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+------------------------------------------------------------------------------
+-- --
+-- GNAT RUN-TIME COMPONENTS --
+-- --
+-- S Y S T E M . T A S K _ L O C K --
+-- --
+-- S p e c --
+-- --
+-- Copyright (C) 1998-2013, AdaCore --
+-- --
+-- 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 3, 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. --
+-- --
+-- 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/>. --
+-- --
+-- GNAT was originally developed by the GNAT team at New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc. --
+-- --
+------------------------------------------------------------------------------
+
+-- 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).
+
+-- Note: this package is in the System hierarchy so that it can be directly
+-- be used by other predefined packages. User access to this package is via
+-- a renaming of this package in GNAT.Task_Lock (file g-tasloc.ads).
+
+package System.Task_Lock is
+ pragma Preelaborate;
+
+ 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:
+ --
+ -- System.Task_Lock.Lock; -- acquires lock
+ -- System.Task_Lock.Lock; -- no effect
+ -- System.Task_Lock.Lock; -- no effect
+ -- System.Task_Lock.Unlock; -- no effect
+ -- System.Task_Lock.Unlock; -- no effect
+ -- System.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.
+ --
+ -- It is an error to call Unlock when there has been no prior call to
+ -- Lock. The effect of such an erroneous call is undefined, and may
+ -- result in deadlock, or other malfunction of the run-time system.
+
+end System.Task_Lock;