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

From: Marco Costalba <mcostalba@gmail.com>
Date: Dec 9, 2006, 23:06 UTC
Message-ID: <e5bfff550612091506g41e40e87n6356b8ddd5e16a5d@mail.gmail.com>
In-Reply-To: <20061209213937.GB12373@steel.home>

On 12/9/06, Alex Riesen <fork0@t-online.de> wrote:

Show 8 quoted lines

>
> 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.

Probably someone more versed in IPC and OS internals could comment on this, I just base my arguments on experimental testing of various IPC systems without going deep in the reasons why the number are like this, also because I don't have the necessary knowledge.

But the fact is that with temporary (in memory) data exchange file the load time has been reduced by 40% against socket based QProcess interface.

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.

  Marco

P.S: I didn't experiment with popen(). Thanks for the hint, I will