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C.7.1 The Package Task_Identification

Static Semantics

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   The following language-defined library package exists:
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package Ada.Task_Identification is
   type Task_ID is private;
   Null_Task_ID : constant Task_ID;
   function  "=" (Left, Right : Task_ID) return Boolean;
3/1
{8652/0070}
   function  Image        (T : Task_ID) return String;
   function  Current_Task return Task_ID;
   procedure Abort_Task   (T : in out Task_ID);
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   function  Is_Terminated(T : Task_ID) return Boolean;
   function  Is_Callable  (T : Task_ID) return Boolean;
private
   ... -- not specified by the language
end Ada.Task_Identification;

Dynamic Semantics

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   A value of the type Task_ID identifies an existent task. The constant Null_Task_ID does not identify any task. Each object of the type Task_ID is default initialized to the value of Null_Task_ID.
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   The function "=" returns True if and only if Left and Right identify the same task or both have the value Null_Task_ID.
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   The function Image returns an implementation-defined string that identifies T. If T equals Null_Task_ID, Image returns an empty string.
7.a
Implementation defined: The result of the Task_Identification.Image attribute.
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   The function Current_Task returns a value that identifies the calling task.
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   The effect of Abort_Task is the same as the abort_statement for the task identified by T. [In addition, if T identifies the environment task, the entire partition is aborted, See E.1.]
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    The functions Is_Terminated and Is_Callable return the value of the corresponding attribute of the task identified by T.
10.a.1/1
Ramification: {8652/0115} These routines can be called with an argument identifying the environment task. Is_Terminated will always be False for such a call, but Is_Callable (usually True) could be False if the environment task is waiting for the termination of dependent tasks. Thus, a dependent task can use Is_Callable to determine if the main subprogram has completed.
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    For a prefix T that is of a task type [(after any implicit dereference)], the following attribute is defined:
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    T'Identity
Yields a value of the type Task_ID that identifies the task denoted by T.
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    For a prefix E that denotes an entry_declaration, the following attribute is defined:
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    E'Caller
Yields a value of the type Task_ID that identifies the task whose call is now being serviced. Use of this attribute is allowed only inside an entry_body or accept_statement corresponding to the entry_declaration denoted by E.
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    {Program_Error (raised by failure of run-time check)} Program_Error is raised if a value of Null_Task_ID is passed as a parameter to Abort_Task, Is_Terminated, and Is_Callable.
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    {potentially blocking operation (Abort_Task) [partial]} {blocking, potentially (Abort_Task) [partial]} Abort_Task is a potentially blocking operation (see 9.5.1).

Bounded (Run-Time) Errors

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    {bounded error (cause) [partial]} It is a bounded error to call the Current_Task function from an entry body or an interrupt handler. {Program_Error (raised by failure of run-time check)} Program_Error is raised, or an implementation-defined value of the type Task_ID is returned.
17.a
Implementation defined: The value of Current_Task when in a protected entry or interrupt handler.
17.b
Implementation Note: This value could be Null_Task_ID, or the ID of some user task, or that of an internal task created by the implementation.

Erroneous Execution

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    {erroneous execution (cause) [partial]} If a value of Task_ID is passed as a parameter to any of the operations declared in this package (or any language-defined child of this package), and the corresponding task object no longer exists, the execution of the program is erroneous.

Documentation Requirements

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    The implementation shall document the effect of calling Current_Task from an entry body or interrupt handler.
19.a
Implementation defined: The effect of calling Current_Task from an entry body or interrupt handler.
NOTES
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10  This package is intended for use in writing user-defined task scheduling packages and constructing server tasks. Current_Task can be used in conjunction with other operations requiring a task as an argument such as Set_Priority (see D.5).
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11  The function Current_Task and the attribute Caller can return a Task_ID value that identifies the environment task.

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