On 12/9/06, Alex Riesen <fork0@t-online.de> wrote:
quoted text
>
> 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
give it a try ;-)
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