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D.11 Asynchronous Task Control

This clause introduces a language-defined package to do asynchronous suspend/resume on tasks. It uses a conceptual held priority value to represent the task's held state.
Static Semantics
The following language-defined library package exists:
       with Ada.Task_Identification;
       package Ada.Asynchronous_Task_Control is
         procedure Hold(T : in Ada.Task_Identification.Task_ID);
         procedure Continue(T : in Ada.Task_Identification.Task_ID);
         function Is_Held(T : Ada.Task_Identification.Task_ID)
          return Boolean;
       end Ada.Asynchronous_Task_Control;
Dynamic Semantics
After the Hold operation has been applied to a task, the task becomes held. For each processor there is a conceptual idle task, which is always ready. The base priority of the idle task is below System.Any_Priority'First. The held priority is a constant of the type integer whose value is below the base priority of the idle task.
The Hold operation sets the state of T to held. For a held task: the task's own base priority does not constitute an inheritance source (see D.1), and the value of the held priority is defined to be such a source instead.
The Continue operation resets the state of T to not-held; T's active priority is then reevaluated as described in D.1. This time, T's base priority is taken into account.
The Is_Held function returns True if and only if T is in the held state.
As part of these operations, a check is made that the task identified by T is not terminated. Tasking_Error is raised if the check fails. Program_Error is raised if the value of T is Null_Task_ID.
Erroneous Execution
If any operation in this package is called with a parameter T that specifies a task object that no longer exists, the execution of the program is erroneous.
Implementation Permissions
An implementation need not support Asynchronous_Task_Control if it is infeasible to support it in the target environment.


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