1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
5 -- S Y S T E M . T A S K I N G . I N I T I A L I Z A T I O N --
9 -- Copyright (C) 1992-2023, Free Software Foundation, Inc. --
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. --
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. --
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/>. --
27 -- GNARL was developed by the GNARL team at Florida State University. --
28 -- Extensive contributions were provided by Ada Core Technologies, Inc. --
30 ------------------------------------------------------------------------------
32 pragma Style_Checks
(All_Checks
);
33 -- Turn off subprogram alpha ordering check, since we group soft link bodies
34 -- and dummy soft link bodies together separately in this unit.
36 with System
.Task_Primitives
;
37 with System
.Task_Primitives
.Operations
;
38 with System
.Soft_Links
;
39 with System
.Soft_Links
.Tasking
;
40 with System
.Tasking
.Debug
;
41 with System
.Tasking
.Task_Attributes
;
43 with System
.Secondary_Stack
;
44 pragma Elaborate_All
(System
.Secondary_Stack
);
45 pragma Unreferenced
(System
.Secondary_Stack
);
46 -- Make sure the body of Secondary_Stack is elaborated before calling
47 -- Init_Tasking_Soft_Links. See comments for this routine for explanation.
49 package body System
.Tasking
.Initialization
is
51 package STPO
renames System
.Task_Primitives
.Operations
;
52 package SSL
renames System
.Soft_Links
;
55 use Task_Primitives
.Operations
;
57 Global_Task_Lock
: aliased System
.Task_Primitives
.RTS_Lock
;
58 -- This is a global lock; it is used to execute in mutual exclusion from
59 -- all other tasks. It is only used by Task_Lock, Task_Unlock, and
62 ----------------------------------------------------------------------
63 -- Tasking versions of some services needed by non-tasking programs --
64 ----------------------------------------------------------------------
66 procedure Abort_Defer
;
67 -- NON-INLINE versions without Self_ID for soft links
69 procedure Abort_Undefer
;
70 -- NON-INLINE versions without Self_ID for soft links
73 -- Locks out other tasks. Preceding a section of code by Task_Lock and
74 -- following it by Task_Unlock creates a critical region. This is used
75 -- for ensuring that a region of non-tasking code (such as code used to
76 -- allocate memory) is tasking safe. Note that it is valid for calls to
77 -- Task_Lock/Task_Unlock to be nested, and this must work properly, i.e.
78 -- only the corresponding outer level Task_Unlock will actually unlock.
80 procedure Task_Unlock
;
81 -- Releases lock previously set by call to Task_Lock. In the nested case,
82 -- all nested locks must be released before other tasks competing for the
83 -- tasking lock are released.
85 function Get_Current_Excep
return SSL
.EOA
;
86 -- Task-safe version of SSL.Get_Current_Excep
88 function Task_Name
return String;
89 -- Returns current task's name
91 ------------------------
92 -- Local Subprograms --
93 ------------------------
95 ----------------------------
96 -- Tasking Initialization --
97 ----------------------------
100 -- This procedure completes the initialization of the GNARL. The first part
101 -- of the initialization is done in the body of System.Tasking. It consists
102 -- of initializing global locks, and installing tasking versions of certain
103 -- operations used by the compiler. Init_RTS is called during elaboration.
105 --------------------------
106 -- Change_Base_Priority --
107 --------------------------
109 -- Call only with abort deferred and holding Self_ID locked
111 procedure Change_Base_Priority
(T
: Task_Id
) is
113 if T
.Common
.Base_Priority
/= T
.New_Base_Priority
then
114 T
.Common
.Base_Priority
:= T
.New_Base_Priority
;
115 Set_Priority
(T
, T
.Common
.Base_Priority
);
117 end Change_Base_Priority
;
119 ------------------------
120 -- Check_Abort_Status --
121 ------------------------
123 function Check_Abort_Status
return Integer is
124 Self_ID
: constant Task_Id
:= Self
;
127 and then Self_ID
.Deferral_Level
= 0
128 and then Self_ID
.Pending_ATC_Level
< Self_ID
.ATC_Nesting_Level
129 and then not Self_ID
.Aborting
135 end Check_Abort_Status
;
141 procedure Defer_Abort
(Self_ID
: Task_Id
) is
147 pragma Assert
(Self_ID
.Deferral_Level
= 0);
150 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level);
152 -- The above check has been useful in detecting mismatched defer/undefer
153 -- pairs. You may uncomment it when testing on systems that support
156 -- If the OS supports preemptive abort (e.g. pthread_kill), it should
157 -- have happened already. A problem is with systems that do not support
158 -- preemptive abort, and so rely on polling. On such systems we may get
159 -- false failures of the assertion, since polling for pending abort does
160 -- no occur until the abort undefer operation.
162 -- Even on systems that only poll for abort, the assertion may be useful
163 -- for catching missed abort completion polling points. The operations
164 -- that undefer abort poll for pending aborts. This covers most of the
165 -- places where the core Ada semantics require abort to be caught,
166 -- without any special attention. However, this generally happens on
167 -- exit from runtime system call, which means a pending abort will not
168 -- be noticed on the way into the runtime system. We considered adding a
169 -- check for pending aborts at this point, but chose not to, because of
170 -- the overhead. Instead, we searched for RTS calls where abort
171 -- completion is required and a task could go farther than Ada allows
172 -- before undeferring abort; we then modified the code to ensure the
173 -- abort would be detected.
175 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
178 --------------------------
179 -- Defer_Abort_Nestable --
180 --------------------------
182 procedure Defer_Abort_Nestable
(Self_ID
: Task_Id
) is
188 -- The following assertion is by default disabled. See the comment in
189 -- Defer_Abort on the situations in which it may be useful to uncomment
190 -- this assertion and enable the test.
193 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level or else
194 -- Self_ID.Deferral_Level > 0);
196 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
197 end Defer_Abort_Nestable
;
203 procedure Abort_Defer
is
210 Self_ID
:= STPO
.Self
;
211 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
214 -----------------------
215 -- Get_Current_Excep --
216 -----------------------
218 function Get_Current_Excep
return SSL
.EOA
is
220 return STPO
.Self
.Common
.Compiler_Data
.Current_Excep
'Access;
221 end Get_Current_Excep
;
223 -----------------------
224 -- Do_Pending_Action --
225 -----------------------
227 -- Call only when holding no locks
229 procedure Do_Pending_Action
(Self_ID
: Task_Id
) is
232 pragma Assert
(Self_ID
= Self
and then Self_ID
.Deferral_Level
= 0);
234 -- Needs loop to recheck for pending action in case a new one occurred
235 -- while we had abort deferred below.
238 -- Temporarily defer abort so that we can lock Self_ID
240 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
242 Write_Lock
(Self_ID
);
243 Self_ID
.Pending_Action
:= False;
246 -- Restore the original Deferral value
248 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
250 if not Self_ID
.Pending_Action
then
251 if Self_ID
.Pending_ATC_Level
< Self_ID
.ATC_Nesting_Level
then
252 if not Self_ID
.Aborting
then
253 Self_ID
.Aborting
:= True;
255 (Debug
.Trace
(Self_ID
, "raise Abort_Signal", 'B'));
256 raise Standard
'Abort_Signal;
258 pragma Assert
(not Self_ID
.ATC_Hack
);
260 elsif Self_ID
.ATC_Hack
then
262 -- The solution really belongs in the Abort_Signal handler
263 -- for async. entry calls. The present hack is very
264 -- fragile. It relies that the very next point after
265 -- Exit_One_ATC_Level at which the task becomes abortable
266 -- will be the call to Undefer_Abort in the
267 -- Abort_Signal handler.
269 Self_ID
.ATC_Hack
:= False;
273 (Self_ID
, "raise Abort_Signal (ATC hack)", 'B'));
274 raise Standard
'Abort_Signal;
281 end Do_Pending_Action
;
283 -----------------------
284 -- Final_Task_Unlock --
285 -----------------------
287 -- This version is only for use in Terminate_Task, when the task is
288 -- relinquishing further rights to its own ATCB.
290 -- There is a very interesting potential race condition there, where the
291 -- old task may run concurrently with a new task that is allocated the old
292 -- tasks (now reused) ATCB. The critical thing here is to not make any
293 -- reference to the ATCB after the lock is released. See also comments on
294 -- Terminate_Task and Unlock.
296 procedure Final_Task_Unlock
(Self_ID
: Task_Id
) is
298 pragma Assert
(Self_ID
.Common
.Global_Task_Lock_Nesting
= 1);
299 Unlock
(Global_Task_Lock
'Access);
300 end Final_Task_Unlock
;
306 procedure Init_RTS
is
311 -- Terminate run time (regular vs restricted) specific initialization
312 -- of the environment task.
314 Self_Id
:= Environment_Task
;
315 Self_Id
.Master_Of_Task
:= Environment_Task_Level
;
316 Self_Id
.Master_Within
:= Self_Id
.Master_Of_Task
+ 1;
318 for L
in Self_Id
.Entry_Calls
'Range loop
319 Self_Id
.Entry_Calls
(L
).Self
:= Self_Id
;
320 Self_Id
.Entry_Calls
(L
).Level
:= L
;
323 Self_Id
.Awake_Count
:= 1;
324 Self_Id
.Alive_Count
:= 1;
326 -- Normally, a task starts out with internal master nesting level one
327 -- larger than external master nesting level. It is incremented to one
328 -- by Enter_Master, which is called in the task body only if the
329 -- compiler thinks the task may have dependent tasks. There is no
330 -- corresponding call to Enter_Master for the environment task, so we
331 -- would need to increment it to 2 here. Instead, we set it to 3. By
332 -- doing this we reserve the level 2 for server tasks of the runtime
333 -- system. The environment task does not need to wait for these server
335 Self_Id
.Master_Within
:= Library_Task_Level
;
337 -- Initialize lock used to implement mutual exclusion between all tasks
339 Initialize_Lock
(Global_Task_Lock
'Access, STPO
.Global_Task_Level
);
341 -- Notify that the tasking run time has been elaborated so that
342 -- the tasking version of the soft links can be used.
345 SSL
.Abort_Defer
:= Abort_Defer
'Access;
346 SSL
.Abort_Undefer
:= Abort_Undefer
'Access;
349 SSL
.Lock_Task
:= Task_Lock
'Access;
350 SSL
.Unlock_Task
:= Task_Unlock
'Access;
351 SSL
.Check_Abort_Status
:= Check_Abort_Status
'Access;
352 SSL
.Task_Name
:= Task_Name
'Access;
353 SSL
.Get_Current_Excep
:= Get_Current_Excep
'Access;
355 -- Initialize the tasking soft links (if not done yet) that are common
356 -- to the full and the restricted run times.
358 SSL
.Tasking
.Init_Tasking_Soft_Links
;
360 -- Abort is deferred in a new ATCB, so we need to undefer abort at this
361 -- stage to make the environment task abortable.
363 Undefer_Abort
(Environment_Task
);
366 ---------------------------
367 -- Locked_Abort_To_Level--
368 ---------------------------
370 -- Abort a task to the specified ATC nesting level.
371 -- Call this only with T locked.
373 -- An earlier version of this code contained a call to Wakeup. That should
374 -- not be necessary here, if Abort_Task is implemented correctly, since
375 -- Abort_Task should include the effect of Wakeup. However, the above call
376 -- was in earlier versions of this file, and at least for some targets
377 -- Abort_Task has not been doing Wakeup. It should not hurt to uncomment
378 -- the above call, until the error is corrected for all targets.
380 -- See extended comments in package body System.Tasking.Abort for the
381 -- overall design of the implementation of task abort.
382 -- ??? there is no such package ???
384 -- If the task is sleeping it will be in an abort-deferred region, and will
385 -- not have Abort_Signal raised by Abort_Task. Such an "abort deferral" is
386 -- just to protect the RTS internals, and not necessarily required to
387 -- enforce Ada semantics. Abort_Task should wake the task up and let it
388 -- decide if it wants to complete the aborted construct immediately.
390 -- Note that the effect of the low-level Abort_Task is not persistent.
391 -- If the target task is not blocked, this wakeup will be missed.
393 -- We don't bother calling Abort_Task if this task is aborting itself,
394 -- since we are inside the RTS and have abort deferred. Similarly, We don't
395 -- bother to call Abort_Task if T is terminated, since there is no need to
396 -- abort a terminated task, and it could be dangerous to try if the task
397 -- has stopped executing.
399 -- Note that an earlier version of this code had some false reasoning about
400 -- being able to reliably wake up a task that had suspended on a blocking
401 -- system call that does not atomically release the task's lock (e.g., UNIX
402 -- nanosleep, which we once thought could be used to implement delays).
403 -- That still left the possibility of missed wakeups.
405 -- We cannot safely call Vulnerable_Complete_Activation here, since that
406 -- requires locking Self_ID.Parent. The anti-deadlock lock ordering rules
407 -- would then require us to release the lock on Self_ID first, which would
408 -- create a timing window for other tasks to lock Self_ID. This is
409 -- significant for tasks that may be aborted before their execution can
410 -- enter the task body, and so they do not get a chance to call
411 -- Complete_Task. The actual work for this case is done in Terminate_Task.
413 procedure Locked_Abort_To_Level
419 if not T
.Aborting
and then T
/= Self_ID
then
420 case T
.Common
.State
is
424 pragma Assert
(Standard
.False);
430 if T
.ATC_Nesting_Level
> Level_No_ATC_Occurring
then
431 -- This scenario occurs when an asynchronous protected entry
432 -- call is canceled during a requeue with abort.
435 (T
.ATC_Nesting_Level
).Cancellation_Attempted
:= True;
438 when Interrupt_Server_Blocked_On_Event_Flag
=>
441 when AST_Server_Sleep
444 | Interrupt_Server_Blocked_Interrupt_Sleep
445 | Interrupt_Server_Idle_Sleep
448 Wakeup
(T
, T
.Common
.State
);
450 when Acceptor_Delay_Sleep
453 T
.Open_Accepts
:= null;
454 Wakeup
(T
, T
.Common
.State
);
456 when Entry_Caller_Sleep
=>
457 pragma Assert
(T
.ATC_Nesting_Level
> Level_No_ATC_Occurring
);
460 (T
.ATC_Nesting_Level
).Cancellation_Attempted
:= True;
461 Wakeup
(T
, T
.Common
.State
);
465 | Master_Completion_Sleep
466 | Master_Phase_2_Sleep
472 if T
.Pending_ATC_Level
> L
then
473 T
.Pending_ATC_Level
:= L
;
474 T
.Pending_Action
:= True;
476 if L
= Level_Completed_Task
then
480 -- This prevents aborted task from accepting calls
484 -- The test above is just a heuristic, to reduce wasteful
485 -- calls to Abort_Task. We are holding T locked, and this
486 -- value will not be set to False except with T also locked,
487 -- inside Exit_One_ATC_Level, so we should not miss wakeups.
489 if T
.Common
.State
= Acceptor_Sleep
491 T
.Common
.State
= Acceptor_Delay_Sleep
493 T
.Open_Accepts
:= null;
496 elsif T
/= Self_ID
and then
497 (T
.Common
.State
= Runnable
498 or else T
.Common
.State
= Interrupt_Server_Blocked_On_Event_Flag
)
500 -- The task is blocked on a system call waiting for the
501 -- completion event. In this case Abort_Task may need to take
502 -- special action in order to succeed.
508 end Locked_Abort_To_Level
;
510 --------------------------------
511 -- Remove_From_All_Tasks_List --
512 --------------------------------
514 procedure Remove_From_All_Tasks_List
(T
: Task_Id
) is
520 (Debug
.Trace
(Self
, "Remove_From_All_Tasks_List", 'C'));
522 Previous
:= Null_Task
;
524 while C
/= Null_Task
loop
526 if Previous
= Null_Task
then
527 All_Tasks_List
:= All_Tasks_List
.Common
.All_Tasks_Link
;
529 Previous
.Common
.All_Tasks_Link
:= C
.Common
.All_Tasks_Link
;
536 C
:= C
.Common
.All_Tasks_Link
;
539 pragma Assert
(Standard
.False);
540 end Remove_From_All_Tasks_List
;
546 procedure Task_Lock
(Self_ID
: Task_Id
) is
548 Self_ID
.Common
.Global_Task_Lock_Nesting
:=
549 Self_ID
.Common
.Global_Task_Lock_Nesting
+ 1;
551 if Self_ID
.Common
.Global_Task_Lock_Nesting
= 1 then
552 Defer_Abort_Nestable
(Self_ID
);
553 Write_Lock
(Global_Task_Lock
'Access);
557 procedure Task_Lock
is
559 Task_Lock
(STPO
.Self
);
566 function Task_Name
return String is
567 Self_Id
: constant Task_Id
:= STPO
.Self
;
569 return Self_Id
.Common
.Task_Image
(1 .. Self_Id
.Common
.Task_Image_Len
);
576 procedure Task_Unlock
(Self_ID
: Task_Id
) is
578 pragma Assert
(Self_ID
.Common
.Global_Task_Lock_Nesting
> 0);
579 Self_ID
.Common
.Global_Task_Lock_Nesting
:=
580 Self_ID
.Common
.Global_Task_Lock_Nesting
- 1;
582 if Self_ID
.Common
.Global_Task_Lock_Nesting
= 0 then
583 Unlock
(Global_Task_Lock
'Access);
584 Undefer_Abort_Nestable
(Self_ID
);
588 procedure Task_Unlock
is
590 Task_Unlock
(STPO
.Self
);
597 -- Precondition : Self does not hold any locks
599 -- Undefer_Abort is called on any abort completion point (aka.
600 -- synchronization point). It performs the following actions if they
601 -- are pending: (1) change the base priority, (2) abort the task.
603 -- The priority change has to occur before abort. Otherwise, it would
604 -- take effect no earlier than the next abort completion point.
606 procedure Undefer_Abort
(Self_ID
: Task_Id
) is
612 pragma Assert
(Self_ID
.Deferral_Level
= 1);
614 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
616 if Self_ID
.Deferral_Level
= 0 then
617 pragma Assert
(Check_No_Locks
(Self_ID
));
619 if Self_ID
.Pending_Action
then
620 Do_Pending_Action
(Self_ID
);
625 ----------------------------
626 -- Undefer_Abort_Nestable --
627 ----------------------------
629 -- An earlier version would re-defer abort if an abort is in progress.
630 -- Then, we modified the effect of the raise statement so that it defers
631 -- abort until control reaches a handler. That was done to prevent
632 -- "skipping over" a handler if another asynchronous abort occurs during
633 -- the propagation of the abort to the handler.
635 -- There has been talk of reversing that decision, based on a newer
636 -- implementation of exception propagation. Care must be taken to evaluate
637 -- how such a change would interact with the above code and all the places
638 -- where abort-deferral is used to bridge over critical transitions, such
639 -- as entry to the scope of a region with a finalizer and entry into the
640 -- body of an accept-procedure.
642 procedure Undefer_Abort_Nestable
(Self_ID
: Task_Id
) is
648 pragma Assert
(Self_ID
.Deferral_Level
> 0);
650 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
652 if Self_ID
.Deferral_Level
= 0 then
654 pragma Assert
(Check_No_Locks
(Self_ID
));
656 if Self_ID
.Pending_Action
then
657 Do_Pending_Action
(Self_ID
);
660 end Undefer_Abort_Nestable
;
666 procedure Abort_Undefer
is
673 Self_ID
:= STPO
.Self
;
675 if Self_ID
.Deferral_Level
= 0 then
677 -- In case there are different views on whether Abort is supported
678 -- between the expander and the run time, we may end up with
679 -- Self_ID.Deferral_Level being equal to zero, when called from
680 -- the procedure created by the expander that corresponds to a
681 -- task body. In this case, there's nothing to be done.
683 -- See related code in System.Tasking.Stages.Create_Task resetting
684 -- Deferral_Level when System.Restrictions.Abort_Allowed is False.
689 pragma Assert
(Self_ID
.Deferral_Level
> 0);
690 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
692 if Self_ID
.Deferral_Level
= 0 then
693 pragma Assert
(Check_No_Locks
(Self_ID
));
695 if Self_ID
.Pending_Action
then
696 Do_Pending_Action
(Self_ID
);
701 --------------------------
702 -- Wakeup_Entry_Caller --
703 --------------------------
705 -- This is called at the end of service of an entry call, to abort the
706 -- caller if he is in an abortable part, and to wake up the caller if it
707 -- is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
709 -- (This enforces the rule that a task must be off-queue if its state is
710 -- Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
712 -- Timed_Call or Simple_Call:
713 -- The caller is waiting on Entry_Caller_Sleep, in
714 -- Wait_For_Completion, or Wait_For_Completion_With_Timeout.
717 -- The caller might be in Wait_For_Completion,
718 -- waiting for a rendezvous (possibly requeued without abort)
721 -- Asynchronous_Call:
722 -- The caller may be executing in the abortable part o
723 -- an async. select, or on a time delay,
724 -- if Entry_Call.State >= Was_Abortable.
726 procedure Wakeup_Entry_Caller
728 Entry_Call
: Entry_Call_Link
;
729 New_State
: Entry_Call_State
)
731 Caller
: constant Task_Id
:= Entry_Call
.Self
;
734 pragma Debug
(Debug
.Trace
735 (Self_ID
, "Wakeup_Entry_Caller", 'E', Caller
));
736 pragma Assert
(New_State
= Done
or else New_State
= Cancelled
);
738 pragma Assert
(Caller
.Common
.State
/= Unactivated
);
740 Entry_Call
.State
:= New_State
;
742 if Entry_Call
.Mode
= Asynchronous_Call
then
744 -- Abort the caller in his abortable part, but do so only if call has
745 -- been queued abortably.
747 if Entry_Call
.State
>= Was_Abortable
or else New_State
= Done
then
748 Locked_Abort_To_Level
(Self_ID
, Caller
, Entry_Call
.Level
- 1);
751 elsif Caller
.Common
.State
= Entry_Caller_Sleep
then
752 Wakeup
(Caller
, Entry_Caller_Sleep
);
754 end Wakeup_Entry_Caller
;
756 -------------------------
757 -- Finalize_Attributes --
758 -------------------------
760 procedure Finalize_Attributes
(T
: Task_Id
) is
761 Attr
: Atomic_Address
;
764 for J
in T
.Attributes
'Range loop
765 Attr
:= T
.Attributes
(J
);
767 if Attr
/= 0 and then Task_Attributes
.Require_Finalization
(J
) then
768 Task_Attributes
.To_Attribute
(Attr
).Free
(Attr
);
769 T
.Attributes
(J
) := 0;
772 end Finalize_Attributes
;
776 end System
.Tasking
.Initialization
;