[Geany-devel] Race condition when saving geany.conf

[Lex Trotman]

On 24 February 2010 20:04, Eugene Arshinov <earshinov at gmail.com> wrote:

> Hi all.
>
> When several instances of Geany quit in the same time, there is a high
> possibility of a conflict. I can reproduce it easily on my machine,
> using either trunk or SM version.
>
> To reproduce: open three instances of geany, "geany", "geany -i" and
> another "geany" (absence of file names implies -i automatically in
> this case). It would be better to open three different files in
> the instances, to distinguish them. Then logout or reboot without
> quitting geany manually. On my machine, after I (in case of
> trunk) or SM code (in case of SM) restart geany, the default session is
> always cleared. Expected behaviour: the default session is managed by
> the first of the three instances and contains the files, which
> were opened in that instance, after restart.
>

The overall issue of preferences, configuration and sessions for multiple
instances is an interesting one (Sorry Eugene, I've got no answers but lots
of questions)

Why is the first necessarily the "master"?
Is this by definition or is there a reason?
What if the first is started with -i?
 And what happens to configuration changes I make in other instances?

You see, I'm forgetful, if I had more than one Geany running (and I can see
good reasons to do that) then I may forget which one is the "master" and
change a preference in a different instance, so what happens to the conf
file?

These are questions beyond just the session manager I know, but maybe the
answer is/should be the same.

Cheers
Lex


>
> I can see two solutions for this problem. The first is an
> additional POSIX process-shared semaphore / mutex for Windows to guard
> geany.conf. This should eliminate the problem completely. AFAIK, there
> are no wrappers for process synchronization primitives in GLib, so I'll
> need to write a thin wrapper myself.
>
> The second option is to change the behaviour of "new instances". If
> such an instance (#1) detects a "main instance" (#2) running, it should
> not touch geany.conf. Actually, to deal with the described issue, it
> is enough to implement this behaviour only when #1 tries to save
> geany.conf while quitting.
>
> The second option is easier to write as it does not require
> additional synchronization primitives and it's possible to reuse the
> code of socket.c. Actually, I already have this option implemented, to
> check whether it indeed solves the problem. But, you see, this
> solution can't prevent the race condition completely, in distinction
> from the first solution. Moreover, some of you may consider the second
> solution "hackish", which is enough to decline it.
>
> So, the first solution is right, but the second is easy :-) What do you
> think?
>
> Best regards,
> Eugene.
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