1------------------------------------------------------------------------------ 2-- -- 3-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS -- 4-- -- 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 -- 6-- -- 7-- B o d y -- 8-- -- 9-- Copyright (C) 1998-2014, Free Software Foundation, Inc. -- 10-- -- 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. -- 17-- -- 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. -- 21-- -- 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/>. -- 26-- -- 27-- GNARL was developed by the GNARL team at Florida State University. -- 28-- Extensive contributions were provided by Ada Core Technologies, Inc. -- 29-- -- 30------------------------------------------------------------------------------ 31 32pragma Polling (Off); 33-- Turn off polling, we do not want ATC polling to take place during 34-- tasking operations. It causes infinite loops and other problems. 35 36with Ada.Unchecked_Conversion; 37with Ada.Task_Identification; 38 39with System.Task_Primitives.Operations; 40with System.Tasking.Utilities; 41with System.Tasking.Initialization; 42with System.Tasking.Debug; 43with System.OS_Primitives; 44with System.Interrupt_Management.Operations; 45with System.Parameters; 46with System.Traces.Tasking; 47 48package body System.Tasking.Async_Delays is 49 50 package STPO renames System.Task_Primitives.Operations; 51 package ST renames System.Tasking; 52 package STU renames System.Tasking.Utilities; 53 package STI renames System.Tasking.Initialization; 54 package OSP renames System.OS_Primitives; 55 56 use Parameters; 57 use System.Traces; 58 use System.Traces.Tasking; 59 60 function To_System is new Ada.Unchecked_Conversion 61 (Ada.Task_Identification.Task_Id, Task_Id); 62 63 Timer_Attention : Boolean := False; 64 pragma Atomic (Timer_Attention); 65 66 task Timer_Server is 67 pragma Interrupt_Priority (System.Any_Priority'Last); 68 end Timer_Server; 69 70 Timer_Server_ID : constant ST.Task_Id := To_System (Timer_Server'Identity); 71 72 -- The timer queue is a circular doubly linked list, ordered by absolute 73 -- wakeup time. The first item in the queue is Timer_Queue.Succ. 74 -- It is given a Resume_Time that is larger than any legitimate wakeup 75 -- time, so that the ordered insertion will always stop searching when it 76 -- gets back to the queue header block. 77 78 Timer_Queue : aliased Delay_Block; 79 80 package Init_Timer_Queue is end Init_Timer_Queue; 81 pragma Unreferenced (Init_Timer_Queue); 82 -- Initialize the Timer_Queue. This is a package to work around the 83 -- fact that statements are syntactically illegal here. We want this 84 -- initialization to happen before the Timer_Server is activated. A 85 -- build-in-place function would also work, but that's not supported 86 -- on all platforms (e.g. cil). 87 88 package body Init_Timer_Queue is 89 begin 90 Timer_Queue.Succ := Timer_Queue'Unchecked_Access; 91 Timer_Queue.Pred := Timer_Queue'Unchecked_Access; 92 Timer_Queue.Resume_Time := Duration'Last; 93 end Init_Timer_Queue; 94 95 ------------------------ 96 -- Cancel_Async_Delay -- 97 ------------------------ 98 99 -- This should (only) be called from the compiler-generated cleanup routine 100 -- for an async. select statement with delay statement as trigger. The 101 -- effect should be to remove the delay from the timer queue, and exit one 102 -- ATC nesting level. 103 -- The usage and logic are similar to Cancel_Protected_Entry_Call, but 104 -- simplified because this is not a true entry call. 105 106 procedure Cancel_Async_Delay (D : Delay_Block_Access) is 107 Dpred : Delay_Block_Access; 108 Dsucc : Delay_Block_Access; 109 110 begin 111 -- Note that we mark the delay as being cancelled 112 -- using a level value that is reserved. 113 114 -- make this operation idempotent 115 116 if D.Level = ATC_Level_Infinity then 117 return; 118 end if; 119 120 D.Level := ATC_Level_Infinity; 121 122 -- remove self from timer queue 123 124 STI.Defer_Abort_Nestable (D.Self_Id); 125 126 if Single_Lock then 127 STPO.Lock_RTS; 128 end if; 129 130 STPO.Write_Lock (Timer_Server_ID); 131 Dpred := D.Pred; 132 Dsucc := D.Succ; 133 Dpred.Succ := Dsucc; 134 Dsucc.Pred := Dpred; 135 D.Succ := D; 136 D.Pred := D; 137 STPO.Unlock (Timer_Server_ID); 138 139 -- Note that the above deletion code is required to be 140 -- idempotent, since the block may have been dequeued 141 -- previously by the Timer_Server. 142 143 -- leave the asynchronous select 144 145 STPO.Write_Lock (D.Self_Id); 146 STU.Exit_One_ATC_Level (D.Self_Id); 147 STPO.Unlock (D.Self_Id); 148 149 if Single_Lock then 150 STPO.Unlock_RTS; 151 end if; 152 153 STI.Undefer_Abort_Nestable (D.Self_Id); 154 end Cancel_Async_Delay; 155 156 ---------------------- 157 -- Enqueue_Duration -- 158 ---------------------- 159 160 function Enqueue_Duration 161 (T : Duration; 162 D : Delay_Block_Access) return Boolean 163 is 164 begin 165 if T <= 0.0 then 166 D.Timed_Out := True; 167 STPO.Yield; 168 return False; 169 170 else 171 -- The corresponding call to Undefer_Abort is performed by the 172 -- expanded code (see exp_ch9). 173 174 STI.Defer_Abort (STPO.Self); 175 Time_Enqueue 176 (STPO.Monotonic_Clock 177 + Duration'Min (T, OSP.Max_Sensible_Delay), D); 178 return True; 179 end if; 180 end Enqueue_Duration; 181 182 ------------------ 183 -- Time_Enqueue -- 184 ------------------ 185 186 -- Allocate a queue element for the wakeup time T and put it in the 187 -- queue in wakeup time order. Assume we are on an asynchronous 188 -- select statement with delay trigger. Put the calling task to 189 -- sleep until either the delay expires or is cancelled. 190 191 -- We use one entry call record for this delay, since we have 192 -- to increment the ATC nesting level, but since it is not a 193 -- real entry call we do not need to use any of the fields of 194 -- the call record. The following code implements a subset of 195 -- the actions for the asynchronous case of Protected_Entry_Call, 196 -- much simplified since we know this never blocks, and does not 197 -- have the full semantics of a protected entry call. 198 199 procedure Time_Enqueue 200 (T : Duration; 201 D : Delay_Block_Access) 202 is 203 Self_Id : constant Task_Id := STPO.Self; 204 Q : Delay_Block_Access; 205 206 use type ST.Task_Id; 207 -- for visibility of operator "=" 208 209 begin 210 pragma Debug (Debug.Trace (Self_Id, "Async_Delay", 'P')); 211 pragma Assert (Self_Id.Deferral_Level = 1, 212 "async delay from within abort-deferred region"); 213 214 if Self_Id.ATC_Nesting_Level = ATC_Level'Last then 215 raise Storage_Error with "not enough ATC nesting levels"; 216 end if; 217 218 Self_Id.ATC_Nesting_Level := Self_Id.ATC_Nesting_Level + 1; 219 220 pragma Debug 221 (Debug.Trace (Self_Id, "ASD: entered ATC level: " & 222 ATC_Level'Image (Self_Id.ATC_Nesting_Level), 'A')); 223 224 D.Level := Self_Id.ATC_Nesting_Level; 225 D.Self_Id := Self_Id; 226 D.Resume_Time := T; 227 228 if Single_Lock then 229 STPO.Lock_RTS; 230 end if; 231 232 STPO.Write_Lock (Timer_Server_ID); 233 234 -- Previously, there was code here to dynamically create 235 -- the Timer_Server task, if one did not already exist. 236 -- That code had a timing window that could allow multiple 237 -- timer servers to be created. Luckily, the need for 238 -- postponing creation of the timer server should now be 239 -- gone, since this package will only be linked in if 240 -- there are calls to enqueue calls on the timer server. 241 242 -- Insert D in the timer queue, at the position determined 243 -- by the wakeup time T. 244 245 Q := Timer_Queue.Succ; 246 247 while Q.Resume_Time < T loop 248 Q := Q.Succ; 249 end loop; 250 251 -- Q is the block that has Resume_Time equal to or greater than 252 -- T. After the insertion we want Q to be the successor of D. 253 254 D.Succ := Q; 255 D.Pred := Q.Pred; 256 D.Pred.Succ := D; 257 Q.Pred := D; 258 259 -- If the new element became the head of the queue, 260 -- signal the Timer_Server to wake up. 261 262 if Timer_Queue.Succ = D then 263 Timer_Attention := True; 264 STPO.Wakeup (Timer_Server_ID, ST.Timer_Server_Sleep); 265 end if; 266 267 STPO.Unlock (Timer_Server_ID); 268 269 if Single_Lock then 270 STPO.Unlock_RTS; 271 end if; 272 end Time_Enqueue; 273 274 --------------- 275 -- Timed_Out -- 276 --------------- 277 278 function Timed_Out (D : Delay_Block_Access) return Boolean is 279 begin 280 return D.Timed_Out; 281 end Timed_Out; 282 283 ------------------ 284 -- Timer_Server -- 285 ------------------ 286 287 task body Timer_Server is 288 Ignore : constant Boolean := STU.Make_Independent; 289 290 -- Local Declarations 291 292 Next_Wakeup_Time : Duration := Duration'Last; 293 Timedout : Boolean; 294 Yielded : Boolean; 295 Now : Duration; 296 Dequeued : Delay_Block_Access; 297 Dequeued_Task : Task_Id; 298 299 pragma Unreferenced (Timedout, Yielded); 300 301 begin 302 pragma Assert (Timer_Server_ID = STPO.Self); 303 304 -- Since this package may be elaborated before System.Interrupt, 305 -- we need to call Setup_Interrupt_Mask explicitly to ensure that 306 -- this task has the proper signal mask. 307 308 Interrupt_Management.Operations.Setup_Interrupt_Mask; 309 310 -- Initialize the timer queue to empty, and make the wakeup time of the 311 -- header node be larger than any real wakeup time we will ever use. 312 313 loop 314 STI.Defer_Abort (Timer_Server_ID); 315 316 if Single_Lock then 317 STPO.Lock_RTS; 318 end if; 319 320 STPO.Write_Lock (Timer_Server_ID); 321 322 -- The timer server needs to catch pending aborts after finalization 323 -- of library packages. If it doesn't poll for it, the server will 324 -- sometimes hang. 325 326 if not Timer_Attention then 327 Timer_Server_ID.Common.State := ST.Timer_Server_Sleep; 328 329 if Next_Wakeup_Time = Duration'Last then 330 Timer_Server_ID.User_State := 1; 331 Next_Wakeup_Time := 332 STPO.Monotonic_Clock + OSP.Max_Sensible_Delay; 333 334 else 335 Timer_Server_ID.User_State := 2; 336 end if; 337 338 STPO.Timed_Sleep 339 (Timer_Server_ID, Next_Wakeup_Time, 340 OSP.Absolute_RT, ST.Timer_Server_Sleep, 341 Timedout, Yielded); 342 Timer_Server_ID.Common.State := ST.Runnable; 343 end if; 344 345 -- Service all of the wakeup requests on the queue whose times have 346 -- been reached, and update Next_Wakeup_Time to next wakeup time 347 -- after that (the wakeup time of the head of the queue if any, else 348 -- a time far in the future). 349 350 Timer_Server_ID.User_State := 3; 351 Timer_Attention := False; 352 353 Now := STPO.Monotonic_Clock; 354 while Timer_Queue.Succ.Resume_Time <= Now loop 355 356 -- Dequeue the waiting task from the front of the queue 357 358 pragma Debug (System.Tasking.Debug.Trace 359 (Timer_Server_ID, "Timer service: waking up waiting task", 'E')); 360 361 Dequeued := Timer_Queue.Succ; 362 Timer_Queue.Succ := Dequeued.Succ; 363 Dequeued.Succ.Pred := Dequeued.Pred; 364 Dequeued.Succ := Dequeued; 365 Dequeued.Pred := Dequeued; 366 367 -- We want to abort the queued task to the level of the async. 368 -- select statement with the delay. To do that, we need to lock 369 -- the ATCB of that task, but to avoid deadlock we need to release 370 -- the lock of the Timer_Server. This leaves a window in which 371 -- another task might perform an enqueue or dequeue operation on 372 -- the timer queue, but that is OK because we always restart the 373 -- next iteration at the head of the queue. 374 375 if Parameters.Runtime_Traces then 376 Send_Trace_Info (E_Kill, Dequeued.Self_Id); 377 end if; 378 379 STPO.Unlock (Timer_Server_ID); 380 STPO.Write_Lock (Dequeued.Self_Id); 381 Dequeued_Task := Dequeued.Self_Id; 382 Dequeued.Timed_Out := True; 383 STI.Locked_Abort_To_Level 384 (Timer_Server_ID, Dequeued_Task, Dequeued.Level - 1); 385 STPO.Unlock (Dequeued_Task); 386 STPO.Write_Lock (Timer_Server_ID); 387 end loop; 388 389 Next_Wakeup_Time := Timer_Queue.Succ.Resume_Time; 390 391 -- Service returns the Next_Wakeup_Time. 392 -- The Next_Wakeup_Time is either an infinity (no delay request) 393 -- or the wakeup time of the queue head. This value is used for 394 -- an actual delay in this server. 395 396 STPO.Unlock (Timer_Server_ID); 397 398 if Single_Lock then 399 STPO.Unlock_RTS; 400 end if; 401 402 STI.Undefer_Abort (Timer_Server_ID); 403 end loop; 404 end Timer_Server; 405 406end System.Tasking.Async_Delays; 407