)
protected void	filterOnOptimisticLockingFailure(CommandContext commandContext, List<LockedExternalTask> tasks)
boolean	isRetryable()	When CockroachDB is used, this command may be retried multiple times until it is successful, or the retries are exhausted.
protected List<QueryOrderingProperty>	orderingPropertiesWithPriority(boolean usePriority, List<QueryOrderingProperty> queryOrderingProperties)
protected void	validateInput()

Methods inherited from class java.lang.Object

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

Field Details

LOG

protected static final EnginePersistenceLogger LOG

workerId

protected String workerId

maxResults

protected int maxResults

orderingProperties

protected List<QueryOrderingProperty> orderingProperties

fetchInstructions

protected Map<String,TopicFetchInstruction> fetchInstructions

Constructor Details

FetchExternalTasksCmd

public FetchExternalTasksCmd(String workerId,
 int maxResults,
 Map<String,TopicFetchInstruction> instructions)

FetchExternalTasksCmd

public FetchExternalTasksCmd(String workerId,
 int maxResults,
 Map<String,TopicFetchInstruction> instructions,
 boolean usePriority,
 List<QueryOrderingProperty> orderingProperties)

Method Details

execute

public List<LockedExternalTask> execute(CommandContext commandContext)

Specified by:

execute in interface Command<List<LockedExternalTask>>

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 FetchExternalTasks command only executes internal code, so we are certain that a retry of a failed external task locking will not impact user data, and may be performed multiple times.

Specified by:

isRetryable in interface Command<List<LockedExternalTask>>

Returns:

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

filterOnOptimisticLockingFailure

protected void filterOnOptimisticLockingFailure(CommandContext commandContext,
 List<LockedExternalTask> tasks)

validateInput

protected void validateInput()

orderingPropertiesWithPriority

protected List<QueryOrderingProperty> orderingPropertiesWithPriority(boolean usePriority,
 List<QueryOrderingProperty> queryOrderingProperties)