D.5.2 Dynamic Priorities for Protected Objects
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This clause specifies how the priority of a protected
object can be modified or queried at run time. Static Semantics
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The following attribute is defined for a prefix
P that denotes a protected object:3/2
P'Priority
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AI95-00327-01}
Denotes a non-aliased
component of the protected object P. This component is of type System.Any_Priority
and its value is the priority of P. P'Priority denotes a variable if
and only if P denotes a variable. A reference to this attribute shall
appear only within the body of P.
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The initial value of this attribute is the initial
value of the priority of the protected object[, and can be changed by
an assignment]. Dynamic Semantics
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If the locking policy Ceiling_Locking (see D.3)
is in effect then the ceiling priority of a protected object P
is set to the value of P'Priority at the end of each protected
action of P.6/2
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If the locking policy Ceiling_Locking is in effect,
then for a protected object P with either an Attach_Handler or
Interrupt_Handler pragma applying to one of its procedures, a check is
made that the value to be assigned to P'Priority is in the range
System.Interrupt_Priority. If the check fails, Program_Error is raised.{Program_Error
(raised by failure of run-time check)} Metrics
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The implementation shall document the following
metric:8/2
- The
difference in execution time of calls to the following procedures in
protected object P:
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protected P is
procedure Do_Not_Set_Ceiling (Pr : System.Any_Priority);
procedure Set_Ceiling (Pr : System.Any_Priority);
end P;
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protected body P is
procedure Do_Not_Set_Ceiling (Pr : System.Any_Priority) is
begin
null;
end;
procedure Set_Ceiling (Pr : System.Any_Priority) is
begin
P'Priority := Pr;
end;
end P;
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Documentation Requirement:
The metrics for setting the priority
of a protected object.
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Since P'Priority is a normal variable, the value
following an assignment to the attribute immediately reflects the new
value even though its impact on the ceiling priority of P is postponed
until completion of the protected action in which it is executed.
Extensions to Ada 95
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{extensions to Ada 95} The
ability to dynamically change and query the priority of a protected object
is new.
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