2.4. Task schedulingΒΆ

When the current executed task reaches a task scheduling point, the implementation may decide to switch from this task to another one from the set of eligible tasks. Task scheduling points may occur at the following locations:

  • in a task generating code
  • in a taskwait directive
  • just after the completion of a task

The fact of switching from a task to a different one is known as task switching and it may imply to begin the execution of a non-previously executed task or resumes the execution of a partially executed task. Task switching is restricted in the following situations:

  • the set of eligible tasks (at a given time) is initially formed by the set of tasks included in the ready task pool (at this time).
  • once a tied task has been executed by a given thread, it can be only resumed by the very same thread (i.e. the set of eligible tasks for a thread does not include tied tasks that has been previously executed by a different thread).
  • when creating a task with the if clause for which expression evaluated to false, the runtime must offer a mechanism to immediately execute this task (usually by the same thread that creates it).
  • when executing in a final context all the encountered task generating codes will execute the task immediately after creating it as if it was a simple routine call (i.e. the set of eligible tasks in this situation is restricted to include only the newly generated task).

Note

Remember that the ready task pool does not include tasks with dependences still not fulfilled (i.e. not all its predecessors have finished yet) or blocked tasks in any other condition (e.g. tasks executing a taskwait with non-finished child tasks).