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) 1992-2018, 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.
37 -- Turn polling off for this package. We don't need polling during any of the
38 -- routines in this package, and more to the point, if we try to poll it can
39 -- cause infinite loops.
41 with System
.Task_Primitives
;
42 with System
.Task_Primitives
.Operations
;
43 with System
.Soft_Links
;
44 with System
.Soft_Links
.Tasking
;
45 with System
.Tasking
.Debug
;
46 with System
.Tasking
.Task_Attributes
;
47 with System
.Parameters
;
49 with System
.Secondary_Stack
;
50 pragma Elaborate_All
(System
.Secondary_Stack
);
51 pragma Unreferenced
(System
.Secondary_Stack
);
52 -- Make sure the body of Secondary_Stack is elaborated before calling
53 -- Init_Tasking_Soft_Links. See comments for this routine for explanation.
55 package body System
.Tasking
.Initialization
is
57 package STPO
renames System
.Task_Primitives
.Operations
;
58 package SSL
renames System
.Soft_Links
;
61 use Task_Primitives
.Operations
;
63 Global_Task_Lock
: aliased System
.Task_Primitives
.RTS_Lock
;
64 -- This is a global lock; it is used to execute in mutual exclusion from
65 -- all other tasks. It is only used by Task_Lock, Task_Unlock, and
68 ----------------------------------------------------------------------
69 -- Tasking versions of some services needed by non-tasking programs --
70 ----------------------------------------------------------------------
72 procedure Abort_Defer
;
73 -- NON-INLINE versions without Self_ID for soft links
75 procedure Abort_Undefer
;
76 -- NON-INLINE versions without Self_ID for soft links
79 -- Locks out other tasks. Preceding a section of code by Task_Lock and
80 -- following it by Task_Unlock creates a critical region. This is used
81 -- for ensuring that a region of non-tasking code (such as code used to
82 -- allocate memory) is tasking safe. Note that it is valid for calls to
83 -- Task_Lock/Task_Unlock to be nested, and this must work properly, i.e.
84 -- only the corresponding outer level Task_Unlock will actually unlock.
86 procedure Task_Unlock
;
87 -- Releases lock previously set by call to Task_Lock. In the nested case,
88 -- all nested locks must be released before other tasks competing for the
89 -- tasking lock are released.
91 function Get_Current_Excep
return SSL
.EOA
;
92 -- Task-safe version of SSL.Get_Current_Excep
94 function Task_Name
return String;
95 -- Returns current task's name
97 ------------------------
98 -- Local Subprograms --
99 ------------------------
101 ----------------------------
102 -- Tasking Initialization --
103 ----------------------------
106 -- This procedure completes the initialization of the GNARL. The first part
107 -- of the initialization is done in the body of System.Tasking. It consists
108 -- of initializing global locks, and installing tasking versions of certain
109 -- operations used by the compiler. Init_RTS is called during elaboration.
111 --------------------------
112 -- Change_Base_Priority --
113 --------------------------
115 -- Call only with abort deferred and holding Self_ID locked
117 procedure Change_Base_Priority
(T
: Task_Id
) is
119 if T
.Common
.Base_Priority
/= T
.New_Base_Priority
then
120 T
.Common
.Base_Priority
:= T
.New_Base_Priority
;
121 Set_Priority
(T
, T
.Common
.Base_Priority
);
123 end Change_Base_Priority
;
125 ------------------------
126 -- Check_Abort_Status --
127 ------------------------
129 function Check_Abort_Status
return Integer is
130 Self_ID
: constant Task_Id
:= Self
;
133 and then Self_ID
.Deferral_Level
= 0
134 and then Self_ID
.Pending_ATC_Level
< Self_ID
.ATC_Nesting_Level
140 end Check_Abort_Status
;
146 procedure Defer_Abort
(Self_ID
: Task_Id
) is
152 pragma Assert
(Self_ID
.Deferral_Level
= 0);
155 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level);
157 -- The above check has been useful in detecting mismatched defer/undefer
158 -- pairs. You may uncomment it when testing on systems that support
161 -- If the OS supports preemptive abort (e.g. pthread_kill), it should
162 -- have happened already. A problem is with systems that do not support
163 -- preemptive abort, and so rely on polling. On such systems we may get
164 -- false failures of the assertion, since polling for pending abort does
165 -- no occur until the abort undefer operation.
167 -- Even on systems that only poll for abort, the assertion may be useful
168 -- for catching missed abort completion polling points. The operations
169 -- that undefer abort poll for pending aborts. This covers most of the
170 -- places where the core Ada semantics require abort to be caught,
171 -- without any special attention. However, this generally happens on
172 -- exit from runtime system call, which means a pending abort will not
173 -- be noticed on the way into the runtime system. We considered adding a
174 -- check for pending aborts at this point, but chose not to, because of
175 -- the overhead. Instead, we searched for RTS calls where abort
176 -- completion is required and a task could go farther than Ada allows
177 -- before undeferring abort; we then modified the code to ensure the
178 -- abort would be detected.
180 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
183 --------------------------
184 -- Defer_Abort_Nestable --
185 --------------------------
187 procedure Defer_Abort_Nestable
(Self_ID
: Task_Id
) is
193 -- The following assertion is by default disabled. See the comment in
194 -- Defer_Abort on the situations in which it may be useful to uncomment
195 -- this assertion and enable the test.
198 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level or else
199 -- Self_ID.Deferral_Level > 0);
201 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
202 end Defer_Abort_Nestable
;
208 procedure Abort_Defer
is
215 Self_ID
:= STPO
.Self
;
216 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
219 -----------------------
220 -- Get_Current_Excep --
221 -----------------------
223 function Get_Current_Excep
return SSL
.EOA
is
225 return STPO
.Self
.Common
.Compiler_Data
.Current_Excep
'Access;
226 end Get_Current_Excep
;
228 -----------------------
229 -- Do_Pending_Action --
230 -----------------------
232 -- Call only when holding no locks
234 procedure Do_Pending_Action
(Self_ID
: Task_Id
) is
237 pragma Assert
(Self_ID
= Self
and then Self_ID
.Deferral_Level
= 0);
239 -- Needs loop to recheck for pending action in case a new one occurred
240 -- while we had abort deferred below.
243 -- Temporarily defer abort so that we can lock Self_ID
245 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
251 Write_Lock
(Self_ID
);
252 Self_ID
.Pending_Action
:= False;
259 -- Restore the original Deferral value
261 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
263 if not Self_ID
.Pending_Action
then
264 if Self_ID
.Pending_ATC_Level
< Self_ID
.ATC_Nesting_Level
then
265 if not Self_ID
.Aborting
then
266 Self_ID
.Aborting
:= True;
268 (Debug
.Trace
(Self_ID
, "raise Abort_Signal", 'B'));
269 raise Standard
'Abort_Signal;
271 pragma Assert
(not Self_ID
.ATC_Hack
);
273 elsif Self_ID
.ATC_Hack
then
275 -- The solution really belongs in the Abort_Signal handler
276 -- for async. entry calls. The present hack is very
277 -- fragile. It relies that the very next point after
278 -- Exit_One_ATC_Level at which the task becomes abortable
279 -- will be the call to Undefer_Abort in the
280 -- Abort_Signal handler.
282 Self_ID
.ATC_Hack
:= False;
286 (Self_ID
, "raise Abort_Signal (ATC hack)", 'B'));
287 raise Standard
'Abort_Signal;
294 end Do_Pending_Action
;
296 -----------------------
297 -- Final_Task_Unlock --
298 -----------------------
300 -- This version is only for use in Terminate_Task, when the task is
301 -- relinquishing further rights to its own ATCB.
303 -- There is a very interesting potential race condition there, where the
304 -- old task may run concurrently with a new task that is allocated the old
305 -- tasks (now reused) ATCB. The critical thing here is to not make any
306 -- reference to the ATCB after the lock is released. See also comments on
307 -- Terminate_Task and Unlock.
309 procedure Final_Task_Unlock
(Self_ID
: Task_Id
) is
311 pragma Assert
(Self_ID
.Common
.Global_Task_Lock_Nesting
= 1);
312 Unlock
(Global_Task_Lock
'Access, Global_Lock
=> True);
313 end Final_Task_Unlock
;
319 procedure Init_RTS
is
324 -- Terminate run time (regular vs restricted) specific initialization
325 -- of the environment task.
327 Self_Id
:= Environment_Task
;
328 Self_Id
.Master_Of_Task
:= Environment_Task_Level
;
329 Self_Id
.Master_Within
:= Self_Id
.Master_Of_Task
+ 1;
331 for L
in Self_Id
.Entry_Calls
'Range loop
332 Self_Id
.Entry_Calls
(L
).Self
:= Self_Id
;
333 Self_Id
.Entry_Calls
(L
).Level
:= L
;
336 Self_Id
.Awake_Count
:= 1;
337 Self_Id
.Alive_Count
:= 1;
339 -- Normally, a task starts out with internal master nesting level one
340 -- larger than external master nesting level. It is incremented to one
341 -- by Enter_Master, which is called in the task body only if the
342 -- compiler thinks the task may have dependent tasks. There is no
343 -- corresponding call to Enter_Master for the environment task, so we
344 -- would need to increment it to 2 here. Instead, we set it to 3. By
345 -- doing this we reserve the level 2 for server tasks of the runtime
346 -- system. The environment task does not need to wait for these server
348 Self_Id
.Master_Within
:= Library_Task_Level
;
350 -- Initialize lock used to implement mutual exclusion between all tasks
352 Initialize_Lock
(Global_Task_Lock
'Access, STPO
.Global_Task_Level
);
354 -- Notify that the tasking run time has been elaborated so that
355 -- the tasking version of the soft links can be used.
358 SSL
.Abort_Defer
:= Abort_Defer
'Access;
359 SSL
.Abort_Undefer
:= Abort_Undefer
'Access;
362 SSL
.Lock_Task
:= Task_Lock
'Access;
363 SSL
.Unlock_Task
:= Task_Unlock
'Access;
364 SSL
.Check_Abort_Status
:= Check_Abort_Status
'Access;
365 SSL
.Task_Name
:= Task_Name
'Access;
366 SSL
.Get_Current_Excep
:= Get_Current_Excep
'Access;
368 -- Initialize the tasking soft links (if not done yet) that are common
369 -- to the full and the restricted run times.
371 SSL
.Tasking
.Init_Tasking_Soft_Links
;
373 -- Abort is deferred in a new ATCB, so we need to undefer abort at this
374 -- stage to make the environment task abortable.
376 Undefer_Abort
(Environment_Task
);
379 ---------------------------
380 -- Locked_Abort_To_Level--
381 ---------------------------
383 -- Abort a task to the specified ATC nesting level.
384 -- Call this only with T locked.
386 -- An earlier version of this code contained a call to Wakeup. That should
387 -- not be necessary here, if Abort_Task is implemented correctly, since
388 -- Abort_Task should include the effect of Wakeup. However, the above call
389 -- was in earlier versions of this file, and at least for some targets
390 -- Abort_Task has not been doing Wakeup. It should not hurt to uncomment
391 -- the above call, until the error is corrected for all targets.
393 -- See extended comments in package body System.Tasking.Abort for the
394 -- overall design of the implementation of task abort.
395 -- ??? there is no such package ???
397 -- If the task is sleeping it will be in an abort-deferred region, and will
398 -- not have Abort_Signal raised by Abort_Task. Such an "abort deferral" is
399 -- just to protect the RTS internals, and not necessarily required to
400 -- enforce Ada semantics. Abort_Task should wake the task up and let it
401 -- decide if it wants to complete the aborted construct immediately.
403 -- Note that the effect of the low-level Abort_Task is not persistent.
404 -- If the target task is not blocked, this wakeup will be missed.
406 -- We don't bother calling Abort_Task if this task is aborting itself,
407 -- since we are inside the RTS and have abort deferred. Similarly, We don't
408 -- bother to call Abort_Task if T is terminated, since there is no need to
409 -- abort a terminated task, and it could be dangerous to try if the task
410 -- has stopped executing.
412 -- Note that an earlier version of this code had some false reasoning about
413 -- being able to reliably wake up a task that had suspended on a blocking
414 -- system call that does not atomically release the task's lock (e.g., UNIX
415 -- nanosleep, which we once thought could be used to implement delays).
416 -- That still left the possibility of missed wakeups.
418 -- We cannot safely call Vulnerable_Complete_Activation here, since that
419 -- requires locking Self_ID.Parent. The anti-deadlock lock ordering rules
420 -- would then require us to release the lock on Self_ID first, which would
421 -- create a timing window for other tasks to lock Self_ID. This is
422 -- significant for tasks that may be aborted before their execution can
423 -- enter the task body, and so they do not get a chance to call
424 -- Complete_Task. The actual work for this case is done in Terminate_Task.
426 procedure Locked_Abort_To_Level
432 if not T
.Aborting
and then T
/= Self_ID
then
433 case T
.Common
.State
is
437 pragma Assert
(False);
443 -- This is needed to cancel an asynchronous protected entry
444 -- call during a requeue with abort.
447 (T
.ATC_Nesting_Level
).Cancellation_Attempted
:= True;
449 when Interrupt_Server_Blocked_On_Event_Flag
=>
452 when AST_Server_Sleep
455 | Interrupt_Server_Blocked_Interrupt_Sleep
456 | Interrupt_Server_Idle_Sleep
459 Wakeup
(T
, T
.Common
.State
);
461 when Acceptor_Delay_Sleep
464 T
.Open_Accepts
:= null;
465 Wakeup
(T
, T
.Common
.State
);
467 when Entry_Caller_Sleep
=>
469 (T
.ATC_Nesting_Level
).Cancellation_Attempted
:= True;
470 Wakeup
(T
, T
.Common
.State
);
474 | Master_Completion_Sleep
475 | Master_Phase_2_Sleep
481 if T
.Pending_ATC_Level
> L
then
482 T
.Pending_ATC_Level
:= L
;
483 T
.Pending_Action
:= True;
489 -- This prevents aborted task from accepting calls
493 -- The test above is just a heuristic, to reduce wasteful
494 -- calls to Abort_Task. We are holding T locked, and this
495 -- value will not be set to False except with T also locked,
496 -- inside Exit_One_ATC_Level, so we should not miss wakeups.
498 if T
.Common
.State
= Acceptor_Sleep
500 T
.Common
.State
= Acceptor_Delay_Sleep
502 T
.Open_Accepts
:= null;
505 elsif T
/= Self_ID
and then
506 (T
.Common
.State
= Runnable
507 or else T
.Common
.State
= Interrupt_Server_Blocked_On_Event_Flag
)
509 -- The task is blocked on a system call waiting for the
510 -- completion event. In this case Abort_Task may need to take
511 -- special action in order to succeed.
517 end Locked_Abort_To_Level
;
519 --------------------------------
520 -- Remove_From_All_Tasks_List --
521 --------------------------------
523 procedure Remove_From_All_Tasks_List
(T
: Task_Id
) is
529 (Debug
.Trace
(Self
, "Remove_From_All_Tasks_List", 'C'));
531 Previous
:= Null_Task
;
533 while C
/= Null_Task
loop
535 if Previous
= Null_Task
then
536 All_Tasks_List
:= All_Tasks_List
.Common
.All_Tasks_Link
;
538 Previous
.Common
.All_Tasks_Link
:= C
.Common
.All_Tasks_Link
;
545 C
:= C
.Common
.All_Tasks_Link
;
548 pragma Assert
(False);
549 end Remove_From_All_Tasks_List
;
555 procedure Task_Lock
(Self_ID
: Task_Id
) is
557 Self_ID
.Common
.Global_Task_Lock_Nesting
:=
558 Self_ID
.Common
.Global_Task_Lock_Nesting
+ 1;
560 if Self_ID
.Common
.Global_Task_Lock_Nesting
= 1 then
561 Defer_Abort_Nestable
(Self_ID
);
562 Write_Lock
(Global_Task_Lock
'Access, Global_Lock
=> True);
566 procedure Task_Lock
is
568 Task_Lock
(STPO
.Self
);
575 function Task_Name
return String is
576 Self_Id
: constant Task_Id
:= STPO
.Self
;
578 return Self_Id
.Common
.Task_Image
(1 .. Self_Id
.Common
.Task_Image_Len
);
585 procedure Task_Unlock
(Self_ID
: Task_Id
) is
587 pragma Assert
(Self_ID
.Common
.Global_Task_Lock_Nesting
> 0);
588 Self_ID
.Common
.Global_Task_Lock_Nesting
:=
589 Self_ID
.Common
.Global_Task_Lock_Nesting
- 1;
591 if Self_ID
.Common
.Global_Task_Lock_Nesting
= 0 then
592 Unlock
(Global_Task_Lock
'Access, Global_Lock
=> True);
593 Undefer_Abort_Nestable
(Self_ID
);
597 procedure Task_Unlock
is
599 Task_Unlock
(STPO
.Self
);
606 -- Precondition : Self does not hold any locks
608 -- Undefer_Abort is called on any abort completion point (aka.
609 -- synchronization point). It performs the following actions if they
610 -- are pending: (1) change the base priority, (2) abort the task.
612 -- The priority change has to occur before abort. Otherwise, it would
613 -- take effect no earlier than the next abort completion point.
615 procedure Undefer_Abort
(Self_ID
: Task_Id
) is
621 pragma Assert
(Self_ID
.Deferral_Level
= 1);
623 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
625 if Self_ID
.Deferral_Level
= 0 then
626 pragma Assert
(Check_No_Locks
(Self_ID
));
628 if Self_ID
.Pending_Action
then
629 Do_Pending_Action
(Self_ID
);
634 ----------------------------
635 -- Undefer_Abort_Nestable --
636 ----------------------------
638 -- An earlier version would re-defer abort if an abort is in progress.
639 -- Then, we modified the effect of the raise statement so that it defers
640 -- abort until control reaches a handler. That was done to prevent
641 -- "skipping over" a handler if another asynchronous abort occurs during
642 -- the propagation of the abort to the handler.
644 -- There has been talk of reversing that decision, based on a newer
645 -- implementation of exception propagation. Care must be taken to evaluate
646 -- how such a change would interact with the above code and all the places
647 -- where abort-deferral is used to bridge over critical transitions, such
648 -- as entry to the scope of a region with a finalizer and entry into the
649 -- body of an accept-procedure.
651 procedure Undefer_Abort_Nestable
(Self_ID
: Task_Id
) is
657 pragma Assert
(Self_ID
.Deferral_Level
> 0);
659 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
661 if Self_ID
.Deferral_Level
= 0 then
663 pragma Assert
(Check_No_Locks
(Self_ID
));
665 if Self_ID
.Pending_Action
then
666 Do_Pending_Action
(Self_ID
);
669 end Undefer_Abort_Nestable
;
675 procedure Abort_Undefer
is
682 Self_ID
:= STPO
.Self
;
684 if Self_ID
.Deferral_Level
= 0 then
686 -- In case there are different views on whether Abort is supported
687 -- between the expander and the run time, we may end up with
688 -- Self_ID.Deferral_Level being equal to zero, when called from
689 -- the procedure created by the expander that corresponds to a
690 -- task body. In this case, there's nothing to be done.
692 -- See related code in System.Tasking.Stages.Create_Task resetting
693 -- Deferral_Level when System.Restrictions.Abort_Allowed is False.
698 pragma Assert
(Self_ID
.Deferral_Level
> 0);
699 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
701 if Self_ID
.Deferral_Level
= 0 then
702 pragma Assert
(Check_No_Locks
(Self_ID
));
704 if Self_ID
.Pending_Action
then
705 Do_Pending_Action
(Self_ID
);
710 --------------------------
711 -- Wakeup_Entry_Caller --
712 --------------------------
714 -- This is called at the end of service of an entry call, to abort the
715 -- caller if he is in an abortable part, and to wake up the caller if it
716 -- is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
718 -- (This enforces the rule that a task must be off-queue if its state is
719 -- Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
721 -- Timed_Call or Simple_Call:
722 -- The caller is waiting on Entry_Caller_Sleep, in
723 -- Wait_For_Completion, or Wait_For_Completion_With_Timeout.
726 -- The caller might be in Wait_For_Completion,
727 -- waiting for a rendezvous (possibly requeued without abort)
730 -- Asynchronous_Call:
731 -- The caller may be executing in the abortable part o
732 -- an async. select, or on a time delay,
733 -- if Entry_Call.State >= Was_Abortable.
735 procedure Wakeup_Entry_Caller
737 Entry_Call
: Entry_Call_Link
;
738 New_State
: Entry_Call_State
)
740 Caller
: constant Task_Id
:= Entry_Call
.Self
;
743 pragma Debug
(Debug
.Trace
744 (Self_ID
, "Wakeup_Entry_Caller", 'E', Caller
));
745 pragma Assert
(New_State
= Done
or else New_State
= Cancelled
);
747 pragma Assert
(Caller
.Common
.State
/= Unactivated
);
749 Entry_Call
.State
:= New_State
;
751 if Entry_Call
.Mode
= Asynchronous_Call
then
753 -- Abort the caller in his abortable part, but do so only if call has
754 -- been queued abortably.
756 if Entry_Call
.State
>= Was_Abortable
or else New_State
= Done
then
757 Locked_Abort_To_Level
(Self_ID
, Caller
, Entry_Call
.Level
- 1);
760 elsif Caller
.Common
.State
= Entry_Caller_Sleep
then
761 Wakeup
(Caller
, Entry_Caller_Sleep
);
763 end Wakeup_Entry_Caller
;
765 -------------------------
766 -- Finalize_Attributes --
767 -------------------------
769 procedure Finalize_Attributes
(T
: Task_Id
) is
770 Attr
: Atomic_Address
;
773 for J
in T
.Attributes
'Range loop
774 Attr
:= T
.Attributes
(J
);
776 if Attr
/= 0 and then Task_Attributes
.Require_Finalization
(J
) then
777 Task_Attributes
.To_Attribute
(Attr
).Free
(Attr
);
778 T
.Attributes
(J
) := 0;
781 end Finalize_Attributes
;
785 end System
.Tasking
.Initialization
;