1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
5 -- S Y S T E M . T A S K I N G --
9 -- Copyright (C) 1992-2007, 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, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, 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
41 -- Exception_Occurrence
43 with System.Parameters;
46 with System.Task_Info;
47 -- used for Task_Info_Type
49 with System.Soft_Links;
52 with System.Task_Primitives;
53 -- used for Private_Data
55 with System.Stack_Usage;
56 -- used for Stack_Analyzer
58 with Ada.Unchecked_Conversion;
60 package System.Tasking is
67 -- The following rules must be followed at all times, to prevent
68 -- deadlock and generally ensure correct operation of locking.
70 -- Never lock a lock unless abort is deferred
72 -- Never undefer abort while holding a lock
74 -- Overlapping critical sections must be properly nested, and locks must
75 -- be released in LIFO order. e.g., the following is not allowed:
85 -- Locks with lower (smaller) level number cannot be locked
86 -- while holding a lock with a higher level number. (The level
88 -- 1. System.Tasking.PO_Simple.Protection.L (any PO lock)
89 -- 2. System.Tasking.Initialization.Global_Task_Lock (in body)
90 -- 3. System.Task_Primitives.Operations.Single_RTS_Lock
91 -- 4. System.Tasking.Ada_Task_Control_Block.LL.L (any TCB lock)
93 -- Clearly, there can be no circular chain of hold-and-wait
94 -- relationships involving locks in different ordering levels.
96 -- We used to have Global_Task_Lock before Protection.L but this was
97 -- clearly wrong since there can be calls to "new" inside protected
98 -- operations. The new ordering prevents these failures.
100 -- Sometimes we need to hold two ATCB locks at the same time. To allow us
101 -- to order the locking, each ATCB is given a unique serial number. If one
102 -- needs to hold locks on several ATCBs at once, the locks with lower
103 -- serial numbers must be locked first.
105 -- We don't always need to check the serial numbers, since the serial
106 -- numbers are assigned sequentially, and so:
108 -- . The parent of a task always has a lower serial number.
109 -- . The activator of a task always has a lower serial number.
110 -- . The environment task has a lower serial number than any other task.
111 -- . If the activator of a task is different from the task's parent,
112 -- the parent always has a lower serial number than the activator.
114 ---------------------------------
115 -- Task_Id related definitions --
116 ---------------------------------
118 type Ada_Task_Control_Block;
120 type Task_Id is access all Ada_Task_Control_Block;
122 Null_Task : constant Task_Id;
124 type Task_List is array (Positive range <>) of Task_Id;
126 function Self return Task_Id;
127 pragma Inline (Self);
128 -- This is the compiler interface version of this function. Do not call
129 -- from the run-time system.
131 function To_Task_Id is
132 new Ada.Unchecked_Conversion (System.Address, Task_Id);
133 function To_Address is
134 new Ada.Unchecked_Conversion (Task_Id, System.Address);
136 -----------------------
137 -- Enumeration types --
138 -----------------------
142 -- Task has been created but has not been activated.
143 -- It cannot be executing.
146 -- For all states from here down, the task has been activated.
147 -- For all states from here down, except for Terminated, the task
149 -- Activator = null iff it has not yet completed activating.
151 -- For all states from here down,
152 -- the task has been activated, and may be executing.
155 -- Task is not blocked for any reason known to Ada.
156 -- (It may be waiting for a mutex, though.)
157 -- It is conceptually "executing" in normal mode.
160 -- The task is terminated, in the sense of ARM 9.3 (5).
161 -- Any dependents that were waiting on terminate
162 -- alternatives have been awakened and have terminated themselves.
165 -- Task is waiting for created tasks to complete activation
168 -- Task is waiting on an accept or selective wait statement
171 -- Task is waiting on an entry call
174 -- Task is waiting to start the abortable part of an
175 -- asynchronous select statement.
178 -- Task is waiting on a select statement with only a delay
181 Master_Completion_Sleep,
182 -- Master completion has two phases.
183 -- In Phase 1 the task is sleeping in Complete_Master
184 -- having completed a master within itself,
185 -- and is waiting for the tasks dependent on that master to become
186 -- terminated or waiting on a terminate Phase.
188 Master_Phase_2_Sleep,
189 -- In Phase 2 the task is sleeping in Complete_Master
190 -- waiting for tasks on terminate alternatives to finish
193 -- The following are special uses of sleep, for server tasks
194 -- within the run-time system.
196 Interrupt_Server_Idle_Sleep,
197 Interrupt_Server_Blocked_Interrupt_Sleep,
202 -- The task has been held by Asynchronous_Task_Control.Hold_Task
204 Interrupt_Server_Blocked_On_Event_Flag
205 -- The task has been blocked on a system call waiting for a
206 -- completion event/signal to occur.
210 (Simple_Call, Conditional_Call, Asynchronous_Call, Timed_Call);
212 type Select_Modes is (Simple_Mode, Else_Mode, Terminate_Mode, Delay_Mode);
214 subtype Delay_Modes is Integer;
216 -------------------------------
217 -- Entry related definitions --
218 -------------------------------
220 Null_Entry : constant := 0;
222 Max_Entry : constant := Integer'Last;
224 Interrupt_Entry : constant := -2;
226 Cancelled_Entry : constant := -1;
228 type Entry_Index is range Interrupt_Entry .. Max_Entry;
230 Null_Task_Entry : constant := Null_Entry;
232 Max_Task_Entry : constant := Max_Entry;
234 type Task_Entry_Index is new Entry_Index
235 range Null_Task_Entry .. Max_Task_Entry;
237 type Entry_Call_Record;
239 type Entry_Call_Link is access all Entry_Call_Record;
241 type Entry_Queue is record
242 Head : Entry_Call_Link;
243 Tail : Entry_Call_Link;
246 type Task_Entry_Queue_Array is
247 array (Task_Entry_Index range <>) of Entry_Queue;
249 ----------------------------------
250 -- Entry_Call_Record definition --
251 ----------------------------------
253 type Entry_Call_State is
255 -- the call is not abortable, and never can be
258 -- the call is not abortable, but may become so
261 -- the call is not abortable, but once was
264 -- the call is abortable
267 -- the call has been completed
270 -- the call was asynchronous, and was cancelled
273 -- Never_Abortable is used for calls that are made in a abort
274 -- deferred region (see ARM 9.8(5-11), 9.8 (20)).
275 -- Such a call is never abortable.
277 -- The Was_ vs. Not_Yet_ distinction is needed to decide whether it
278 -- is OK to advance into the abortable part of an async. select stmt.
279 -- That is allowed iff the mode is Now_ or Was_.
281 -- Done indicates the call has been completed, without cancellation,
282 -- or no call has been made yet at this ATC nesting level,
283 -- and so aborting the call is no longer an issue.
284 -- Completion of the call does not necessarily indicate "success";
285 -- the call may be returning an exception if Exception_To_Raise is
288 -- Cancelled indicates the call was cancelled,
289 -- and so aborting the call is no longer an issue.
291 -- The call is on an entry queue unless
292 -- State >= Done, in which case it may or may not be still Onqueue.
294 -- Please do not modify the order of the values, without checking
295 -- all uses of this type. We rely on partial "monotonicity" of
296 -- Entry_Call_Record.State to avoid locking when we access this
297 -- value for certain tests. In particular:
299 -- 1) Once State >= Done, we can rely that the call has been
300 -- completed. If State >= Done, it will not
301 -- change until the task does another entry call at this level.
303 -- 2) Once State >= Was_Abortable, we can rely that the call has
304 -- been queued abortably at least once, and so the check for
305 -- whether it is OK to advance to the abortable part of an
306 -- async. select statement does not need to lock anything.
308 type Restricted_Entry_Call_Record is record
314 State : Entry_Call_State;
315 pragma Atomic (State);
316 -- Indicates part of the state of the call.
318 -- Protection: If the call is not on a queue, it should only be
319 -- accessed by Self, and Self does not need any lock to modify this
322 -- Once the call is on a queue, the value should be something other
323 -- than Done unless it is cancelled, and access is controller by the
324 -- "server" of the queue -- i.e., the lock of Checked_To_Protection
325 -- (Call_Target) if the call record is on the queue of a PO, or the
326 -- lock of Called_Target if the call is on the queue of a task. See
327 -- comments on type declaration for more details.
329 Uninterpreted_Data : System.Address;
330 -- Data passed by the compiler
332 Exception_To_Raise : Ada.Exceptions.Exception_Id;
333 -- The exception to raise once this call has been completed without
336 pragma Suppress_Initialization (Restricted_Entry_Call_Record);
338 -------------------------------------------
339 -- Task termination procedure definition --
340 -------------------------------------------
342 -- We need to redefine here these types (already defined in
343 -- Ada.Task_Termination) for avoiding circular dependencies.
345 type Cause_Of_Termination is (Normal, Abnormal, Unhandled_Exception);
346 -- Possible causes for task termination:
348 -- Normal means that the task terminates due to completing the
349 -- last sentence of its body, or as a result of waiting on a
350 -- terminate alternative.
352 -- Abnormal means that the task terminates because it is being aborted
354 -- handled_Exception means that the task terminates because of exception
355 -- raised by by the execution of its task_body.
357 type Termination_Handler is access protected procedure
358 (Cause : Cause_Of_Termination;
360 X : Ada.Exceptions.Exception_Occurrence);
361 -- Used to represent protected procedures to be executed when task
364 ------------------------------------
365 -- Task related other definitions --
366 ------------------------------------
368 type Activation_Chain is limited private;
369 -- Linked list of to-be-activated tasks, linked through
370 -- Activation_Link. The order of tasks on the list is irrelevant, because
371 -- the priority rules will ensure that they actually start activating in
374 type Activation_Chain_Access is access all Activation_Chain;
376 type Task_Procedure_Access is access procedure (Arg : System.Address);
378 type Access_Boolean is access all Boolean;
380 function Detect_Blocking return Boolean;
381 pragma Inline (Detect_Blocking);
382 -- Return whether the Detect_Blocking pragma is enabled
384 function Storage_Size (T : Task_Id) return System.Parameters.Size_Type;
385 -- Retrieve from the TCB of the task the allocated size of its stack,
386 -- either the system default or the size specified by a pragma. This
387 -- is in general a non-static value that can depend on discriminants
390 ----------------------------------------------
391 -- Ada_Task_Control_Block (ATCB) definition --
392 ----------------------------------------------
394 -- Notes on protection (synchronization) of TRTS data structures
396 -- Any field of the TCB can be written by the activator of a task when the
397 -- task is created, since no other task can access the new task's
398 -- state until creation is complete.
400 -- The protection for each field is described in a comment starting with
403 -- When a lock is used to protect an ATCB field, this lock is simply named
405 -- Some protection is described in terms of tasks related to the
406 -- ATCB being protected. These are:
408 -- Self: The task which is controlled by this ATCB
409 -- Acceptor: A task accepting a call from Self
410 -- Caller: A task calling an entry of Self
411 -- Parent: The task executing the master on which Self depends
412 -- Dependent: A task dependent on Self
413 -- Activator: The task that created Self and initiated its activation
414 -- Created: A task created and activated by Self
416 -- Note: The order of the fields is important to implement efficiently
417 -- tasking support under gdb.
418 -- Currently gdb relies on the order of the State, Parent, Base_Priority,
419 -- Task_Image, Task_Image_Len, Call and LL fields.
421 -------------------------
422 -- Common ATCB section --
423 -------------------------
425 -- Section used by all GNARL implementations (regular and restricted)
427 type Common_ATCB is record
429 pragma Atomic (State);
430 -- Encodes some basic information about the state of a task,
431 -- including whether it has been activated, whether it is sleeping,
432 -- and whether it is terminated.
434 -- Protection: Self.L
437 -- The task on which this task depends.
438 -- See also Master_Level and Master_Within.
440 Base_Priority : System.Any_Priority;
441 -- Base priority, not changed during entry calls, only changed
442 -- via dynamic priorities package.
444 -- Protection: Only written by Self, accessed by anyone
446 Current_Priority : System.Any_Priority;
447 -- Active priority, except that the effects of protected object
448 -- priority ceilings are not reflected. This only reflects explicit
449 -- priority changes and priority inherited through task activation
452 -- Ada 95 notes: In Ada 95, this field will be transferred to the
453 -- Priority field of an Entry_Calls component when an entry call
454 -- is initiated. The Priority of the Entry_Calls component will not
455 -- change for the duration of the call. The accepting task can
456 -- use it to boost its own priority without fear of its changing in
459 -- This can safely be used in the priority ordering
460 -- of entry queues. Once a call is queued, its priority does not
463 -- Since an entry call cannot be made while executing
464 -- a protected action, the priority of a task will never reflect a
465 -- priority ceiling change at the point of an entry call.
467 -- Protection: Only written by Self, and only accessed when Acceptor
468 -- accepts an entry or when Created activates, at which points Self is
471 Protected_Action_Nesting : Natural;
472 pragma Atomic (Protected_Action_Nesting);
473 -- The dynamic level of protected action nesting for this task. This
474 -- field is needed for checking whether potentially blocking operations
475 -- are invoked from protected actions. pragma Atomic is used because it
476 -- can be read/written from protected interrupt handlers.
478 Task_Image : String (1 .. System.Parameters.Max_Task_Image_Length);
479 -- Hold a string that provides a readable id for task,
480 -- built from the variable of which it is a value or component.
482 Task_Image_Len : Natural;
483 -- Actual length of Task_Image
485 Call : Entry_Call_Link;
486 -- The entry call that has been accepted by this task.
488 -- Protection: Self.L. Self will modify this field when Self.Accepting
489 -- is False, and will not need the mutex to do so. Once a task sets
490 -- Pending_ATC_Level = 0, no other task can access this field.
492 LL : aliased Task_Primitives.Private_Data;
493 -- Control block used by the underlying low-level tasking service
496 -- Protection: This is used only by the GNULLI implementation, which
497 -- takes care of all of its synchronization.
499 Task_Arg : System.Address;
500 -- The argument to task procedure. Provide a handle for discriminant
503 -- Protection: Part of the synchronization between Self and Activator.
504 -- Activator writes it, once, before Self starts executing. Thereafter,
505 -- Self only reads it.
507 Task_Entry_Point : Task_Procedure_Access;
508 -- Information needed to call the procedure containing the code for
509 -- the body of this task.
511 -- Protection: Part of the synchronization between Self and Activator.
512 -- Activator writes it, once, before Self starts executing. Self reads
513 -- it, once, as part of its execution.
515 Compiler_Data : System.Soft_Links.TSD;
516 -- Task-specific data needed by the compiler to store per-task
519 -- Protection: Only accessed by Self
521 All_Tasks_Link : Task_Id;
522 -- Used to link this task to the list of all tasks in the system
524 -- Protection: RTS_Lock
526 Activation_Link : Task_Id;
527 -- Used to link this task to a list of tasks to be activated
529 -- Protection: Only used by Activator
532 -- The task that created this task, either by declaring it as a task
533 -- object or by executing a task allocator. The value is null iff Self
534 -- has completed activation.
536 -- Protection: Set by Activator before Self is activated, and only read
537 -- and modified by Self after that.
539 Wait_Count : Integer;
540 -- This count is used by a task that is waiting for other tasks. At all
541 -- other times, the value should be zero. It is used differently in
542 -- several different states. Since a task cannot be in more than one of
543 -- these states at the same time, a single counter suffices.
545 -- Protection: Self.L
549 -- This is the number of tasks that this task is activating, i.e. the
550 -- children that have started activation but have not completed it.
552 -- Protection: Self.L and Created.L. Both mutexes must be locked, since
553 -- Self.Activation_Count and Created.State must be synchronized.
555 -- Master_Completion_Sleep (phase 1)
557 -- This is the number dependent tasks of a master being completed by
558 -- Self that are not activated, not terminated, and not waiting on a
559 -- terminate alternative.
561 -- Master_Completion_2_Sleep (phase 2)
563 -- This is the count of tasks dependent on a master being completed by
564 -- Self which are waiting on a terminate alternative.
566 Elaborated : Access_Boolean;
567 -- Pointer to a flag indicating that this task's body has been
568 -- elaborated. The flag is created and managed by the
569 -- compiler-generated code.
571 -- Protection: The field itself is only accessed by Activator. The flag
572 -- that it points to is updated by Master and read by Activator; access
573 -- is assumed to be atomic.
575 Activation_Failed : Boolean;
576 -- Set to True if activation of a chain of tasks fails,
577 -- so that the activator should raise Tasking_Error.
579 Task_Info : System.Task_Info.Task_Info_Type;
580 -- System-specific attributes of the task as specified by the
583 Analyzer : System.Stack_Usage.Stack_Analyzer;
584 -- For storing informations used to measure the stack usage
586 Global_Task_Lock_Nesting : Natural;
587 -- This is the current nesting level of calls to
588 -- System.Tasking.Initialization.Lock_Task. This allows a task to call
589 -- Lock_Task multiple times without deadlocking. A task only locks
590 -- Global_Task_Lock when its Global_Task_Lock_Nesting goes from 0 to 1,
591 -- and only unlocked when it goes from 1 to 0.
593 -- Protection: Only accessed by Self
595 Fall_Back_Handler : Termination_Handler;
596 -- This is the fall-back handler that applies to the dependent tasks of
599 -- Protection: Self.L
601 Specific_Handler : Termination_Handler;
602 -- This is the specific handler that applies only to this task, and not
603 -- any of its dependent tasks.
605 -- Protection: Self.L
608 ---------------------------------------
609 -- Restricted_Ada_Task_Control_Block --
610 ---------------------------------------
612 -- This type should only be used by the restricted GNARLI and by
613 -- restricted GNULL implementations to allocate an ATCB (see
614 -- System.Task_Primitives.Operations.New_ATCB) that will take
615 -- significantly less memory.
617 -- Note that the restricted GNARLI should only access fields that are
618 -- present in the Restricted_Ada_Task_Control_Block structure.
620 type Restricted_Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is
622 Common : Common_ATCB;
623 -- The common part between various tasking implementations
625 Entry_Call : aliased Restricted_Entry_Call_Record;
626 -- Protection: This field is used on entry call "queues" associated
627 -- with protected objects, and is protected by the protected object
630 pragma Suppress_Initialization (Restricted_Ada_Task_Control_Block);
632 Interrupt_Manager_ID : Task_Id;
633 -- This task ID is declared here to break circular dependencies.
634 -- Also declare Interrupt_Manager_ID after Task_Id is known, to avoid
635 -- generating unneeded finalization code.
637 -----------------------
638 -- List of all Tasks --
639 -----------------------
641 All_Tasks_List : Task_Id;
642 -- Global linked list of all tasks
644 ------------------------------------------
645 -- Regular (non restricted) definitions --
646 ------------------------------------------
648 --------------------------------
649 -- Master Related Definitions --
650 --------------------------------
652 subtype Master_Level is Integer;
653 subtype Master_ID is Master_Level;
655 -- Normally, a task starts out with internal master nesting level one
656 -- larger than external master nesting level. It is incremented to one by
657 -- Enter_Master, which is called in the task body only if the compiler
658 -- thinks the task may have dependent tasks. It is set to 1 for the
659 -- environment task, the level 2 is reserved for server tasks of the
660 -- run-time system (the so called "independent tasks"), and the level 3 is
661 -- for the library level tasks. Foreign threads which are detected by
662 -- the run-time have a level of 0, allowing these tasks to be easily
663 -- distinguished if needed.
665 Foreign_Task_Level : constant Master_Level := 0;
666 Environment_Task_Level : constant Master_Level := 1;
667 Independent_Task_Level : constant Master_Level := 2;
668 Library_Task_Level : constant Master_Level := 3;
670 ------------------------------
671 -- Task size, priority info --
672 ------------------------------
674 Unspecified_Priority : constant Integer := System.Priority'First - 1;
676 Priority_Not_Boosted : constant Integer := System.Priority'First - 1;
677 -- Definition of Priority actually has to come from the RTS configuration
679 subtype Rendezvous_Priority is Integer
680 range Priority_Not_Boosted .. System.Any_Priority'Last;
682 ------------------------------------
683 -- Rendezvous related definitions --
684 ------------------------------------
686 No_Rendezvous : constant := 0;
688 Max_Select : constant Integer := Integer'Last;
691 subtype Select_Index is Integer range No_Rendezvous .. Max_Select;
692 -- type Select_Index is range No_Rendezvous .. Max_Select;
694 subtype Positive_Select_Index is
695 Select_Index range 1 .. Select_Index'Last;
697 type Accept_Alternative is record
699 S : Task_Entry_Index;
703 array (Positive_Select_Index range <>) of Accept_Alternative;
705 type Accept_List_Access is access constant Accept_List;
707 -----------------------------------
708 -- ATC_Level related definitions --
709 -----------------------------------
711 Max_ATC_Nesting : constant Natural := 20;
713 subtype ATC_Level_Base is Integer range 0 .. Max_ATC_Nesting;
715 ATC_Level_Infinity : constant ATC_Level_Base := ATC_Level_Base'Last;
717 subtype ATC_Level is ATC_Level_Base range 0 .. ATC_Level_Base'Last - 1;
719 subtype ATC_Level_Index is ATC_Level range 1 .. ATC_Level'Last;
721 ----------------------------------
722 -- Entry_Call_Record definition --
723 ----------------------------------
725 type Entry_Call_Record is record
731 State : Entry_Call_State;
732 pragma Atomic (State);
733 -- Indicates part of the state of the call
735 -- Protection: If the call is not on a queue, it should only be
736 -- accessed by Self, and Self does not need any lock to modify this
737 -- field. Once the call is on a queue, the value should be something
738 -- other than Done unless it is cancelled, and access is controller by
739 -- the "server" of the queue -- i.e., the lock of Checked_To_Protection
740 -- (Call_Target) if the call record is on the queue of a PO, or the
741 -- lock of Called_Target if the call is on the queue of a task. See
742 -- comments on type declaration for more details.
744 Uninterpreted_Data : System.Address;
745 -- Data passed by the compiler
747 Exception_To_Raise : Ada.Exceptions.Exception_Id;
748 -- The exception to raise once this call has been completed without
751 Prev : Entry_Call_Link;
753 Next : Entry_Call_Link;
756 -- One of Self and Level are redundant in this implementation, since
757 -- each Entry_Call_Record is at Self.Entry_Calls (Level). Since we must
758 -- have access to the entry call record to be reading this, we could
759 -- get Self from Level, or Level from Self. However, this requires
760 -- non-portable address arithmetic.
764 Prio : System.Any_Priority;
766 -- The above fields are those that there may be some hope of packing.
767 -- They are gathered together to allow for compilers that lay records
768 -- out contiguously, to allow for such packing.
770 Called_Task : Task_Id;
771 pragma Atomic (Called_Task);
772 -- Use for task entry calls. The value is null if the call record is
773 -- not in use. Conversely, unless State is Done and Onqueue is false,
774 -- Called_Task points to an ATCB.
776 -- Protection: Called_Task.L
778 Called_PO : System.Address;
779 pragma Atomic (Called_PO);
780 -- Similar to Called_Task but for protected objects
782 -- Note that the previous implementation tried to merge both
783 -- Called_Task and Called_PO but this ended up in many unexpected
784 -- complications (e.g having to add a magic number in the ATCB, which
785 -- caused gdb lots of confusion) with no real gain since the
786 -- Lock_Server implementation still need to loop around chasing for
787 -- pointer changes even with a single pointer.
789 Acceptor_Prev_Call : Entry_Call_Link;
790 -- For task entry calls only
792 Acceptor_Prev_Priority : Rendezvous_Priority := Priority_Not_Boosted;
793 -- For task entry calls only. The priority of the most recent prior
794 -- call being serviced. For protected entry calls, this function should
795 -- be performed by GNULLI ceiling locking.
797 Cancellation_Attempted : Boolean := False;
798 pragma Atomic (Cancellation_Attempted);
799 -- Cancellation of the call has been attempted.
800 -- Consider merging this into State???
802 With_Abort : Boolean := False;
803 -- Tell caller whether the call may be aborted
804 -- ??? consider merging this with Was_Abortable state
806 Needs_Requeue : Boolean := False;
807 -- Temporary to tell acceptor of task entry call that
808 -- Exceptional_Complete_Rendezvous needs to do requeue.
811 ------------------------------------
812 -- Task related other definitions --
813 ------------------------------------
815 type Access_Address is access all System.Address;
816 -- Comment on what this is used for ???
818 pragma No_Strict_Aliasing (Access_Address);
819 -- This type is used in contexts where aliasing may be an issue (see
820 -- for example s-tataat.adb), so we avoid any incorrect aliasing
823 ----------------------------------------------
824 -- Ada_Task_Control_Block (ATCB) definition --
825 ----------------------------------------------
827 type Entry_Call_Array is array (ATC_Level_Index) of
828 aliased Entry_Call_Record;
830 type Direct_Index is range 0 .. Parameters.Default_Attribute_Count;
831 subtype Direct_Index_Range is Direct_Index range 1 .. Direct_Index'Last;
832 -- Attributes with indices in this range are stored directly in the task
833 -- control block. Such attributes must be Address-sized. Other attributes
834 -- will be held in dynamically allocated records chained off of the task
837 type Direct_Attribute_Element is mod Memory_Size;
838 pragma Atomic (Direct_Attribute_Element);
840 type Direct_Attribute_Array is
841 array (Direct_Index_Range) of aliased Direct_Attribute_Element;
843 type Direct_Index_Vector is mod 2 ** Parameters.Default_Attribute_Count;
844 -- This is a bit-vector type, used to store information about
845 -- the usage of the direct attribute fields.
847 type Task_Serial_Number is mod 2 ** 64;
848 -- Used to give each task a unique serial number
850 type Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is record
851 Common : Common_ATCB;
852 -- The common part between various tasking implementations
854 Entry_Calls : Entry_Call_Array;
855 -- An array of entry calls
857 -- Protection: The elements of this array are on entry call queues
858 -- associated with protected objects or task entries, and are protected
859 -- by the protected object lock or Acceptor.L, respectively.
861 New_Base_Priority : System.Any_Priority;
862 -- New value for Base_Priority (for dynamic priorities package)
864 -- Protection: Self.L
866 Open_Accepts : Accept_List_Access;
867 -- This points to the Open_Accepts array of accept alternatives passed
868 -- to the RTS by the compiler-generated code to Selective_Wait. It is
869 -- non-null iff this task is ready to accept an entry call.
871 -- Protection: Self.L
873 Chosen_Index : Select_Index;
874 -- The index in Open_Accepts of the entry call accepted by a selective
875 -- wait executed by this task.
877 -- Protection: Written by both Self and Caller. Usually protected by
878 -- Self.L. However, once the selection is known to have been written it
879 -- can be accessed without protection. This happens after Self has
880 -- updated it itself using information from a suspended Caller, or
881 -- after Caller has updated it and awakened Self.
883 Master_of_Task : Master_Level;
884 -- The task executing the master of this task, and the ID of this task's
885 -- master (unique only among masters currently active within Parent).
887 -- Protection: Set by Activator before Self is activated, and read
888 -- after Self is activated.
890 Master_Within : Master_Level;
891 -- The ID of the master currently executing within this task; that is,
892 -- the most deeply nested currently active master.
894 -- Protection: Only written by Self, and only read by Self or by
895 -- dependents when Self is attempting to exit a master. Since Self will
896 -- not write this field until the master is complete, the
897 -- synchronization should be adequate to prevent races.
899 Alive_Count : Integer := 0;
900 -- Number of tasks directly dependent on this task (including itself)
901 -- that are still "alive", i.e. not terminated.
903 -- Protection: Self.L
905 Awake_Count : Integer := 0;
906 -- Number of tasks directly dependent on this task (including itself)
907 -- still "awake", i.e., are not terminated and not waiting on a
908 -- terminate alternative.
910 -- Invariant: Awake_Count <= Alive_Count
912 -- Protection: Self.L
914 -- Beginning of flags
916 Aborting : Boolean := False;
917 pragma Atomic (Aborting);
918 -- Self is in the process of aborting. While set, prevents multiple
919 -- abort signals from being sent by different aborter while abort
920 -- is acted upon. This is essential since an aborter which calls
921 -- Abort_To_Level could set the Pending_ATC_Level to yet a lower level
922 -- (than the current level), may be preempted and would send the
923 -- abort signal when resuming execution. At this point, the abortee
924 -- may have completed abort to the proper level such that the
925 -- signal (and resulting abort exception) are not handled any more.
926 -- In other words, the flag prevents a race between multiple aborters
928 -- Protection: protected by atomic access.
930 ATC_Hack : Boolean := False;
931 pragma Atomic (ATC_Hack);
933 -- Temporary fix, to allow Undefer_Abort to reset Aborting in the
934 -- handler for Abort_Signal that encloses an async. entry call.
935 -- For the longer term, this should be done via code in the
938 Callable : Boolean := True;
939 -- It is OK to call entries of this task
941 Dependents_Aborted : Boolean := False;
942 -- This is set to True by whichever task takes responsibility for
943 -- aborting the dependents of this task.
945 -- Protection: Self.L
947 Interrupt_Entry : Boolean := False;
948 -- Indicates if one or more Interrupt Entries are attached to the task.
949 -- This flag is needed for cleaning up the Interrupt Entry bindings.
951 Pending_Action : Boolean := False;
952 -- Unified flag indicating some action needs to be take when abort
953 -- next becomes undeferred. Currently set if:
954 -- . Pending_Priority_Change is set
955 -- . Pending_ATC_Level is changed
956 -- . Requeue involving POs
957 -- (Abortable field may have changed and the Wait_Until_Abortable
958 -- has to recheck the abortable status of the call.)
959 -- . Exception_To_Raise is non-null
961 -- Protection: Self.L
963 -- This should never be reset back to False outside of the procedure
964 -- Do_Pending_Action, which is called by Undefer_Abort. It should only
965 -- be set to True by Set_Priority and Abort_To_Level.
967 Pending_Priority_Change : Boolean := False;
968 -- Flag to indicate pending priority change (for dynamic priorities
969 -- package). The base priority is updated on the next abort
970 -- completion point (aka. synchronization point).
972 -- Protection: Self.L
974 Terminate_Alternative : Boolean := False;
975 -- Task is accepting Select with Terminate Alternative
977 -- Protection: Self.L
981 -- Beginning of counts
983 ATC_Nesting_Level : ATC_Level := 1;
984 -- The dynamic level of ATC nesting (currently executing nested
985 -- asynchronous select statements) in this task.
987 -- Protection: Self_ID.L. Only Self reads or updates this field.
988 -- Decrementing it deallocates an Entry_Calls component, and care must
989 -- be taken that all references to that component are eliminated before
990 -- doing the decrement. This in turn will require locking a protected
991 -- object (for a protected entry call) or the Acceptor's lock (for a
992 -- task entry call). No other task should attempt to read or modify
995 Deferral_Level : Natural := 1;
996 -- This is the number of times that Defer_Abort has been called by
997 -- this task without a matching Undefer_Abort call. Abortion is only
998 -- allowed when this zero. It is initially 1, to protect the task at
1001 -- Protection: Only updated by Self; access assumed to be atomic
1003 Pending_ATC_Level : ATC_Level_Base := ATC_Level_Infinity;
1004 -- The ATC level to which this task is currently being aborted. If the
1005 -- value is zero, the entire task has "completed". That may be via
1006 -- abort, exception propagation, or normal exit. If the value is
1007 -- ATC_Level_Infinity, the task is not being aborted to any level. If
1008 -- the value is positive, the task has not completed. This should ONLY
1009 -- be modified by Abort_To_Level and Exit_One_ATC_Level.
1011 -- Protection: Self.L
1013 Serial_Number : Task_Serial_Number;
1014 -- A growing number to provide some way to check locking rules/ordering
1016 Known_Tasks_Index : Integer := -1;
1017 -- Index in the System.Tasking.Debug.Known_Tasks array
1019 User_State : Long_Integer := 0;
1020 -- User-writeable location, for use in debugging tasks; also provides a
1021 -- simple task specific data.
1023 Direct_Attributes : Direct_Attribute_Array;
1024 -- For task attributes that have same size as Address
1026 Is_Defined : Direct_Index_Vector := 0;
1027 -- Bit I is 1 iff Direct_Attributes (I) is defined
1029 Indirect_Attributes : Access_Address;
1030 -- A pointer to chain of records for other attributes that are not
1031 -- address-sized, including all tagged types.
1033 Entry_Queues : Task_Entry_Queue_Array (1 .. Entry_Num);
1034 -- An array of task entry queues
1036 -- Protection: Self.L. Once a task has set Self.Stage to Completing, it
1037 -- has exclusive access to this field.
1040 --------------------
1041 -- Initialization --
1042 --------------------
1044 procedure Initialize;
1045 -- This procedure constitutes the first part of the initialization of the
1046 -- GNARL. This includes creating data structures to make the initial thread
1047 -- into the environment task. The last part of the initialization is done
1048 -- in System.Tasking.Initialization or System.Tasking.Restricted.Stages.
1049 -- All the initializations used to be in Tasking.Initialization, but this
1050 -- is no longer possible with the run time simplification (including
1051 -- optimized PO and the restricted run time) since one cannot rely on
1052 -- System.Tasking.Initialization being present, as was done before.
1054 procedure Initialize_ATCB
1056 Task_Entry_Point : Task_Procedure_Access;
1057 Task_Arg : System.Address;
1059 Elaborated : Access_Boolean;
1060 Base_Priority : System.Any_Priority;
1061 Task_Info : System.Task_Info.Task_Info_Type;
1062 Stack_Size : System.Parameters.Size_Type;
1064 Success : out Boolean);
1065 -- Initialize fields of a TCB and link into global TCB structures Call
1066 -- this only with abort deferred and holding RTS_Lock. Need more
1067 -- documentation, mention T, and describe Success ???
1071 Null_Task : constant Task_Id := null;
1073 type Activation_Chain is limited record
1077 -- Activation_Chain is an in-out parameter of initialization procedures and
1078 -- it must be passed by reference because the init proc may terminate
1079 -- abnormally after creating task components, and these must be properly
1080 -- registered for removal (Expunge_Unactivated_Tasks). The "limited" forces
1081 -- Activation_Chain to be a by-reference type; see RM-6.2(4).