org.gridgain.grid
Interface GridJob

All Superinterfaces:

Serializable

All Known Subinterfaces:

GridAffinityJob<A>, GridCoherenceAffinityJob<A>

All Known Implementing Classes:

GridAffinityJobAdapter, GridCoherenceAffinityJobAdapter, GridifyJobAdapter, GridJobAdapter

@Apache20LicenseCompatible
public interface GridJob
extends Serializable

Defines executable unit for GridTask.

Description

Grid job is an executable unit of GridTask. Grid task gets split into jobs when GridTask.map(List, Object) method is called. This method returns all jobs for the task mapped to their corresponding grid nodes for execution. Grid will then serialize this jobs and send them to requested nodes for execution. When a node receives a request to execute a job, the following sequence of events takes place:

1. Job gets put on waiting list which is passed to underlying GridCollisionSpi SPI.
2. The Collision SPI will decide one of the following scheduling policies:
   • Job will be kept on waiting list. In this case, job will not get a chance to execute until next time the Collision SPI is called.
   • Job will be moved to active list. In this case system will proceed with job execution.
   • Job will be rejected. In this case the GridJobResult passed into GridTask.result(GridJobResult, List) method will contain GridExecutionRejectedException exception. If you are using any of the task adapters shipped with GridGain, then job will be failed over automatically for execution on another node.
3. For activated jobs, an instance of distributed task session (see GridTaskSession) will be injected.
4. System will execute the job by calling GridJob.execute() method.
5. If job gets cancelled while executing then GridJob.cancel() method will be called. Note that just like with Thread.interrupt() method, grid job cancellation serves as a hint that a job should stop executing or exhibit some other user defined behavior. Generally it is up to a job to decide whether it wants to react to cancellation or ignore it. Job cancellation can happen for several reasons:
   • Collision SPI cancelled an active job.
   • Parent task has completed without waiting for this job's result.
   • User cancelled task by calling GridTaskFuture.cancel() method.
6. Once job execution is complete, the return value will be sent back to parent task and will be passed into GridTask.result(GridJobResult, List) method via GridJobResult instance. If job execution resulted in a checked exception, then GridJobResult.getException() method will contain that exception. If job execution threw a runtime exception or error, then it will be wrapped into GridUserUndeclaredException exception.

Resource Injection

Grid job implementation can be injected using IoC (dependency injection) with grid resources. Both, field and method based injection are supported. The following grid resources can be injected:

• GridTaskSessionResource
• GridJobContextResource
• GridInstanceResource
• GridLoggerResource
• GridHomeResource
• GridExecutorServiceResource
• GridLocalNodeIdResource
• GridMBeanServerResource
• GridMarshallerResource
• GridSpringApplicationContextResource
• GridSpringResource

Refer to corresponding resource documentation for more information.

GridJobAdapter

GridGain comes with convenience GridJobAdapter adapter that provides default empty implementation for GridJob.cancel() method and also allows user to set and get job argument, if there is one.

Distributed Session Attributes

Jobs can communicate with parent task and with other job siblings from the same task by setting session attributes (see GridTaskSession). Other jobs can wait for an attribute to be set either synchronously or asynchronously. Such functionality allows jobs to synchronize their execution with other jobs at any point and can be useful when other jobs within task need to be made aware of certain event or state change that occurred during job execution.

Distributed task session can be injected into GridJob implementation using @GridTaskSessionResource annotation. Both, field and method based injections are supported. Refer to GridTaskSession documentation for more information on session functionality.

Saving Checkpoints

Long running jobs may wish to save intermediate checkpoints to protect themselves from failures. There are three checkpoint management methods:

• GridTaskSession.saveCheckpoint(String, Serializable, GridCheckpointScope, long)
• GridTaskSession.loadCheckpoint(String)
• GridTaskSession.removeCheckpoint(String)

Jobs that utilize checkpoint functionality should attempt to load a check point at the beginning of execution. If a non-null value is returned, then job can continue from where it failed last time, otherwise it would start from scratch. Throughout it's execution job should periodically save its intermediate state to avoid starting from scratch in case of a failure.



See Also:

Documentation
Email Support
Online Forums
Issue Tracking

Author: 2005-2008 Copyright © GridGain Systems. All Rights Reserved. ver. 2.1.0

	Nikita Ivanov, GridGain Systems nivanov@gridgain.com
	Dmitriy Setrakyan, GridGain Systems dsetrakyan@gridgain.com
	Alexander Magdenko, GridGain Systems amagdenko@gridgain.com
	Boris Suchodoev, GridGain Systems bsuchodoev@gridgain.com
	Denis Kharlamov, GridGain Systems dkharlamov@gridgain.com
	close

Method Summary

void	cancel() This method is called when when system detects that completion of this job can no longer alter the overall outcome (for example, when parent task has already reduced the results).
Serializable	execute() Executes this job.

Method Detail

cancel

void cancel()

This method is called when when system detects that completion of this job can no longer alter the overall outcome (for example, when parent task has already reduced the results). Job is also cancelled when GridTaskFuture.cancel() is called.

Note that job cancellation is only a hint, and just like with Thread.interrupt() method, it is really upto the actual job instance to gracefully finish execution and exit.

execute

Serializable execute()
                     throws GridException

Executes this job.

Throws:

GridException - If job execution caused an exception. This exception will be returned in GridJobResult.getException() method passed into GridTask.result(GridJobResult, List) method into task on caller node. If execution produces a RuntimeException or Error, then it will be wrapped into GridException.

Returns:

Job execution result (possibly null). This result will be returned in GridJobResult.getData() method passed into GridTask.result(GridJobResult, List) method into task on caller node.