Re: Easy shell question: how to make a script killing all his childs when killed?

Marco Costalba, Sun, Dec 10, 2006 00:06:34 +0100:

On 12/9/06, Alex Riesen [off-list ref] wrote:

quoted

Why do you need to save it in temporary file at all? Why don't you
read the output like gitk does?  You can take a look at popen(3). It's
known to be portable among operating systems and libc's.  Or, BTW, why
don't you just read qprocess.h, use processIdentifier()/pid(),
read*()-methods and the like?  (though, looking at the QProcess in
qt3, I wouldn't really blame you)

Well, I _used_ QProcess interface until last week. It's socket based
and it's quite fast (much more then gitk BTW), but due to some
internal buffering not so fast as reading from a file (in my last post
regarding git-rev-list access there are some performance numbers to
document this). It seems that socket/pipe based IPC is not as fast as
file write/read. Of course we are talking of OS cached files, no disk
access must be involved to keep the speed.

Oh, I see now ("Fast access git-rev-list output...").

BTW, I just cannot reproduce that at all (on Linux):

    time { git rev-list --all > /tmp/ggg; cat /tmp/ggg >/dev/null; }

tends to be somewhat slower than

    time git rev-list --all | cat >/dev/null

QProcess must be doing something stupid.

Regarding gitk we are at least one order of magnitude faster both with
QProcess and, more, with temporary files, so it's not a useful
reference in this case.

Dunno. It's hard to assess on "small" repos, like kernel. They feel
almost equally fast (maybe because qgit checks working directory too).
Haven't tried QGit on Windows yet (does it work there?).

P.S: I didn't experiment with popen(). Thanks for the hint, I will
give it a try ;-)

popen(3) usually uses pipe(2). It's also awkward with regard to
shell metacharacters and signals (as system(3) is). You can use your'
own buffers (setvbuf) so that could be a win against QProcess.