Using Streams in conjunction with Spawn and Gnat.Expect

Using Streams in conjunction with Spawn and Gnat.Expect

[Jean François Martinez]

Problem is:  I have a program that spawns another (Non_Blocking_Spawn in Gnat.Expect) and communicates with it by sending it variable length strings preceeding by a token telling the son what to do with it.  I would like they did it by exchanging objects through the 'Output and 'Input atribute.

Problem is: Non_Blocking_Spawn works with Process_Descriptors from them you can get a File_Descriptor (from Gnat.Os_Lib.File_Descriptor) but I have been unable to find a way for mapping a Stream on a File_Descriptor.

Any ideas?

Jean François Martinez

PS: I could resort to forget about Objects and Streams and just parse input in son, in fact that is what I did in a previous version but that is sooo crude and unelegant.  That is why I would like to use Objects and Streamas.

Re: Using Streams in conjunction with Spawn and Gnat.Expect

[Dmitry A. Kazakov]

On Mon, 9 Feb 2015 08:38:27 -0800 (PST), Jean François Martinez wrote:

> Problem is:  I have a program that spawns another (Non_Blocking_Spawn in
> Gnat.Expect) and communicates with it by sending it variable length
> strings preceeding by a token telling the son what to do with it.  I would
> like they did it by exchanging objects through the 'Output and 'Input
> atribute.
> 
> Problem is: Non_Blocking_Spawn works with Process_Descriptors from them
> you can get a File_Descriptor (from Gnat.Os_Lib.File_Descriptor) but I
> have been unable to find a way for mapping a Stream on a File_Descriptor.

You could possibly convert file descriptor to Ada's file using
GNAT-specific libraries and then get a stream to it. Or else use low-level
I/O on the descriptor and then use a custom stream or else a memory-mapped
stream object to fed with data.

> Any ideas?

I am using GTK's Glib facilities which are more comfortable. The Ada
bindings has Input/Output/Error calls for data exchange.

It might be difficult to use 'Input 'Output attributes from concurrent
tasks if you wanted run it as proper pipes.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de