1 ------------------------------------------------------------------------------
3 -- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
5 -- S Y S T E M . T A S K I N G . A S Y N C _ D E L A Y S --
9 -- Copyright (C) 1998-2004, 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 2, or (at your option) any later ver- --
14 -- sion. GNARL 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. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNARL; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
29 -- GNARL was developed by the GNARL team at Florida State University. --
30 -- Extensive contributions were provided by Ada Core Technologies, Inc. --
32 ------------------------------------------------------------------------------
35 -- Turn off polling, we do not want ATC polling to take place during
36 -- tasking operations. It causes infinite loops and other problems.
39 -- Used for Raise_Exception
41 with System.Task_Primitives.Operations;
42 -- Used for Write_Lock,
51 with System.Tasking.Utilities;
52 -- Used for Make_Independent
54 with System.Tasking.Initialization;
55 -- Used for Defer_Abort
58 with System.Tasking.Debug;
61 with System.OS_Primitives;
62 -- used for Max_Sensible_Delay
64 with Ada.Task_Identification;
65 -- used for Task_Id type
67 with System.Parameters;
68 -- used for Single_Lock
71 with System.Traces.Tasking;
72 -- used for Send_Trace_Info
74 with Unchecked_Conversion;
76 package body System.Tasking.Async_Delays is
78 package STPO renames System.Task_Primitives.Operations;
79 package ST renames System.Tasking;
80 package STU renames System.Tasking.Utilities;
81 package STI renames System.Tasking.Initialization;
82 package OSP renames System.OS_Primitives;
86 use System.Traces.Tasking;
88 function To_System is new Unchecked_Conversion
89 (Ada.Task_Identification.Task_Id, Task_Id);
91 Timer_Server_ID : ST.Task_Id;
93 Timer_Attention : Boolean := False;
94 pragma Atomic (Timer_Attention);
97 pragma Interrupt_Priority (System.Any_Priority'Last);
100 -- The timer queue is a circular doubly linked list, ordered by absolute
101 -- wakeup time. The first item in the queue is Timer_Queue.Succ.
102 -- It is given a Resume_Time that is larger than any legitimate wakeup
103 -- time, so that the ordered insertion will always stop searching when it
104 -- gets back to the queue header block.
106 Timer_Queue : aliased Delay_Block;
108 ------------------------
109 -- Cancel_Async_Delay --
110 ------------------------
112 -- This should (only) be called from the compiler-generated cleanup routine
113 -- for an async. select statement with delay statement as trigger. The
114 -- effect should be to remove the delay from the timer queue, and exit one
115 -- ATC nesting level.
116 -- The usage and logic are similar to Cancel_Protected_Entry_Call, but
117 -- simplified because this is not a true entry call.
119 procedure Cancel_Async_Delay (D : Delay_Block_Access) is
120 Dpred : Delay_Block_Access;
121 Dsucc : Delay_Block_Access;
124 -- Note that we mark the delay as being cancelled
125 -- using a level value that is reserved.
127 -- make this operation idempotent
129 if D.Level = ATC_Level_Infinity then
133 D.Level := ATC_Level_Infinity;
135 -- remove self from timer queue
137 STI.Defer_Abort_Nestable (D.Self_Id);
143 STPO.Write_Lock (Timer_Server_ID);
150 STPO.Unlock (Timer_Server_ID);
152 -- Note that the above deletion code is required to be
153 -- idempotent, since the block may have been dequeued
154 -- previously by the Timer_Server.
156 -- leave the asynchronous select
158 STPO.Write_Lock (D.Self_Id);
159 STU.Exit_One_ATC_Level (D.Self_Id);
160 STPO.Unlock (D.Self_Id);
166 STI.Undefer_Abort_Nestable (D.Self_Id);
167 end Cancel_Async_Delay;
169 ---------------------------
170 -- Enqueue_Time_Duration --
171 ---------------------------
173 function Enqueue_Duration
175 D : Delay_Block_Access)
185 -- The corresponding call to Undefer_Abort is performed by the
186 -- expanded code (see exp_ch9).
188 STI.Defer_Abort (STPO.Self);
190 (STPO.Monotonic_Clock
191 + Duration'Min (T, OSP.Max_Sensible_Delay), D);
194 end Enqueue_Duration;
200 -- Allocate a queue element for the wakeup time T and put it in the
201 -- queue in wakeup time order. Assume we are on an asynchronous
202 -- select statement with delay trigger. Put the calling task to
203 -- sleep until either the delay expires or is cancelled.
205 -- We use one entry call record for this delay, since we have
206 -- to increment the ATC nesting level, but since it is not a
207 -- real entry call we do not need to use any of the fields of
208 -- the call record. The following code implements a subset of
209 -- the actions for the asynchronous case of Protected_Entry_Call,
210 -- much simplified since we know this never blocks, and does not
211 -- have the full semantics of a protected entry call.
213 procedure Time_Enqueue
215 D : Delay_Block_Access)
217 Self_Id : constant Task_Id := STPO.Self;
218 Q : Delay_Block_Access;
221 -- for visibility of operator "="
224 pragma Debug (Debug.Trace (Self_Id, "Async_Delay", 'P'));
225 pragma Assert (Self_Id.Deferral_Level = 1,
226 "async delay from within abort-deferred region");
228 if Self_Id.ATC_Nesting_Level = ATC_Level'Last then
229 Ada.Exceptions.Raise_Exception (Storage_Error'Identity,
230 "not enough ATC nesting levels");
233 Self_Id.ATC_Nesting_Level := Self_Id.ATC_Nesting_Level + 1;
236 (Debug.Trace (Self_Id, "ASD: entered ATC level: " &
237 ATC_Level'Image (Self_Id.ATC_Nesting_Level), 'A'));
239 D.Level := Self_Id.ATC_Nesting_Level;
240 D.Self_Id := Self_Id;
247 STPO.Write_Lock (Timer_Server_ID);
249 -- Previously, there was code here to dynamically create
250 -- the Timer_Server task, if one did not already exist.
251 -- That code had a timing window that could allow multiple
252 -- timer servers to be created. Luckily, the need for
253 -- postponing creation of the timer server should now be
254 -- gone, since this package will only be linked in if
255 -- there are calls to enqueue calls on the timer server.
257 -- Insert D in the timer queue, at the position determined
258 -- by the wakeup time T.
260 Q := Timer_Queue.Succ;
262 while Q.Resume_Time < T loop
266 -- Q is the block that has Resume_Time equal to or greater than
267 -- T. After the insertion we want Q to be the successor of D.
274 -- If the new element became the head of the queue,
275 -- signal the Timer_Server to wake up.
277 if Timer_Queue.Succ = D then
278 Timer_Attention := True;
279 STPO.Wakeup (Timer_Server_ID, ST.Timer_Server_Sleep);
282 STPO.Unlock (Timer_Server_ID);
293 function Timed_Out (D : Delay_Block_Access) return Boolean is
302 task body Timer_Server is
303 function Get_Next_Wakeup_Time return Duration;
304 -- Used to initialize Next_Wakeup_Time, but also to ensure that
305 -- Make_Independent is called during the elaboration of this task
307 --------------------------
308 -- Get_Next_Wakeup_Time --
309 --------------------------
311 function Get_Next_Wakeup_Time return Duration is
313 STU.Make_Independent;
314 return Duration'Last;
315 end Get_Next_Wakeup_Time;
317 Next_Wakeup_Time : Duration := Get_Next_Wakeup_Time;
321 Dequeued : Delay_Block_Access;
322 Dequeued_Task : Task_Id;
325 Timer_Server_ID := STPO.Self;
327 -- Initialize the timer queue to empty, and make the wakeup time of the
328 -- header node be larger than any real wakeup time we will ever use.
331 STI.Defer_Abort (Timer_Server_ID);
337 STPO.Write_Lock (Timer_Server_ID);
339 -- The timer server needs to catch pending aborts after finalization
340 -- of library packages. If it doesn't poll for it, the server will
343 if not Timer_Attention then
344 Timer_Server_ID.Common.State := ST.Timer_Server_Sleep;
346 if Next_Wakeup_Time = Duration'Last then
347 Timer_Server_ID.User_State := 1;
349 STPO.Monotonic_Clock + OSP.Max_Sensible_Delay;
352 Timer_Server_ID.User_State := 2;
356 (Timer_Server_ID, Next_Wakeup_Time,
357 OSP.Absolute_RT, ST.Timer_Server_Sleep,
359 Timer_Server_ID.Common.State := ST.Runnable;
362 -- Service all of the wakeup requests on the queue whose times have
363 -- been reached, and update Next_Wakeup_Time to next wakeup time
364 -- after that (the wakeup time of the head of the queue if any, else
365 -- a time far in the future).
367 Timer_Server_ID.User_State := 3;
368 Timer_Attention := False;
370 Now := STPO.Monotonic_Clock;
372 while Timer_Queue.Succ.Resume_Time <= Now loop
374 -- Dequeue the waiting task from the front of the queue.
376 pragma Debug (System.Tasking.Debug.Trace
377 (Timer_Server_ID, "Timer service: waking up waiting task", 'E'));
379 Dequeued := Timer_Queue.Succ;
380 Timer_Queue.Succ := Dequeued.Succ;
381 Dequeued.Succ.Pred := Dequeued.Pred;
382 Dequeued.Succ := Dequeued;
383 Dequeued.Pred := Dequeued;
385 -- We want to abort the queued task to the level of the async.
386 -- select statement with the delay. To do that, we need to lock
387 -- the ATCB of that task, but to avoid deadlock we need to release
388 -- the lock of the Timer_Server. This leaves a window in which
389 -- another task might perform an enqueue or dequeue operation on
390 -- the timer queue, but that is OK because we always restart the
391 -- next iteration at the head of the queue.
393 if Parameters.Runtime_Traces then
394 Send_Trace_Info (E_Kill, Dequeued.Self_Id);
397 STPO.Unlock (Timer_Server_ID);
398 STPO.Write_Lock (Dequeued.Self_Id);
399 Dequeued_Task := Dequeued.Self_Id;
400 Dequeued.Timed_Out := True;
401 STI.Locked_Abort_To_Level
402 (Timer_Server_ID, Dequeued_Task, Dequeued.Level - 1);
403 STPO.Unlock (Dequeued_Task);
404 STPO.Write_Lock (Timer_Server_ID);
407 Next_Wakeup_Time := Timer_Queue.Succ.Resume_Time;
409 -- Service returns the Next_Wakeup_Time.
410 -- The Next_Wakeup_Time is either an infinity (no delay request)
411 -- or the wakeup time of the queue head. This value is used for
412 -- an actual delay in this server.
414 STPO.Unlock (Timer_Server_ID);
420 STI.Undefer_Abort (Timer_Server_ID);
424 ------------------------------
425 -- Package Body Elaboration --
426 ------------------------------
429 Timer_Queue.Succ := Timer_Queue'Unchecked_Access;
430 Timer_Queue.Pred := Timer_Queue'Unchecked_Access;
431 Timer_Queue.Resume_Time := Duration'Last;
432 Timer_Server_ID := To_System (Timer_Server'Identity);
433 end System.Tasking.Async_Delays;