Re: Reading the while standard input into a String

[Natasha Kerensikova <lithiumcat@gmail.com>]

Hello,

On 2011-06-06, Ludovic Brenta <ludovic@ludovic-brenta.org> wrote:
> Ludovic Brenta wrote on comp.lang.ada:
>> Natasha Kerensikova wrote on comp.lang.ada:
>>> However I thought that something similar to C's fread(), which can use
>>> efficient bulk memory copy, would be better than a loop of single
>>> character read (even when buffered in memory).
>>
>> How about:
>>
>> procedure Read_In_Chunks (Stream : in out
>> Ada.Streams.Root_Stream_Type'Class;
>>                           Result : out
>> Ada.Strings.Unbounded.Unbounded_String) is
> [...]
>
> I think I'm guilty of premature optimization.  I'd be curious to know
> whether Read_In_Chunks is actually faster than simply reading one
> character at a time and appending it to Result.  Only a benchmark
> could tell for sure.

The problem with benchmarks is that they are highly dependant on platform
and situation.

For what it's worth, I tried on my development system (Ubuntu Lucid),
using 1 KiB chunk size to read 10 MiB on random data, alternating calls
to each test program, 10 times each discarding the result (to warm up
caches) and then 10 times each gathering the results.

I got 100-160 ms spent in system mode for both, 90-110 ms in user mode
for your reader, and 440-490 ms in user mode for mine.

Using on-the-fly concatenation of 10 times the original 10 MiB file,
piped into the test programs, I get roughly the same ranges times ten.

So it looks like your optimization was justiified after all.



Thanks a lot for the idea,
Natasha