------------------------------------------------------------------------------ -- -- -- 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) 1992-2007, 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 2, or (at your option) any later ver- -- -- sion. GNARL 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. See the GNU General Public License -- -- for more details. You should have received a copy of the GNU General -- -- Public License distributed with GNARL; see file COPYING. If not, write -- -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, -- -- Boston, MA 02110-1301, USA. -- -- -- -- As a special exception, if other files instantiate generics from this -- -- unit, or you link this unit with other files to produce an executable, -- -- this unit does not by itself cause the resulting executable to be -- -- covered by the GNU General Public License. This exception does not -- -- however invalidate any other reasons why the executable file might be -- -- covered by the GNU Public License. -- -- -- -- 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; -- Used for Exception_Occurrence_Access with System.Task_Primitives; -- Used for Lock with System.Task_Primitives.Operations; -- Used for Set_Priority -- Write_Lock -- Unlock -- Initialize_Lock with System.Soft_Links; -- Used for the non-tasking routines (*_NT) that refer to global data. -- They are needed here before the tasking run time has been elaborated. with System.Soft_Links.Tasking; -- Used for Init_Tasking_Soft_Links with System.Tasking.Debug; -- Used for Trace with System.Stack_Checking; with System.Parameters; -- used for Single_Lock 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_Stack_Info return Stack_Checking.Stack_Access; -- Get access to the current task's Stack_Info 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; -- pragma Assert -- ((Self_ID.Pending_ATC_Level >= Self_ID.ATC_Nesting_Level or else -- Self_ID.Deferral_Level > 0)); -- See comment in Defer_Abort on the situations in which it may be -- useful to uncomment the above assertion. 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; Self_Id.Master_Within := Library_Task_Level; -- 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 -- 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.Get_Stack_Info := Get_Stack_Info'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 beek 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 lowl-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 relase 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 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 => 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 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 Bodies -- ---------------------- function Get_Stack_Info return Stack_Checking.Stack_Access is begin return STPO.Self.Common.Compiler_Data.Pri_Stack_Info'Access; end Get_Stack_Info; ----------------------- -- 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;