Re: [Qemu-devel] [PATCH 2/2] qemu-ga: Add the guest-suspend command

[Daniel P. Berrange]

On Mon, Jan 16, 2012 at 03:08:53PM -0200, Luiz Capitulino wrote:
> On Fri, 13 Jan 2012 14:48:04 -0700
> Eric Blake <address@hidden> wrote:
> 
> > > +
> > > +        pid = fork();
> > > +        if (!pid) {
> > > +            char buf[32];
> > > +            FILE *sysfile;
> > > +            const char *arg;
> > > +            const char *pmutils_bin = "pm-is-supported";
> > > +
> > > +            if (strcmp(mode, "hibernate") == 0) {
> > 
> > Strangely enough, POSIX doesn't include strcmp() in its list of
> > async-signal-safe functions (which is what you should be restricting
> > yourself to, if qemu-ga is multi-threaded), but in practice, I think
> > that is a bug of omission in POSIX, and not something you have to change
> > in your code.
> 
> memset() ins't either... sigaction() either, which begins to get
> annoying.
> 
> For those familiar with glib: isn't it possible to confirm it's using
> threads and/or acquire a global mutex or something?

The most that GLib says is

  "The GLib threading system used to be initialized with g_thread_init().
   This is no longer necessary. Since version 2.32, the GLib threading
   system is automatically initialized at the start of your program,
   and all thread-creation functions and synchronization primitives
   are available right away.

   Note that it is not safe to assume that your program has no threads
   even if you don't call g_thread_new() yourself. GLib and GIO can
   and will create threads for their own purposes in some cases, such
   as when using g_unix_signal_source_new() or when using GDBus. "

The latter paragraph is rather fuzzy, which is probably intentional.
So I think the only safe thing, in order to be future proof wrt later
GLib releases, is to just assume you have threads at all times.


Daniel
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