Dexecutor

Execute Dependent tasks in a reliable way

Example

Lets take a look at an example, here is the content of DefaultDependentTasksExecutorTest, which would help you understand the API

@Test
public void testDependentTaskExecution() {

	DefaultDependentTasksExecutor<Integer> executor = newTaskExecutor();

    executor.addDependency(1, 2);
    executor.addDependency(1, 3);
    executor.addDependency(3, 4);
    executor.addDependency(3, 5);
    executor.addDependency(3, 6);
    //executor.addDependency(10, 2); // cycle
    executor.addDependency(2, 7);
    executor.addDependency(2, 9);
    executor.addDependency(2, 8);
    executor.addDependency(9, 10);
    executor.addDependency(12, 13);
    executor.addDependency(13, 4);
    executor.addDependency(13, 14);
    executor.addIndependent(11);

    executor.execute();
}

private DefaultDependentTasksExecutor<Integer> newTaskExecutor() {
	return new DefaultDependentTasksExecutor<Integer>(newExecutor(), new SleepyTaskProvider<Integer>());
}

private ExecutorService newExecutor() {
	return Executors.newCachedThreadPool();
}

private static class SleepyTaskProvider<T> implements TaskProvider<T> {

	public Task provid(T id) {

		return new Task() {

			public void execute() {
				try {
					Thread.sleep(500);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
	}		
}

As can be seen above, DefaultDependentTasksExecutor requires two things

1. Instance of ExecutorService API would use this Service to schedule tasks
2. Instance of TaskProvider, API represents graph using just the basic information (could be task id), it consults the TaskProvider to provide the task when it comes to actual execution.

##There are two phases

1. Graph construction: When you say executor.addDependency(1, 2) it means tasks 1 should finish before task 2can start, executor.addIndependent(11) means neither task 11 depend on any task nor any other task depend on task 11.

   executor.addDependency(1, 2); executor.addDependency(1, 3); executor.addDependency(3, 4); executor.addDependency(3, 5); executor.addDependency(3, 6); //executor.addDependency(10, 2); // cycle executor.addDependency(2, 7); executor.addDependency(2, 9); executor.addDependency(2, 8); executor.addDependency(9, 10); executor.addDependency(12, 13); executor.addDependency(13, 4); executor.addDependency(13, 14); executor.addIndependent(11);

Which would generate the following graph

2. Tasks execution

executor.execute()

Console Output

19:57:43.705 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 1 node
19:57:43.710 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 11 node
19:57:43.710 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 12 node
19:57:44.212 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 1 done
19:57:44.213 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 2 node
19:57:44.214 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 3 node
19:57:44.215 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 11 done
19:57:44.216 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 12 done
19:57:44.217 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 13 node
19:57:44.717 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 2 done
19:57:44.718 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 7 node
19:57:44.719 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 9 node
19:57:44.720 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 8 node
19:57:44.721 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 3 done
19:57:44.722 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 83 - node 4 depends on [3, 13]
19:57:44.724 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 5 node
19:57:44.726 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 6 node
19:57:44.728 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 13 done
19:57:44.729 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 4 node
19:57:44.730 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 14 node
19:57:45.219 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 7 done
19:57:45.221 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 9 done
19:57:45.223 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doExecute 80 - Going to schedule 10 node
19:57:45.225 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 8 done
19:57:45.227 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 5 done
19:57:45.228 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 6 done
19:57:45.234 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 4 done
19:57:45.235 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 14 done
19:57:45.725 [main] DEBUG c.n.e.DefaultDependentTasksExecutor.doWaitForExecution 105 - Processing of node 10 done
19:57:45.726 [main] INFO  c.n.e.DefaultDependentTasksExecutor.execute 69 - Total Time taken to process 14 jobs each taking 500 ms is 2022 ms instead of 7000 ms
19:57:45.728 [main] INFO  c.n.e.DefaultDependentTasksExecutor.execute 70 - [1, 11, 12, 2, 3, 13, 7, 9, 8, 5, 6, 4, 14, 10]