Re: File output and buffering

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 19 Sie, 22:27, Maciej Sobczak <see.my.homep...@gmail.com> wrote:

> It seems to me that the file output in standard Ada library is not
> buffered:
> 1. There is no buffer-related operation in the whole library.
> 2. The semantics of output operations is defined in terms of the
> effects on external file.
> 3. The performance of simple test is consistent with what can be
> obtained in equivalent C code that flushes the channel after every
> operation (ie. some 15-20x slower than with default buffering).

Now I'm puzzled, because it looks like the files are written in chunks
of 32kB. In other words, nothing is written to the file until the
total output accumulated to 32kB and the step is preserved for each
future write - this indicates that the buffering is actually in use.

My original observations become questions:

1. Why there is no buffer-related operation in the whole library?
In particular: how can I *flush* the buffer?
This is very important for log files. I have discovered this exactly
because the log is not written synchronously with Put operations,
which makes it "a bit" less useful. How can I make sure that what I
Put is actually written? Closing a file after each Put does not make
much sense.

2. What about the semantics of Put?

3. Why is buffered Ada.Text_IO as slow as non-buffered C's stdio? Who
is eating the 20x factor?

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com

Database Access Library for Ada: www.inspirel.com/soci-ada