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) 1992-2016, 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.
43 with System
.Task_Primitives
;
44 with System
.Task_Primitives
.Operations
;
45 with System
.Soft_Links
;
46 with System
.Soft_Links
.Tasking
;
47 with System
.Tasking
.Debug
;
48 with System
.Tasking
.Task_Attributes
;
49 with System
.Parameters
;
51 with System
.Secondary_Stack
;
52 pragma Elaborate_All
(System
.Secondary_Stack
);
53 pragma Unreferenced
(System
.Secondary_Stack
);
54 -- Make sure the body of Secondary_Stack is elaborated before calling
55 -- Init_Tasking_Soft_Links. See comments for this routine for explanation.
57 package body System
.Tasking
.Initialization
is
59 package STPO
renames System
.Task_Primitives
.Operations
;
60 package SSL
renames System
.Soft_Links
;
63 use Task_Primitives
.Operations
;
65 Global_Task_Lock
: aliased System
.Task_Primitives
.RTS_Lock
;
66 -- This is a global lock; it is used to execute in mutual exclusion from
67 -- all other tasks. It is only used by Task_Lock, Task_Unlock, and
70 ----------------------------------------------------------------------
71 -- Tasking versions of some services needed by non-tasking programs --
72 ----------------------------------------------------------------------
74 procedure Abort_Defer
;
75 -- NON-INLINE versions without Self_ID for soft links
77 procedure Abort_Undefer
;
78 -- NON-INLINE versions without Self_ID for soft links
81 -- Locks out other tasks. Preceding a section of code by Task_Lock and
82 -- following it by Task_Unlock creates a critical region. This is used
83 -- for ensuring that a region of non-tasking code (such as code used to
84 -- allocate memory) is tasking safe. Note that it is valid for calls to
85 -- Task_Lock/Task_Unlock to be nested, and this must work properly, i.e.
86 -- only the corresponding outer level Task_Unlock will actually unlock.
88 procedure Task_Unlock
;
89 -- Releases lock previously set by call to Task_Lock. In the nested case,
90 -- all nested locks must be released before other tasks competing for the
91 -- tasking lock are released.
93 function Get_Current_Excep
return SSL
.EOA
;
94 -- Task-safe version of SSL.Get_Current_Excep
96 function Task_Name
return String;
97 -- Returns current task's name
99 ------------------------
100 -- Local Subprograms --
101 ------------------------
103 ----------------------------
104 -- Tasking Initialization --
105 ----------------------------
108 -- This procedure completes the initialization of the GNARL. The first part
109 -- of the initialization is done in the body of System.Tasking. It consists
110 -- of initializing global locks, and installing tasking versions of certain
111 -- operations used by the compiler. Init_RTS is called during elaboration.
113 --------------------------
114 -- Change_Base_Priority --
115 --------------------------
117 -- Call only with abort deferred and holding Self_ID locked
119 procedure Change_Base_Priority
(T
: Task_Id
) is
121 if T
.Common
.Base_Priority
/= T
.New_Base_Priority
then
122 T
.Common
.Base_Priority
:= T
.New_Base_Priority
;
123 Set_Priority
(T
, T
.Common
.Base_Priority
);
125 end Change_Base_Priority
;
127 ------------------------
128 -- Check_Abort_Status --
129 ------------------------
131 function Check_Abort_Status
return Integer is
132 Self_ID
: constant Task_Id
:= Self
;
135 and then Self_ID
.Deferral_Level
= 0
136 and then Self_ID
.Pending_ATC_Level
< Self_ID
.ATC_Nesting_Level
142 end Check_Abort_Status
;
148 procedure Defer_Abort
(Self_ID
: Task_Id
) is
154 pragma Assert
(Self_ID
.Deferral_Level
= 0);
157 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level);
159 -- The above check has been useful in detecting mismatched defer/undefer
160 -- pairs. You may uncomment it when testing on systems that support
163 -- If the OS supports preemptive abort (e.g. pthread_kill), it should
164 -- have happened already. A problem is with systems that do not support
165 -- preemptive abort, and so rely on polling. On such systems we may get
166 -- false failures of the assertion, since polling for pending abort does
167 -- no occur until the abort undefer operation.
169 -- Even on systems that only poll for abort, the assertion may be useful
170 -- for catching missed abort completion polling points. The operations
171 -- that undefer abort poll for pending aborts. This covers most of the
172 -- places where the core Ada semantics require abort to be caught,
173 -- without any special attention. However, this generally happens on
174 -- exit from runtime system call, which means a pending abort will not
175 -- be noticed on the way into the runtime system. We considered adding a
176 -- check for pending aborts at this point, but chose not to, because of
177 -- the overhead. Instead, we searched for RTS calls where abort
178 -- completion is required and a task could go farther than Ada allows
179 -- before undeferring abort; we then modified the code to ensure the
180 -- abort would be detected.
182 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
185 --------------------------
186 -- Defer_Abort_Nestable --
187 --------------------------
189 procedure Defer_Abort_Nestable
(Self_ID
: Task_Id
) is
195 -- The following assertion is by default disabled. See the comment in
196 -- Defer_Abort on the situations in which it may be useful to uncomment
197 -- this assertion and enable the test.
200 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level or else
201 -- Self_ID.Deferral_Level > 0);
203 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
204 end Defer_Abort_Nestable
;
210 procedure Abort_Defer
is
217 Self_ID
:= STPO
.Self
;
218 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
221 -----------------------
222 -- Get_Current_Excep --
223 -----------------------
225 function Get_Current_Excep
return SSL
.EOA
is
227 return STPO
.Self
.Common
.Compiler_Data
.Current_Excep
'Access;
228 end Get_Current_Excep
;
230 -----------------------
231 -- Do_Pending_Action --
232 -----------------------
234 -- Call only when holding no locks
236 procedure Do_Pending_Action
(Self_ID
: Task_Id
) is
237 use type Ada
.Exceptions
.Exception_Id
;
240 pragma Assert
(Self_ID
= Self
and then Self_ID
.Deferral_Level
= 0);
242 -- Needs loop to recheck for pending action in case a new one occurred
243 -- while we had abort deferred below.
246 -- Temporarily defer abort so that we can lock Self_ID
248 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
+ 1;
254 Write_Lock
(Self_ID
);
255 Self_ID
.Pending_Action
:= False;
262 -- Restore the original Deferral value
264 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
266 if not Self_ID
.Pending_Action
then
267 if Self_ID
.Pending_ATC_Level
< Self_ID
.ATC_Nesting_Level
then
268 if not Self_ID
.Aborting
then
269 Self_ID
.Aborting
:= True;
271 (Debug
.Trace
(Self_ID
, "raise Abort_Signal", 'B'));
272 raise Standard
'Abort_Signal;
274 pragma Assert
(not Self_ID
.ATC_Hack
);
276 elsif Self_ID
.ATC_Hack
then
278 -- The solution really belongs in the Abort_Signal handler
279 -- for async. entry calls. The present hack is very
280 -- fragile. It relies that the very next point after
281 -- Exit_One_ATC_Level at which the task becomes abortable
282 -- will be the call to Undefer_Abort in the
283 -- Abort_Signal handler.
285 Self_ID
.ATC_Hack
:= False;
289 (Self_ID
, "raise Abort_Signal (ATC hack)", 'B'));
290 raise Standard
'Abort_Signal;
297 end Do_Pending_Action
;
299 -----------------------
300 -- Final_Task_Unlock --
301 -----------------------
303 -- This version is only for use in Terminate_Task, when the task is
304 -- relinquishing further rights to its own ATCB.
306 -- There is a very interesting potential race condition there, where the
307 -- old task may run concurrently with a new task that is allocated the old
308 -- tasks (now reused) ATCB. The critical thing here is to not make any
309 -- reference to the ATCB after the lock is released. See also comments on
310 -- Terminate_Task and Unlock.
312 procedure Final_Task_Unlock
(Self_ID
: Task_Id
) is
314 pragma Assert
(Self_ID
.Common
.Global_Task_Lock_Nesting
= 1);
315 Unlock
(Global_Task_Lock
'Access, Global_Lock
=> True);
316 end Final_Task_Unlock
;
322 procedure Init_RTS
is
327 -- Terminate run time (regular vs restricted) specific initialization
328 -- of the environment task.
330 Self_Id
:= Environment_Task
;
331 Self_Id
.Master_of_Task
:= Environment_Task_Level
;
332 Self_Id
.Master_Within
:= Self_Id
.Master_of_Task
+ 1;
334 for L
in Self_Id
.Entry_Calls
'Range loop
335 Self_Id
.Entry_Calls
(L
).Self
:= Self_Id
;
336 Self_Id
.Entry_Calls
(L
).Level
:= L
;
339 Self_Id
.Awake_Count
:= 1;
340 Self_Id
.Alive_Count
:= 1;
342 -- Normally, a task starts out with internal master nesting level one
343 -- larger than external master nesting level. It is incremented to one
344 -- by Enter_Master, which is called in the task body only if the
345 -- compiler thinks the task may have dependent tasks. There is no
346 -- corresponding call to Enter_Master for the environment task, so we
347 -- would need to increment it to 2 here. Instead, we set it to 3. By
348 -- doing this we reserve the level 2 for server tasks of the runtime
349 -- system. The environment task does not need to wait for these server
351 Self_Id
.Master_Within
:= Library_Task_Level
;
353 -- Initialize lock used to implement mutual exclusion between all tasks
355 Initialize_Lock
(Global_Task_Lock
'Access, STPO
.Global_Task_Level
);
357 -- Notify that the tasking run time has been elaborated so that
358 -- the tasking version of the soft links can be used.
361 SSL
.Abort_Defer
:= Abort_Defer
'Access;
362 SSL
.Abort_Undefer
:= Abort_Undefer
'Access;
365 SSL
.Lock_Task
:= Task_Lock
'Access;
366 SSL
.Unlock_Task
:= Task_Unlock
'Access;
367 SSL
.Check_Abort_Status
:= Check_Abort_Status
'Access;
368 SSL
.Task_Name
:= Task_Name
'Access;
369 SSL
.Get_Current_Excep
:= Get_Current_Excep
'Access;
371 -- Initialize the tasking soft links (if not done yet) that are common
372 -- to the full and the restricted run times.
374 SSL
.Tasking
.Init_Tasking_Soft_Links
;
376 -- Abort is deferred in a new ATCB, so we need to undefer abort at this
377 -- stage to make the environment task abortable.
379 Undefer_Abort
(Environment_Task
);
382 ---------------------------
383 -- Locked_Abort_To_Level--
384 ---------------------------
386 -- Abort a task to the specified ATC nesting level.
387 -- Call this only with T locked.
389 -- An earlier version of this code contained a call to Wakeup. That should
390 -- not be necessary here, if Abort_Task is implemented correctly, since
391 -- Abort_Task should include the effect of Wakeup. However, the above call
392 -- was in earlier versions of this file, and at least for some targets
393 -- Abort_Task has not been doing Wakeup. It should not hurt to uncomment
394 -- the above call, until the error is corrected for all targets.
396 -- See extended comments in package body System.Tasking.Abort for the
397 -- overall design of the implementation of task abort.
398 -- ??? there is no such package ???
400 -- If the task is sleeping it will be in an abort-deferred region, and will
401 -- not have Abort_Signal raised by Abort_Task. Such an "abort deferral" is
402 -- just to protect the RTS internals, and not necessarily required to
403 -- enforce Ada semantics. Abort_Task should wake the task up and let it
404 -- decide if it wants to complete the aborted construct immediately.
406 -- Note that the effect of the low-level Abort_Task is not persistent.
407 -- If the target task is not blocked, this wakeup will be missed.
409 -- We don't bother calling Abort_Task if this task is aborting itself,
410 -- since we are inside the RTS and have abort deferred. Similarly, We don't
411 -- bother to call Abort_Task if T is terminated, since there is no need to
412 -- abort a terminated task, and it could be dangerous to try if the task
413 -- has stopped executing.
415 -- Note that an earlier version of this code had some false reasoning about
416 -- being able to reliably wake up a task that had suspended on a blocking
417 -- system call that does not atomically release the task's lock (e.g., UNIX
418 -- nanosleep, which we once thought could be used to implement delays).
419 -- That still left the possibility of missed wakeups.
421 -- We cannot safely call Vulnerable_Complete_Activation here, since that
422 -- requires locking Self_ID.Parent. The anti-deadlock lock ordering rules
423 -- would then require us to release the lock on Self_ID first, which would
424 -- create a timing window for other tasks to lock Self_ID. This is
425 -- significant for tasks that may be aborted before their execution can
426 -- enter the task body, and so they do not get a chance to call
427 -- Complete_Task. The actual work for this case is done in Terminate_Task.
429 procedure Locked_Abort_To_Level
435 if not T
.Aborting
and then T
/= Self_ID
then
436 case T
.Common
.State
is
440 pragma Assert
(False);
446 -- This is needed to cancel an asynchronous protected entry
447 -- call during a requeue with abort.
450 (T
.ATC_Nesting_Level
).Cancellation_Attempted
:= True;
452 when Interrupt_Server_Blocked_On_Event_Flag
=>
455 when AST_Server_Sleep
458 | Interrupt_Server_Blocked_Interrupt_Sleep
459 | Interrupt_Server_Idle_Sleep
462 Wakeup
(T
, T
.Common
.State
);
464 when Acceptor_Delay_Sleep
467 T
.Open_Accepts
:= null;
468 Wakeup
(T
, T
.Common
.State
);
470 when Entry_Caller_Sleep
=>
472 (T
.ATC_Nesting_Level
).Cancellation_Attempted
:= True;
473 Wakeup
(T
, T
.Common
.State
);
477 | Master_Completion_Sleep
478 | Master_Phase_2_Sleep
484 if T
.Pending_ATC_Level
> L
then
485 T
.Pending_ATC_Level
:= L
;
486 T
.Pending_Action
:= True;
492 -- This prevents aborted task from accepting calls
496 -- The test above is just a heuristic, to reduce wasteful
497 -- calls to Abort_Task. We are holding T locked, and this
498 -- value will not be set to False except with T also locked,
499 -- inside Exit_One_ATC_Level, so we should not miss wakeups.
501 if T
.Common
.State
= Acceptor_Sleep
503 T
.Common
.State
= Acceptor_Delay_Sleep
505 T
.Open_Accepts
:= null;
508 elsif T
/= Self_ID
and then
509 (T
.Common
.State
= Runnable
510 or else T
.Common
.State
= Interrupt_Server_Blocked_On_Event_Flag
)
512 -- The task is blocked on a system call waiting for the
513 -- completion event. In this case Abort_Task may need to take
514 -- special action in order to succeed.
520 end Locked_Abort_To_Level
;
522 --------------------------------
523 -- Remove_From_All_Tasks_List --
524 --------------------------------
526 procedure Remove_From_All_Tasks_List
(T
: Task_Id
) is
532 (Debug
.Trace
(Self
, "Remove_From_All_Tasks_List", 'C'));
534 Previous
:= Null_Task
;
536 while C
/= Null_Task
loop
538 if Previous
= Null_Task
then
539 All_Tasks_List
:= All_Tasks_List
.Common
.All_Tasks_Link
;
541 Previous
.Common
.All_Tasks_Link
:= C
.Common
.All_Tasks_Link
;
548 C
:= C
.Common
.All_Tasks_Link
;
551 pragma Assert
(False);
552 end Remove_From_All_Tasks_List
;
558 procedure Task_Lock
(Self_ID
: Task_Id
) is
560 Self_ID
.Common
.Global_Task_Lock_Nesting
:=
561 Self_ID
.Common
.Global_Task_Lock_Nesting
+ 1;
563 if Self_ID
.Common
.Global_Task_Lock_Nesting
= 1 then
564 Defer_Abort_Nestable
(Self_ID
);
565 Write_Lock
(Global_Task_Lock
'Access, Global_Lock
=> True);
569 procedure Task_Lock
is
571 Task_Lock
(STPO
.Self
);
578 function Task_Name
return String is
579 Self_Id
: constant Task_Id
:= STPO
.Self
;
581 return Self_Id
.Common
.Task_Image
(1 .. Self_Id
.Common
.Task_Image_Len
);
588 procedure Task_Unlock
(Self_ID
: Task_Id
) is
590 pragma Assert
(Self_ID
.Common
.Global_Task_Lock_Nesting
> 0);
591 Self_ID
.Common
.Global_Task_Lock_Nesting
:=
592 Self_ID
.Common
.Global_Task_Lock_Nesting
- 1;
594 if Self_ID
.Common
.Global_Task_Lock_Nesting
= 0 then
595 Unlock
(Global_Task_Lock
'Access, Global_Lock
=> True);
596 Undefer_Abort_Nestable
(Self_ID
);
600 procedure Task_Unlock
is
602 Task_Unlock
(STPO
.Self
);
609 -- Precondition : Self does not hold any locks
611 -- Undefer_Abort is called on any abort completion point (aka.
612 -- synchronization point). It performs the following actions if they
613 -- are pending: (1) change the base priority, (2) abort the task.
615 -- The priority change has to occur before abort. Otherwise, it would
616 -- take effect no earlier than the next abort completion point.
618 procedure Undefer_Abort
(Self_ID
: Task_Id
) is
624 pragma Assert
(Self_ID
.Deferral_Level
= 1);
626 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
628 if Self_ID
.Deferral_Level
= 0 then
629 pragma Assert
(Check_No_Locks
(Self_ID
));
631 if Self_ID
.Pending_Action
then
632 Do_Pending_Action
(Self_ID
);
637 ----------------------------
638 -- Undefer_Abort_Nestable --
639 ----------------------------
641 -- An earlier version would re-defer abort if an abort is in progress.
642 -- Then, we modified the effect of the raise statement so that it defers
643 -- abort until control reaches a handler. That was done to prevent
644 -- "skipping over" a handler if another asynchronous abort occurs during
645 -- the propagation of the abort to the handler.
647 -- There has been talk of reversing that decision, based on a newer
648 -- implementation of exception propagation. Care must be taken to evaluate
649 -- how such a change would interact with the above code and all the places
650 -- where abort-deferral is used to bridge over critical transitions, such
651 -- as entry to the scope of a region with a finalizer and entry into the
652 -- body of an accept-procedure.
654 procedure Undefer_Abort_Nestable
(Self_ID
: Task_Id
) is
660 pragma Assert
(Self_ID
.Deferral_Level
> 0);
662 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
664 if Self_ID
.Deferral_Level
= 0 then
666 pragma Assert
(Check_No_Locks
(Self_ID
));
668 if Self_ID
.Pending_Action
then
669 Do_Pending_Action
(Self_ID
);
672 end Undefer_Abort_Nestable
;
678 procedure Abort_Undefer
is
685 Self_ID
:= STPO
.Self
;
687 if Self_ID
.Deferral_Level
= 0 then
689 -- In case there are different views on whether Abort is supported
690 -- between the expander and the run time, we may end up with
691 -- Self_ID.Deferral_Level being equal to zero, when called from
692 -- the procedure created by the expander that corresponds to a
693 -- task body. In this case, there's nothing to be done.
695 -- See related code in System.Tasking.Stages.Create_Task resetting
696 -- Deferral_Level when System.Restrictions.Abort_Allowed is False.
701 pragma Assert
(Self_ID
.Deferral_Level
> 0);
702 Self_ID
.Deferral_Level
:= Self_ID
.Deferral_Level
- 1;
704 if Self_ID
.Deferral_Level
= 0 then
705 pragma Assert
(Check_No_Locks
(Self_ID
));
707 if Self_ID
.Pending_Action
then
708 Do_Pending_Action
(Self_ID
);
713 --------------------------
714 -- Wakeup_Entry_Caller --
715 --------------------------
717 -- This is called at the end of service of an entry call, to abort the
718 -- caller if he is in an abortable part, and to wake up the caller if it
719 -- is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
721 -- (This enforces the rule that a task must be off-queue if its state is
722 -- Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
724 -- Timed_Call or Simple_Call:
725 -- The caller is waiting on Entry_Caller_Sleep, in
726 -- Wait_For_Completion, or Wait_For_Completion_With_Timeout.
729 -- The caller might be in Wait_For_Completion,
730 -- waiting for a rendezvous (possibly requeued without abort)
733 -- Asynchronous_Call:
734 -- The caller may be executing in the abortable part o
735 -- an async. select, or on a time delay,
736 -- if Entry_Call.State >= Was_Abortable.
738 procedure Wakeup_Entry_Caller
740 Entry_Call
: Entry_Call_Link
;
741 New_State
: Entry_Call_State
)
743 Caller
: constant Task_Id
:= Entry_Call
.Self
;
746 pragma Debug
(Debug
.Trace
747 (Self_ID
, "Wakeup_Entry_Caller", 'E', Caller
));
748 pragma Assert
(New_State
= Done
or else New_State
= Cancelled
);
750 pragma Assert
(Caller
.Common
.State
/= Unactivated
);
752 Entry_Call
.State
:= New_State
;
754 if Entry_Call
.Mode
= Asynchronous_Call
then
756 -- Abort the caller in his abortable part, but do so only if call has
757 -- been queued abortably.
759 if Entry_Call
.State
>= Was_Abortable
or else New_State
= Done
then
760 Locked_Abort_To_Level
(Self_ID
, Caller
, Entry_Call
.Level
- 1);
763 elsif Caller
.Common
.State
= Entry_Caller_Sleep
then
764 Wakeup
(Caller
, Entry_Caller_Sleep
);
766 end Wakeup_Entry_Caller
;
768 -------------------------
769 -- Finalize_Attributes --
770 -------------------------
772 procedure Finalize_Attributes
(T
: Task_Id
) is
773 Attr
: Atomic_Address
;
776 for J
in T
.Attributes
'Range loop
777 Attr
:= T
.Attributes
(J
);
779 if Attr
/= 0 and then Task_Attributes
.Require_Finalization
(J
) then
780 Task_Attributes
.To_Attribute
(Attr
).Free
(Attr
);
781 T
.Attributes
(J
) := 0;
784 end Finalize_Attributes
;
788 end System
.Tasking
.Initialization
;