1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
5 -- S Y S T E M . T A S K I N G . E N T R Y _ C A L L S --
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 with System.Task_Primitives.Operations;
33 with System.Tasking.Initialization;
34 with System.Tasking.Protected_Objects.Entries;
35 with System.Tasking.Protected_Objects.Operations;
36 with System.Tasking.Queuing;
37 with System.Tasking.Utilities;
38 with System.Parameters;
41 package body System.Tasking.Entry_Calls is
43 package STPO renames System.Task_Primitives.Operations;
47 use Protected_Objects.Entries;
48 use Protected_Objects.Operations;
51 -- DO NOT use Protected_Objects.Lock or Protected_Objects.Unlock
52 -- internally. Those operations will raise Program_Error, which
53 -- we are not prepared to handle inside the RTS. Instead, use
54 -- System.Task_Primitives lock operations directly on Protection.L.
56 -----------------------
57 -- Local Subprograms --
58 -----------------------
60 procedure Lock_Server (Entry_Call : Entry_Call_Link);
62 -- This locks the server targeted by Entry_Call
64 -- This may be a task or a protected object, depending on the target of the
65 -- original call or any subsequent requeues.
67 -- This routine is needed because the field specifying the server for this
68 -- call must be protected by the server's mutex. If it were protected by
69 -- the caller's mutex, accessing the server's queues would require locking
70 -- the caller to get the server, locking the server, and then accessing the
71 -- queues. This involves holding two ATCB locks at once, something which we
72 -- can guarantee that it will always be done in the same order, or locking
73 -- a protected object while we hold an ATCB lock, something which is not
74 -- permitted. Since the server cannot be obtained reliably, it must be
75 -- obtained unreliably and then checked again once it has been locked.
77 -- If Single_Lock and server is a PO, release RTS_Lock
79 -- This should only be called by the Entry_Call.Self.
80 -- It should be holding no other ATCB locks at the time.
82 procedure Unlock_Server (Entry_Call : Entry_Call_Link);
83 -- STPO.Unlock the server targeted by Entry_Call. The server must
84 -- be locked before calling this.
86 -- If Single_Lock and server is a PO, take RTS_Lock on exit.
88 procedure Unlock_And_Update_Server
90 Entry_Call : Entry_Call_Link);
91 -- Similar to Unlock_Server, but services entry calls if the
92 -- server is a protected object.
94 -- If Single_Lock and server is a PO, take RTS_Lock on exit.
96 procedure Check_Pending_Actions_For_Entry_Call
98 Entry_Call : Entry_Call_Link);
99 -- This procedure performs priority change of a queued call and dequeuing
100 -- of an entry call when the call is cancelled. If the call is dequeued the
101 -- state should be set to Cancelled. Call only with abort deferred and
102 -- holding lock of Self_ID. This is a bit of common code for all entry
103 -- calls. The effect is to do any deferred base priority change operation,
104 -- in case some other task called STPO.Set_Priority while the current task
105 -- had abort deferred, and to dequeue the call if the call has been
108 procedure Poll_Base_Priority_Change_At_Entry_Call
110 Entry_Call : Entry_Call_Link);
111 pragma Inline (Poll_Base_Priority_Change_At_Entry_Call);
112 -- A specialized version of Poll_Base_Priority_Change, that does the
113 -- optional entry queue reordering. Has to be called with the Self_ID's
114 -- ATCB write-locked. May temporarily release the lock.
116 ---------------------
117 -- Check_Exception --
118 ---------------------
120 procedure Check_Exception
122 Entry_Call : Entry_Call_Link)
124 pragma Warnings (Off, Self_ID);
126 use type Ada.Exceptions.Exception_Id;
128 procedure Internal_Raise (X : Ada.Exceptions.Exception_Id);
129 pragma Import (C, Internal_Raise, "__gnat_raise_with_msg");
131 E : constant Ada.Exceptions.Exception_Id :=
132 Entry_Call.Exception_To_Raise;
134 -- pragma Assert (Self_ID.Deferral_Level = 0);
136 -- The above may be useful for debugging, but the Florist packages
137 -- contain critical sections that defer abort and then do entry calls,
138 -- which causes the above Assert to trip.
140 if E /= Ada.Exceptions.Null_Id then
145 ------------------------------------------
146 -- Check_Pending_Actions_For_Entry_Call --
147 ------------------------------------------
149 procedure Check_Pending_Actions_For_Entry_Call
151 Entry_Call : Entry_Call_Link)
154 pragma Assert (Self_ID = Entry_Call.Self);
156 Poll_Base_Priority_Change_At_Entry_Call (Self_ID, Entry_Call);
158 if Self_ID.Pending_ATC_Level < Self_ID.ATC_Nesting_Level
159 and then Entry_Call.State = Now_Abortable
161 STPO.Unlock (Self_ID);
162 Lock_Server (Entry_Call);
164 if Queuing.Onqueue (Entry_Call)
165 and then Entry_Call.State = Now_Abortable
167 Queuing.Dequeue_Call (Entry_Call);
169 if Entry_Call.Cancellation_Attempted then
170 Entry_Call.State := Cancelled;
172 Entry_Call.State := Done;
175 Unlock_And_Update_Server (Self_ID, Entry_Call);
178 Unlock_Server (Entry_Call);
181 STPO.Write_Lock (Self_ID);
183 end Check_Pending_Actions_For_Entry_Call;
189 procedure Lock_Server (Entry_Call : Entry_Call_Link) is
191 Test_PO : Protection_Entries_Access;
192 Ceiling_Violation : Boolean;
193 Failures : Integer := 0;
196 Test_Task := Entry_Call.Called_Task;
199 if Test_Task = null then
201 -- Entry_Call was queued on a protected object, or in transition,
202 -- when we last fetched Test_Task.
204 Test_PO := To_Protection (Entry_Call.Called_PO);
206 if Test_PO = null then
208 -- We had very bad luck, interleaving with TWO different
209 -- requeue operations. Go around the loop and try again.
224 Lock_Entries (Test_PO, Ceiling_Violation);
228 -- The following code allows Lock_Server to be called when
229 -- cancelling a call, to allow for the possibility that the
230 -- priority of the caller has been raised beyond that of the
231 -- protected entry call by Ada.Dynamic_Priorities.Set_Priority.
233 -- If the current task has a higher priority than the ceiling
234 -- of the protected object, temporarily lower it. It will
235 -- be reset in Unlock.
237 if Ceiling_Violation then
239 Current_Task : constant Task_Id := STPO.Self;
240 Old_Base_Priority : System.Any_Priority;
247 STPO.Write_Lock (Current_Task);
248 Old_Base_Priority := Current_Task.Common.Base_Priority;
249 Current_Task.New_Base_Priority := Test_PO.Ceiling;
250 System.Tasking.Initialization.Change_Base_Priority
252 STPO.Unlock (Current_Task);
258 -- Following lock should not fail
260 Lock_Entries (Test_PO);
262 Test_PO.Old_Base_Priority := Old_Base_Priority;
263 Test_PO.Pending_Action := True;
267 exit when To_Address (Test_PO) = Entry_Call.Called_PO;
268 Unlock_Entries (Test_PO);
276 STPO.Write_Lock (Test_Task);
277 exit when Test_Task = Entry_Call.Called_Task;
278 STPO.Unlock (Test_Task);
281 Test_Task := Entry_Call.Called_Task;
282 Failures := Failures + 1;
283 pragma Assert (Failures <= 5);
287 ---------------------------------------------
288 -- Poll_Base_Priority_Change_At_Entry_Call --
289 ---------------------------------------------
291 procedure Poll_Base_Priority_Change_At_Entry_Call
293 Entry_Call : Entry_Call_Link)
296 if Self_ID.Pending_Priority_Change then
298 -- Check for ceiling violations ???
300 Self_ID.Pending_Priority_Change := False;
302 -- Requeue the entry call at the new priority. We need to requeue
303 -- even if the new priority is the same than the previous (see ACATS
306 STPO.Unlock (Self_ID);
307 Lock_Server (Entry_Call);
308 Queuing.Requeue_Call_With_New_Prio
309 (Entry_Call, STPO.Get_Priority (Self_ID));
310 Unlock_And_Update_Server (Self_ID, Entry_Call);
311 STPO.Write_Lock (Self_ID);
313 end Poll_Base_Priority_Change_At_Entry_Call;
319 procedure Reset_Priority
321 Acceptor_Prev_Priority : Rendezvous_Priority)
324 pragma Assert (Acceptor = STPO.Self);
326 -- Since we limit this kind of "active" priority change to be done
327 -- by the task for itself, we don't need to lock Acceptor.
329 if Acceptor_Prev_Priority /= Priority_Not_Boosted then
330 STPO.Set_Priority (Acceptor, Acceptor_Prev_Priority,
331 Loss_Of_Inheritance => True);
335 ------------------------------
336 -- Try_To_Cancel_Entry_Call --
337 ------------------------------
339 procedure Try_To_Cancel_Entry_Call (Succeeded : out Boolean) is
340 Entry_Call : Entry_Call_Link;
341 Self_ID : constant Task_Id := STPO.Self;
343 use type Ada.Exceptions.Exception_Id;
346 Entry_Call := Self_ID.Entry_Calls (Self_ID.ATC_Nesting_Level)'Access;
348 -- Experimentation has shown that abort is sometimes (but not
349 -- always) already deferred when Cancel_xxx_Entry_Call is called.
350 -- That may indicate an error. Find out what is going on. ???
352 pragma Assert (Entry_Call.Mode = Asynchronous_Call);
353 Initialization.Defer_Abort_Nestable (Self_ID);
359 STPO.Write_Lock (Self_ID);
360 Entry_Call.Cancellation_Attempted := True;
362 if Self_ID.Pending_ATC_Level >= Entry_Call.Level then
363 Self_ID.Pending_ATC_Level := Entry_Call.Level - 1;
366 Entry_Calls.Wait_For_Completion (Entry_Call);
367 STPO.Unlock (Self_ID);
373 Succeeded := Entry_Call.State = Cancelled;
375 Initialization.Undefer_Abort_Nestable (Self_ID);
377 -- Ideally, abort should no longer be deferred at this point, so we
378 -- should be able to call Check_Exception. The loop below should be
379 -- considered temporary, to work around the possibility that abort
380 -- may be deferred more than one level deep ???
382 if Entry_Call.Exception_To_Raise /= Ada.Exceptions.Null_Id then
383 while Self_ID.Deferral_Level > 0 loop
384 System.Tasking.Initialization.Undefer_Abort_Nestable (Self_ID);
387 Entry_Calls.Check_Exception (Self_ID, Entry_Call);
389 end Try_To_Cancel_Entry_Call;
391 ------------------------------
392 -- Unlock_And_Update_Server --
393 ------------------------------
395 procedure Unlock_And_Update_Server
397 Entry_Call : Entry_Call_Link)
399 Called_PO : Protection_Entries_Access;
403 if Entry_Call.Called_Task /= null then
404 STPO.Unlock (Entry_Call.Called_Task);
406 Called_PO := To_Protection (Entry_Call.Called_PO);
407 PO_Service_Entries (Self_ID, Called_PO, False);
409 if Called_PO.Pending_Action then
410 Called_PO.Pending_Action := False;
417 STPO.Write_Lock (Caller);
418 Caller.New_Base_Priority := Called_PO.Old_Base_Priority;
419 Initialization.Change_Base_Priority (Caller);
420 STPO.Unlock (Caller);
427 Unlock_Entries (Called_PO);
433 end Unlock_And_Update_Server;
439 procedure Unlock_Server (Entry_Call : Entry_Call_Link) is
441 Called_PO : Protection_Entries_Access;
444 if Entry_Call.Called_Task /= null then
445 STPO.Unlock (Entry_Call.Called_Task);
447 Called_PO := To_Protection (Entry_Call.Called_PO);
449 if Called_PO.Pending_Action then
450 Called_PO.Pending_Action := False;
457 STPO.Write_Lock (Caller);
458 Caller.New_Base_Priority := Called_PO.Old_Base_Priority;
459 Initialization.Change_Base_Priority (Caller);
460 STPO.Unlock (Caller);
467 Unlock_Entries (Called_PO);
475 -------------------------
476 -- Wait_For_Completion --
477 -------------------------
479 procedure Wait_For_Completion (Entry_Call : Entry_Call_Link) is
480 Self_Id : constant Task_Id := Entry_Call.Self;
483 -- If this is a conditional call, it should be cancelled when it
484 -- becomes abortable. This is checked in the loop below.
486 if Parameters.Runtime_Traces then
487 Send_Trace_Info (W_Completion);
490 Self_Id.Common.State := Entry_Caller_Sleep;
492 -- Try to remove calls to Sleep in the loop below by letting the caller
493 -- a chance of getting ready immediately, using Unlock & Yield.
494 -- See similar action in Wait_For_Call & Timed_Selective_Wait.
499 STPO.Unlock (Self_Id);
502 if Entry_Call.State < Done then
509 STPO.Write_Lock (Self_Id);
513 Check_Pending_Actions_For_Entry_Call (Self_Id, Entry_Call);
515 exit when Entry_Call.State >= Done;
517 STPO.Sleep (Self_Id, Entry_Caller_Sleep);
520 Self_Id.Common.State := Runnable;
521 Utilities.Exit_One_ATC_Level (Self_Id);
523 if Parameters.Runtime_Traces then
524 Send_Trace_Info (M_Call_Complete);
526 end Wait_For_Completion;
528 --------------------------------------
529 -- Wait_For_Completion_With_Timeout --
530 --------------------------------------
532 procedure Wait_For_Completion_With_Timeout
533 (Entry_Call : Entry_Call_Link;
534 Wakeup_Time : Duration;
536 Yielded : out Boolean)
538 Self_Id : constant Task_Id := Entry_Call.Self;
539 Timedout : Boolean := False;
541 use type Ada.Exceptions.Exception_Id;
544 -- This procedure waits for the entry call to be served, with a timeout.
545 -- It tries to cancel the call if the timeout expires before the call is
548 -- If we wake up from the timed sleep operation here, it may be for
549 -- several possible reasons:
551 -- 1) The entry call is done being served.
552 -- 2) There is an abort or priority change to be served.
553 -- 3) The timeout has expired (Timedout = True)
554 -- 4) There has been a spurious wakeup.
556 -- Once the timeout has expired we may need to continue to wait if the
557 -- call is already being serviced. In that case, we want to go back to
558 -- sleep, but without any timeout. The variable Timedout is used to
559 -- control this. If the Timedout flag is set, we do not need to
560 -- STPO.Sleep with a timeout. We just sleep until we get a wakeup for
561 -- some status change.
563 -- The original call may have become abortable after waking up. We want
564 -- to check Check_Pending_Actions_For_Entry_Call again in any case.
566 pragma Assert (Entry_Call.Mode = Timed_Call);
569 Self_Id.Common.State := Entry_Caller_Sleep;
571 -- Looping is necessary in case the task wakes up early from the timed
572 -- sleep, due to a "spurious wakeup". Spurious wakeups are a weakness of
573 -- POSIX condition variables. A thread waiting for a condition variable
574 -- is allowed to wake up at any time, not just when the condition is
575 -- signaled. See same loop in the ordinary Wait_For_Completion, above.
577 if Parameters.Runtime_Traces then
578 Send_Trace_Info (WT_Completion, Wakeup_Time);
582 Check_Pending_Actions_For_Entry_Call (Self_Id, Entry_Call);
583 exit when Entry_Call.State >= Done;
585 STPO.Timed_Sleep (Self_Id, Wakeup_Time, Mode,
586 Entry_Caller_Sleep, Timedout, Yielded);
589 if Parameters.Runtime_Traces then
590 Send_Trace_Info (E_Timeout);
593 -- Try to cancel the call (see Try_To_Cancel_Entry_Call for
594 -- corresponding code in the ATC case).
596 Entry_Call.Cancellation_Attempted := True;
598 if Self_Id.Pending_ATC_Level >= Entry_Call.Level then
599 Self_Id.Pending_ATC_Level := Entry_Call.Level - 1;
602 -- The following loop is the same as the loop and exit code
603 -- from the ordinary Wait_For_Completion. If we get here, we
604 -- have timed out but we need to keep waiting until the call
605 -- has actually completed or been cancelled successfully.
608 Check_Pending_Actions_For_Entry_Call (Self_Id, Entry_Call);
609 exit when Entry_Call.State >= Done;
610 STPO.Sleep (Self_Id, Entry_Caller_Sleep);
613 Self_Id.Common.State := Runnable;
614 Utilities.Exit_One_ATC_Level (Self_Id);
620 -- This last part is the same as ordinary Wait_For_Completion,
621 -- and is only executed if the call completed without timing out.
623 if Parameters.Runtime_Traces then
624 Send_Trace_Info (M_Call_Complete);
627 Self_Id.Common.State := Runnable;
628 Utilities.Exit_One_ATC_Level (Self_Id);
629 end Wait_For_Completion_With_Timeout;
631 --------------------------
632 -- Wait_Until_Abortable --
633 --------------------------
635 procedure Wait_Until_Abortable
637 Call : Entry_Call_Link)
640 pragma Assert (Self_ID.ATC_Nesting_Level > 0);
641 pragma Assert (Call.Mode = Asynchronous_Call);
643 if Parameters.Runtime_Traces then
644 Send_Trace_Info (W_Completion);
647 STPO.Write_Lock (Self_ID);
648 Self_ID.Common.State := Entry_Caller_Sleep;
651 Check_Pending_Actions_For_Entry_Call (Self_ID, Call);
652 exit when Call.State >= Was_Abortable;
653 STPO.Sleep (Self_ID, Async_Select_Sleep);
656 Self_ID.Common.State := Runnable;
657 STPO.Unlock (Self_ID);
659 if Parameters.Runtime_Traces then
660 Send_Trace_Info (M_Call_Complete);
662 end Wait_Until_Abortable;
664 end System.Tasking.Entry_Calls;