org.apache.ignite.services

Interface Service

All Superinterfaces:

Serializable

All Known Implementing Classes:

TensorFlowClusterMaintainer

public interface Service
extends Serializable

An instance of grid-managed service.

Description

Grid-managed services may be deployed from IgniteServices facade or directly from grid configuration at startup.

Deployment

Whenever service is deployed, Ignite will automatically calculate how many instances of this service should be deployed on each node within the cluster. Whenever service is deployed on a cluster node, Ignite will call execute(ServiceContext) method on that service. It is up to the user to control whenever the service should exit from the execute method. For example, user may choose to implement service as follows:

 public class MyIgniteService implements Service {
      ...
      // Example of ignite resource injection. All resources are optional.
      // You should inject resources only as needed.
      @IgniteInstanceResource
      private Ignite ignite;
      ...
      @Override public void cancel(ServiceContext ctx) {
          // No-op.
      }

      @Override public void execute(ServiceContext ctx) {
          // Loop until service is cancelled.
          while (!ctx.isCancelled()) {
              // Do something.
              ...
          }
      }
  }
 

Consecutively, this service can be deployed as follows:

 ...
 IgniteServices svcs = ignite.services();

 svcs.deployClusterSingleton("mySingleton", new MyIgniteService());
 

Or from grid configuration on startup:

 IgniteConfiguration gridCfg = new IgniteConfiguration();

 IgniteServiceConfiguration svcCfg = new IgniteServiceConfiguration();

 // Configuration for cluster-singleton service.
 svcCfg.setName("mySingleton");
 svcCfg.setMaxPerNodeCount(1);
 svcCfg.setTotalCount(1);
 svcCfg.setService(new MyIgniteService());

 gridCfg.setServiceConfiguration(svcCfg);
 ...
 Ignition.start(gridCfg);
 

Cancellation

Services can be cancelled by calling any of the cancel methods on IgniteServices API. Whenever a deployed service is cancelled, Ignite will automatically call cancel(ServiceContext) method on that service.

Note that Ignite cannot guarantee that the service exits from execute(ServiceContext) method whenever cancel(ServiceContext) is called. It is up to the user to make sure that the service code properly reacts to cancellations.

Method Summary

Modifier and Type	Method and Description
void	cancel(ServiceContext ctx) Cancels this service.
void	execute(ServiceContext ctx) Starts execution of this service.
void	init(ServiceContext ctx) Pre-initializes service before execution.

Method Detail

cancel

void cancel(ServiceContext ctx)

Cancels this service. Ignite will automatically call this method whenever any of the cancel methods on IgniteServices API are called.

Note that Ignite cannot guarantee that the service exits from execute(ServiceContext) method whenever cancel(ServiceContext) method is called. It is up to the user to make sure that the service code properly reacts to cancellations.

Parameters:

ctx - Service execution context.

init

void init(ServiceContext ctx)
   throws Exception

Pre-initializes service before execution. This method is guaranteed to be called before service deployment is complete (this guarantees that this method will be called before method execute(ServiceContext) is called).

Parameters:

ctx - Service execution context.

Throws:

Exception - If service initialization failed.

execute

void execute(ServiceContext ctx)
      throws Exception

Starts execution of this service. This method is automatically invoked whenever an instance of the service is deployed on a grid node. Note that service is considered deployed even after it exits the execute method and can be cancelled (or undeployed) only by calling any of the cancel methods on IgniteServices API. Also note that service is not required to exit from execute method until cancel(ServiceContext) method was called.

Parameters:

ctx - Service execution context.

Throws:

Exception - If service execution failed. Not that service will still remain deployed, until IgniteServices.cancel(String) method will be called.