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) 1992-2009, 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.Parameters;
50 package body System.Tasking.Initialization is
52 package STPO renames System.Task_Primitives.Operations;
53 package SSL renames System.Soft_Links;
54 package AE renames Ada.Exceptions;
57 use Task_Primitives.Operations;
59 Global_Task_Lock : aliased System.Task_Primitives.RTS_Lock;
60 -- This is a global lock; it is used to execute in mutual exclusion from
61 -- all other tasks. It is only used by Task_Lock, Task_Unlock, and
64 ----------------------------------------------------------------------
65 -- Tasking versions of some services needed by non-tasking programs --
66 ----------------------------------------------------------------------
68 procedure Abort_Defer;
69 -- NON-INLINE versions without Self_ID for soft links
71 procedure Abort_Undefer;
72 -- NON-INLINE versions without Self_ID for soft links
75 -- Locks out other tasks. Preceding a section of code by Task_Lock and
76 -- following it by Task_Unlock creates a critical region. This is used
77 -- for ensuring that a region of non-tasking code (such as code used to
78 -- allocate memory) is tasking safe. Note that it is valid for calls to
79 -- Task_Lock/Task_Unlock to be nested, and this must work properly, i.e.
80 -- only the corresponding outer level Task_Unlock will actually unlock.
82 procedure Task_Unlock;
83 -- Releases lock previously set by call to Task_Lock. In the nested case,
84 -- all nested locks must be released before other tasks competing for the
85 -- tasking lock are released.
87 function Get_Current_Excep return SSL.EOA;
88 -- Task-safe version of SSL.Get_Current_Excep
90 procedure Update_Exception
91 (X : AE.Exception_Occurrence := SSL.Current_Target_Exception);
92 -- Handle exception setting and check for pending actions
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
194 -- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level or else
195 -- Self_ID.Deferral_Level > 0);
197 -- See comment in Defer_Abort on the situations in which it may be
198 -- useful to uncomment the above assertion.
200 Self_ID.Deferral_Level := Self_ID.Deferral_Level + 1;
201 end Defer_Abort_Nestable;
207 procedure Abort_Defer is
214 Self_ID := STPO.Self;
215 Self_ID.Deferral_Level := Self_ID.Deferral_Level + 1;
218 -----------------------
219 -- Get_Current_Excep --
220 -----------------------
222 function Get_Current_Excep return SSL.EOA is
224 return STPO.Self.Common.Compiler_Data.Current_Excep'Access;
225 end Get_Current_Excep;
227 -----------------------
228 -- Do_Pending_Action --
229 -----------------------
231 -- Call only when holding no locks
233 procedure Do_Pending_Action (Self_ID : Task_Id) is
234 use type Ada.Exceptions.Exception_Id;
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.Update_Exception := Update_Exception'Access;
367 SSL.Get_Current_Excep := Get_Current_Excep'Access;
369 -- Initialize the tasking soft links (if not done yet) that are common
370 -- to the full and the restricted run times.
372 SSL.Tasking.Init_Tasking_Soft_Links;
374 -- Abort is deferred in a new ATCB, so we need to undefer abort at this
375 -- stage to make the environment task abortable.
377 Undefer_Abort (Environment_Task);
380 ---------------------------
381 -- Locked_Abort_To_Level--
382 ---------------------------
384 -- Abort a task to the specified ATC nesting level.
385 -- Call this only with T locked.
387 -- An earlier version of this code contained a call to Wakeup. That should
388 -- not be necessary here, if Abort_Task is implemented correctly, since
389 -- Abort_Task should include the effect of Wakeup. However, the above call
390 -- was in earlier versions of this file, and at least for some targets
391 -- Abort_Task has not been doing Wakeup. It should not hurt to uncomment
392 -- the above call, until the error is corrected for all targets.
394 -- See extended comments in package body System.Tasking.Abort for the
395 -- overall design of the implementation of task abort.
396 -- ??? there is no such package ???
398 -- If the task is sleeping it will be in an abort-deferred region, and will
399 -- not have Abort_Signal raised by Abort_Task. Such an "abort deferral" is
400 -- just to protect the RTS internals, and not necessarily required to
401 -- enforce Ada semantics. Abort_Task should wake the task up and let it
402 -- decide if it wants to complete the aborted construct immediately.
404 -- Note that the effect of the low-level Abort_Task is not persistent.
405 -- If the target task is not blocked, this wakeup will be missed.
407 -- We don't bother calling Abort_Task if this task is aborting itself,
408 -- since we are inside the RTS and have abort deferred. Similarly, We don't
409 -- bother to call Abort_Task if T is terminated, since there is no need to
410 -- abort a terminated task, and it could be dangerous to try if the task
411 -- has stopped executing.
413 -- Note that an earlier version of this code had some false reasoning about
414 -- being able to reliably wake up a task that had suspended on a blocking
415 -- system call that does not atomically release the task's lock (e.g., UNIX
416 -- nanosleep, which we once thought could be used to implement delays).
417 -- That still left the possibility of missed wakeups.
419 -- We cannot safely call Vulnerable_Complete_Activation here, since that
420 -- requires locking Self_ID.Parent. The anti-deadlock lock ordering rules
421 -- would then require us to release the lock on Self_ID first, which would
422 -- create a timing window for other tasks to lock Self_ID. This is
423 -- significant for tasks that may be aborted before their execution can
424 -- enter the task body, and so they do not get a chance to call
425 -- Complete_Task. The actual work for this case is done in Terminate_Task.
427 procedure Locked_Abort_To_Level
433 if not T.Aborting and then T /= Self_ID then
434 case T.Common.State is
435 when Unactivated | Terminated =>
436 pragma Assert (False);
439 when Activating | Runnable =>
441 -- This is needed to cancel an asynchronous protected entry
442 -- call during a requeue with abort.
445 (T.ATC_Nesting_Level).Cancellation_Attempted := True;
447 when Interrupt_Server_Blocked_On_Event_Flag =>
452 Interrupt_Server_Idle_Sleep |
453 Interrupt_Server_Blocked_Interrupt_Sleep |
456 Wakeup (T, T.Common.State);
458 when Acceptor_Sleep | Acceptor_Delay_Sleep =>
459 T.Open_Accepts := null;
460 Wakeup (T, T.Common.State);
462 when Entry_Caller_Sleep =>
464 (T.ATC_Nesting_Level).Cancellation_Attempted := True;
465 Wakeup (T, T.Common.State);
467 when Activator_Sleep |
468 Master_Completion_Sleep |
469 Master_Phase_2_Sleep |
475 if T.Pending_ATC_Level > L then
476 T.Pending_ATC_Level := L;
477 T.Pending_Action := True;
483 -- This prevents aborted task from accepting calls
487 -- The test above is just a heuristic, to reduce wasteful
488 -- calls to Abort_Task. We are holding T locked, and this
489 -- value will not be set to False except with T also locked,
490 -- inside Exit_One_ATC_Level, so we should not miss wakeups.
492 if T.Common.State = Acceptor_Sleep
494 T.Common.State = Acceptor_Delay_Sleep
496 T.Open_Accepts := null;
499 elsif T /= Self_ID and then
500 (T.Common.State = Runnable
501 or else T.Common.State = Interrupt_Server_Blocked_On_Event_Flag)
503 -- The task is blocked on a system call waiting for the
504 -- completion event. In this case Abort_Task may need to take
505 -- special action in order to succeed. Example system: VMS.
511 end Locked_Abort_To_Level;
513 --------------------------------
514 -- Remove_From_All_Tasks_List --
515 --------------------------------
517 procedure Remove_From_All_Tasks_List (T : Task_Id) is
523 (Debug.Trace (Self, "Remove_From_All_Tasks_List", 'C'));
525 Previous := Null_Task;
527 while C /= Null_Task loop
529 if Previous = Null_Task then
530 All_Tasks_List := All_Tasks_List.Common.All_Tasks_Link;
532 Previous.Common.All_Tasks_Link := C.Common.All_Tasks_Link;
539 C := C.Common.All_Tasks_Link;
542 pragma Assert (False);
543 end Remove_From_All_Tasks_List;
549 procedure Task_Lock (Self_ID : Task_Id) is
551 Self_ID.Common.Global_Task_Lock_Nesting :=
552 Self_ID.Common.Global_Task_Lock_Nesting + 1;
554 if Self_ID.Common.Global_Task_Lock_Nesting = 1 then
555 Defer_Abort_Nestable (Self_ID);
556 Write_Lock (Global_Task_Lock'Access, Global_Lock => True);
560 procedure Task_Lock is
562 Task_Lock (STPO.Self);
569 function Task_Name return String is
570 Self_Id : constant Task_Id := STPO.Self;
572 return Self_Id.Common.Task_Image (1 .. Self_Id.Common.Task_Image_Len);
579 procedure Task_Unlock (Self_ID : Task_Id) is
581 pragma Assert (Self_ID.Common.Global_Task_Lock_Nesting > 0);
582 Self_ID.Common.Global_Task_Lock_Nesting :=
583 Self_ID.Common.Global_Task_Lock_Nesting - 1;
585 if Self_ID.Common.Global_Task_Lock_Nesting = 0 then
586 Unlock (Global_Task_Lock'Access, Global_Lock => True);
587 Undefer_Abort_Nestable (Self_ID);
591 procedure Task_Unlock is
593 Task_Unlock (STPO.Self);
600 -- Precondition : Self does not hold any locks!
602 -- Undefer_Abort is called on any abort completion point (aka.
603 -- synchronization point). It performs the following actions if they
604 -- are pending: (1) change the base priority, (2) abort the task.
606 -- The priority change has to occur before abort. Otherwise, it would
607 -- take effect no earlier than the next abort completion point.
609 procedure Undefer_Abort (Self_ID : Task_Id) is
615 pragma Assert (Self_ID.Deferral_Level = 1);
617 Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
619 if Self_ID.Deferral_Level = 0 then
620 pragma Assert (Check_No_Locks (Self_ID));
622 if Self_ID.Pending_Action then
623 Do_Pending_Action (Self_ID);
628 ----------------------------
629 -- Undefer_Abort_Nestable --
630 ----------------------------
632 -- An earlier version would re-defer abort if an abort is in progress.
633 -- Then, we modified the effect of the raise statement so that it defers
634 -- abort until control reaches a handler. That was done to prevent
635 -- "skipping over" a handler if another asynchronous abort occurs during
636 -- the propagation of the abort to the handler.
638 -- There has been talk of reversing that decision, based on a newer
639 -- implementation of exception propagation. Care must be taken to evaluate
640 -- how such a change would interact with the above code and all the places
641 -- where abort-deferral is used to bridge over critical transitions, such
642 -- as entry to the scope of a region with a finalizer and entry into the
643 -- body of an accept-procedure.
645 procedure Undefer_Abort_Nestable (Self_ID : Task_Id) is
651 pragma Assert (Self_ID.Deferral_Level > 0);
653 Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
655 if Self_ID.Deferral_Level = 0 then
657 pragma Assert (Check_No_Locks (Self_ID));
659 if Self_ID.Pending_Action then
660 Do_Pending_Action (Self_ID);
663 end Undefer_Abort_Nestable;
669 procedure Abort_Undefer is
676 Self_ID := STPO.Self;
678 if Self_ID.Deferral_Level = 0 then
680 -- In case there are different views on whether Abort is supported
681 -- between the expander and the run time, we may end up with
682 -- Self_ID.Deferral_Level being equal to zero, when called from
683 -- the procedure created by the expander that corresponds to a
686 -- In this case, there's nothing to be done
688 -- See related code in System.Tasking.Stages.Create_Task resetting
689 -- Deferral_Level when System.Restrictions.Abort_Allowed is False.
694 pragma Assert (Self_ID.Deferral_Level > 0);
695 Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
697 if Self_ID.Deferral_Level = 0 then
698 pragma Assert (Check_No_Locks (Self_ID));
700 if Self_ID.Pending_Action then
701 Do_Pending_Action (Self_ID);
706 ----------------------
707 -- Update_Exception --
708 ----------------------
710 -- Call only when holding no locks
712 procedure Update_Exception
713 (X : AE.Exception_Occurrence := SSL.Current_Target_Exception)
715 Self_Id : constant Task_Id := Self;
719 Save_Occurrence (Self_Id.Common.Compiler_Data.Current_Excep, X);
721 if Self_Id.Deferral_Level = 0 then
722 if Self_Id.Pending_Action then
723 Self_Id.Pending_Action := False;
724 Self_Id.Deferral_Level := Self_Id.Deferral_Level + 1;
730 Write_Lock (Self_Id);
731 Self_Id.Pending_Action := False;
738 Self_Id.Deferral_Level := Self_Id.Deferral_Level - 1;
740 if Self_Id.Pending_ATC_Level < Self_Id.ATC_Nesting_Level then
741 if not Self_Id.Aborting then
742 Self_Id.Aborting := True;
743 raise Standard'Abort_Signal;
748 end Update_Exception;
750 --------------------------
751 -- Wakeup_Entry_Caller --
752 --------------------------
754 -- This is called at the end of service of an entry call, to abort the
755 -- caller if he is in an abortable part, and to wake up the caller if it
756 -- is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
758 -- (This enforces the rule that a task must be off-queue if its state is
759 -- Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
761 -- Timed_Call or Simple_Call:
762 -- The caller is waiting on Entry_Caller_Sleep, in
763 -- Wait_For_Completion, or Wait_For_Completion_With_Timeout.
766 -- The caller might be in Wait_For_Completion,
767 -- waiting for a rendezvous (possibly requeued without abort)
770 -- Asynchronous_Call:
771 -- The caller may be executing in the abortable part o
772 -- an async. select, or on a time delay,
773 -- if Entry_Call.State >= Was_Abortable.
775 procedure Wakeup_Entry_Caller
777 Entry_Call : Entry_Call_Link;
778 New_State : Entry_Call_State)
780 Caller : constant Task_Id := Entry_Call.Self;
783 pragma Debug (Debug.Trace
784 (Self_ID, "Wakeup_Entry_Caller", 'E', Caller));
785 pragma Assert (New_State = Done or else New_State = Cancelled);
787 pragma Assert (Caller.Common.State /= Unactivated);
789 Entry_Call.State := New_State;
791 if Entry_Call.Mode = Asynchronous_Call then
793 -- Abort the caller in his abortable part, but do so only if call has
794 -- been queued abortably.
796 if Entry_Call.State >= Was_Abortable or else New_State = Done then
797 Locked_Abort_To_Level (Self_ID, Caller, Entry_Call.Level - 1);
800 elsif Caller.Common.State = Entry_Caller_Sleep then
801 Wakeup (Caller, Entry_Caller_Sleep);
803 end Wakeup_Entry_Caller;
805 -----------------------
806 -- Soft-Link Dummies --
807 -----------------------
809 -- These are dummies for subprograms that are only needed by certain
810 -- optional run-time system packages. If they are needed, the soft links
811 -- will be redirected to the real subprogram by elaboration of the
812 -- subprogram body where the real subprogram is declared.
814 procedure Finalize_Attributes (T : Task_Id) is
815 pragma Unreferenced (T);
818 end Finalize_Attributes;
820 procedure Initialize_Attributes (T : Task_Id) is
821 pragma Unreferenced (T);
824 end Initialize_Attributes;
828 end System.Tasking.Initialization;