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Diffstat (limited to 'gcc/ada/s-tasloc.ads')
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diff --git a/gcc/ada/s-tasloc.ads b/gcc/ada/s-tasloc.ads new file mode 100755 index 00000000000..804eca0a7fe --- /dev/null +++ b/gcc/ada/s-tasloc.ads @@ -0,0 +1,100 @@ +------------------------------------------------------------------------------ +-- -- +-- GNAT RUN-TIME COMPONENTS -- +-- -- +-- S Y S T E M . T A S K _ L O C K -- +-- -- +-- S p e c -- +-- -- +-- Copyright (C) 1998-2007, 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 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, 51 Franklin Street, Fifth Floor, -- +-- Boston, MA 02110-1301, 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 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 Elaborate_Body; + + 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; |