Re: GNAT/Ada95 Streams Performance Issue

[hebisch@math.uni.wroc.pl (Waldek Hebisch)]

Warren W. Gay VE3WWG (ve3wwg@cogeco.ca) wrote:
: 3. The individual characters that make up Msg are written
:      out to stream S, using individual calls to Character'Write.

: Step # 3 is the performance killer.

: To help in this regard, APQ 1.2 (not released yet) now supports
: two new functions for performance reasons:

:       String_Output to substitute for String'Output
:       String_Input to substitute for String'Input

: These routines deal with the array of characters as
: one block of data.

: But this is really just a patch over part of a much
: larger problem.

: How have other people dealt with this type of streams
: performance issue?  Or do people generally avoid
: streams when performance is important?

Well, I just toyed with a simple cat program:

        loop
                Ada.Text_IO.Get_Line( Line, Last );
                Ada.Text_IO.Put_Line( Line(1..Last) );
        end loop;

Using GNAT (gcc 3.1.1), I get very bad performance (about 10 MB/s, raw 
system calls (in C) give 450MB/s). I looked at the sources, and while 
Put_Line essentialy outputs the block (it makes a copy and modifies it 
slightly) Get_Line works with single characters. The problem is that to 
cooperate nicely with C Ada has to go trough C stdio interface. Since Ada 
and C semantics differ Ada cannot use C block input. The problem is magnified 
becouse each C stdio function performs locking. 

--
                              Waldek Hebisch
hebisch@math.uni.wroc.pl    or hebisch@hera.math.uni.wroc.pl