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175 | ------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . T A S K I N G . P R O T E C T E D _ O B J E C T S --
-- --
-- B o d y --
-- --
-- Copyright (C) 1992-2023, Free Software Foundation, Inc. --
-- --
-- GNARL is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNARL was developed by the GNARL team at Florida State University. --
-- Extensive contributions were provided by Ada Core Technologies, Inc. --
-- --
------------------------------------------------------------------------------
-- This is the Ravenscar version of this package
with System.Task_Primitives.Operations;
-- Used for Set_Priority
-- Get_Priority
-- Self
package body System.Tasking.Protected_Objects is
use System.Task_Primitives.Operations;
use System.Multiprocessors;
Multiprocessor : constant Boolean := CPU'Range_Length /= 1;
-- Set true if on multiprocessor (more than one CPU)
---------------------------
-- Initialize_Protection --
---------------------------
procedure Initialize_Protection
(Object : Protection_Access;
Ceiling_Priority : Integer)
is
Init_Priority : Integer := Ceiling_Priority;
begin
if Init_Priority = Unspecified_Priority then
Init_Priority := System.Priority'Last;
end if;
Object.Ceiling := System.Any_Priority (Init_Priority);
Object.Caller_Priority := System.Any_Priority'First;
Object.Owner := Null_Task;
-- Only for multiprocessor
if Multiprocessor then
Multiprocessors.Fair_Locks.Initialize (Object.Lock);
end if;
end Initialize_Protection;
----------
-- Lock --
----------
procedure Lock (Object : Protection_Access) is
Self_Id : constant Task_Id := Self;
Caller_Priority : constant Any_Priority := Get_Priority (Self_Id);
begin
-- For this run time, pragma Detect_Blocking is always active. As
-- described in ARM 9.5.1, par. 15, an external call on a protected
-- subprogram with the same target object as that of the protected
-- action that is currently in progress (i.e., if the caller is
-- already the protected object's owner) is a potentially blocking
-- operation, and hence Program_Error must be raised.
if Object.Owner = Self_Id then
raise Program_Error;
end if;
-- Check ceiling locking violation. It is perfectly correct to stay at
-- the same priority because a running task will never be preempted by
-- another task at the same priority (no potentially blocking operation,
-- no time slicing).
if Caller_Priority > Object.Ceiling then
raise Program_Error;
end if;
Set_Priority (Self_Id, Object.Ceiling);
-- Locking for multiprocessor systems
-- This lock ensure mutual exclusion of tasks from different processors,
-- not for tasks on the same processors. But, because of the ceiling
-- priority, this case never occurs.
if Multiprocessor then
-- Only for multiprocessor
Multiprocessors.Fair_Locks.Lock (Object.Lock);
end if;
-- Update the protected object's owner
Object.Owner := Self_Id;
-- Store caller's active priority so that it can be later
-- restored when finishing the protected action.
Object.Caller_Priority := Caller_Priority;
-- We are entering in a protected action, so that we increase the
-- protected object nesting level.
Self_Id.Common.Protected_Action_Nesting :=
Self_Id.Common.Protected_Action_Nesting + 1;
end Lock;
------------
-- Unlock --
------------
procedure Unlock (Object : Protection_Access) is
Self_Id : constant Task_Id := Self;
Caller_Priority : constant Any_Priority := Object.Caller_Priority;
begin
-- Calls to this procedure can only take place when being within a
-- protected action and when the caller is the protected object's
-- owner.
pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
and then Object.Owner = Self_Id);
-- Remove ownership of the protected object
Object.Owner := Null_Task;
-- We are exiting from a protected action, so that we decrease the
-- protected object nesting level.
Self_Id.Common.Protected_Action_Nesting :=
Self_Id.Common.Protected_Action_Nesting - 1;
-- Locking for multiprocessor systems
if Multiprocessor then
-- Only for multiprocessor
Multiprocessors.Fair_Locks.Unlock (Object.Lock);
end if;
Set_Priority (Self_Id, Caller_Priority);
end Unlock;
begin
-- Ensure that tasking is initialized when using protected objects
Tasking.Initialize;
end System.Tasking.Protected_Objects;
|