Grid Event Management Example

Every significant action in GridGain generates event. These events can be queried by:

Looking through collection of events stored on local node by definining event filter
Defining listener that is triggered at event occurence

This example demonstrates both aproaches.

(will be available with 1.6.2 release)

Package:
org.gridgain.examples.helloworld.gridify.failover

There are three classes implemented for this example:

GridEventsListenerExample.java
GridEventsQuerytExample.java
GridEventsExampleTask.java

Running Grid Node

This example will need one remote node to be running. Note that you don't need another machine for it - you can start remote node on the same machine you are running example on.

To start a remote node open the terminal window on Linux/Mac OS X or Command Prompt on Windows, change directory to ${GRIDGAIN_HOME}/bin and run the gridgain.{sh|bat} script. It takes 2-3 seconds for grid node to start and if everything worked fine you should see starting log ending with successful start acknowledgment.

GridEventsListenerExample.java

1. Import GridGain classes.

import org.gridgain.grid.*;

2. Add Grid Start and Stop.

GridFactory.start();
        
try {
    ...
}
finally {
    GridFactory.stop(true);
}

finally clause allows for graceful grid shutdown in case of the exceptions.

3. Define Event Listener.

Implementation of GridLocalEventListener ^Javadoc interface simply prints event information.

GridLocalEventListener listener = new GridLocalEventListener() {
    /**
     * {@inheritDoc}
     */
    public void onEvent(GridEvent evt) {
        System.out.println(">>> Grid event occurred: " + evt);
    }
};

4. Register listener on the grid.

grid.addLocalEventListener(listener);

5. Execute task on the grid.

grid.execute(GridEventsExampleTask.class, null).get();

6. Unregister listener from the grid.

grid.removeLocalEventListener(listener);

Full Source Code

GridEventsQuerytExample.java

package org.gridgain.examples.events;

import org.gridgain.grid.*;

public final class GridEventsQuerytExample {
    /**
     * Ensure singleton.
     */
    private GridEventsQuerytExample() {
        // No-op.
    }

    /**
     * Executes an example task on the grid in order to generate events and then lists
     * all events that have occured from task execution.
     *
     * @param args Command line arguments, none required but if provided
     *      first one should point to the Spring configuration file. See
     *      <tt>"examples/config/"</tt> for configuration file examples.
     * @throws GridException If example execution failed.
     */
    public static void main(String[] args) throws GridException {
        if (args.length == 0) {
            GridFactory.start();
        }
        else {
            GridFactory.start(args[0]);
        }

        try {
            Grid grid = GridFactory.getGrid();

            // Execute example task to generate events.
            grid.execute(GridEventsExampleTask.class, null).get();

            // Define event filter.
            GridEventFilter evtFilter = new GridEventFilter() {
                public boolean accept(GridEvent evt) {
                    return true;
                }
            };

            // Retrieve and filter local node events.
            for(GridEvent evt : grid.queryLocalEvents(evtFilter)) {
                System.out.println(">>> Found grid event: " + evt);
            }

            System.out.println(">>>");
            System.out.println(">>> Finished executing Grid Events Query Example.");
            System.out.println(">>> Check local node output.");
            System.out.println(">>>");
        }
        finally {
            GridFactory.stop(true);
        }
    }
}

GridEventsQuerytExample.java

1. Import GridGain classes.

import org.gridgain.grid.*;

2. Add Grid Start and Stop.

GridFactory.start();
        
try {
    ...
}
finally {
    GridFactory.stop(true);
}

finally clause allows for graceful grid shutdown in case of the exceptions.

3. Execute task on the grid.

Execute task to generate events on the grid.

grid.execute(GridEventsExampleTask.class, null).get();

4. Define Event Filter.

Implementation of GridEventFilter ^Javadoc interface simply accepts all events.

GridEventFilter evtFilter = new GridEventFilter() {
    public boolean accept(GridEvent evt) {
        return true;
    }
};

5. Retrieve all local events on the grid.

for(GridEvent evt : grid.queryLocalEvents(evtFilter)) {
    System.out.println(">>> Found grid event: " + evt);
}

Full Source Code

GridEventsQuerytExample.java

package org.gridgain.examples.events;

import org.gridgain.grid.*;

public final class GridEventsQuerytExample {
    /**
     * Ensure singleton.
     */
    private GridEventsQuerytExample() {
        // No-op.
    }

    /**
     * Executes an example task on the grid in order to generate events and then lists
     * all events that have occured from task execution.
     *
     * @param args Command line arguments, none required but if provided
     *      first one should point to the Spring configuration file. See
     *      <tt>"examples/config/"</tt> for configuration file examples.
     * @throws GridException If example execution failed.
     */
    public static void main(String[] args) throws GridException {
        if (args.length == 0) {
            GridFactory.start();
        }
        else {
            GridFactory.start(args[0]);
        }

        try {
            Grid grid = GridFactory.getGrid();

            // Execute example task to generate events.
            grid.execute(GridEventsExampleTask.class, null).get();

            // Define event filter.
            GridEventFilter evtFilter = new GridEventFilter() {
                public boolean accept(GridEvent evt) {
                    return true;
                }
            };

            // Retrieve and filter local node events.
            for(GridEvent evt : grid.queryLocalEvents(evtFilter)) {
                System.out.println(">>> Found grid event: " + evt);
            }

            System.out.println(">>>");
            System.out.println(">>> Finished executing Grid Events Query Example.");
            System.out.println(">>> Check local node output.");
            System.out.println(">>>");
        }
        finally {
            GridFactory.stop(true);
        }
    }
}

GridEventsExampleTask.java

1. Import GridGain classes.

import org.gridgain.grid.*;
import org.gridgain.grid.logger.*;
import org.gridgain.grid.resources.*;

2. Split Logic.

This is a grid task implementation that is responsible map and reduce logic. Note that this task implements GridTask ^Javadoc interface. Main two methods that are implemented here are map and reduce. Method reduce is empty since this task has no return value.

Full Source Code

GridEventsExampleTask.java

package org.gridgain.examples.events;

import java.io.*;
import java.util.*;
import org.gridgain.grid.*;
import org.gridgain.grid.logger.*;
import org.gridgain.grid.resources.*;

/**
 * Example task used to generate events for event demonstration example.
 *
 */
public class GridEventsExampleTask extends GridTaskAdapter<String> {
    /** Grid logger. */
    @GridLoggerResource
    private GridLogger log = null;

    /** Instance of grid. */
    @GridInstanceResource
    private Grid grid = null;

    /**
     * {@inheritDoc}
     */
    public Map<? extends GridJob, GridNode> map(List<GridNode> subgrid, String arg) throws GridException {
        GridJob job = new GridJobAdapter() {
            /*
             * Simply prints the job's argument.
             */
            public Serializable execute() {
                if (log.isInfoEnabled() == true) {
                    log.info(">>> Exectuting event example job on this node.");
                }

                // This job does not return any result.
                return null;
            }
        };

        Map<GridJob, GridNode> jobs = new HashMap<GridJob, GridNode>(1);

        // Use only local node for this example.
        jobs.put(job, grid.getLocalNode());

        return jobs;
    }

    /**
     * {@inheritDoc}
     */
    public Serializable reduce(List<GridJobResult> results) throws GridException {
        // Nothing to reduce.
        return null;
    }
}

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