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RE: stpd and stdout
- From: "Stone, Joshua I" <joshua dot i dot stone at intel dot com>
- To: "Hien Nguyen" <hien at us dot ibm dot com>, "Martin Hunt" <hunt at redhat dot com>, "SystemTAP" <systemtap at sources dot redhat dot com>
- Date: Tue, 9 May 2006 15:57:20 -0700
- Subject: RE: stpd and stdout
On Tuesday, May 09, 2006 3:21 PM, Hien Nguyen wrote:
> While working on the the systemtap GUI we run into the problem of
> getting the stdout to the gui app in a timely fashion. We does get the
> output as a blob of text once in a while (looks like data were only
> flushed out when the buffer is full). To recreate the problem you can
> try this
>
> stap -e 'probe syscall.open{ log(filename) }' | tee
>
> Anyway, I added one line of code to flushout the data as soon as the
> stpd gets it. It seems to solve the above problem. To avoid
> unnecessary performance issues for others, perhaps we should have
> that as an option. What do you think?
I've run into this with Perl scripts before -- Perl normally
line-buffers output to STDOUT and block-buffers otherwise (e.g. to a
pipe or socket). Their solution for this problem is an autoflush
option:
http://perldoc.perl.org/perlvar.html#HANDLE->autoflush(EXPR)
I think it would be very reasonable to support a similar command-line
option in stap/stpd.
Josh