Java Application Examples

The following examples illustrate some application interactions that use the Java language bindings. You can find additional examples on the “How To” section of the Grid Engine Community Site.

Example 6–4 Starting and Stopping a Session

The following code segment shows the most basic DRMAA Java language binding program.

Everything that you as a programmer do with DRMAA, you do through a Session object. You get the Session object from a SessionFactory. You get the SessionFactory from the static SessionFactory.getFactory() method. The reason for this chain is that the org.ggf.drmaa.* classes should be considered an immutable package to be used by every DRMAA Java language binding implementation. Because the package is immutable, to load a specific implementation, the SessionFactory uses a system property to find the implementation's session factory, which it then loads. That session factory is then responsible for creating the session in whatever way it sees fit. It should be noted that even though there is a session factory, only one session may exist at a time.

On line 9, SessionFactory.getFactory() gets a session factory instance . On line 10, SessionFactory.getSession() gets the session instance. On line 13, Session.init() initializes the session. "" is passed in as the contact string to create a new session because no initialization arguments are needed.

Session.init() creates a session and starts an event client listener thread. The session is used for organizing jobs submitted through DRMAA, and the thread is used to receive updates from the queue master about the state of jobs and the system in general. Once Session.init() has been called successfully, the calling application must also call Session.exit() before terminating. If an application does not call Session.exit() before terminating, the queue master might be left with a dead event client handle, which can decrease queue master performance. Use the Runtime.addShutdownHook() method to make sure Session.exit() gets called.

At the end of the program, on line 14, Session.exit() cleans up the session and stops the event client listener thread. Most other DRMAA methods must be called before Session.exit(). Some functions, like Session.getContact(), can be called after Session.exit(), but these functions only provide general information. Any function that performs an action, such as Session.runJob() or Session.wait() must be called before Session.exit() is called. If such a function is called after Session.exit() is called, it will throw a NoActiveSessionException.

01: package com.sun.grid.drmaa.howto;
02:
03: import org.ggf.drmaa.DrmaaException;
04: import org.ggf.drmaa.Session;
05: import org.ggf.drmaa.SessionFactory;
06:
07: public class Howto1 {
08:    public static void main(String[] args) {
09:       SessionFactory factory = SessionFactory.getFactory();
10:       Session session = factory.getSession();
11:
12:       try {
13:          session.init("");
14:          session.exit();
15:       } catch (DrmaaException e) {
16:          System.out.println("Error: " + e.getMessage());
17:       }
18:    }
19: }

Example 6–5 Running a Job

The following code segment shows how to use the DRMAA Java language binding to submit a job to N1 Grid Engine. The beginning and end of this program are the same as Example 6–4. The differences are on lines 16-24.

On line 16 , DRMAA allocates a JobTemplate. A JobTemplate is an object that is used to store information about a job to be submitted. The same template can be reused for multiple calls to Session.runJob() or Session.runBulkJobs().

On line 17, the remoteCommand attribute is set. This attribute tells DRMAA where to find the program to run. Its value is the path to the executable. The path can be relative or absolute. If relative, the path is relative to the workingDirectory attribute, which defaults to the user's home directory. For more information on DRMAA attributes, see the DRMAA Javadoc or the drmaa_attributes man page. For this program to work, the script sleeper.sh must be in your default path.

On line 18, the args attribute is set. This attribute tells DRMAA what arguments to pass to the executable. For more information on DRMAA attributes, see the DRMAA Javadoc or the drmaa_attributes man page.

On line 20, Session.runJob() submits the job. This method returns the ID assigned to the job by the queue master. The job is now running as though submitted by qsub. At this point, calling Session.exit() or terminating the program will have no effect on the job.

To clean things up, the job template is deleted on line 24. This action frees the memory DRMAA set aside for the job template, but has no effect on submitted jobs.

01: package com.sun.grid.drmaa.howto;
02:
03: import java.util.Collections;
04: import org.ggf.drmaa.DrmaaException;
05: import org.ggf.drmaa.JobTemplate;
06: import org.ggf.drmaa.Session;
07: import org.ggf.drmaa.SessionFactory;
08:
09: public class Howto2 {
10:    public static void main(String[] args) {
11:       SessionFactory factory = SessionFactory.getFactory();
12:       Session session = factory.getSession();
13:
14:       try {
15:          session.init("");
16:          JobTemplate jt = session.createJobTemplate();
17:          jt.setRemoteCommand("sleeper.sh");
18:          jt.setArgs(Collections.singletonList("5"));
19:
20:          String id = session.runJob(jt);
21:
22:          System.out.println("Your job has been submitted with id " + id);
23:
24:          session.deleteJobTemplate(jt);
25:          session.exit();
26:       } catch (DrmaaException e) {
27:          System.out.println("Error: " + e.getMessage());
28:       }
29:    }
30: }