C.7.3 The Package Task_Termination
Static Semantics
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The following language-defined library package
exists: 2/2
with Ada.Task_Identification;
with Ada.Exceptions;
package Ada.Task_Termination is
pragma Preelaborate(Task_Termination);
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type Cause_Of_Termination is (Normal, Abnormal, Unhandled_Exception);
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type Termination_Handler is access protected procedure
(Cause : in Cause_Of_Termination;
T : in Ada.Task_Identification.Task_Id;
X : in Ada.Exceptions.Exception_Occurrence);
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procedure Set_Dependents_Fallback_Handler
(Handler: in Termination_Handler);
function Current_Task_Fallback_Handler return Termination_Handler;
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procedure Set_Specific_Handler
(T : in Ada.Task_Identification.Task_Id;
Handler : in Termination_Handler);
function Specific_Handler (T : Ada.Task_Identification.Task_Id)
return Termination_Handler;
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end Ada.Task_Termination;
Dynamic Semantics
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{termination handler}
{handler (termination)}
The type Termination_Handler identifies a protected
procedure to be executed by the implementation when a task terminates.
Such a protected procedure is called a handler. In all cases T
identifies the task that is terminating. If the task terminates due to
completing the last statement of its body, or as a result of waiting
on a terminate alternative, then Cause is set to Normal and X is set
to Null_Occurrence. If the task terminates because it is being aborted,
then Cause is set to Abnormal and X is set to Null_Occurrence. If the
task terminates because of an exception raised by the execution of its
task_body, then Cause is set to Unhandled_Exception
and X is set to the associated exception occurrence.9/2
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{fall-back handler}
{termination handler
(fall-back)} {specific
handler} {termination
handler (specific)} {set
(termination handler)} {cleared
(termination handler)} Each task has two
termination handlers, a fall-back handler and a specific handler.
The specific handler applies only to the task itself, while the fall-back
handler applies only to the dependent tasks of the task. A handler is
said to be set if it is associated with a non-null value of type
Termination_Handler, and cleared otherwise. When a task is created,
its specific handler and fall-back handler are cleared.10/2
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The procedure Set_Dependents_Fallback_Handler changes
the fall-back handler for the calling task; if Handler is null,
that fall-back handler is cleared, otherwise it is set to be Handler.all.
If a fall-back handler had previously been set it is replaced.11/2
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The function Current_Task_Fallback_Handler returns
the fall-back handler that is currently set for the calling task, if
one is set; otherwise it returns null.12/2
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The procedure Set_Specific_Handler changes the
specific handler for the task identified by T; if Handler is null,
that specific handler is cleared, otherwise it is set to be Handler.all.
If a specific handler had previously been set it is replaced.13/2
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The function Specific_Handler returns the specific
handler that is currently set for the task identified by T, if one is
set; otherwise it returns null.14/2
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As part of the finalization of a task_body,
after performing the actions specified in 7.6
for finalization of a master, the specific handler for the task, if one
is set, is executed. If the specific handler is cleared, a search for
a fall-back handler proceeds by recursively following the master relationship
for the task. If a task is found whose fall-back handler is set, that
handler is executed; otherwise, no handler is executed.15/2
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For Set_Specific_Handler or Specific_Handler, Tasking_Error
is raised if the task identified by T has already terminated. Program_Error
is raised if the value of T is Ada.Task_Identification.Null_Task_Id.16/2
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An exception propagated from a handler that is
invoked as part of the termination of a task has no effect.Erroneous Execution
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For a call of Set_Specific_Handler or Specific_Handler,
if the task identified by T no longer exists, the execution of the program
is erroneous. Extensions to Ada 95
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{extensions to Ada 95} Package
Task_Termination is new.
Sponsored by Ada-Europe