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------------------------------------------------------------------------------
-- --
-- GNAT 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 --
-- --
-- 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. --
-- --
------------------------------------------------------------------------------
-- 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;
with System.Tasking.Initialization;
package body System.Tasking.Queuing is
use Task_Primitives.Operations;
use Protected_Objects;
use Protected_Objects.Entries;
-- 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
function Check_Queue (E : Entry_Queue) return Boolean;
-- Check the validity of E.
-- Return True if E is valid, raise Assert_Failure if assertions are
-- enabled and False otherwise.
-----------------------------
-- 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;
-----------------
-- Check_Queue --
-----------------
function Check_Queue (E : Entry_Queue) return Boolean is
Valid : Boolean := True;
C, Prev : Entry_Call_Link;
begin
if E.Head = null then
if E.Tail /= null then
Valid := False;
pragma Assert (Valid);
end if;
else
if E.Tail = null
or else E.Tail.Next /= E.Head
then
Valid := False;
pragma Assert (Valid);
else
C := E.Head;
loop
Prev := C;
C := C.Next;
if C = null then
Valid := False;
pragma Assert (Valid);
exit;
end if;
if Prev /= C.Prev then
Valid := False;
pragma Assert (Valid);
exit;
end if;
exit when C = E.Head;
end loop;
if Prev /= E.Tail then
Valid := False;
pragma Assert (Valid);
end if;
end if;
end if;
return Valid;
end Check_Queue;
-------------------
-- Count_Waiting --
-------------------
-- Return number of calls on the waiting queue of E
function Count_Waiting (E : Entry_Queue) return Natural is
Count : Natural;
Temp : Entry_Call_Link;
begin
pragma Assert (Check_Queue (E));
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;
-------------
-- Dequeue --
-------------
-- Dequeue call from entry_queue E
procedure Dequeue (E : in out Entry_Queue; Call : Entry_Call_Link) is
begin
pragma Assert (Check_Queue (E));
pragma Assert (Call /= null);
-- If empty queue, simply return
if E.Head = null then
return;
end if;
pragma Assert (Call.Prev /= null);
pragma Assert (Call.Next /= null);
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;
pragma Assert (Check_Queue (E));
end Dequeue;
------------------
-- Dequeue_Call --
------------------
procedure Dequeue_Call (Entry_Call : Entry_Call_Link) is
Called_PO : Protection_Entries_Access;
begin
pragma Assert (Entry_Call /= null);
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;
------------------
-- 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
pragma Assert (Check_Queue (E));
-- 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
pragma Assert (Temp /= null);
pragma Assert (Temp.Next /= null);
pragma Assert (Temp.Prev /= null);
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;
pragma Assert (Check_Queue (E));
end Dequeue_Head;
-------------
-- 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
pragma Assert (Check_Queue (E));
pragma Assert (Call /= null);
-- 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;
pragma Assert (Call.Prev /= null);
pragma Assert (Call.Next /= null);
Call.Prev.Next := Call;
Call.Next.Prev := Call;
end if;
pragma Assert (Check_Queue (E));
return;
end if;
-- FIFO 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;
pragma Assert (Check_Queue (E));
end Enqueue;
------------------
-- Enqueue_Call --
------------------
procedure Enqueue_Call (Entry_Call : Entry_Call_Link) is
Called_PO : Protection_Entries_Access;
begin
pragma Assert (Entry_Call /= null);
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;
----------
-- Head --
----------
-- Return the head of entry_queue E
function Head (E : Entry_Queue) return Entry_Call_Link is
begin
pragma Assert (Check_Queue (E));
return E.Head;
end Head;
-------------
-- Onqueue --
-------------
-- Return True if Call is on any entry_queue at all
function Onqueue (Call : Entry_Call_Link) return Boolean is
begin
pragma Assert (Call /= null);
-- 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;
--------------------------------
-- Requeue_Call_With_New_Prio --
--------------------------------
procedure Requeue_Call_With_New_Prio
(Entry_Call : Entry_Call_Link; Prio : System.Any_Priority) is
begin
pragma Assert (Entry_Call /= null);
-- 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;
---------------------------------
-- 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 := Null_Entry; -- stop warning
begin
Entry_Call := null;
begin
-- Priority queuing case
if Priority_Queuing then
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;
-- FIFO queueing case
else
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
Temp_Call := Entry_Call;
Dequeue_Head (Object.Entry_Queues (Entry_Index), Entry_Call);
pragma Assert (Temp_Call = Entry_Call);
end if;
Call := Entry_Call;
end Select_Protected_Entry_Call;
----------------------------
-- 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 := Task_Entry_Index'First;
Temp_Entry : Task_Entry_Index;
begin
Open_Alternative := False;
Entry_Call := null;
Selection := No_Rendezvous;
if Priority_Queuing then
-- Priority queueing case
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 case
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
Dequeue_Head (Acceptor.Entry_Queues (Entry_Index), Entry_Call);
-- Guard is open
end if;
Call := Entry_Call;
end Select_Task_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);
Initialization.Wakeup_Entry_Caller (Self_ID, Entry_Call, Done);
Unlock (Caller);
end Send_Program_Error;
end System.Tasking.Queuing;