Daily bump.
[official-gcc.git] / gcc / ada / s-taprop.ads
blob6f15ce7f55e93302317107d89e90d76029409daf
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
4 -- --
5 -- S Y S T E M . T A S K _ P R I M I T I V E S .O P E R A T I O N S --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 1992-2011, Free Software Foundation, Inc. --
10 -- --
11 -- GNARL 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 -- GNARL was developed by the GNARL team at Florida State University. --
28 -- Extensive contributions were provided by Ada Core Technologies, Inc. --
29 -- --
30 ------------------------------------------------------------------------------
32 -- This package contains all the GNULL primitives that interface directly with
33 -- the underlying OS.
35 with System.Parameters;
36 with System.Tasking;
37 with System.OS_Interface;
39 package System.Task_Primitives.Operations is
40 pragma Preelaborate;
42 package ST renames System.Tasking;
43 package OSI renames System.OS_Interface;
45 procedure Initialize (Environment_Task : ST.Task_Id);
46 -- Perform initialization and set up of the environment task for proper
47 -- operation of the tasking run-time. This must be called once, before any
48 -- other subprograms of this package are called.
50 procedure Create_Task
51 (T : ST.Task_Id;
52 Wrapper : System.Address;
53 Stack_Size : System.Parameters.Size_Type;
54 Priority : System.Any_Priority;
55 Succeeded : out Boolean);
56 pragma Inline (Create_Task);
57 -- Create a new low-level task with ST.Task_Id T and place other needed
58 -- information in the ATCB.
60 -- A new thread of control is created, with a stack of at least Stack_Size
61 -- storage units, and the procedure Wrapper is called by this new thread
62 -- of control. If Stack_Size = Unspecified_Storage_Size, choose a default
63 -- stack size; this may be effectively "unbounded" on some systems.
65 -- The newly created low-level task is associated with the ST.Task_Id T
66 -- such that any subsequent call to Self from within the context of the
67 -- low-level task returns T.
69 -- The caller is responsible for ensuring that the storage of the Ada
70 -- task control block object pointed to by T persists for the lifetime
71 -- of the new task.
73 -- Succeeded is set to true unless creation of the task failed,
74 -- as it may if there are insufficient resources to create another task.
76 procedure Enter_Task (Self_ID : ST.Task_Id);
77 pragma Inline (Enter_Task);
78 -- Initialize data structures specific to the calling task. Self must be
79 -- the ID of the calling task. It must be called (once) by the task
80 -- immediately after creation, while abort is still deferred. The effects
81 -- of other operations defined below are not defined unless the caller has
82 -- previously called Initialize_Task.
84 procedure Exit_Task;
85 pragma Inline (Exit_Task);
86 -- Destroy the thread of control. Self must be the ID of the calling task.
87 -- The effects of further calls to operations defined below on the task
88 -- are undefined thereafter.
90 ----------------------------------
91 -- ATCB allocation/deallocation --
92 ----------------------------------
94 package ATCB_Allocation is
96 function New_ATCB (Entry_Num : ST.Task_Entry_Index) return ST.Task_Id;
97 pragma Inline (New_ATCB);
98 -- Allocate a new ATCB with the specified number of entries
100 procedure Free_ATCB (T : ST.Task_Id);
101 pragma Inline (Free_ATCB);
102 -- Deallocate an ATCB previously allocated by New_ATCB
104 end ATCB_Allocation;
106 function New_ATCB (Entry_Num : ST.Task_Entry_Index) return ST.Task_Id
107 renames ATCB_Allocation.New_ATCB;
109 procedure Initialize_TCB (Self_ID : ST.Task_Id; Succeeded : out Boolean);
110 pragma Inline (Initialize_TCB);
111 -- Initialize all fields of the TCB
113 procedure Finalize_TCB (T : ST.Task_Id);
114 pragma Inline (Finalize_TCB);
115 -- Finalizes Private_Data of ATCB, and then deallocates it. This is also
116 -- responsible for recovering any storage or other resources that were
117 -- allocated by Create_Task (the one in this package). This should only be
118 -- called from Free_Task. After it is called there should be no further
119 -- reference to the ATCB that corresponds to T.
121 procedure Abort_Task (T : ST.Task_Id);
122 pragma Inline (Abort_Task);
123 -- Abort the task specified by T (the target task). This causes the target
124 -- task to asynchronously raise Abort_Signal if abort is not deferred, or
125 -- if it is blocked on an interruptible system call.
127 -- precondition:
128 -- the calling task is holding T's lock and has abort deferred
130 -- postcondition:
131 -- the calling task is holding T's lock and has abort deferred.
133 -- ??? modify GNARL to skip wakeup and always call Abort_Task
135 function Self return ST.Task_Id;
136 pragma Inline (Self);
137 -- Return a pointer to the Ada Task Control Block of the calling task
139 type Lock_Level is
140 (PO_Level,
141 Global_Task_Level,
142 RTS_Lock_Level,
143 ATCB_Level);
144 -- Type used to describe kind of lock for second form of Initialize_Lock
145 -- call specified below. See locking rules in System.Tasking (spec) for
146 -- more details.
148 procedure Initialize_Lock
149 (Prio : System.Any_Priority;
150 L : not null access Lock);
151 procedure Initialize_Lock
152 (L : not null access RTS_Lock;
153 Level : Lock_Level);
154 pragma Inline (Initialize_Lock);
155 -- Initialize a lock object
157 -- For Lock, Prio is the ceiling priority associated with the lock. For
158 -- RTS_Lock, the ceiling is implicitly Priority'Last.
160 -- If the underlying system does not support priority ceiling
161 -- locking, the Prio parameter is ignored.
163 -- The effect of either initialize operation is undefined unless is a lock
164 -- object that has not been initialized, or which has been finalized since
165 -- it was last initialized.
167 -- The effects of the other operations on lock objects are undefined
168 -- unless the lock object has been initialized and has not since been
169 -- finalized.
171 -- Initialization of the per-task lock is implicit in Create_Task
173 -- These operations raise Storage_Error if a lack of storage is detected
175 procedure Finalize_Lock (L : not null access Lock);
176 procedure Finalize_Lock (L : not null access RTS_Lock);
177 pragma Inline (Finalize_Lock);
178 -- Finalize a lock object, freeing any resources allocated by the
179 -- corresponding Initialize_Lock operation.
181 procedure Write_Lock
182 (L : not null access Lock;
183 Ceiling_Violation : out Boolean);
184 procedure Write_Lock
185 (L : not null access RTS_Lock;
186 Global_Lock : Boolean := False);
187 procedure Write_Lock
188 (T : ST.Task_Id);
189 pragma Inline (Write_Lock);
190 -- Lock a lock object for write access. After this operation returns,
191 -- the calling task holds write permission for the lock object. No other
192 -- Write_Lock or Read_Lock operation on the same lock object will return
193 -- until this task executes an Unlock operation on the same object. The
194 -- effect is undefined if the calling task already holds read or write
195 -- permission for the lock object L.
197 -- For the operation on Lock, Ceiling_Violation is set to true iff the
198 -- operation failed, which will happen if there is a priority ceiling
199 -- violation.
201 -- For the operation on RTS_Lock, Global_Lock should be set to True
202 -- if L is a global lock (Single_RTS_Lock, Global_Task_Lock).
204 -- For the operation on ST.Task_Id, the lock is the special lock object
205 -- associated with that task's ATCB. This lock has effective ceiling
206 -- priority high enough that it is safe to call by a task with any
207 -- priority in the range System.Priority. It is implicitly initialized
208 -- by task creation. The effect is undefined if the calling task already
209 -- holds T's lock, or has interrupt-level priority. Finalization of the
210 -- per-task lock is implicit in Exit_Task.
212 procedure Read_Lock
213 (L : not null access Lock;
214 Ceiling_Violation : out Boolean);
215 pragma Inline (Read_Lock);
216 -- Lock a lock object for read access. After this operation returns,
217 -- the calling task has non-exclusive read permission for the logical
218 -- resources that are protected by the lock. No other Write_Lock operation
219 -- on the same object will return until this task and any other tasks with
220 -- read permission for this lock have executed Unlock operation(s) on the
221 -- lock object. A Read_Lock for a lock object may return immediately while
222 -- there are tasks holding read permission, provided there are no tasks
223 -- holding write permission for the object. The effect is undefined if
224 -- the calling task already holds read or write permission for L.
226 -- Alternatively: An implementation may treat Read_Lock identically to
227 -- Write_Lock. This simplifies the implementation, but reduces the level
228 -- of concurrency that can be achieved.
230 -- Note that Read_Lock is not defined for RT_Lock and ST.Task_Id.
231 -- That is because (1) so far Read_Lock has always been implemented
232 -- the same as Write_Lock, (2) most lock usage inside the RTS involves
233 -- potential write access, and (3) implementations of priority ceiling
234 -- locking that make a reader-writer distinction have higher overhead.
236 procedure Unlock
237 (L : not null access Lock);
238 procedure Unlock
239 (L : not null access RTS_Lock;
240 Global_Lock : Boolean := False);
241 procedure Unlock
242 (T : ST.Task_Id);
243 pragma Inline (Unlock);
244 -- Unlock a locked lock object
246 -- The effect is undefined unless the calling task holds read or write
247 -- permission for the lock L, and L is the lock object most recently
248 -- locked by the calling task for which the calling task still holds
249 -- read or write permission. (That is, matching pairs of Lock and Unlock
250 -- operations on each lock object must be properly nested.)
252 -- For the operation on RTS_Lock, Global_Lock should be set to True if L
253 -- is a global lock (Single_RTS_Lock, Global_Task_Lock).
255 -- Note that Write_Lock for RTS_Lock does not have an out-parameter.
256 -- RTS_Locks are used in situations where we have not made provision for
257 -- recovery from ceiling violations. We do not expect them to occur inside
258 -- the runtime system, because all RTS locks have ceiling Priority'Last.
260 -- There is one way there can be a ceiling violation. That is if the
261 -- runtime system is called from a task that is executing in the
262 -- Interrupt_Priority range.
264 -- It is not clear what to do about ceiling violations due to RTS calls
265 -- done at interrupt priority. In general, it is not acceptable to give
266 -- all RTS locks interrupt priority, since that would give terrible
267 -- performance on systems where this has the effect of masking hardware
268 -- interrupts, though we could get away allowing Interrupt_Priority'last
269 -- where we are layered on an OS that does not allow us to mask interrupts.
270 -- Ideally, we would like to raise Program_Error back at the original point
271 -- of the RTS call, but this would require a lot of detailed analysis and
272 -- recoding, with almost certain performance penalties.
274 -- For POSIX systems, we considered just skipping setting priority ceiling
275 -- on RTS locks. This would mean there is no ceiling violation, but we
276 -- would end up with priority inversions inside the runtime system,
277 -- resulting in failure to satisfy the Ada priority rules, and possible
278 -- missed validation tests. This could be compensated-for by explicit
279 -- priority-change calls to raise the caller to Priority'Last whenever it
280 -- first enters the runtime system, but the expected overhead seems high,
281 -- though it might be lower than using locks with ceilings if the
282 -- underlying implementation of ceiling locks is an inefficient one.
284 -- This issue should be reconsidered whenever we get around to checking
285 -- for calls to potentially blocking operations from within protected
286 -- operations. If we check for such calls and catch them on entry to the
287 -- OS, it may be that we can eliminate the possibility of ceiling
288 -- violations inside the RTS. For this to work, we would have to forbid
289 -- explicitly setting the priority of a task to anything in the
290 -- Interrupt_Priority range, at least. We would also have to check that
291 -- there are no RTS-lock operations done inside any operations that are
292 -- not treated as potentially blocking.
294 -- The latter approach seems to be the best, i.e. to check on entry to RTS
295 -- calls that may need to use locks that the priority is not in the
296 -- interrupt range. If there are RTS operations that NEED to be called
297 -- from interrupt handlers, those few RTS locks should then be converted
298 -- to PO-type locks, with ceiling Interrupt_Priority'Last.
300 -- For now, we will just shut down the system if there is ceiling violation
302 procedure Set_Ceiling
303 (L : not null access Lock;
304 Prio : System.Any_Priority);
305 pragma Inline (Set_Ceiling);
306 -- Change the ceiling priority associated to the lock
308 -- The effect is undefined unless the calling task holds read or write
309 -- permission for the lock L, and L is the lock object most recently
310 -- locked by the calling task for which the calling task still holds
311 -- read or write permission. (That is, matching pairs of Lock and Unlock
312 -- operations on each lock object must be properly nested.)
314 procedure Yield (Do_Yield : Boolean := True);
315 pragma Inline (Yield);
316 -- Yield the processor. Add the calling task to the tail of the ready queue
317 -- for its active_priority. On most platforms, Yield is a no-op if Do_Yield
318 -- is False. But on some platforms (notably VxWorks), Do_Yield is ignored.
319 -- This is only used in some very rare cases where a Yield should have an
320 -- effect on a specific target and not on regular ones.
322 procedure Set_Priority
323 (T : ST.Task_Id;
324 Prio : System.Any_Priority;
325 Loss_Of_Inheritance : Boolean := False);
326 pragma Inline (Set_Priority);
327 -- Set the priority of the task specified by T to T.Current_Priority. The
328 -- priority set is what would correspond to the Ada concept of "base
329 -- priority" in the terms of the lower layer system, but the operation may
330 -- be used by the upper layer to implement changes in "active priority"
331 -- that are not due to lock effects. The effect should be consistent with
332 -- the Ada Reference Manual. In particular, when a task lowers its
333 -- priority due to the loss of inherited priority, it goes at the head of
334 -- the queue for its new priority (RM D.2.2 par 9). Loss_Of_Inheritance
335 -- helps the underlying implementation to do it right when the OS doesn't.
337 function Get_Priority (T : ST.Task_Id) return System.Any_Priority;
338 pragma Inline (Get_Priority);
339 -- Returns the priority last set by Set_Priority for this task
341 function Monotonic_Clock return Duration;
342 pragma Inline (Monotonic_Clock);
343 -- Returns "absolute" time, represented as an offset relative to "the
344 -- Epoch", which is Jan 1, 1970. This clock implementation is immune to
345 -- the system's clock changes.
347 function RT_Resolution return Duration;
348 pragma Inline (RT_Resolution);
349 -- Returns resolution of the underlying clock used to implement RT_Clock
351 ----------------
352 -- Extensions --
353 ----------------
355 -- Whoever calls either of the Sleep routines is responsible for checking
356 -- for pending aborts before the call. Pending priority changes are handled
357 -- internally.
359 procedure Sleep
360 (Self_ID : ST.Task_Id;
361 Reason : System.Tasking.Task_States);
362 pragma Inline (Sleep);
363 -- Wait until the current task, T, is signaled to wake up
365 -- precondition:
366 -- The calling task is holding its own ATCB lock
367 -- and has abort deferred
369 -- postcondition:
370 -- The calling task is holding its own ATCB lock and has abort deferred.
372 -- The effect is to atomically unlock T's lock and wait, so that another
373 -- task that is able to lock T's lock can be assured that the wait has
374 -- actually commenced, and that a Wakeup operation will cause the waiting
375 -- task to become ready for execution once again. When Sleep returns, the
376 -- waiting task will again hold its own ATCB lock. The waiting task may
377 -- become ready for execution at any time (that is, spurious wakeups are
378 -- permitted), but it will definitely become ready for execution when a
379 -- Wakeup operation is performed for the same task.
381 procedure Timed_Sleep
382 (Self_ID : ST.Task_Id;
383 Time : Duration;
384 Mode : ST.Delay_Modes;
385 Reason : System.Tasking.Task_States;
386 Timedout : out Boolean;
387 Yielded : out Boolean);
388 -- Combination of Sleep (above) and Timed_Delay
390 procedure Timed_Delay
391 (Self_ID : ST.Task_Id;
392 Time : Duration;
393 Mode : ST.Delay_Modes);
394 -- Implement the semantics of the delay statement.
395 -- The caller should be abort-deferred and should not hold any locks.
397 procedure Wakeup
398 (T : ST.Task_Id;
399 Reason : System.Tasking.Task_States);
400 pragma Inline (Wakeup);
401 -- Wake up task T if it is waiting on a Sleep call (of ordinary
402 -- or timed variety), making it ready for execution once again.
403 -- If the task T is not waiting on a Sleep, the operation has no effect.
405 function Environment_Task return ST.Task_Id;
406 pragma Inline (Environment_Task);
407 -- Return the task ID of the environment task
408 -- Consider putting this into a variable visible directly
409 -- by the rest of the runtime system. ???
411 function Get_Thread_Id (T : ST.Task_Id) return OSI.Thread_Id;
412 -- Return the thread id of the specified task
414 function Is_Valid_Task return Boolean;
415 pragma Inline (Is_Valid_Task);
416 -- Does the calling thread have an ATCB?
418 function Register_Foreign_Thread return ST.Task_Id;
419 -- Allocate and initialize a new ATCB for the current thread
421 -----------------------
422 -- RTS Entrance/Exit --
423 -----------------------
425 -- Following two routines are used for possible operations needed to be
426 -- setup/cleared upon entrance/exit of RTS while maintaining a single
427 -- thread of control in the RTS. Since we intend these routines to be used
428 -- for implementing the Single_Lock RTS, Lock_RTS should follow the first
429 -- Defer_Abort operation entering RTS. In the same fashion Unlock_RTS
430 -- should precede the last Undefer_Abort exiting RTS.
432 -- These routines also replace the functions Lock/Unlock_All_Tasks_List
434 procedure Lock_RTS;
435 -- Take the global RTS lock
437 procedure Unlock_RTS;
438 -- Release the global RTS lock
440 --------------------
441 -- Stack Checking --
442 --------------------
444 -- Stack checking in GNAT is done using the concept of stack probes. A
445 -- stack probe is an operation that will generate a storage error if
446 -- an insufficient amount of stack space remains in the current task.
448 -- The exact mechanism for a stack probe is target dependent. Typical
449 -- possibilities are to use a load from a non-existent page, a store to a
450 -- read-only page, or a comparison with some stack limit constant. Where
451 -- possible we prefer to use a trap on a bad page access, since this has
452 -- less overhead. The generation of stack probes is either automatic if
453 -- the ABI requires it (as on for example DEC Unix), or is controlled by
454 -- the gcc parameter -fstack-check.
456 -- When we are using bad-page accesses, we need a bad page, called guard
457 -- page, at the end of each task stack. On some systems, this is provided
458 -- automatically, but on other systems, we need to create the guard page
459 -- ourselves, and the procedure Stack_Guard is provided for this purpose.
461 procedure Stack_Guard (T : ST.Task_Id; On : Boolean);
462 -- Ensure guard page is set if one is needed and the underlying thread
463 -- system does not provide it. The procedure is as follows:
465 -- 1. When we create a task adjust its size so a guard page can
466 -- safely be set at the bottom of the stack.
468 -- 2. When the thread is created (and its stack allocated by the
469 -- underlying thread system), get the stack base (and size, depending
470 -- how the stack is growing), and create the guard page taking care
471 -- of page boundaries issues.
473 -- 3. When the task is destroyed, remove the guard page.
475 -- If On is true then protect the stack bottom (i.e make it read only)
476 -- else unprotect it (i.e. On is True for the call when creating a task,
477 -- and False when a task is destroyed).
479 -- The call to Stack_Guard has no effect if guard pages are not used on
480 -- the target, or if guard pages are automatically provided by the system.
482 ------------------------
483 -- Suspension objects --
484 ------------------------
486 -- These subprograms provide the functionality required for synchronizing
487 -- on a suspension object. Tasks can suspend execution and relinquish the
488 -- processors until the condition is signaled.
490 function Current_State (S : Suspension_Object) return Boolean;
491 -- Return the state of the suspension object
493 procedure Set_False (S : in out Suspension_Object);
494 -- Set the state of the suspension object to False
496 procedure Set_True (S : in out Suspension_Object);
497 -- Set the state of the suspension object to True. If a task were
498 -- suspended on the protected object then this task is released (and
499 -- the state of the suspension object remains set to False).
501 procedure Suspend_Until_True (S : in out Suspension_Object);
502 -- If the state of the suspension object is True then the calling task
503 -- continues its execution, and the state is set to False. If the state
504 -- of the object is False then the task is suspended on the suspension
505 -- object until a Set_True operation is executed. Program_Error is raised
506 -- if another task is already waiting on that suspension object.
508 procedure Initialize (S : in out Suspension_Object);
509 -- Initialize the suspension object
511 procedure Finalize (S : in out Suspension_Object);
512 -- Finalize the suspension object
514 -----------------------------------------
515 -- Runtime System Debugging Interfaces --
516 -----------------------------------------
518 -- These interfaces have been added to assist in debugging the
519 -- tasking runtime system.
521 function Check_Exit (Self_ID : ST.Task_Id) return Boolean;
522 pragma Inline (Check_Exit);
523 -- Check that the current task is holding only Global_Task_Lock
525 function Check_No_Locks (Self_ID : ST.Task_Id) return Boolean;
526 pragma Inline (Check_No_Locks);
527 -- Check that current task is holding no locks
529 function Suspend_Task
530 (T : ST.Task_Id;
531 Thread_Self : OSI.Thread_Id) return Boolean;
532 -- Suspend a specific task when the underlying thread library provides this
533 -- functionality, unless the thread associated with T is Thread_Self. Such
534 -- functionality is needed by gdb on some targets (e.g VxWorks) Return True
535 -- is the operation is successful. On targets where this operation is not
536 -- available, a dummy body is present which always returns False.
538 function Resume_Task
539 (T : ST.Task_Id;
540 Thread_Self : OSI.Thread_Id) return Boolean;
541 -- Resume a specific task when the underlying thread library provides
542 -- such functionality, unless the thread associated with T is Thread_Self.
543 -- Such functionality is needed by gdb on some targets (e.g VxWorks)
544 -- Return True is the operation is successful
546 procedure Stop_All_Tasks;
547 -- Stop all tasks when the underlying thread library provides such
548 -- functionality. Such functionality is needed by gdb on some targets (e.g
549 -- VxWorks) This function can be run from an interrupt handler. Return True
550 -- is the operation is successful
552 function Stop_Task (T : ST.Task_Id) return Boolean;
553 -- Stop a specific task when the underlying thread library provides
554 -- such functionality. Such functionality is needed by gdb on some targets
555 -- (e.g VxWorks). Return True is the operation is successful.
557 function Continue_Task (T : ST.Task_Id) return Boolean;
558 -- Continue a specific task when the underlying thread library provides
559 -- such functionality. Such functionality is needed by gdb on some targets
560 -- (e.g VxWorks) Return True is the operation is successful
562 -------------------
563 -- Task affinity --
564 -------------------
566 procedure Set_Task_Affinity (T : ST.Task_Id);
567 -- Enforce at the operating system level the task affinity defined in the
568 -- Ada Task Control Block. Has no effect if the underlying operating system
569 -- does not support this capability.
571 end System.Task_Primitives.Operations;