D.5.2 Dynamic Priorities for Protected Objects
This clause 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
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 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
The implementation shall document the following
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);
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;
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