org.apache.ignite.services

## Interface Service

All Superinterfaces:
  Serializable

All Known Subinterfaces:
  PlatformDotNetService, PlatformService

All Known Implementing Classes:
  PlatformAbstractService, PlatformDotNetServiceImpl

    public interface Service
    extends Serializable

An instance of grid-managed service. 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

All Methods Instance Methods Abstract Methods
`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.

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Ignite Database and Caching Platform | : ver. 2.10.0
Release Date | : March 10 2021