Job Dependencies demo

What does the sample do?

This demo leverages the built-in job dependencies feature and provides a easy and intuitive way to define a graph of jobs with dependencies. It supports any non-cyclic dependency graph and will work even when the jobs in the dependency graph are submitted from multiple JPPF clients running on multiple machines.

How do I run it?

1. Grid setup

• start a JPPF server and at least one node. For information on how to set up a node and server, please refer to the JPPF documentation.

2. Running the demo

• open a command prompt in the JPPF-x.y.z-samples-pack/JobDependencies folder
• start the demo by entering "run.bat" on Windows, "./run.sh" on Linux/Unix or by launching the Ant script "ant run"
• During the demo, the console output will show the jobs that complete, along with their execution results

3. Defining your own dependency graph

• The jobs graph is defined in the file JobDependencies/dependency_graph.txt
• for example, the dependency graph defined in the vanilla version of this sample is defined as:
  

  Configuration	Corresponding graph
  Job F ==> Job A, Job B, Job E | root Job E ==> Job C, Job D Job D ==> Job B, Job C Job C ==> Job A Job B ==> Job A Job A ==>

4. Detection of cycles in the dependency graph

When a cycle is detected, the server will print a message to the console, similar to this:

[2016-05-09 21:48:00.621] cycle detected while adding dependency 'Job C' to 'Job A' :
Job A ==> Job B ==> Job C ==> Job A

5. Distributed scenario: submitting jobs in the dependency graph from separate clients

As mentioned above, this demo will work even when the jobs are submitted from multiple client applications. To illustrate this, we will proceed as follows:

• Make a copy of the JPPF-x.y.z-samples-pack/JobDependencies folder, let's call it JobDependencies2 for this exercise
• in JobDependencies/dependency_graph.txt, remove or comment out the last 3 declared dependencies, so the dependencies should look like this:

  Job F ==> Job A, Job B, Job E | root
  Job E ==> Job C, Job D
  Job D ==> Job B, Job C
  

• in JobDependencies2/dependency_graph.txt, remove or comment out the first 3 declared dependencies, the dependencies should look like this:

  Job C ==> Job A
  Job B ==> Job A
  Job A ==>
  

• if not already done, start a server and at least one node
• start the demo in JobDependencies with "run.bat" or "./run.sh". You will observe that it prints the following message:

  [2016-07-22 08:51:33.667] runner: ***** awaiting results for 'Job F' *****

• start the demo in JobDependencies2 with "run.bat" or "./run.sh". It will print completion messages for the jobs A, B and C
• now if you get back to the console for JobDependencies, you will see that jobs D, E, F were completed as well, following the completion of their dependencies submitted by the other instance of the demo in JobDependencies2

Source files

• JobDependenciesRunner.java: the entry point for the demo, reads the dependency graph and submits multiple jobs accordingly
• DependencyDescriptor.java: represents information of a job and its dependencies, parsed from the dependency graph definition file
• MyTask.java: a very simple JPPF task implementation, an instance of which is added to each job in the dependency graph
• Utils.java: utility methods to print messages and parse the graph definition file

I have additional questions and comments, where can I go?

If you need more insight into the code of this demo, you can consult the Java source files located in the CustomLoadBalancer/src folder.

In addition, There are 2 privileged places you can go to:

• The JPPF Forums
• The JPPF documentation