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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:
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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. 
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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.
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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.

Metrics

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The implementation shall document the following metric:
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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;
NOTES
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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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