File : s-tasini.adb
------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . T A S K I N G . I N I T I A L I Z A T I O N --
-- --
-- B o d y --
-- --
-- Copyright (C) 1992-2009, Free Software Foundation, Inc. --
-- --
-- GNARL is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- --
-- --
-- --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNARL was developed by the GNARL team at Florida State University. --
-- Extensive contributions were provided by Ada Core Technologies, Inc. --
-- --
------------------------------------------------------------------------------
pragma Style_Checks (All_Checks);
-- Turn off subprogram alpha ordering check, since we group soft link bodies
-- and dummy soft link bodies together separately in this unit.
pragma Polling (Off);
-- Turn polling off for this package. We don't need polling during any of the
-- routines in this package, and more to the point, if we try to poll it can
-- cause infinite loops.
with Ada.Exceptions;
with System.Task_Primitives;
with System.Task_Primitives.Operations;
with System.Soft_Links;
with System.Soft_Links.Tasking;
with System.Tasking.Debug;
with System.Parameters;
package body System.Tasking.Initialization is
package STPO renames System.Task_Primitives.Operations;
package SSL renames System.Soft_Links;
package AE renames Ada.Exceptions;
use Parameters;
use Task_Primitives.Operations;
Global_Task_Lock : aliased System.Task_Primitives.RTS_Lock;
-- This is a global lock; it is used to execute in mutual exclusion from
-- all other tasks. It is only used by Task_Lock, Task_Unlock, and
-- Final_Task_Unlock.
----------------------------------------------------------------------
-- Tasking versions of some services needed by non-tasking programs --
----------------------------------------------------------------------
procedure Abort_Defer;
-- NON-INLINE versions without Self_ID for soft links
procedure Abort_Undefer;
-- NON-INLINE versions without Self_ID for soft links
procedure Task_Lock;
-- Locks out other tasks. Preceding a section of code by Task_Lock and
-- following it by Task_Unlock creates a critical region. This is used
-- for ensuring that a region of non-tasking code (such as code used to
-- allocate memory) is tasking safe. Note that it is valid for calls to
-- Task_Lock/Task_Unlock to be nested, and this must work properly, i.e.
-- only the corresponding outer level Task_Unlock will actually unlock.
procedure Task_Unlock;
-- Releases lock previously set by call to Task_Lock. In the nested case,
-- all nested locks must be released before other tasks competing for the
-- tasking lock are released.
function Get_Current_Excep return SSL.EOA;
-- Task-safe version of SSL.Get_Current_Excep
procedure Update_Exception
(X : AE.Exception_Occurrence := SSL.Current_Target_Exception);
-- Handle exception setting and check for pending actions
function Task_Name return String;
-- Returns current task's name
------------------------
-- Local Subprograms --
------------------------
----------------------------
-- Tasking Initialization --
----------------------------
procedure Init_RTS;
-- This procedure completes the initialization of the GNARL. The first part
-- of the initialization is done in the body of System.Tasking. It consists
-- of initializing global locks, and installing tasking versions of certain
-- operations used by the compiler. Init_RTS is called during elaboration.
--------------------------
-- Change_Base_Priority --
--------------------------
-- Call only with abort deferred and holding Self_ID locked
procedure Change_Base_Priority (T : Task_Id) is
begin
if T.Common.Base_Priority /= T.New_Base_Priority then
T.Common.Base_Priority := T.New_Base_Priority;
Set_Priority (T, T.Common.Base_Priority);
end if;
end Change_Base_Priority;
------------------------
-- Check_Abort_Status --
------------------------
function Check_Abort_Status return Integer is
Self_ID : constant Task_Id := Self;
begin
if Self_ID /= null
and then Self_ID.Deferral_Level = 0
and then Self_ID.Pending_ATC_Level < Self_ID.ATC_Nesting_Level
then
return 1;
else
return 0;
end if;
end Check_Abort_Status;
-----------------
-- Defer_Abort --
-----------------
procedure Defer_Abort (Self_ID : Task_Id) is
begin
if No_Abort then
return;
end if;
pragma Assert (Self_ID.Deferral_Level = 0);
-- pragma Assert
-- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level);
-- The above check has been useful in detecting mismatched defer/undefer
-- pairs. You may uncomment it when testing on systems that support
-- preemptive abort.
-- If the OS supports preemptive abort (e.g. pthread_kill), it should
-- have happened already. A problem is with systems that do not support
-- preemptive abort, and so rely on polling. On such systems we may get
-- false failures of the assertion, since polling for pending abort does
-- no occur until the abort undefer operation.
-- Even on systems that only poll for abort, the assertion may be useful
-- for catching missed abort completion polling points. The operations
-- that undefer abort poll for pending aborts. This covers most of the
-- places where the core Ada semantics require abort to be caught,
-- without any special attention. However, this generally happens on
-- exit from runtime system call, which means a pending abort will not
-- be noticed on the way into the runtime system. We considered adding a
-- check for pending aborts at this point, but chose not to, because of
-- the overhead. Instead, we searched for RTS calls where abort
-- completion is required and a task could go farther than Ada allows
-- before undeferring abort; we then modified the code to ensure the
-- abort would be detected.
Self_ID.Deferral_Level := Self_ID.Deferral_Level + 1;
end Defer_Abort;
--------------------------
-- Defer_Abort_Nestable --
--------------------------
procedure Defer_Abort_Nestable (Self_ID : Task_Id) is
begin
if No_Abort then
return;
end if;
-- The following assertion is by default disabled. See the comment in
-- Defer_Abort on the situations in which it may be useful to uncomment
-- this assertion and enable the test.
-- pragma Assert
-- (Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level or else
-- Self_ID.Deferral_Level > 0);
Self_ID.Deferral_Level := Self_ID.Deferral_Level + 1;
end Defer_Abort_Nestable;
-----------------
-- Abort_Defer --
-----------------
procedure Abort_Defer is
Self_ID : Task_Id;
begin
if No_Abort then
return;
end if;
Self_ID := STPO.Self;
Self_ID.Deferral_Level := Self_ID.Deferral_Level + 1;
end Abort_Defer;
-----------------------
-- Get_Current_Excep --
-----------------------
function Get_Current_Excep return SSL.EOA is
begin
return STPO.Self.Common.Compiler_Data.Current_Excep'Access;
end Get_Current_Excep;
-----------------------
-- Do_Pending_Action --
-----------------------
-- Call only when holding no locks
procedure Do_Pending_Action (Self_ID : Task_Id) is
use type Ada.Exceptions.Exception_Id;
begin
pragma Assert (Self_ID = Self and then Self_ID.Deferral_Level = 0);
-- Needs loop to recheck for pending action in case a new one occurred
-- while we had abort deferred below.
loop
-- Temporarily defer abort so that we can lock Self_ID
Self_ID.Deferral_Level := Self_ID.Deferral_Level + 1;
if Single_Lock then
Lock_RTS;
end if;
Write_Lock (Self_ID);
Self_ID.Pending_Action := False;
Unlock (Self_ID);
if Single_Lock then
Unlock_RTS;
end if;
-- Restore the original Deferral value
Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
if not Self_ID.Pending_Action then
if Self_ID.Pending_ATC_Level < Self_ID.ATC_Nesting_Level then
if not Self_ID.Aborting then
Self_ID.Aborting := True;
pragma Debug
(Debug.Trace (Self_ID, "raise Abort_Signal", 'B'));
raise Standard'Abort_Signal;
pragma Assert (not Self_ID.ATC_Hack);
elsif Self_ID.ATC_Hack then
-- The solution really belongs in the Abort_Signal handler
-- for async. entry calls. The present hack is very
-- fragile. It relies that the very next point after
-- Exit_One_ATC_Level at which the task becomes abortable
-- will be the call to Undefer_Abort in the
-- Abort_Signal handler.
Self_ID.ATC_Hack := False;
pragma Debug
(Debug.Trace
(Self_ID, "raise Abort_Signal (ATC hack)", 'B'));
raise Standard'Abort_Signal;
end if;
end if;
return;
end if;
end loop;
end Do_Pending_Action;
-----------------------
-- Final_Task_Unlock --
-----------------------
-- This version is only for use in Terminate_Task, when the task is
-- relinquishing further rights to its own ATCB.
-- There is a very interesting potential race condition there, where the
-- old task may run concurrently with a new task that is allocated the old
-- tasks (now reused) ATCB. The critical thing here is to not make any
-- reference to the ATCB after the lock is released. See also comments on
-- Terminate_Task and Unlock.
procedure Final_Task_Unlock (Self_ID : Task_Id) is
begin
pragma Assert (Self_ID.Common.Global_Task_Lock_Nesting = 1);
Unlock (Global_Task_Lock'Access, Global_Lock => True);
end Final_Task_Unlock;
--------------
-- Init_RTS --
--------------
procedure Init_RTS is
Self_Id : Task_Id;
begin
Tasking.Initialize;
-- Terminate run time (regular vs restricted) specific initialization
-- of the environment task.
Self_Id := Environment_Task;
Self_Id.Master_of_Task := Environment_Task_Level;
Self_Id.Master_Within := Self_Id.Master_of_Task + 1;
for L in Self_Id.Entry_Calls'Range loop
Self_Id.Entry_Calls (L).Self := Self_Id;
Self_Id.Entry_Calls (L).Level := L;
end loop;
Self_Id.Awake_Count := 1;
Self_Id.Alive_Count := 1;
-- Normally, a task starts out with internal master nesting level one
-- larger than external master nesting level. It is incremented to one
-- by Enter_Master, which is called in the task body only if the
-- compiler thinks the task may have dependent tasks. There is no
-- corresponding call to Enter_Master for the environment task, so we
-- would need to increment it to 2 here. Instead, we set it to 3. By
-- doing this we reserve the level 2 for server tasks of the runtime
-- system. The environment task does not need to wait for these server
Self_Id.Master_Within := Library_Task_Level;
-- Initialize lock used to implement mutual exclusion between all tasks
Initialize_Lock (Global_Task_Lock'Access, STPO.Global_Task_Level);
-- Notify that the tasking run time has been elaborated so that
-- the tasking version of the soft links can be used.
if not No_Abort then
SSL.Abort_Defer := Abort_Defer'Access;
SSL.Abort_Undefer := Abort_Undefer'Access;
end if;
SSL.Lock_Task := Task_Lock'Access;
SSL.Unlock_Task := Task_Unlock'Access;
SSL.Check_Abort_Status := Check_Abort_Status'Access;
SSL.Task_Name := Task_Name'Access;
SSL.Update_Exception := Update_Exception'Access;
SSL.Get_Current_Excep := Get_Current_Excep'Access;
-- Initialize the tasking soft links (if not done yet) that are common
-- to the full and the restricted run times.
SSL.Tasking.Init_Tasking_Soft_Links;
-- Abort is deferred in a new ATCB, so we need to undefer abort at this
-- stage to make the environment task abortable.
Undefer_Abort (Environment_Task);
end Init_RTS;
---------------------------
-- Locked_Abort_To_Level--
---------------------------
-- Abort a task to the specified ATC nesting level.
-- Call this only with T locked.
-- An earlier version of this code contained a call to Wakeup. That should
-- not be necessary here, if Abort_Task is implemented correctly, since
-- Abort_Task should include the effect of Wakeup. However, the above call
-- was in earlier versions of this file, and at least for some targets
-- Abort_Task has not been doing Wakeup. It should not hurt to uncomment
-- the above call, until the error is corrected for all targets.
-- See extended comments in package body System.Tasking.Abort for the
-- overall design of the implementation of task abort.
-- ??? there is no such package ???
-- If the task is sleeping it will be in an abort-deferred region, and will
-- not have Abort_Signal raised by Abort_Task. Such an "abort deferral" is
-- just to protect the RTS internals, and not necessarily required to
-- enforce Ada semantics. Abort_Task should wake the task up and let it
-- decide if it wants to complete the aborted construct immediately.
-- Note that the effect of the low-level Abort_Task is not persistent.
-- If the target task is not blocked, this wakeup will be missed.
-- We don't bother calling Abort_Task if this task is aborting itself,
-- since we are inside the RTS and have abort deferred. Similarly, We don't
-- bother to call Abort_Task if T is terminated, since there is no need to
-- abort a terminated task, and it could be dangerous to try if the task
-- has stopped executing.
-- Note that an earlier version of this code had some false reasoning about
-- being able to reliably wake up a task that had suspended on a blocking
-- system call that does not atomically release the task's lock (e.g., UNIX
-- nanosleep, which we once thought could be used to implement delays).
-- That still left the possibility of missed wakeups.
-- We cannot safely call Vulnerable_Complete_Activation here, since that
-- requires locking Self_ID.Parent. The anti-deadlock lock ordering rules
-- would then require us to release the lock on Self_ID first, which would
-- create a timing window for other tasks to lock Self_ID. This is
-- significant for tasks that may be aborted before their execution can
-- enter the task body, and so they do not get a chance to call
-- Complete_Task. The actual work for this case is done in Terminate_Task.
procedure Locked_Abort_To_Level
(Self_ID : Task_Id;
T : Task_Id;
L : ATC_Level)
is
begin
if not T.Aborting and then T /= Self_ID then
case T.Common.State is
when Unactivated | Terminated =>
pragma Assert (False);
null;
when Activating | Runnable =>
-- This is needed to cancel an asynchronous protected entry
-- call during a requeue with abort.
T.Entry_Calls
(T.ATC_Nesting_Level).Cancellation_Attempted := True;
when Interrupt_Server_Blocked_On_Event_Flag =>
null;
when Delay_Sleep |
Async_Select_Sleep |
Interrupt_Server_Idle_Sleep |
Interrupt_Server_Blocked_Interrupt_Sleep |
Timer_Server_Sleep |
AST_Server_Sleep =>
Wakeup (T, T.Common.State);
when Acceptor_Sleep | Acceptor_Delay_Sleep =>
T.Open_Accepts := null;
Wakeup (T, T.Common.State);
when Entry_Caller_Sleep =>
T.Entry_Calls
(T.ATC_Nesting_Level).Cancellation_Attempted := True;
Wakeup (T, T.Common.State);
when Activator_Sleep |
Master_Completion_Sleep |
Master_Phase_2_Sleep |
Asynchronous_Hold =>
null;
end case;
end if;
if T.Pending_ATC_Level > L then
T.Pending_ATC_Level := L;
T.Pending_Action := True;
if L = 0 then
T.Callable := False;
end if;
-- This prevents aborted task from accepting calls
if T.Aborting then
-- The test above is just a heuristic, to reduce wasteful
-- calls to Abort_Task. We are holding T locked, and this
-- value will not be set to False except with T also locked,
-- inside Exit_One_ATC_Level, so we should not miss wakeups.
if T.Common.State = Acceptor_Sleep
or else
T.Common.State = Acceptor_Delay_Sleep
then
T.Open_Accepts := null;
end if;
elsif T /= Self_ID and then
(T.Common.State = Runnable
or else T.Common.State = Interrupt_Server_Blocked_On_Event_Flag)
-- The task is blocked on a system call waiting for the
-- completion event. In this case Abort_Task may need to take
-- special action in order to succeed. Example system: VMS.
then
Abort_Task (T);
end if;
end if;
end Locked_Abort_To_Level;
--------------------------------
-- Remove_From_All_Tasks_List --
--------------------------------
procedure Remove_From_All_Tasks_List (T : Task_Id) is
C : Task_Id;
Previous : Task_Id;
begin
pragma Debug
(Debug.Trace (Self, "Remove_From_All_Tasks_List", 'C'));
Previous := Null_Task;
C := All_Tasks_List;
while C /= Null_Task loop
if C = T then
if Previous = Null_Task then
All_Tasks_List := All_Tasks_List.Common.All_Tasks_Link;
else
Previous.Common.All_Tasks_Link := C.Common.All_Tasks_Link;
end if;
return;
end if;
Previous := C;
C := C.Common.All_Tasks_Link;
end loop;
pragma Assert (False);
end Remove_From_All_Tasks_List;
---------------
-- Task_Lock --
---------------
procedure Task_Lock (Self_ID : Task_Id) is
begin
Self_ID.Common.Global_Task_Lock_Nesting :=
Self_ID.Common.Global_Task_Lock_Nesting + 1;
if Self_ID.Common.Global_Task_Lock_Nesting = 1 then
Defer_Abort_Nestable (Self_ID);
Write_Lock (Global_Task_Lock'Access, Global_Lock => True);
end if;
end Task_Lock;
procedure Task_Lock is
begin
Task_Lock (STPO.Self);
end Task_Lock;
---------------
-- Task_Name --
---------------
function Task_Name return String is
Self_Id : constant Task_Id := STPO.Self;
begin
return Self_Id.Common.Task_Image (1 .. Self_Id.Common.Task_Image_Len);
end Task_Name;
-----------------
-- Task_Unlock --
-----------------
procedure Task_Unlock (Self_ID : Task_Id) is
begin
pragma Assert (Self_ID.Common.Global_Task_Lock_Nesting > 0);
Self_ID.Common.Global_Task_Lock_Nesting :=
Self_ID.Common.Global_Task_Lock_Nesting - 1;
if Self_ID.Common.Global_Task_Lock_Nesting = 0 then
Unlock (Global_Task_Lock'Access, Global_Lock => True);
Undefer_Abort_Nestable (Self_ID);
end if;
end Task_Unlock;
procedure Task_Unlock is
begin
Task_Unlock (STPO.Self);
end Task_Unlock;
-------------------
-- Undefer_Abort --
-------------------
-- Precondition : Self does not hold any locks!
-- Undefer_Abort is called on any abort completion point (aka.
-- synchronization point). It performs the following actions if they
-- are pending: (1) change the base priority, (2) abort the task.
-- The priority change has to occur before abort. Otherwise, it would
-- take effect no earlier than the next abort completion point.
procedure Undefer_Abort (Self_ID : Task_Id) is
begin
if No_Abort then
return;
end if;
pragma Assert (Self_ID.Deferral_Level = 1);
Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
if Self_ID.Deferral_Level = 0 then
pragma Assert (Check_No_Locks (Self_ID));
if Self_ID.Pending_Action then
Do_Pending_Action (Self_ID);
end if;
end if;
end Undefer_Abort;
----------------------------
-- Undefer_Abort_Nestable --
----------------------------
-- An earlier version would re-defer abort if an abort is in progress.
-- Then, we modified the effect of the raise statement so that it defers
-- abort until control reaches a handler. That was done to prevent
-- "skipping over" a handler if another asynchronous abort occurs during
-- the propagation of the abort to the handler.
-- There has been talk of reversing that decision, based on a newer
-- implementation of exception propagation. Care must be taken to evaluate
-- how such a change would interact with the above code and all the places
-- where abort-deferral is used to bridge over critical transitions, such
-- as entry to the scope of a region with a finalizer and entry into the
-- body of an accept-procedure.
procedure Undefer_Abort_Nestable (Self_ID : Task_Id) is
begin
if No_Abort then
return;
end if;
pragma Assert (Self_ID.Deferral_Level > 0);
Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
if Self_ID.Deferral_Level = 0 then
pragma Assert (Check_No_Locks (Self_ID));
if Self_ID.Pending_Action then
Do_Pending_Action (Self_ID);
end if;
end if;
end Undefer_Abort_Nestable;
-------------------
-- Abort_Undefer --
-------------------
procedure Abort_Undefer is
Self_ID : Task_Id;
begin
if No_Abort then
return;
end if;
Self_ID := STPO.Self;
if Self_ID.Deferral_Level = 0 then
-- In case there are different views on whether Abort is supported
-- between the expander and the run time, we may end up with
-- Self_ID.Deferral_Level being equal to zero, when called from
-- the procedure created by the expander that corresponds to a
-- task body.
-- In this case, there's nothing to be done
-- See related code in System.Tasking.Stages.Create_Task resetting
-- Deferral_Level when System.Restrictions.Abort_Allowed is False.
return;
end if;
pragma Assert (Self_ID.Deferral_Level > 0);
Self_ID.Deferral_Level := Self_ID.Deferral_Level - 1;
if Self_ID.Deferral_Level = 0 then
pragma Assert (Check_No_Locks (Self_ID));
if Self_ID.Pending_Action then
Do_Pending_Action (Self_ID);
end if;
end if;
end Abort_Undefer;
----------------------
-- Update_Exception --
----------------------
-- Call only when holding no locks
procedure Update_Exception
(X : AE.Exception_Occurrence := SSL.Current_Target_Exception)
is
Self_Id : constant Task_Id := Self;
use Ada.Exceptions;
begin
Save_Occurrence (Self_Id.Common.Compiler_Data.Current_Excep, X);
if Self_Id.Deferral_Level = 0 then
if Self_Id.Pending_Action then
Self_Id.Pending_Action := False;
Self_Id.Deferral_Level := Self_Id.Deferral_Level + 1;
if Single_Lock then
Lock_RTS;
end if;
Write_Lock (Self_Id);
Self_Id.Pending_Action := False;
Unlock (Self_Id);
if Single_Lock then
Unlock_RTS;
end if;
Self_Id.Deferral_Level := Self_Id.Deferral_Level - 1;
if Self_Id.Pending_ATC_Level < Self_Id.ATC_Nesting_Level then
if not Self_Id.Aborting then
Self_Id.Aborting := True;
raise Standard'Abort_Signal;
end if;
end if;
end if;
end if;
end Update_Exception;
--------------------------
-- Wakeup_Entry_Caller --
--------------------------
-- This is called at the end of service of an entry call, to abort the
-- caller if he is in an abortable part, and to wake up the caller if it
-- is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
-- (This enforces the rule that a task must be off-queue if its state is
-- Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
-- Timed_Call or Simple_Call:
-- The caller is waiting on Entry_Caller_Sleep, in
-- Wait_For_Completion, or Wait_For_Completion_With_Timeout.
-- Conditional_Call:
-- The caller might be in Wait_For_Completion,
-- waiting for a rendezvous (possibly requeued without abort)
-- to complete.
-- Asynchronous_Call:
-- The caller may be executing in the abortable part o
-- an async. select, or on a time delay,
-- if Entry_Call.State >= Was_Abortable.
procedure Wakeup_Entry_Caller
(Self_ID : Task_Id;
Entry_Call : Entry_Call_Link;
New_State : Entry_Call_State)
is
Caller : constant Task_Id := Entry_Call.Self;
begin
pragma Debug (Debug.Trace
(Self_ID, "Wakeup_Entry_Caller", 'E', Caller));
pragma Assert (New_State = Done or else New_State = Cancelled);
pragma Assert (Caller.Common.State /= Unactivated);
Entry_Call.State := New_State;
if Entry_Call.Mode = Asynchronous_Call then
-- Abort the caller in his abortable part, but do so only if call has
-- been queued abortably.
if Entry_Call.State >= Was_Abortable or else New_State = Done then
Locked_Abort_To_Level (Self_ID, Caller, Entry_Call.Level - 1);
end if;
elsif Caller.Common.State = Entry_Caller_Sleep then
Wakeup (Caller, Entry_Caller_Sleep);
end if;
end Wakeup_Entry_Caller;
-----------------------
-- Soft-Link Dummies --
-----------------------
-- These are dummies for subprograms that are only needed by certain
-- optional run-time system packages. If they are needed, the soft links
-- will be redirected to the real subprogram by elaboration of the
-- subprogram body where the real subprogram is declared.
procedure Finalize_Attributes (T : Task_Id) is
pragma Unreferenced (T);
begin
null;
end Finalize_Attributes;
procedure Initialize_Attributes (T : Task_Id) is
pragma Unreferenced (T);
begin
null;
end Initialize_Attributes;
begin
Init_RTS;
end System.Tasking.Initialization;