Re: request for review: Doing direct file I/O in Emacs Lisp

[John Wiegley <johnw@gnu.org>]

Richard Stallman <rms@gnu.org> writes:

> Since save-buffer calls write-region, both the fastest and the
> slowest method use write-region.  What is the difference between
> these two methods?

Hmm.. that IS curious.  In the save-buffer case, I call
insert-and-inherit in a temp buffer thousands of times, then one call
to save-buffer.  In the write-region case, I am calling write-region
thousands of times.  I think the difference is the constant filesystem
access in the latter case.

>     However, the real slowdown is with start-process, as others
>     mentioned.  Here are the times for doing the same cat, but using
>     the system's cat:
>
> Sorry, I do not understand what that means.
>
>      ~952s  file-handle-write
>       ...s  save-buffer (the current method)
>
> I can't understand what alternatives you have compared.
> Could you please explain them more concretely?

If I start a process with start-process (/usr/bin/cat) and redirect
its output to a file, it is far slower than if I simply output the
same data to a file (eshell/cat) -- even though the resulting "output"
in both cases is the same.  Why is receiving output via a process
sentinel so slow?

> start-process takes a certain amount of time, but it should be a
> fixed amount, and less than a second.  How many times did you start
> a process here?

I am only starting the system cat once.

John