Handling a sequence of tasks

When we want to handle an error

Sometimes we are in the situation when we don't want to run the second task if the first one fails. We do this by setting the 'fatal' flag on the first task i.e.

myTask.setFatal(true);

We can test this by setting the code for the task to some code that has an error in it e.g.

Runnable code = new Thread() {
  public void run() {
    System.out.println("Running code for My Task");
    String[] = new String[3];
    String[4] = "Error"; //This will generate an array out of bounds error
    System.out.println("Completed code for My Task");
  }
}

Now when we run the task manager we see -

Running code for My Task

i.e. the first task failed before it wrote that it was completed and the second task did not run.

Sometimes when there is an error we want to do something different. We can do this by setting the onFailureCode for the task e.g. -

Runnable failCode = new Thread() {
  public void run() {
    System.out.println("MyTask has failed");
  }
};
myTask.setOnFailureCode(failCode)

Our console output will now read -

Running code for My Task
MyTask has failed

This code will be run whether the task is marked as fatal or not.

We can also add code that will run if our task completes its code successfully -
Runnable successCode = new Thread() {
  public void run() {
    System.out.println("MyTask has been successful");
  }
};
myTask.setOnSuccessCode(failCode)

Running tasks in parallel
Sometimes we have a number of tasks that it is safe enough to run sequentially - for example we might be printing reports on two different printers. Here is the code for the main method of the NormalDemo class in the com.virtualmachinery.taskmanager.demos.

/**
* Starts the application.
* @param args an array of command-line arguments
*/
public static void main(java.lang.String[] args) {

  TaskManagerInterface demoTaskManager = new TaskManager();
  show("Normal Demo - Demonstrates the features of the Task Manager using a normal scenario with 4 tasks, 1 with sequence number 1, 2 with 2 and 1 with 4.");

  try {
    demoTaskManager.addTask(createTask1());// Sequence 1, non-fatal, named TASK 1, wait 5ms
    demoTaskManager.addTask(createTask2a());// Sequence 2, non-fatal, named TASK 2a, wait 50ms
    demoTaskManager.addTask(createTask2b());// Sequence 2, non-fatal, named TASK 2b,wait 5ms
    demoTaskManager.addTask(createTask4());// Sequence 4, non-fatal, named TASK 4, wait 5ms
    demoTaskManager.startTasks(true);
  }
  catch (TaskManagerFatalFailureException te) {
    show("Fatal Failure - task execution halted "+te);
  }
  catch (TaskManagerException te) {
    show("Exception adding tasks in main "+te);
  }

  showStatus(demoTaskManager);
}

Other features