Mercurial > hg > CbC > CbC_gcc
comparison gcc/ada/libgnat/s-tasloc.ads @ 111:04ced10e8804
gcc 7
| author | kono |
|---|---|
| date | Fri, 27 Oct 2017 22:46:09 +0900 |
| parents | |
| children | 84e7813d76e9 |
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| 68:561a7518be6b | 111:04ced10e8804 |
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| 1 ------------------------------------------------------------------------------ | |
| 2 -- -- | |
| 3 -- GNAT RUN-TIME COMPONENTS -- | |
| 4 -- -- | |
| 5 -- S Y S T E M . T A S K _ L O C K -- | |
| 6 -- -- | |
| 7 -- S p e c -- | |
| 8 -- -- | |
| 9 -- Copyright (C) 1998-2017, AdaCore -- | |
| 10 -- -- | |
| 11 -- GNAT is free software; you can redistribute it and/or modify it under -- | |
| 12 -- terms of the GNU General Public License as published by the Free Soft- -- | |
| 13 -- ware Foundation; either version 3, or (at your option) any later ver- -- | |
| 14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- | |
| 15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- | |
| 16 -- or FITNESS FOR A PARTICULAR PURPOSE. -- | |
| 17 -- -- | |
| 18 -- As a special exception under Section 7 of GPL version 3, you are granted -- | |
| 19 -- additional permissions described in the GCC Runtime Library Exception, -- | |
| 20 -- version 3.1, as published by the Free Software Foundation. -- | |
| 21 -- -- | |
| 22 -- You should have received a copy of the GNU General Public License and -- | |
| 23 -- a copy of the GCC Runtime Library Exception along with this program; -- | |
| 24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- | |
| 25 -- <http://www.gnu.org/licenses/>. -- | |
| 26 -- -- | |
| 27 -- GNAT was originally developed by the GNAT team at New York University. -- | |
| 28 -- Extensive contributions were provided by Ada Core Technologies Inc. -- | |
| 29 -- -- | |
| 30 ------------------------------------------------------------------------------ | |
| 31 | |
| 32 -- Simple task lock and unlock routines | |
| 33 | |
| 34 -- A small package containing a task lock and unlock routines for creating | |
| 35 -- a critical region. The lock involved is a global lock, shared by all | |
| 36 -- tasks, and by all calls to these routines, so these routines should be | |
| 37 -- used with care to avoid unnecessary reduction of concurrency. | |
| 38 | |
| 39 -- These routines may be used in a non-tasking program, and in that case | |
| 40 -- they have no effect (they do NOT cause the tasking runtime to be loaded). | |
| 41 | |
| 42 -- Note: this package is in the System hierarchy so that it can be directly | |
| 43 -- be used by other predefined packages. User access to this package is via | |
| 44 -- a renaming of this package in GNAT.Task_Lock (file g-tasloc.ads). | |
| 45 | |
| 46 package System.Task_Lock is | |
| 47 pragma Preelaborate; | |
| 48 | |
| 49 procedure Lock; | |
| 50 pragma Inline (Lock); | |
| 51 -- Acquires the global lock, starts the execution of a critical region | |
| 52 -- which no other task can enter until the locking task calls Unlock | |
| 53 | |
| 54 procedure Unlock; | |
| 55 pragma Inline (Unlock); | |
| 56 -- Releases the global lock, allowing another task to successfully | |
| 57 -- complete a Lock operation. Terminates the critical region. | |
| 58 -- | |
| 59 -- The recommended protocol for using these two procedures is as | |
| 60 -- follows: | |
| 61 -- | |
| 62 -- Locked_Processing : begin | |
| 63 -- Lock; | |
| 64 -- ... | |
| 65 -- TSL.Unlock; | |
| 66 -- | |
| 67 -- exception | |
| 68 -- when others => | |
| 69 -- Unlock; | |
| 70 -- raise; | |
| 71 -- end Locked_Processing; | |
| 72 -- | |
| 73 -- This ensures that the lock is not left set if an exception is raised | |
| 74 -- explicitly or implicitly during the critical locked region. | |
| 75 -- | |
| 76 -- Note on multiple calls to Lock: It is permissible to call Lock | |
| 77 -- more than once with no intervening Unlock from a single task, | |
| 78 -- and the lock will not be released until the corresponding number | |
| 79 -- of Unlock operations has been performed. For example: | |
| 80 -- | |
| 81 -- System.Task_Lock.Lock; -- acquires lock | |
| 82 -- System.Task_Lock.Lock; -- no effect | |
| 83 -- System.Task_Lock.Lock; -- no effect | |
| 84 -- System.Task_Lock.Unlock; -- no effect | |
| 85 -- System.Task_Lock.Unlock; -- no effect | |
| 86 -- System.Task_Lock.Unlock; -- releases lock | |
| 87 -- | |
| 88 -- However, as previously noted, the Task_Lock facility should only | |
| 89 -- be used for very local locks where the probability of conflict is | |
| 90 -- low, so usually this kind of nesting is not a good idea in any case. | |
| 91 -- In more complex locking situations, it is more appropriate to define | |
| 92 -- an appropriate protected type to provide the required locking. | |
| 93 -- | |
| 94 -- It is an error to call Unlock when there has been no prior call to | |
| 95 -- Lock. The effect of such an erroneous call is undefined, and may | |
| 96 -- result in deadlock, or other malfunction of the run-time system. | |
| 97 | |
| 98 end System.Task_Lock; |