New Language: Ada

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@45955 138bc75d-0d04-0410-961f-82ee72b054a4

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+------------------------------------------------------------------------------
+--                                                                          --
+--                         GNAT RUN-TIME COMPONENTS                         --
+--                                                                          --
+--                       G N A T . T A S K _ L O C K                        --
+--                                                                          --
+--                                 S p e c                                  --
+--                                                                          --
+--                            $Revision: 1.5 $
+--                                                                          --
+--            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;