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257 | ------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . T A S K I N G . P R O T E C T E D _ O B J E C T S . --
-- S I N G L E _ E N T R Y --
-- --
-- B o d y --
-- --
-- Copyright (C) 1998-2023, AdaCore --
-- --
-- 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. 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. --
-- --
-- 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. --
-- --
------------------------------------------------------------------------------
pragma Style_Checks (All_Checks);
-- Turn off subprogram ordering check, since restricted GNARLI
-- subprograms are gathered together at end.
-- This package provides an optimized version of Protected_Objects.Operations
-- and Protected_Objects.Entries making the following assumptions:
--
-- PO have only one entry
-- There is only one caller at a time (No_Entry_Queue)
-- There is no dynamic priority support (No_Dynamic_Priorities)
-- No Abort Statements
-- (No_Abort_Statements, Max_Asynchronous_Select_Nesting => 0)
-- PO are at library level
-- No Requeue
-- None of the tasks will terminate (no need for finalization)
--
-- This interface is intended to be used in the ravenscar and restricted
-- profiles, the compiler is responsible for ensuring that the conditions
-- mentioned above are respected, except for the No_Entry_Queue restriction
-- that is checked dynamically in this package, since the check cannot be
-- performed at compile time (see Protected_Single_Entry_Call, Service_Entry).
pragma Suppress (All_Checks);
with System.Multiprocessors;
with System.Task_Primitives.Operations;
-- used for Self
-- Get_Priority
-- Set_Priority
with System.Tasking.Protected_Objects.Multiprocessors;
package body System.Tasking.Protected_Objects.Single_Entry is
use System.Multiprocessors;
package STPO renames System.Task_Primitives.Operations;
package STPOM renames System.Tasking.Protected_Objects.Multiprocessors;
Multiprocessor : constant Boolean := CPU'Range_Length /= 1;
---------------------------------
-- Initialize_Protection_Entry --
---------------------------------
procedure Initialize_Protection_Entry
(Object : Protection_Entry_Access;
Ceiling_Priority : Integer;
Compiler_Info : System.Address;
Entry_Body : Entry_Body_Access)
is
begin
Initialize_Protection (Object.Common'Access, Ceiling_Priority);
Object.Compiler_Info := Compiler_Info;
Object.Call_In_Progress := null;
Object.Entry_Body := Entry_Body;
Object.Entry_Queue := null;
end Initialize_Protection_Entry;
----------------
-- Lock_Entry --
----------------
procedure Lock_Entry (Object : Protection_Entry_Access) is
begin
Lock (Object.Common'Access);
end Lock_Entry;
---------------------------
-- Protected_Count_Entry --
---------------------------
function Protected_Count_Entry (Object : Protection_Entry) return Natural is
begin
return Boolean'Pos (Object.Entry_Queue /= null);
end Protected_Count_Entry;
---------------------------------
-- Protected_Single_Entry_Call --
---------------------------------
procedure Protected_Single_Entry_Call
(Object : Protection_Entry_Access;
Uninterpreted_Data : System.Address)
is
Self_Id : constant Task_Id := STPO.Self;
begin
-- For this run time, pragma Detect_Blocking is always active, so we
-- must raise Program_Error if this potentially blocking operation is
-- called from a protected action.
if Self_Id.Common.Protected_Action_Nesting > 0 then
raise Program_Error;
end if;
Lock_Entry (Object);
Self_Id.Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
if Object.Entry_Body.Barrier (Object.Compiler_Info, 1) then
-- No other task can be executing an entry within this protected
-- object. On a single processor implementation (such as this one),
-- the ceiling priority protocol and the strictly preemptive priority
-- scheduling policy guarantee that protected objects are always
-- available when any task tries to use them (otherwise, either the
-- currently executing task would not have had a high enough priority
-- to be executing, or a blocking operation would have been called
-- from within the entry body).
pragma Assert (Object.Call_In_Progress = null);
Object.Call_In_Progress := Self_Id.Entry_Call'Access;
Object.Entry_Body.Action
(Object.Compiler_Info, Self_Id.Entry_Call.Uninterpreted_Data, 1);
Object.Call_In_Progress := null;
-- Entry call is over
Unlock_Entry (Object);
else
if Object.Entry_Queue /= null then
-- This violates the No_Entry_Queue restriction, raise
-- Program_Error.
Unlock_Entry (Object);
raise Program_Error;
end if;
-- There is a potential race condition between the Unlock_Entry and
-- the Sleep below (the Wakeup may be called before the Sleep). This
-- case is explicitly handled in the Sleep and Wakeup procedures:
-- Sleep won't block if Wakeup has been called before.
Object.Entry_Queue := Self_Id.Entry_Call'Access;
Unlock_Entry (Object);
-- Suspend until entry call has been completed.
-- On exit, the call will not be queued.
Self_Id.Common.State := Entry_Caller_Sleep;
STPO.Sleep (Self_Id, Entry_Caller_Sleep);
Self_Id.Common.State := Runnable;
end if;
end Protected_Single_Entry_Call;
-----------------------------------
-- Protected_Single_Entry_Caller --
-----------------------------------
function Protected_Single_Entry_Caller
(Object : Protection_Entry) return Task_Id
is
begin
return Object.Call_In_Progress.Self;
end Protected_Single_Entry_Caller;
-------------------
-- Service_Entry --
-------------------
procedure Service_Entry (Object : Protection_Entry_Access) is
Entry_Call : constant Entry_Call_Link := Object.Entry_Queue;
Caller : Task_Id;
begin
if Entry_Call /= null
and then Object.Entry_Body.Barrier (Object.Compiler_Info, 1)
then
Object.Entry_Queue := null;
-- No other task can be executing an entry within this protected
-- object. On a single processor implementation (such as this one),
-- the ceiling priority protocol and the strictly preemptive
-- priority scheduling policy guarantee that protected objects are
-- always available when any task tries to use them (otherwise,
-- either the currently executing task would not have had a high
-- enough priority to be executing, or a blocking operation would
-- have been called from within the entry body).
pragma Assert (Object.Call_In_Progress = null);
Object.Call_In_Progress := Entry_Call;
Object.Entry_Body.Action
(Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
Object.Call_In_Progress := null;
Caller := Entry_Call.Self;
Unlock_Entry (Object);
-- Signal the entry caller that the entry is completed
if not Multiprocessor
or else Caller.Common.Base_CPU = STPO.Self.Common.Base_CPU
then
-- Entry caller and servicing tasks are on the same CPU.
-- We are allowed to directly wake up the task.
STPO.Wakeup (Caller, Entry_Caller_Sleep);
else
-- The entry caller is on a different CPU.
STPOM.Served (Entry_Call);
end if;
else
-- Just unlock the entry
Unlock_Entry (Object);
end if;
end Service_Entry;
------------------
-- Unlock_Entry --
------------------
procedure Unlock_Entry (Object : Protection_Entry_Access) is
begin
Unlock (Object.Common'Access);
end Unlock_Entry;
end System.Tasking.Protected_Objects.Single_Entry;
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