THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
Another example is the Task Scheduler. Getting commands from users using the REST API, it allocates multiple Evaluators and submits Tasks.
It is a basic Task Scheduler example using Reef-webserver. The application receives the Task (shell command) list from user and execute the Tasks in a FIFO order.
REST API
Users can send the HTTP request to the server via URL :
http://{address}:{port}/reef-example-scheduler/v1
And the possible requests are as follows:
/list: lists all the Tasks’ statuses./clear: clears all the Tasks waiting in the queue and returns the number of Tasks that have been removed./submit?cmd=COMMAND: submits a Task to execute COMMAND and returns the Task id./status?id=ID: returns the status of the Task with the id, “ID”./cancel?id=ID: cancels the Task with the id, “ID”./max-eval?num={num}: sets the maximum number of Evaluators.
The result of each task is written in the log files - both in the driver’s and the evaluators’.
Reusing the Evaluators
You can find the method retainEvaluator() in SchedulerDriver:
/**
* Retain the complete evaluators submitting another task
* until there is no need to reuse them.
*/
private synchronized void retainEvaluator(final ActiveContext context) {
if (scheduler.hasPendingTasks()) {
scheduler.submitTask(context);
} else if (nActiveEval > 1) {
nActiveEval--;
context.close();
} else {
state = State.READY;
waitForCommands(context);
}
}
When a Task completes, the
EventHandler for the CompletedTask event is invoked. An instance of CompletedTask is then passed using the parameter to get the ActiveContext object from the CompletedTask. We can reuse this Evaluator by submitting another Task to it if there is a Task to launch.Using the -retain false argument disables this functionality and allocates a new Evaluator for every Task.