org.apache.ignite.services

## Interface Service

- All Superinterfaces:
    Serializable

      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
    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.

2020 Copyright © Apache Software Foundation
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Ignite Database and Caching Platform | : ver. 2.9.1
Release Date | : December 9 2020