File : s-tasque.adb
------------------------------------------------------------------------------
-- --
-- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . T A S K I N G . Q U E U I N G --
-- --
-- B o d y --
-- --
-- $Revision: 1.35 $
-- --
-- Copyright (C) 1991-1999, Florida State University --
-- --
-- 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, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, 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. It is --
-- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
-- State University (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
-- This version of the body implements queueing policy according to the
-- policy specified by the pragma Queuing_Policy. When no such pragma
-- is specified FIFO policy is used as default.
with System.Task_Primitives.Operations;
-- used for Write_Lock
-- Unlock
with System.Tasking.Initialization;
-- used for Wakeup_Entry_Caller
package body System.Tasking.Queuing is
use System.Task_Primitives.Operations;
use System.Tasking.Protected_Objects;
use System.Tasking.Protected_Objects.Entries;
procedure Wakeup_Entry_Caller
(Self_ID : Task_ID;
Entry_Call : Entry_Call_Link;
New_State : Entry_Call_State)
renames Initialization.Wakeup_Entry_Caller;
-- Entry Queues implemented as doubly linked list.
Queuing_Policy : Character;
pragma Import (C, Queuing_Policy, "__gl_queuing_policy");
Priority_Queuing : constant Boolean := Queuing_Policy = 'P';
procedure Send_Program_Error
(Self_ID : Task_ID;
Entry_Call : Entry_Call_Link);
-- Raise Program_Error in the caller of the specified entry call
------------------------
-- Send_Program_Error --
------------------------
procedure Send_Program_Error
(Self_ID : Task_ID;
Entry_Call : Entry_Call_Link)
is
Caller : Task_ID;
begin
Caller := Entry_Call.Self;
Entry_Call.Exception_To_Raise := Program_Error'Identity;
Write_Lock (Caller);
Wakeup_Entry_Caller (Self_ID, Entry_Call, Done);
Unlock (Caller);
end Send_Program_Error;
-----------------------------
-- Broadcast_Program_Error --
-----------------------------
procedure Broadcast_Program_Error
(Self_ID : Task_ID;
Object : Protection_Entries_Access;
Pending_Call : Entry_Call_Link)
is
Entry_Call : Entry_Call_Link;
begin
if Pending_Call /= null then
Send_Program_Error (Self_ID, Pending_Call);
end if;
for E in Object.Entry_Queues'Range loop
Dequeue_Head (Object.Entry_Queues (E), Entry_Call);
while Entry_Call /= null loop
pragma Assert (Entry_Call.Mode /= Conditional_Call);
Send_Program_Error (Self_ID, Entry_Call);
Dequeue_Head (Object.Entry_Queues (E), Entry_Call);
end loop;
end loop;
end Broadcast_Program_Error;
-------------
-- Enqueue --
-------------
-- Enqueue call at the end of entry_queue E, for FIFO queuing policy.
-- Enqueue call priority ordered, FIFO at same priority level, for
-- Priority queuing policy.
procedure Enqueue (E : in out Entry_Queue; Call : Entry_Call_Link) is
Temp : Entry_Call_Link := E.Head;
begin
-- Priority Queuing
if Priority_Queuing then
if Temp = null then
Call.Prev := Call;
Call.Next := Call;
E.Head := Call;
E.Tail := Call;
else
loop
-- Find the entry that the new guy should precede
exit when Call.Prio > Temp.Prio;
Temp := Temp.Next;
if Temp = E.Head then
Temp := null;
exit;
end if;
end loop;
if Temp = null then
-- Insert at tail
Call.Prev := E.Tail;
Call.Next := E.Head;
E.Tail := Call;
else
Call.Prev := Temp.Prev;
Call.Next := Temp;
-- Insert at head
if Temp = E.Head then
E.Head := Call;
end if;
end if;
Call.Prev.Next := Call;
Call.Next.Prev := Call;
end if;
return;
end if;
-- Priority Queuing
if E.Head = null then
E.Head := Call;
else
E.Tail.Next := Call;
Call.Prev := E.Tail;
end if;
E.Head.Prev := Call;
E.Tail := Call;
Call.Next := E.Head;
end Enqueue;
-------------
-- Dequeue --
-------------
-- Dequeue call from entry_queue E
procedure Dequeue (E : in out Entry_Queue; Call : Entry_Call_Link) is
begin
-- If empty queue, simply return
if E.Head = null then
return;
end if;
Call.Prev.Next := Call.Next;
Call.Next.Prev := Call.Prev;
if E.Head = Call then
-- Case of one element
if E.Tail = Call then
E.Head := null;
E.Tail := null;
-- More than one element
else
E.Head := Call.Next;
end if;
elsif E.Tail = Call then
E.Tail := Call.Prev;
end if;
-- Successfully dequeued
Call.Prev := null;
Call.Next := null;
end Dequeue;
----------
-- Head --
----------
-- Return the head of entry_queue E
function Head (E : in Entry_Queue) return Entry_Call_Link is
begin
return E.Head;
end Head;
------------------
-- Dequeue_Head --
------------------
-- Remove and return the head of entry_queue E
procedure Dequeue_Head
(E : in out Entry_Queue;
Call : out Entry_Call_Link)
is
Temp : Entry_Call_Link;
begin
-- If empty queue, return null pointer
if E.Head = null then
Call := null;
return;
end if;
Temp := E.Head;
-- Case of one element
if E.Head = E.Tail then
E.Head := null;
E.Tail := null;
-- More than one element
else
E.Head := Temp.Next;
Temp.Prev.Next := Temp.Next;
Temp.Next.Prev := Temp.Prev;
end if;
-- Successfully dequeued
Temp.Prev := null;
Temp.Next := null;
Call := Temp;
end Dequeue_Head;
-------------
-- Onqueue --
-------------
-- Return True if Call is on any entry_queue at all
function Onqueue (Call : Entry_Call_Link) return Boolean is
begin
-- Utilize the fact that every queue is circular, so if Call
-- is on any queue at all, Call.Next must NOT be null.
return Call.Next /= null;
end Onqueue;
-------------------
-- Count_Waiting --
-------------------
-- Return number of calls on the waiting queue of E
function Count_Waiting (E : in Entry_Queue) return Natural is
Count : Natural;
Temp : Entry_Call_Link;
begin
Count := 0;
if E.Head /= null then
Temp := E.Head;
loop
Count := Count + 1;
exit when E.Tail = Temp;
Temp := Temp.Next;
end loop;
end if;
return Count;
end Count_Waiting;
----------------------------
-- Select_Task_Entry_Call --
----------------------------
-- Select an entry for rendezvous. Selection depends on the queuing policy
-- being used.
procedure Select_Task_Entry_Call
(Acceptor : Task_ID;
Open_Accepts : Accept_List_Access;
Call : out Entry_Call_Link;
Selection : out Select_Index;
Open_Alternative : out Boolean)
is
Entry_Call : Entry_Call_Link;
Temp_Call : Entry_Call_Link;
Entry_Index : Task_Entry_Index;
Temp_Entry : Task_Entry_Index;
begin
Open_Alternative := False;
Entry_Call := null;
if Priority_Queuing then
-- Priority Queuing
for J in Open_Accepts'Range loop
Temp_Entry := Open_Accepts (J).S;
if Temp_Entry /= Null_Task_Entry then
Open_Alternative := True;
Temp_Call := Head (Acceptor.Entry_Queues (Temp_Entry));
if Temp_Call /= null and then
(Entry_Call = null or else
Entry_Call.Prio < Temp_Call.Prio)
then
Entry_Call := Head (Acceptor.Entry_Queues (Temp_Entry));
Entry_Index := Temp_Entry;
Selection := J;
end if;
end if;
end loop;
else
-- FIFO Queuing
for J in Open_Accepts'Range loop
Temp_Entry := Open_Accepts (J).S;
if Temp_Entry /= Null_Task_Entry then
Open_Alternative := True;
Temp_Call := Head (Acceptor.Entry_Queues (Temp_Entry));
if Temp_Call /= null then
Entry_Call := Head (Acceptor.Entry_Queues (Temp_Entry));
Entry_Index := Temp_Entry;
Selection := J;
exit;
end if;
end if;
end loop;
end if;
if Entry_Call = null then
Selection := No_Rendezvous;
else
Dequeue_Head (Acceptor.Entry_Queues (Entry_Index), Entry_Call);
-- Guard is open
end if;
Call := Entry_Call;
end Select_Task_Entry_Call;
---------------------------------
-- Select_Protected_Entry_Call --
---------------------------------
-- Select an entry of a protected object. Selection depends on the
-- queuing policy being used.
procedure Select_Protected_Entry_Call
(Self_ID : Task_ID;
Object : Protection_Entries_Access;
Call : out Entry_Call_Link)
is
Entry_Call : Entry_Call_Link;
Temp_Call : Entry_Call_Link;
Entry_Index : Protected_Entry_Index;
begin
Entry_Call := null;
begin
if Priority_Queuing then
-- Priority queuing
for J in Object.Entry_Queues'Range loop
Temp_Call := Head (Object.Entry_Queues (J));
if Temp_Call /= null and then
Object.Entry_Bodies (
Object.Find_Body_Index (Object.Compiler_Info, J)).
Barrier (Object.Compiler_Info, J)
then
if (Entry_Call = null or else
Entry_Call.Prio < Temp_Call.Prio)
then
Entry_Call := Temp_Call;
Entry_Index := J;
end if;
end if;
end loop;
else
-- FIFO queuing
for J in Object.Entry_Queues'Range loop
Temp_Call := Head (Object.Entry_Queues (J));
if Temp_Call /= null and then
Object.Entry_Bodies (
Object.Find_Body_Index (Object.Compiler_Info, J)).
Barrier (Object.Compiler_Info, J)
then
Entry_Call := Temp_Call;
Entry_Index := J;
exit;
end if;
end loop;
end if;
exception
when others =>
Broadcast_Program_Error (Self_ID, Object, null);
end;
-- If a call was selected, dequeue it and return it for service.
if Entry_Call /= null then
Dequeue_Head (Object.Entry_Queues (Entry_Index), Entry_Call);
end if;
Call := Entry_Call;
end Select_Protected_Entry_Call;
------------------
-- Enqueue_Call --
------------------
procedure Enqueue_Call (Entry_Call : Entry_Call_Link) is
Called_PO : Protection_Entries_Access;
begin
if Entry_Call.Called_Task /= null then
Enqueue
(Entry_Call.Called_Task.Entry_Queues
(Task_Entry_Index (Entry_Call.E)),
Entry_Call);
else
Called_PO := To_Protection (Entry_Call.Called_PO);
Enqueue (Called_PO.Entry_Queues
(Protected_Entry_Index (Entry_Call.E)),
Entry_Call);
end if;
end Enqueue_Call;
------------------
-- Dequeue_Call --
------------------
procedure Dequeue_Call (Entry_Call : Entry_Call_Link) is
Called_PO : Protection_Entries_Access;
begin
if Entry_Call.Called_Task /= null then
Dequeue
(Entry_Call.Called_Task.Entry_Queues
(Task_Entry_Index (Entry_Call.E)),
Entry_Call);
else
Called_PO := To_Protection (Entry_Call.Called_PO);
Dequeue (Called_PO.Entry_Queues
(Protected_Entry_Index (Entry_Call.E)),
Entry_Call);
end if;
end Dequeue_Call;
--------------------------------
-- Requeue_Call_With_New_Prio --
--------------------------------
procedure Requeue_Call_With_New_Prio
(Entry_Call : Entry_Call_Link; Prio : System.Any_Priority)
is
begin
-- Perform a queue reordering only when the policy being used is the
-- Priority Queuing.
if Priority_Queuing then
if Onqueue (Entry_Call) then
Dequeue_Call (Entry_Call);
Entry_Call.Prio := Prio;
Enqueue_Call (Entry_Call);
end if;
end if;
end Requeue_Call_With_New_Prio;
end System.Tasking.Queuing;