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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- G N A T . T A S K _ L O C K --
-- --
-- S p e c --
-- --
-- --
-- Copyright (C) 1998-2001 Ada Core Technologies, Inc. --
-- --
-- GNAT 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 2, or (at your option) any later ver- --
-- sion. GNAT 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. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
-- Public License distributed with GNAT; see file COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
-- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
-- --
-- GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
-- Simple task lock and unlock routines
-- A small package containing a task lock and unlock routines for creating
-- a critical region. The lock involved is a global lock, shared by all
-- tasks, and by all calls to these routines, so these routines should be
-- used with care to avoid unnecessary reduction of concurrency.
-- These routines may be used in a non-tasking program, and in that case
-- they have no effect (they do NOT cause the tasking runtime to be loaded).
package GNAT.Task_Lock is
pragma Elaborate_Body (Task_Lock);
procedure Lock;
pragma Inline (Lock);
-- Acquires the global lock, starts the execution of a critical region
-- which no other task can enter until the locking task calls Unlock
procedure Unlock;
pragma Inline (Unlock);
-- Releases the global lock, allowing another task to successfully
-- complete a Lock operation. Terminates the critical region.
-- The recommended protocol for using these two procedures is as
-- follows:
-- Locked_Processing : begin
-- Lock;
-- ...
-- TSL.Unlock;
--
-- exception
-- when others =>
-- Unlock;
-- raise;
-- end Locked_Processing;
-- This ensures that the lock is not left set if an exception is raised
-- explicitly or implicitly during the critical locked region.
-- Note on multiple calls to Lock: It is permissible to call Lock
-- more than once with no intervening Unlock from a single task,
-- and the lock will not be released until the corresponding number
-- of Unlock operations has been performed. For example:
-- GNAT.Task_Lock.Lock; -- acquires lock
-- GNAT.Task_Lock.Lock; -- no effect
-- GNAT.Task_Lock.Lock; -- no effect
-- GNAT.Task_Lock.Unlock; -- no effect
-- GNAT.Task_Lock.Unlock; -- no effect
-- GNAT.Task_Lock.Unlock; -- releases lock
-- However, as previously noted, the Task_Lock facility should only
-- be used for very local locks where the probability of conflict is
-- low, so usually this kind of nesting is not a good idea in any case.
-- In more complex locking situations, it is more appropriate to define
-- an appropriate protected type to provide the required locking.
end GNAT.Task_Lock;
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