D.5.2 Dynamic Priorities for Protected Objects
This subclause specifies how the priority of a protected
object can be modified or queried at run time.
Static Semantics
The following attribute
is defined for a
prefix
P that denotes a protected object:
P'Priority
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.
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
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.
If the locking policy Ceiling_Locking is in effect,
then for a protected object
P with either an Attach_Handler or
Interrupt_Handler aspect specified for 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.
Metrics
The implementation
shall document the following metric:
The difference in
execution time of calls to the following procedures in protected object
P:
protected P is
procedure Do_Not_Set_Ceiling (Pr : System.Any_Priority);
procedure Set_Ceiling (Pr : System.Any_Priority);
end P;
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;
31 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.
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