Creating PMI Handlers

The basic form of a PMI handler is a CacheEntryForEach handler. Inherit from CacheEntryForEach and register your class as an invocation event handler to accept PMI requests from clients.

Prerequisites

• ScaleOut StateServer Pro license

Procedure

Note

This sample in its entirety is available on our GitHub Samples Repo.

1. Determine the type parameters to use with your ForEach handler.

   • A PMI operation evaluates objects stored in a ScaleOut Cache. Caches in the library are strongly-typed, so invocation handlers are also strongly-typed.

   • This example analyzes a cache that tracks the most recent login date for an application’s users. The cache’s key type is a string (representing a User ID), and its value type is a long (representing a login time).

2. Create a class that inherits from ForEach<TKey, TValue>.

   package com.scaleout.client.samples.compute;
   
   import com.scaleout.client.caching.CacheEntryForEachHandler;
   import com.scaleout.client.caching.OperationContext;
   
   public class FindInactiveUsersForEachHandler implements CacheEntryForEachHandler<String, Long, Void> {
           @Override
           public void evaluate(String key, OperationContext<String, Long, Void> operationContext) {
                   //
           }
   }
   

3. Implement your custom evaluation code.

   • During a PMI operation, your Evaluate method will be called for every object in the ScaleOut cache.

   • Your method can read, modify, delete, or perform any needed cache operation. In this example, login times are retrieved to identify inactive users.

   // Use the cache in the PMI context to retrieve the object being evaluated:
   var readResponse = operationContext.getCache().read(key);
   if (readResponse.getStatus() == RequestStatus.ObjectNotFound)
   {
           System.out.println(key + " removed by another client during PMI operation.");
           return;
   }
   else if (readResponse.getStatus() != RequestStatus.ObjectRetrieved)
   {
           System.out.println("Unexpected error (" + readResponse.getStatus() + ") while reading key: " + key);
           return;
   }
   
   // Perform analysis:
   long lastLoginEpochMs = readResponse.getValue();
   long inactiveTimeMs = System.currentTimeMillis() - lastLoginEpochMs;
   if (inactiveTimeMs > Duration.ofDays(7).toMillis())
   {
           System.out.println(key + " inactive for {inactiveTime.TotalDays} days.");
   }
   

4. At application startup, register the class as an invocation handler. If you are running your handler in an Invocation Grid, this code should be put in your project’s InvocationGridStartup.configure() method.

   Tip

   A PMI application can have multiple invocation handlers registered against multiple caches.

   package com.scaleout.client.samples.compute;
   
   import com.scaleout.client.GridConnectException;
   import com.scaleout.client.GridConnection;
   import com.scaleout.client.ServiceEvents;
   import com.scaleout.client.ServiceEventsException;
   import com.scaleout.client.caching.Cache;
   import com.scaleout.client.caching.CacheBuilder;
   
   import java.io.IOException;
   
   public class PMIHandlerSample {
       public static void main(String[] args) throws GridConnectException, ServiceEventsException, IOException {
           GridConnection connection = GridConnection.connect("bootstrapGateways=localhost");
           Cache<String, Long> cache = new CacheBuilder<String, Long>(connection, "PMISample", String.class)
                   .build();
   
           ServiceEvents.setForEachEventHandler(cache, "Find inactive users", new FindInactiveUsersForEachHandler());
           System.out.println("Waiting for events...");
           System.out.println("Press any key to exit.");
           System.in.read();
       }
   }
   

5. Build your handler application and deploy it to all the servers in your farm that are running the ScaleOut service.

   • Once your handler app is running on all your ScaleOut hosts, you are ready to process PMI requests.