1 ------------------------------------------------------------------------------
3 -- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
5 -- S Y S T E M . T A S K I N G --
9 -- Copyright (C) 1992-2004, 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 ------------------------------------------------------------------------------
34 -- This package provides necessary type definitions for compiler interface.
36 -- Note: the compiler generates direct calls to this interface, via Rtsfind.
37 -- Any changes to this interface may require corresponding compiler changes.
40 -- Used for: Exception_Id
42 with System.Parameters;
45 with System.Task_Info;
46 -- used for Task_Info_Type
48 with System.Soft_Links;
51 with System.Task_Primitives;
52 -- used for Private_Data
54 with Unchecked_Conversion;
56 package System.Tasking is
62 -- The following rules must be followed at all times, to prevent
63 -- deadlock and generally ensure correct operation of locking.
65 -- . Never lock a lock unless abort is deferred.
67 -- . Never undefer abort while holding a lock.
69 -- . Overlapping critical sections must be properly nested,
70 -- and locks must be released in LIFO order.
71 -- e.g., the following is not allowed:
81 -- Locks with lower (smaller) level number cannot be locked
82 -- while holding a lock with a higher level number. (The level
83 -- number is the number at the left.)
85 -- 1. System.Tasking.PO_Simple.Protection.L (any PO lock)
86 -- 2. System.Tasking.Initialization.Global_Task_Lock (in body)
87 -- 3. System.Task_Primitives.Operations.Single_RTS_Lock
88 -- 4. System.Tasking.Ada_Task_Control_Block.LL.L (any TCB lock)
90 -- Clearly, there can be no circular chain of hold-and-wait
91 -- relationships involving locks in different ordering levels.
93 -- We used to have Global_Task_Lock before Protection.L but this was
94 -- clearly wrong since there can be calls to "new" inside protected
95 -- operations. The new ordering prevents these failures.
97 -- Sometimes we need to hold two ATCB locks at the same time. To allow
98 -- us to order the locking, each ATCB is given a unique serial
99 -- number. If one needs to hold locks on several ATCBs at once,
100 -- the locks with lower serial numbers must be locked first.
102 -- We don't always need to check the serial numbers, since
103 -- the serial numbers are assigned sequentially, and so:
105 -- . The parent of a task always has a lower serial number.
106 -- . The activator of a task always has a lower serial number.
107 -- . The environment task has a lower serial number than any other task.
108 -- . If the activator of a task is different from the task's parent,
109 -- the parent always has a lower serial number than the activator.
111 ---------------------------------
112 -- Task_Id related definitions --
113 ---------------------------------
115 type Ada_Task_Control_Block;
117 type Task_Id is access all Ada_Task_Control_Block;
119 Null_Task : constant Task_Id;
121 type Task_List is array (Positive range <>) of Task_Id;
123 function Self return Task_Id;
124 pragma Inline (Self);
125 -- This is the compiler interface version of this function. Do not call
126 -- from the run-time system.
128 function To_Task_Id is new Unchecked_Conversion (System.Address, Task_Id);
129 function To_Address is new Unchecked_Conversion (Task_Id, System.Address);
131 -----------------------
132 -- Enumeration types --
133 -----------------------
137 -- Task has been created but has not been activated.
138 -- It cannot be executing.
141 -- For all states from here down, the task has been activated.
142 -- For all states from here down, except for Terminated, the task
144 -- Activator = null iff it has not yet completed activating.
146 -- For all states from here down,
147 -- the task has been activated, and may be executing.
150 -- Task is not blocked for any reason known to Ada.
151 -- (It may be waiting for a mutex, though.)
152 -- It is conceptually "executing" in normal mode.
155 -- The task is terminated, in the sense of ARM 9.3 (5).
156 -- Any dependents that were waiting on terminate
157 -- alternatives have been awakened and have terminated themselves.
160 -- Task is waiting for created tasks to complete activation.
163 -- Task is waiting on an accept or selective wait statement.
166 -- Task is waiting on an entry call.
169 -- Task is waiting to start the abortable part of an
170 -- asynchronous select statement.
173 -- Task is waiting on a select statement with only a delay
176 Master_Completion_Sleep,
177 -- Master completion has two phases.
178 -- In Phase 1 the task is sleeping in Complete_Master
179 -- having completed a master within itself,
180 -- and is waiting for the tasks dependent on that master to become
181 -- terminated or waiting on a terminate Phase.
183 Master_Phase_2_Sleep,
184 -- In Phase 2 the task is sleeping in Complete_Master
185 -- waiting for tasks on terminate alternatives to finish
188 -- The following are special uses of sleep, for server tasks
189 -- within the run-time system.
191 Interrupt_Server_Idle_Sleep,
192 Interrupt_Server_Blocked_Interrupt_Sleep,
197 -- The task has been held by Asynchronous_Task_Control.Hold_Task
199 Interrupt_Server_Blocked_On_Event_Flag
200 -- The task has been blocked on a system call waiting for the
205 (Simple_Call, Conditional_Call, Asynchronous_Call, Timed_Call);
207 type Select_Modes is (Simple_Mode, Else_Mode, Terminate_Mode, Delay_Mode);
209 subtype Delay_Modes is Integer;
211 -------------------------------
212 -- Entry related definitions --
213 -------------------------------
215 Null_Entry : constant := 0;
217 Max_Entry : constant := Integer'Last;
219 Interrupt_Entry : constant := -2;
221 Cancelled_Entry : constant := -1;
223 type Entry_Index is range Interrupt_Entry .. Max_Entry;
225 Null_Task_Entry : constant := Null_Entry;
227 Max_Task_Entry : constant := Max_Entry;
229 type Task_Entry_Index is new Entry_Index
230 range Null_Task_Entry .. Max_Task_Entry;
232 type Entry_Call_Record;
234 type Entry_Call_Link is access all Entry_Call_Record;
236 type Entry_Queue is record
237 Head : Entry_Call_Link;
238 Tail : Entry_Call_Link;
241 type Task_Entry_Queue_Array is
242 array (Task_Entry_Index range <>) of Entry_Queue;
244 ----------------------------------
245 -- Entry_Call_Record definition --
246 ----------------------------------
248 type Entry_Call_State is
250 -- the call is not abortable, and never can be
253 -- the call is not abortable, but may become so
256 -- the call is not abortable, but once was
259 -- the call is abortable
262 -- the call has been completed
265 -- the call was asynchronous, and was cancelled
268 -- Never_Abortable is used for calls that are made in a abort
269 -- deferred region (see ARM 9.8(5-11), 9.8 (20)).
270 -- Such a call is never abortable.
272 -- The Was_ vs. Not_Yet_ distinction is needed to decide whether it
273 -- is OK to advance into the abortable part of an async. select stmt.
274 -- That is allowed iff the mode is Now_ or Was_.
276 -- Done indicates the call has been completed, without cancellation,
277 -- or no call has been made yet at this ATC nesting level,
278 -- and so aborting the call is no longer an issue.
279 -- Completion of the call does not necessarily indicate "success";
280 -- the call may be returning an exception if Exception_To_Raise is
283 -- Cancelled indicates the call was cancelled,
284 -- and so aborting the call is no longer an issue.
286 -- The call is on an entry queue unless
287 -- State >= Done, in which case it may or may not be still Onqueue.
289 -- Please do not modify the order of the values, without checking
290 -- all uses of this type. We rely on partial "monotonicity" of
291 -- Entry_Call_Record.State to avoid locking when we access this
292 -- value for certain tests. In particular:
294 -- 1) Once State >= Done, we can rely that the call has been
295 -- completed. If State >= Done, it will not
296 -- change until the task does another entry call at this level.
298 -- 2) Once State >= Was_Abortable, we can rely that the call has
299 -- been queued abortably at least once, and so the check for
300 -- whether it is OK to advance to the abortable part of an
301 -- async. select statement does not need to lock anything.
303 type Restricted_Entry_Call_Record is record
309 State : Entry_Call_State;
310 pragma Atomic (State);
311 -- Indicates part of the state of the call.
313 -- If the call is not on a queue, it should
314 -- only be accessed by Self, and Self does not need any
315 -- lock to modify this field.
316 -- Once the call is on a queue, the value should be
317 -- something other than Done unless it is cancelled, and access is
318 -- controller by the "server" of the queue -- i.e., the lock
319 -- of Checked_To_Protection (Call_Target)
320 -- if the call record is on the queue of a PO, or the lock
321 -- of Called_Target if the call is on the queue of a task.
322 -- See comments on type declaration for more details.
324 Uninterpreted_Data : System.Address;
325 -- Data passed by the compiler.
327 Exception_To_Raise : Ada.Exceptions.Exception_Id;
328 -- The exception to raise once this call has been completed without
331 pragma Suppress_Initialization (Restricted_Entry_Call_Record);
333 ------------------------------------
334 -- Task related other definitions --
335 ------------------------------------
337 type Activation_Chain is limited private;
339 type Activation_Chain_Access is access all Activation_Chain;
341 type Task_Procedure_Access is access procedure (Arg : System.Address);
343 type Access_Boolean is access all Boolean;
345 ----------------------------------------------
346 -- Ada_Task_Control_Block (ATCB) definition --
347 ----------------------------------------------
349 -- Notes on protection (synchronization) of TRTS data structures.
351 -- Any field of the TCB can be written by the activator of a task when the
352 -- task is created, since no other task can access the new task's
353 -- state until creation is complete.
355 -- The protection for each field is described in a comment starting with
358 -- When a lock is used to protect an ATCB field, this lock is simply named.
360 -- Some protection is described in terms of tasks related to the
361 -- ATCB being protected. These are:
363 -- Self: The task which is controlled by this ATCB
364 -- Acceptor: A task accepting a call from Self
365 -- Caller: A task calling an entry of Self
366 -- Parent: The task executing the master on which Self depends
367 -- Dependent: A task dependent on Self
368 -- Activator: The task that created Self and initiated its activation
369 -- Created: A task created and activated by Self
371 -- Note: The order of the fields is important to implement efficiently
372 -- tasking support under gdb.
373 -- Currently gdb relies on the order of the State, Parent, Base_Priority,
374 -- Task_Image, Task_Image_Len, Call and LL fields.
376 -------------------------
377 -- Common ATCB section --
378 -------------------------
380 -- Section used by all GNARL implementations (regular and restricted)
382 type Common_ATCB is record
384 pragma Atomic (State);
385 -- Encodes some basic information about the state of a task,
386 -- including whether it has been activated, whether it is sleeping,
387 -- and whether it is terminated.
388 -- Protection: Self.L.
391 -- The task on which this task depends.
392 -- See also Master_Level and Master_Within.
394 Base_Priority : System.Any_Priority;
395 -- Base priority, not changed during entry calls, only changed
396 -- via dynamic priorities package.
397 -- Protection: Only written by Self, accessed by anyone.
399 Current_Priority : System.Any_Priority;
400 -- Active priority, except that the effects of protected object
401 -- priority ceilings are not reflected. This only reflects explicit
402 -- priority changes and priority inherited through task activation
405 -- Ada 95 notes: In Ada 95, this field will be transferred to the
406 -- Priority field of an Entry_Calls component when an entry call
407 -- is initiated. The Priority of the Entry_Calls component will not
408 -- change for the duration of the call. The accepting task can
409 -- use it to boost its own priority without fear of its changing in
412 -- This can safely be used in the priority ordering
413 -- of entry queues. Once a call is queued, its priority does not
416 -- Since an entry call cannot be made while executing
417 -- a protected action, the priority of a task will never reflect a
418 -- priority ceiling change at the point of an entry call.
420 -- Protection: Only written by Self, and only accessed when Acceptor
421 -- accepts an entry or when Created activates, at which points Self is
424 Task_Image : String (1 .. 32);
425 -- Hold a string that provides a readable id for task,
426 -- built from the variable of which it is a value or component.
428 Task_Image_Len : Natural;
429 -- Actual length of Task_Image.
431 Call : Entry_Call_Link;
432 -- The entry call that has been accepted by this task.
433 -- Protection: Self.L. Self will modify this field
434 -- when Self.Accepting is False, and will not need the mutex to do so.
435 -- Once a task sets Pending_ATC_Level = 0, no other task can access
438 LL : aliased Task_Primitives.Private_Data;
439 -- Control block used by the underlying low-level tasking
441 -- Protection: This is used only by the GNULLI implementation, which
442 -- takes care of all of its synchronization.
444 Task_Arg : System.Address;
445 -- The argument to task procedure. Provide a handle for discriminant
447 -- Protection: Part of the synchronization between Self and
448 -- Activator. Activator writes it, once, before Self starts
449 -- executing. Thereafter, Self only reads it.
451 Task_Entry_Point : Task_Procedure_Access;
452 -- Information needed to call the procedure containing the code for
453 -- the body of this task.
454 -- Protection: Part of the synchronization between Self and
455 -- Activator. Activator writes it, once, before Self starts
456 -- executing. Self reads it, once, as part of its execution.
458 Compiler_Data : System.Soft_Links.TSD;
459 -- Task-specific data needed by the compiler to store
460 -- per-task structures.
461 -- Protection: Only accessed by Self.
463 All_Tasks_Link : Task_Id;
464 -- Used to link this task to the list of all tasks in the system.
465 -- Protection: RTS_Lock.
467 Activation_Link : Task_Id;
468 -- Used to link this task to a list of tasks to be activated.
469 -- Protection: Only used by Activator.
472 -- The task that created this task, either by declaring it as a task
473 -- object or by executing a task allocator.
474 -- The value is null iff Self has completed activation.
475 -- Protection: Set by Activator before Self is activated, and
476 -- only read and modified by Self after that.
478 Wait_Count : Integer;
479 -- This count is used by a task that is waiting for other tasks.
480 -- At all other times, the value should be zero.
481 -- It is used differently in several different states.
482 -- Since a task cannot be in more than one of these states at the
483 -- same time, a single counter suffices.
484 -- Protection: Self.L.
488 -- This is the number of tasks that this task is activating, i.e. the
489 -- children that have started activation but have not completed it.
490 -- Protection: Self.L and Created.L. Both mutexes must be locked,
491 -- since Self.Activation_Count and Created.State must be synchronized.
493 -- Master_Completion_Sleep (phase 1)
495 -- This is the number dependent tasks of a master being
496 -- completed by Self that are not activated, not terminated, and
497 -- not waiting on a terminate alternative.
499 -- Master_Completion_2_Sleep (phase 2)
501 -- This is the count of tasks dependent on a master being
502 -- completed by Self which are waiting on a terminate alternative.
504 Elaborated : Access_Boolean;
505 -- Pointer to a flag indicating that this task's body has been
506 -- elaborated. The flag is created and managed by the
507 -- compiler-generated code.
508 -- Protection: The field itself is only accessed by Activator. The flag
509 -- that it points to is updated by Master and read by Activator; access
510 -- is assumed to be atomic.
512 Activation_Failed : Boolean;
513 -- Set to True if activation of a chain of tasks fails,
514 -- so that the activator should raise Tasking_Error.
516 Task_Info : System.Task_Info.Task_Info_Type;
517 -- System-specific attributes of the task as specified by the
521 ---------------------------------------
522 -- Restricted_Ada_Task_Control_Block --
523 ---------------------------------------
525 -- This type should only be used by the restricted GNARLI and by
526 -- restricted GNULL implementations to allocate an ATCB (see
527 -- System.Task_Primitives.Operations.New_ATCB) that will take
528 -- significantly less memory.
529 -- Note that the restricted GNARLI should only access fields that are
530 -- present in the Restricted_Ada_Task_Control_Block structure.
532 type Restricted_Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is
534 Common : Common_ATCB;
535 -- The common part between various tasking implementations
537 Entry_Call : aliased Restricted_Entry_Call_Record;
538 -- Protection: This field is used on entry call "queues" associated
539 -- with protected objects, and is protected by the protected object
542 pragma Suppress_Initialization (Restricted_Ada_Task_Control_Block);
544 Interrupt_Manager_ID : Task_Id;
545 -- This task ID is declared here to break circular dependencies.
546 -- Also declare Interrupt_Manager_ID after Task_Id is known, to avoid
547 -- generating unneeded finalization code.
549 -----------------------
550 -- List of all Tasks --
551 -----------------------
553 All_Tasks_List : Task_Id;
554 -- Global linked list of all tasks.
556 ------------------------------------------
557 -- Regular (non restricted) definitions --
558 ------------------------------------------
560 --------------------------------
561 -- Master Related Definitions --
562 --------------------------------
564 subtype Master_Level is Integer;
565 subtype Master_ID is Master_Level;
567 -- Normally, a task starts out with internal master nesting level
568 -- one larger than external master nesting level. It is incremented
569 -- to one by Enter_Master, which is called in the task body only if
570 -- the compiler thinks the task may have dependent tasks. It is set to 1
571 -- for the environment task, the level 2 is reserved for server tasks of
572 -- the run-time system (the so called "independent tasks"), and the level
573 -- 3 is for the library level tasks.
575 Environment_Task_Level : constant Master_Level := 1;
576 Independent_Task_Level : constant Master_Level := 2;
577 Library_Task_Level : constant Master_Level := 3;
579 ------------------------------
580 -- Task size, priority info --
581 ------------------------------
583 Unspecified_Priority : constant Integer := System.Priority'First - 1;
585 Priority_Not_Boosted : constant Integer := System.Priority'First - 1;
586 -- Definition of Priority actually has to come from the RTS configuration.
588 subtype Rendezvous_Priority is Integer
589 range Priority_Not_Boosted .. System.Any_Priority'Last;
591 ------------------------------------
592 -- Rendezvous related definitions --
593 ------------------------------------
595 No_Rendezvous : constant := 0;
597 Max_Select : constant Integer := Integer'Last;
600 subtype Select_Index is Integer range No_Rendezvous .. Max_Select;
601 -- type Select_Index is range No_Rendezvous .. Max_Select;
603 subtype Positive_Select_Index is
604 Select_Index range 1 .. Select_Index'Last;
606 type Accept_Alternative is record
608 S : Task_Entry_Index;
612 array (Positive_Select_Index range <>) of Accept_Alternative;
614 type Accept_List_Access is access constant Accept_List;
616 -----------------------------------
617 -- ATC_Level related definitions --
618 -----------------------------------
620 Max_ATC_Nesting : constant Natural := 20;
622 subtype ATC_Level_Base is Integer range 0 .. Max_ATC_Nesting;
624 ATC_Level_Infinity : constant ATC_Level_Base := ATC_Level_Base'Last;
626 subtype ATC_Level is ATC_Level_Base range 0 .. ATC_Level_Base'Last - 1;
628 subtype ATC_Level_Index is ATC_Level range 1 .. ATC_Level'Last;
630 ----------------------------------
631 -- Entry_Call_Record definition --
632 ----------------------------------
634 type Entry_Call_Record is record
640 State : Entry_Call_State;
641 pragma Atomic (State);
642 -- Indicates part of the state of the call.
644 -- If the call is not on a queue, it should
645 -- only be accessed by Self, and Self does not need any
646 -- lock to modify this field.
647 -- Once the call is on a queue, the value should be
648 -- something other than Done unless it is cancelled, and access is
649 -- controller by the "server" of the queue -- i.e., the lock
650 -- of Checked_To_Protection (Call_Target)
651 -- if the call record is on the queue of a PO, or the lock
652 -- of Called_Target if the call is on the queue of a task.
653 -- See comments on type declaration for more details.
655 Uninterpreted_Data : System.Address;
656 -- Data passed by the compiler.
658 Exception_To_Raise : Ada.Exceptions.Exception_Id;
659 -- The exception to raise once this call has been completed without
662 Prev : Entry_Call_Link;
664 Next : Entry_Call_Link;
667 -- One of Self and Level are redundant in this implementation, since
668 -- each Entry_Call_Record is at Self.Entry_Calls (Level). Since we must
669 -- have access to the entry call record to be reading this, we could
670 -- get Self from Level, or Level from Self. However, this requires
671 -- non-portable address arithmetic.
675 Prio : System.Any_Priority;
677 -- The above fields are those that there may be some hope of packing.
678 -- They are gathered together to allow for compilers that lay records
679 -- out contiguously, to allow for such packing.
681 Called_Task : Task_Id;
682 pragma Atomic (Called_Task);
683 -- Use for task entry calls.
684 -- The value is null if the call record is not in use.
685 -- Conversely, unless State is Done and Onqueue is false,
686 -- Called_Task points to an ATCB.
687 -- Protection: Called_Task.L.
689 Called_PO : System.Address;
690 pragma Atomic (Called_PO);
691 -- Similar to Called_Task but for protected objects.
692 -- Note that the previous implementation tried to merge both
693 -- Called_Task and Called_PO but this ended up in many unexpected
694 -- complications (e.g having to add a magic number in the ATCB, which
695 -- caused gdb lots of confusion) with no real gain since the Lock_Server
696 -- implementation still need to loop around chasing for pointer changes
697 -- even with a single pointer.
699 Acceptor_Prev_Call : Entry_Call_Link;
700 -- For task entry calls only.
702 Acceptor_Prev_Priority : Rendezvous_Priority := Priority_Not_Boosted;
703 -- For task entry calls only.
704 -- The priority of the most recent prior call being serviced.
705 -- For protected entry calls, this function should be performed by
706 -- GNULLI ceiling locking.
708 Cancellation_Attempted : Boolean := False;
709 pragma Atomic (Cancellation_Attempted);
710 -- Cancellation of the call has been attempted.
711 -- If it has succeeded, State = Cancelled.
713 -- Consider merging this into State?
715 Requeue_With_Abort : Boolean := False;
716 -- Temporary to tell caller whether requeue is with abort.
718 -- Find a better way of doing this.
720 Needs_Requeue : Boolean := False;
721 -- Temporary to tell acceptor of task entry call that
722 -- Exceptional_Complete_Rendezvous needs to do requeue.
725 ------------------------------------
726 -- Task related other definitions --
727 ------------------------------------
729 type Access_Address is access all System.Address;
730 -- Comment on what this is used for ???
732 pragma No_Strict_Aliasing (Access_Address);
733 -- This type is used in contexts where aliasing may be an issue (see
734 -- for example s-tataat.adb), so we avoid any incorrect aliasing
737 ----------------------------------------------
738 -- Ada_Task_Control_Block (ATCB) definition --
739 ----------------------------------------------
741 type Entry_Call_Array is array (ATC_Level_Index) of
742 aliased Entry_Call_Record;
744 type Direct_Index is range 0 .. Parameters.Default_Attribute_Count;
745 subtype Direct_Index_Range is Direct_Index range 1 .. Direct_Index'Last;
746 -- Attributes with indices in this range are stored directly in
747 -- the task control block. Such attributes must be Address-sized.
748 -- Other attributes will be held in dynamically allocated records
749 -- chained off of the task control block.
751 type Direct_Attribute_Element is mod Memory_Size;
752 pragma Atomic (Direct_Attribute_Element);
754 type Direct_Attribute_Array is
755 array (Direct_Index_Range) of aliased Direct_Attribute_Element;
757 type Direct_Index_Vector is mod 2 ** Parameters.Default_Attribute_Count;
758 -- This is a bit-vector type, used to store information about
759 -- the usage of the direct attribute fields.
761 type Task_Serial_Number is mod 2 ** 64;
762 -- Used to give each task a unique serial number.
764 type Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is record
765 Common : Common_ATCB;
766 -- The common part between various tasking implementations
768 Entry_Calls : Entry_Call_Array;
769 -- An array of entry calls.
770 -- Protection: The elements of this array are on entry call queues
771 -- associated with protected objects or task entries, and are protected
772 -- by the protected object lock or Acceptor.L, respectively.
774 New_Base_Priority : System.Any_Priority;
775 -- New value for Base_Priority (for dynamic priorities package).
776 -- Protection: Self.L.
778 Global_Task_Lock_Nesting : Natural := 0;
779 -- This is the current nesting level of calls to
780 -- System.Tasking.Stages.Lock_Task_T.
781 -- This allows a task to call Lock_Task_T multiple times without
782 -- deadlocking. A task only locks All_Task_Lock when its
783 -- All_Tasks_Nesting goes from 0 to 1, and only unlocked when it
785 -- Protection: Only accessed by Self.
787 Open_Accepts : Accept_List_Access;
788 -- This points to the Open_Accepts array of accept alternatives passed
789 -- to the RTS by the compiler-generated code to Selective_Wait.
790 -- It is non-null iff this task is ready to accept an entry call.
791 -- Protection: Self.L.
793 Chosen_Index : Select_Index;
794 -- The index in Open_Accepts of the entry call accepted by a selective
795 -- wait executed by this task.
796 -- Protection: Written by both Self and Caller. Usually protected
797 -- by Self.L. However, once the selection is known to have been
798 -- written it can be accessed without protection. This happens
799 -- after Self has updated it itself using information from a suspended
800 -- Caller, or after Caller has updated it and awakened Self.
802 Master_of_Task : Master_Level;
803 -- The task executing the master of this task, and the ID of this task's
804 -- master (unique only among masters currently active within Parent).
805 -- Protection: Set by Activator before Self is activated, and
806 -- read after Self is activated.
808 Master_Within : Master_Level;
809 -- The ID of the master currently executing within this task; that is,
810 -- the most deeply nested currently active master.
811 -- Protection: Only written by Self, and only read by Self or by
812 -- dependents when Self is attempting to exit a master. Since Self
813 -- will not write this field until the master is complete, the
814 -- synchronization should be adequate to prevent races.
816 Alive_Count : Integer := 0;
817 -- Number of tasks directly dependent on this task (including itself)
818 -- that are still "alive", i.e. not terminated.
819 -- Protection: Self.L.
821 Awake_Count : Integer := 0;
822 -- Number of tasks directly dependent on this task (including itself)
823 -- still "awake", i.e., are not terminated and not waiting on a
824 -- terminate alternative.
825 -- Invariant: Awake_Count <= Alive_Count
826 -- Protection: Self.L.
828 -- beginning of flags
830 Aborting : Boolean := False;
831 pragma Atomic (Aborting);
832 -- Self is in the process of aborting. While set, prevents multiple
833 -- abortion signals from being sent by different aborter while abortion
834 -- is acted upon. This is essential since an aborter which calls
835 -- Abort_To_Level could set the Pending_ATC_Level to yet a lower level
836 -- (than the current level), may be preempted and would send the
837 -- abortion signal when resuming execution. At this point, the abortee
838 -- may have completed abortion to the proper level such that the
839 -- signal (and resulting abortion exception) are not handled any more.
840 -- In other words, the flag prevents a race between multiple aborters
842 -- Protection: protected by atomic access.
844 ATC_Hack : Boolean := False;
845 pragma Atomic (ATC_Hack);
847 -- Temporary fix, to allow Undefer_Abort to reset Aborting in the
848 -- handler for Abort_Signal that encloses an async. entry call.
849 -- For the longer term, this should be done via code in the
852 Callable : Boolean := True;
853 -- It is OK to call entries of this task.
855 Dependents_Aborted : Boolean := False;
856 -- This is set to True by whichever task takes responsibility
857 -- for aborting the dependents of this task.
858 -- Protection: Self.L.
860 Interrupt_Entry : Boolean := False;
861 -- Indicates if one or more Interrupt Entries are attached to
862 -- the task. This flag is needed for cleaning up the Interrupt
865 Pending_Action : Boolean := False;
866 -- Unified flag indicating some action needs to be take when abort
867 -- next becomes undeferred. Currently set if:
868 -- . Pending_Priority_Change is set
869 -- . Pending_ATC_Level is changed
870 -- . Requeue involving POs
871 -- (Abortable field may have changed and the Wait_Until_Abortable
872 -- has to recheck the abortable status of the call.)
873 -- . Exception_To_Raise is non-null
874 -- Protection: Self.L.
875 -- This should never be reset back to False outside of the
876 -- procedure Do_Pending_Action, which is called by Undefer_Abort.
877 -- It should only be set to True by Set_Priority and Abort_To_Level.
879 Pending_Priority_Change : Boolean := False;
880 -- Flag to indicate pending priority change (for dynamic priorities
881 -- package). The base priority is updated on the next abortion
882 -- completion point (aka. synchronization point).
883 -- Protection: Self.L.
885 Terminate_Alternative : Boolean := False;
886 -- Task is accepting Select with Terminate Alternative.
887 -- Protection: Self.L.
891 -- beginning of counts
893 ATC_Nesting_Level : ATC_Level := 1;
894 -- The dynamic level of ATC nesting (currently executing nested
895 -- asynchronous select statements) in this task.
896 -- Protection: Self_ID.L.
897 -- Only Self reads or updates this field.
898 -- Decrementing it deallocates an Entry_Calls component, and care must
899 -- be taken that all references to that component are eliminated
900 -- before doing the decrement. This in turn will require locking
901 -- a protected object (for a protected entry call) or the Acceptor's
902 -- lock (for a task entry call).
903 -- No other task should attempt to read or modify this value.
905 Deferral_Level : Natural := 1;
906 -- This is the number of times that Defer_Abortion has been called by
907 -- this task without a matching Undefer_Abortion call. Abortion is
908 -- only allowed when this zero.
909 -- It is initially 1, to protect the task at startup.
910 -- Protection: Only updated by Self; access assumed to be atomic.
912 Pending_ATC_Level : ATC_Level_Base := ATC_Level_Infinity;
913 -- The ATC level to which this task is currently being aborted.
914 -- If the value is zero, the entire task has "completed".
915 -- That may be via abort, exception propagation, or normal exit.
916 -- If the value is ATC_Level_Infinity, the task is not being
917 -- aborted to any level.
918 -- If the value is positive, the task has not completed.
919 -- This should ONLY be modified by
920 -- Abort_To_Level and Exit_One_ATC_Level.
921 -- Protection: Self.L.
923 Serial_Number : Task_Serial_Number;
924 -- A growing number to provide some way to check locking
927 Known_Tasks_Index : Integer := -1;
928 -- Index in the System.Tasking.Debug.Known_Tasks array.
930 User_State : Long_Integer := 0;
931 -- User-writeable location, for use in debugging tasks;
932 -- also provides a simple task specific data.
934 Direct_Attributes : Direct_Attribute_Array;
935 -- For task attributes that have same size as Address
937 Is_Defined : Direct_Index_Vector := 0;
938 -- Bit I is 1 iff Direct_Attributes (I) is defined
940 Indirect_Attributes : Access_Address;
941 -- A pointer to chain of records for other attributes that
942 -- are not address-sized, including all tagged types.
944 Entry_Queues : Task_Entry_Queue_Array (1 .. Entry_Num);
945 -- An array of task entry queues.
946 -- Protection: Self.L. Once a task has set Self.Stage to Completing, it
947 -- has exclusive access to this field.
950 ---------------------
951 -- Initialize_ATCB --
952 ---------------------
954 procedure Initialize_ATCB
956 Task_Entry_Point : Task_Procedure_Access;
957 Task_Arg : System.Address;
959 Elaborated : Access_Boolean;
960 Base_Priority : System.Any_Priority;
961 Task_Info : System.Task_Info.Task_Info_Type;
962 Stack_Size : System.Parameters.Size_Type;
964 Success : out Boolean);
965 -- Initialize fields of a TCB and link into global TCB structures
966 -- Call this only with abort deferred and holding RTS_Lock.
970 Null_Task : constant Task_Id := null;
972 type Activation_Chain is record
975 pragma Volatile (Activation_Chain);
977 -- Activation_chain is an in-out parameter of initialization procedures
978 -- and it must be passed by reference because the init proc may terminate
979 -- abnormally after creating task components, and these must be properly
980 -- registered for removal (Expunge_Unactivated_Tasks).