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.
The following attribute is defined for a prefix
P that denotes a protected object:
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].
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
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.
The implementation shall document the following metric:
The difference in
execution time of calls to the following procedures in protected object
protected P is
procedure Do_Not_Set_Ceiling (Pr : System.Any_Priority);
procedure Set_Ceiling (Pr : System.Any_Priority);
protected body P is
procedure Do_Not_Set_Ceiling (Pr : System.Any_Priority) is
procedure Set_Ceiling (Pr : System.Any_Priority) is
P'Priority := Pr;
Documentation Requirement: The metrics
for setting the priority of a protected object.
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
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe