| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS -- |
| -- -- |
| -- S Y S T E M . T A S K I N G . E N T R Y _ C A L L S -- |
| -- -- |
| -- B o d y -- |
| -- -- |
| -- Copyright (C) 1992-2021, 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. -- |
| -- -- |
| -- As a special exception under Section 7 of GPL version 3, you are granted -- |
| -- additional permissions described in the GCC Runtime Library Exception, -- |
| -- version 3.1, as published by the Free Software Foundation. -- |
| -- -- |
| -- 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. -- |
| -- -- |
| ------------------------------------------------------------------------------ |
| |
| with System.Task_Primitives.Operations; |
| with System.Tasking.Initialization; |
| with System.Tasking.Protected_Objects.Entries; |
| with System.Tasking.Protected_Objects.Operations; |
| with System.Tasking.Queuing; |
| with System.Tasking.Utilities; |
| |
| package body System.Tasking.Entry_Calls is |
| |
| package STPO renames System.Task_Primitives.Operations; |
| |
| use Protected_Objects.Entries; |
| use Protected_Objects.Operations; |
| |
| -- DO NOT use Protected_Objects.Lock or Protected_Objects.Unlock |
| -- internally. Those operations will raise Program_Error, which |
| -- we are not prepared to handle inside the RTS. Instead, use |
| -- System.Task_Primitives lock operations directly on Protection.L. |
| |
| ----------------------- |
| -- Local Subprograms -- |
| ----------------------- |
| |
| procedure Lock_Server (Entry_Call : Entry_Call_Link); |
| |
| -- This locks the server targeted by Entry_Call |
| -- |
| -- This may be a task or a protected object, depending on the target of the |
| -- original call or any subsequent requeues. |
| -- |
| -- This routine is needed because the field specifying the server for this |
| -- call must be protected by the server's mutex. If it were protected by |
| -- the caller's mutex, accessing the server's queues would require locking |
| -- the caller to get the server, locking the server, and then accessing the |
| -- queues. This involves holding two ATCB locks at once, something which we |
| -- can guarantee that it will always be done in the same order, or locking |
| -- a protected object while we hold an ATCB lock, something which is not |
| -- permitted. Since the server cannot be obtained reliably, it must be |
| -- obtained unreliably and then checked again once it has been locked. |
| -- |
| -- This should only be called by the Entry_Call.Self. |
| -- It should be holding no other ATCB locks at the time. |
| |
| procedure Unlock_Server (Entry_Call : Entry_Call_Link); |
| -- STPO.Unlock the server targeted by Entry_Call. The server must |
| -- be locked before calling this. |
| |
| procedure Unlock_And_Update_Server |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link); |
| -- Similar to Unlock_Server, but services entry calls if the |
| -- server is a protected object. |
| |
| procedure Check_Pending_Actions_For_Entry_Call |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link); |
| -- This procedure performs priority change of a queued call and dequeuing |
| -- of an entry call when the call is cancelled. If the call is dequeued the |
| -- state should be set to Cancelled. Call only with abort deferred and |
| -- holding lock of Self_ID. This is a bit of common code for all entry |
| -- calls. The effect is to do any deferred base priority change operation, |
| -- in case some other task called STPO.Set_Priority while the current task |
| -- had abort deferred, and to dequeue the call if the call has been |
| -- aborted. |
| |
| procedure Poll_Base_Priority_Change_At_Entry_Call |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link); |
| pragma Inline (Poll_Base_Priority_Change_At_Entry_Call); |
| -- A specialized version of Poll_Base_Priority_Change, that does the |
| -- optional entry queue reordering. Has to be called with the Self_ID's |
| -- ATCB write-locked. May temporarily release the lock. |
| |
| --------------------- |
| -- Check_Exception -- |
| --------------------- |
| |
| procedure Check_Exception |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link) |
| is |
| pragma Warnings (Off, Self_ID); |
| |
| use type Ada.Exceptions.Exception_Id; |
| |
| procedure Internal_Raise (X : Ada.Exceptions.Exception_Id); |
| pragma Import (C, Internal_Raise, "__gnat_raise_with_msg"); |
| |
| E : constant Ada.Exceptions.Exception_Id := |
| Entry_Call.Exception_To_Raise; |
| begin |
| -- pragma Assert (Self_ID.Deferral_Level = 0); |
| |
| -- The above may be useful for debugging, but the Florist packages |
| -- contain critical sections that defer abort and then do entry calls, |
| -- which causes the above Assert to trip. |
| |
| if E /= Ada.Exceptions.Null_Id then |
| Internal_Raise (E); |
| end if; |
| end Check_Exception; |
| |
| ------------------------------------------ |
| -- Check_Pending_Actions_For_Entry_Call -- |
| ------------------------------------------ |
| |
| procedure Check_Pending_Actions_For_Entry_Call |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link) |
| is |
| begin |
| pragma Assert (Self_ID = Entry_Call.Self); |
| |
| Poll_Base_Priority_Change_At_Entry_Call (Self_ID, Entry_Call); |
| |
| if Self_ID.Pending_ATC_Level < Self_ID.ATC_Nesting_Level |
| and then Entry_Call.State = Now_Abortable |
| then |
| STPO.Unlock (Self_ID); |
| Lock_Server (Entry_Call); |
| |
| if Queuing.Onqueue (Entry_Call) |
| and then Entry_Call.State = Now_Abortable |
| then |
| Queuing.Dequeue_Call (Entry_Call); |
| Entry_Call.State := |
| (if Entry_Call.Cancellation_Attempted then Cancelled else Done); |
| Unlock_And_Update_Server (Self_ID, Entry_Call); |
| |
| else |
| Unlock_Server (Entry_Call); |
| end if; |
| |
| STPO.Write_Lock (Self_ID); |
| end if; |
| end Check_Pending_Actions_For_Entry_Call; |
| |
| ----------------- |
| -- Lock_Server -- |
| ----------------- |
| |
| procedure Lock_Server (Entry_Call : Entry_Call_Link) is |
| Test_Task : Task_Id; |
| Test_PO : Protection_Entries_Access; |
| Ceiling_Violation : Boolean; |
| Failures : Integer := 0; |
| |
| begin |
| Test_Task := Entry_Call.Called_Task; |
| |
| loop |
| if Test_Task = null then |
| |
| -- Entry_Call was queued on a protected object, or in transition, |
| -- when we last fetched Test_Task. |
| |
| Test_PO := To_Protection (Entry_Call.Called_PO); |
| |
| if Test_PO = null then |
| |
| -- We had very bad luck, interleaving with TWO different |
| -- requeue operations. Go around the loop and try again. |
| |
| STPO.Yield; |
| |
| else |
| Lock_Entries_With_Status (Test_PO, Ceiling_Violation); |
| |
| -- ??? |
| |
| -- The following code allows Lock_Server to be called when |
| -- cancelling a call, to allow for the possibility that the |
| -- priority of the caller has been raised beyond that of the |
| -- protected entry call by Ada.Dynamic_Priorities.Set_Priority. |
| |
| -- If the current task has a higher priority than the ceiling |
| -- of the protected object, temporarily lower it. It will |
| -- be reset in Unlock. |
| |
| if Ceiling_Violation then |
| declare |
| Current_Task : constant Task_Id := STPO.Self; |
| Old_Base_Priority : System.Any_Priority; |
| |
| begin |
| STPO.Write_Lock (Current_Task); |
| Old_Base_Priority := Current_Task.Common.Base_Priority; |
| Current_Task.New_Base_Priority := Test_PO.Ceiling; |
| System.Tasking.Initialization.Change_Base_Priority |
| (Current_Task); |
| STPO.Unlock (Current_Task); |
| |
| -- Following lock should not fail |
| |
| Lock_Entries (Test_PO); |
| |
| Test_PO.Old_Base_Priority := Old_Base_Priority; |
| Test_PO.Pending_Action := True; |
| end; |
| end if; |
| |
| exit when To_Address (Test_PO) = Entry_Call.Called_PO; |
| Unlock_Entries (Test_PO); |
| end if; |
| |
| else |
| STPO.Write_Lock (Test_Task); |
| exit when Test_Task = Entry_Call.Called_Task; |
| STPO.Unlock (Test_Task); |
| end if; |
| |
| Test_Task := Entry_Call.Called_Task; |
| Failures := Failures + 1; |
| pragma Assert (Failures <= 5); |
| end loop; |
| end Lock_Server; |
| |
| --------------------------------------------- |
| -- Poll_Base_Priority_Change_At_Entry_Call -- |
| --------------------------------------------- |
| |
| procedure Poll_Base_Priority_Change_At_Entry_Call |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link) |
| is |
| begin |
| if Self_ID.Pending_Priority_Change then |
| |
| -- Check for ceiling violations ??? |
| |
| Self_ID.Pending_Priority_Change := False; |
| |
| -- Requeue the entry call at the new priority. We need to requeue |
| -- even if the new priority is the same than the previous (see ACATS |
| -- test cxd4006). |
| |
| STPO.Unlock (Self_ID); |
| Lock_Server (Entry_Call); |
| Queuing.Requeue_Call_With_New_Prio |
| (Entry_Call, STPO.Get_Priority (Self_ID)); |
| Unlock_And_Update_Server (Self_ID, Entry_Call); |
| STPO.Write_Lock (Self_ID); |
| end if; |
| end Poll_Base_Priority_Change_At_Entry_Call; |
| |
| -------------------- |
| -- Reset_Priority -- |
| -------------------- |
| |
| procedure Reset_Priority |
| (Acceptor : Task_Id; |
| Acceptor_Prev_Priority : Rendezvous_Priority) |
| is |
| begin |
| pragma Assert (Acceptor = STPO.Self); |
| |
| -- Since we limit this kind of "active" priority change to be done |
| -- by the task for itself, we don't need to lock Acceptor. |
| |
| if Acceptor_Prev_Priority /= Priority_Not_Boosted then |
| STPO.Set_Priority (Acceptor, Acceptor_Prev_Priority, |
| Loss_Of_Inheritance => True); |
| end if; |
| end Reset_Priority; |
| |
| ------------------------------ |
| -- Try_To_Cancel_Entry_Call -- |
| ------------------------------ |
| |
| procedure Try_To_Cancel_Entry_Call (Succeeded : out Boolean) is |
| Entry_Call : Entry_Call_Link; |
| Self_ID : constant Task_Id := STPO.Self; |
| |
| use type Ada.Exceptions.Exception_Id; |
| |
| begin |
| Entry_Call := Self_ID.Entry_Calls (Self_ID.ATC_Nesting_Level)'Access; |
| |
| -- Experimentation has shown that abort is sometimes (but not |
| -- always) already deferred when Cancel_xxx_Entry_Call is called. |
| -- That may indicate an error. Find out what is going on. ??? |
| |
| pragma Assert (Entry_Call.Mode = Asynchronous_Call); |
| Initialization.Defer_Abort_Nestable (Self_ID); |
| STPO.Write_Lock (Self_ID); |
| Entry_Call.Cancellation_Attempted := True; |
| |
| if Self_ID.Pending_ATC_Level >= Entry_Call.Level then |
| Self_ID.Pending_ATC_Level := Entry_Call.Level - 1; |
| end if; |
| |
| Entry_Calls.Wait_For_Completion (Entry_Call); |
| STPO.Unlock (Self_ID); |
| Succeeded := Entry_Call.State = Cancelled; |
| Initialization.Undefer_Abort_Nestable (Self_ID); |
| |
| -- Ideally, abort should no longer be deferred at this point, so we |
| -- should be able to call Check_Exception. The loop below should be |
| -- considered temporary, to work around the possibility that abort |
| -- may be deferred more than one level deep ??? |
| |
| if Entry_Call.Exception_To_Raise /= Ada.Exceptions.Null_Id then |
| while Self_ID.Deferral_Level > 0 loop |
| System.Tasking.Initialization.Undefer_Abort_Nestable (Self_ID); |
| end loop; |
| |
| Entry_Calls.Check_Exception (Self_ID, Entry_Call); |
| end if; |
| end Try_To_Cancel_Entry_Call; |
| |
| ------------------------------ |
| -- Unlock_And_Update_Server -- |
| ------------------------------ |
| |
| procedure Unlock_And_Update_Server |
| (Self_ID : Task_Id; |
| Entry_Call : Entry_Call_Link) |
| is |
| Called_PO : Protection_Entries_Access; |
| Caller : Task_Id; |
| |
| begin |
| if Entry_Call.Called_Task /= null then |
| STPO.Unlock (Entry_Call.Called_Task); |
| else |
| Called_PO := To_Protection (Entry_Call.Called_PO); |
| PO_Service_Entries (Self_ID, Called_PO, False); |
| |
| if Called_PO.Pending_Action then |
| Called_PO.Pending_Action := False; |
| Caller := STPO.Self; |
| STPO.Write_Lock (Caller); |
| Caller.New_Base_Priority := Called_PO.Old_Base_Priority; |
| Initialization.Change_Base_Priority (Caller); |
| STPO.Unlock (Caller); |
| end if; |
| |
| Unlock_Entries (Called_PO); |
| end if; |
| end Unlock_And_Update_Server; |
| |
| ------------------- |
| -- Unlock_Server -- |
| ------------------- |
| |
| procedure Unlock_Server (Entry_Call : Entry_Call_Link) is |
| Caller : Task_Id; |
| Called_PO : Protection_Entries_Access; |
| |
| begin |
| if Entry_Call.Called_Task /= null then |
| STPO.Unlock (Entry_Call.Called_Task); |
| else |
| Called_PO := To_Protection (Entry_Call.Called_PO); |
| |
| if Called_PO.Pending_Action then |
| Called_PO.Pending_Action := False; |
| Caller := STPO.Self; |
| STPO.Write_Lock (Caller); |
| Caller.New_Base_Priority := Called_PO.Old_Base_Priority; |
| Initialization.Change_Base_Priority (Caller); |
| STPO.Unlock (Caller); |
| end if; |
| |
| Unlock_Entries (Called_PO); |
| end if; |
| end Unlock_Server; |
| |
| ------------------------- |
| -- Wait_For_Completion -- |
| ------------------------- |
| |
| procedure Wait_For_Completion (Entry_Call : Entry_Call_Link) is |
| Self_Id : constant Task_Id := Entry_Call.Self; |
| |
| begin |
| -- If this is a conditional call, it should be cancelled when it |
| -- becomes abortable. This is checked in the loop below. |
| |
| Self_Id.Common.State := Entry_Caller_Sleep; |
| |
| -- Try to remove calls to Sleep in the loop below by letting the caller |
| -- a chance of getting ready immediately, using Unlock & Yield. |
| -- See similar action in Wait_For_Call & Timed_Selective_Wait. |
| |
| STPO.Unlock (Self_Id); |
| |
| if Entry_Call.State < Done then |
| STPO.Yield; |
| end if; |
| |
| STPO.Write_Lock (Self_Id); |
| |
| loop |
| Check_Pending_Actions_For_Entry_Call (Self_Id, Entry_Call); |
| |
| exit when Entry_Call.State >= Done; |
| |
| STPO.Sleep (Self_Id, Entry_Caller_Sleep); |
| end loop; |
| |
| Self_Id.Common.State := Runnable; |
| Utilities.Exit_One_ATC_Level (Self_Id); |
| end Wait_For_Completion; |
| |
| -------------------------------------- |
| -- Wait_For_Completion_With_Timeout -- |
| -------------------------------------- |
| |
| procedure Wait_For_Completion_With_Timeout |
| (Entry_Call : Entry_Call_Link; |
| Wakeup_Time : Duration; |
| Mode : Delay_Modes; |
| Yielded : out Boolean) |
| is |
| Self_Id : constant Task_Id := Entry_Call.Self; |
| Timedout : Boolean := False; |
| |
| begin |
| -- This procedure waits for the entry call to be served, with a timeout. |
| -- It tries to cancel the call if the timeout expires before the call is |
| -- served. |
| |
| -- If we wake up from the timed sleep operation here, it may be for |
| -- several possible reasons: |
| |
| -- 1) The entry call is done being served. |
| -- 2) There is an abort or priority change to be served. |
| -- 3) The timeout has expired (Timedout = True) |
| -- 4) There has been a spurious wakeup. |
| |
| -- Once the timeout has expired we may need to continue to wait if the |
| -- call is already being serviced. In that case, we want to go back to |
| -- sleep, but without any timeout. The variable Timedout is used to |
| -- control this. If the Timedout flag is set, we do not need to |
| -- STPO.Sleep with a timeout. We just sleep until we get a wakeup for |
| -- some status change. |
| |
| -- The original call may have become abortable after waking up. We want |
| -- to check Check_Pending_Actions_For_Entry_Call again in any case. |
| |
| pragma Assert (Entry_Call.Mode = Timed_Call); |
| |
| Yielded := False; |
| Self_Id.Common.State := Entry_Caller_Sleep; |
| |
| -- Looping is necessary in case the task wakes up early from the timed |
| -- sleep, due to a "spurious wakeup". Spurious wakeups are a weakness of |
| -- POSIX condition variables. A thread waiting for a condition variable |
| -- is allowed to wake up at any time, not just when the condition is |
| -- signaled. See same loop in the ordinary Wait_For_Completion, above. |
| |
| loop |
| Check_Pending_Actions_For_Entry_Call (Self_Id, Entry_Call); |
| exit when Entry_Call.State >= Done; |
| |
| STPO.Timed_Sleep (Self_Id, Wakeup_Time, Mode, |
| Entry_Caller_Sleep, Timedout, Yielded); |
| |
| if Timedout then |
| -- Try to cancel the call (see Try_To_Cancel_Entry_Call for |
| -- corresponding code in the ATC case). |
| |
| Entry_Call.Cancellation_Attempted := True; |
| |
| -- Reset Entry_Call.State so that the call is marked as cancelled |
| -- by Check_Pending_Actions_For_Entry_Call below. |
| |
| if Entry_Call.State < Was_Abortable then |
| Entry_Call.State := Now_Abortable; |
| end if; |
| |
| if Self_Id.Pending_ATC_Level >= Entry_Call.Level then |
| Self_Id.Pending_ATC_Level := Entry_Call.Level - 1; |
| end if; |
| |
| -- The following loop is the same as the loop and exit code |
| -- from the ordinary Wait_For_Completion. If we get here, we |
| -- have timed out but we need to keep waiting until the call |
| -- has actually completed or been cancelled successfully. |
| |
| loop |
| Check_Pending_Actions_For_Entry_Call (Self_Id, Entry_Call); |
| exit when Entry_Call.State >= Done; |
| STPO.Sleep (Self_Id, Entry_Caller_Sleep); |
| end loop; |
| |
| Self_Id.Common.State := Runnable; |
| Utilities.Exit_One_ATC_Level (Self_Id); |
| |
| return; |
| end if; |
| end loop; |
| |
| -- This last part is the same as ordinary Wait_For_Completion, |
| -- and is only executed if the call completed without timing out. |
| |
| Self_Id.Common.State := Runnable; |
| Utilities.Exit_One_ATC_Level (Self_Id); |
| end Wait_For_Completion_With_Timeout; |
| |
| -------------------------- |
| -- Wait_Until_Abortable -- |
| -------------------------- |
| |
| procedure Wait_Until_Abortable |
| (Self_ID : Task_Id; |
| Call : Entry_Call_Link) |
| is |
| begin |
| pragma Assert (Self_ID.ATC_Nesting_Level > Level_No_ATC_Occurring); |
| pragma Assert (Call.Mode = Asynchronous_Call); |
| |
| STPO.Write_Lock (Self_ID); |
| Self_ID.Common.State := Entry_Caller_Sleep; |
| |
| loop |
| Check_Pending_Actions_For_Entry_Call (Self_ID, Call); |
| exit when Call.State >= Was_Abortable; |
| STPO.Sleep (Self_ID, Async_Select_Sleep); |
| end loop; |
| |
| Self_ID.Common.State := Runnable; |
| STPO.Unlock (Self_ID); |
| |
| end Wait_Until_Abortable; |
| |
| end System.Tasking.Entry_Calls; |
