From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on
	ip-172-31-74-118.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.5-pre1
Path: eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED.IIfIc3CB/+nKo+wKq8+a0g.user.gioia.aioe.org!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: is there a version of unix written in Ada
Date: Tue, 28 Jul 2020 17:48:46 +0100
Organization: Aioe.org NNTP Server
Message-ID: <lyd04fegb5.fsf@pushface.org>
References: <e3c51e65-b71e-4623-bd58-c94cdbcc3ba6o@googlegroups.com>
	<27b1bda0-bf22-4bd1-a5f9-2085c8ff2014n@googlegroups.com>
	<rfkmhc$1k12$1@gioia.aioe.org> <rfkvao$nvt$1@dont-email.me>
	<5f20233c$0$24260$426a74cc@news.free.fr>
NNTP-Posting-Host: IIfIc3CB/+nKo+wKq8+a0g.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain
X-Complaints-To: abuse@aioe.org
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (darwin)
X-Notice: Filtered by postfilter v. 0.9.2
Cancel-Lock: sha1:wDvsz4x9dR+T7aHrU6q/GQnG5bo=
Xref: reader01.eternal-september.org comp.lang.ada:59574
List-Id: <comp.lang.ada>

DrPi <314@drpi.fr> writes:

> Ada has embedded thread scheduling. What's the usefulness of m2os ?

The Ada language defines the syntax and semantics of tasking, but
whether an implementation supports tasking is a different matter.

If tasking is supported, there will be a runtime system that provides
it, and the compiler knows how to translate the code you write into
calls on that runtime system. If you write 'task T;' the code generated
by GNAT (in a Ravenscar system) will call

   procedure Create_Restricted_Task
     (Priority             :        Integer;
      Stack_Address        :        System.Address;
      Size                 :        System.Parameters.Size_Type;
      Sec_Stack_Address    :        System.Secondary_Stack.SS_Stack_Ptr;
      Secondary_Stack_Size :        System.Parameters.Size_Type;
      Task_Info            :        System.Task_Info.Task_Info_Type;
      CPU                  :        Integer;
      State                :        Task_Procedure_Access;
      Discriminants        :        System.Address;
      Elaborated           :        Access_Boolean;
      Chain                : in out Activation_Chain;
      Task_Image           :        String;
      Created_Task         :        Task_Id);

The procedure body is the business of the specific runtime system.

M2OS doesn't support Ada tasking at all. Instead, it provides a set of
primitive operations or API (see the web site); to create a "task", you
provide an initialization procedure and a body procedure and call an API
operation to register the code so that it can be called when necessary.

A higher-level facility can translate your code using (some?) Ada
tasking constructs into equivalent code calling the M2OS API.

The advantage claimed is that the memory footprint is much reduced, so
that the application will fit into a smaller MCU.