From: William FRANCK <william.franck@free.fr>
Subject: Re: How to transfer Class-Wide object to a Task ?
Date: Mon, 14 Oct 2019 22:58:42 +0200
Date: 2019-10-14T22:58:42+02:00 [thread overview]
Message-ID: <5da4e182$0$20321$426a74cc@news.free.fr> (raw)
In-Reply-To: qo2k18$4hh$1@gioia.aioe.org
On 2019-10-14 19:58:34 +0000, Dmitry A. Kazakov said:
> On 2019-10-14 21:41, William FRANCK wrote:
>
>> Here is a nice issue I have with Ada (GNAT 2012) when trying to do OO
>> dispatching with streams in different tasks ...
>>
>> Here it is :
>> I'd like to get from a task RdV (Entry-Access) an object which could be
>> any subclass of a root'Class, and pass it to another task
>>
>> Context : read (Root'Class'Input() ) tagged records from an input
>> stream, and send them to anther task which will write
>> (Root'Class'Output() ) the given records to another output stream.
>
> Strange design, why not to pipe streams using a FIFO?
>
>> I'm stuck with task memory isolation with does NOT allow to pass any
>> access object to a Root'Class.
>>
>> Should I try to use a protected object ?
>> (not shore this solves the passing of a Class-wide object ...)
>
> Yes, if using FIFO, a protected object can be used to signal
> non-empty/not-full events at the FIFO ends.
>
> Otherwise, use a reference-counted handle or a plain access type to the
> target object. The reader task allocates the object in the pool and
> passes a handle or access to it to the writer. The writer task writes
> the object and then disposes it.
Thanks you Dimitry for your follow-up.
Here is the multitasking part (simplified) (working, no issue)
for reading the datafile, and writing it back (after some data-process)
My first intention was : while Writing.Bloc is busy writing on the
output file, Reading.Bloc can take 1 record in advance
Now I have to insert the class-wide object passing in the Bloc.
As You mentionned, should I use a protected type (FIFO) instead of 2
// tasks ?
--================
with Ada.Text_io;
procedure main_tasks is
task reading is
entry Open;
entry Bloc;
entry Stop;
end reading;
task writing is
entry Create;
entry Bloc;
entry Stop;
end writing;
task body reading is
begin
loop
select
accept Open;
Ada.Text_IO.put_line("Opening file ...");
or
accept Bloc do
Ada.Text_IO.put_line("Reading ...");
end Bloc;
or
accept Stop;
Ada.Text_IO.put_line("Reading Stopped !");
exit;
end select;
end loop;
end reading;
task body writing is
begin
loop
select
accept Create;
Ada.Text_IO.put_line("Creating file ...");
or
accept Bloc do
Ada.Text_IO.put_line("Got bloc !");
end Bloc;
Ada.Text_IO.put_line("Writing bloc ...");
or
accept Stop;
Ada.Text_IO.put_line("Writing Stopped !");
exit;
end select;
end loop;
end writing;
begin
Writing.Create;
Reading.Open;
for i in 1..10 loop -- While not end_of_file()
Reading.Bloc;
Writing.Bloc;
end loop;
Reading.Stop;
Writing.Stop;
end main_tasks;
next prev parent reply other threads:[~2019-10-14 20:58 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-14 19:41 How to transfer Class-Wide object to a Task ? William FRANCK
2019-10-14 19:55 ` Shark8
2019-10-14 20:48 ` William FRANCK
2019-10-14 22:01 ` Shark8
2019-10-15 5:13 ` William FRANCK
2019-10-14 19:58 ` Dmitry A. Kazakov
2019-10-14 20:58 ` William FRANCK [this message]
2019-10-15 4:40 ` Per Sandberg
2019-10-15 5:40 ` William FRANCK
2019-10-16 20:04 ` William FRANCK
2019-10-16 23:43 ` Anh Vo
2019-10-17 9:28 ` William FRANCK
2019-10-17 10:00 ` Dmitry A. Kazakov
2019-10-17 10:45 ` William FRANCK
2019-10-15 7:21 ` Dmitry A. Kazakov
2019-10-15 14:31 ` Optikos
2019-10-15 19:41 ` William FRANCK
2019-10-15 20:03 ` Shark8
2019-10-14 20:21 ` William FRANCK
2019-10-14 20:32 ` Dmitry A. Kazakov
2019-10-14 21:04 ` William FRANCK
2019-10-14 21:57 ` Shark8
2019-10-15 5:43 ` William FRANCK
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