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Date: Tue, 3 Mar 2015 10:57:25 -0300
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Adrian Hunter <adrian.hunter@intel.com>, Borislav Petkov <bp@suse.de>,
        David Ahern <dsahern@gmail.com>, Don Zickus <dzickus@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Jiri Olsa <jolsa@redhat.com>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 19/20] perf tools: Reference count struct thread
Message-ID: <20150303135725.GE5187@kernel.org>
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 <1425353169-21436-20-git-send-email-acme@kernel.org>
 <20150303134214.GB27046@danjae>
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Em Tue, Mar 03, 2015 at 10:42:14PM +0900, Namhyung Kim escreveu:
> On Tue, Mar 03, 2015 at 12:26:08AM -0300, Arnaldo Carvalho de Melo wrote:
> > +++ b/tools/perf/util/thread.c
> > @@ -82,6 +82,20 @@ void thread__delete(struct thread *thread)

> > +struct thread *thread__get(struct thread *thread)
> > +{
> > +	++thread->refcnt;
> > +	return thread;
> > +}

> > +void thread__put(struct thread *thread)
> > +{
> > +	if (thread && --thread->refcnt == 0) {
> > +		list_del_init(&thread->node);
> > +		thread__delete(thread);
> > +	}
> > +}
 
> I think we need to protect refcnt from concurrent accesses from
> multiple threads.  Not to mention my multi-thread work, perf top
> already uses two threads.

Sure
 
> For perf top case, hist_entry__new() will be called from main thread
> and hist_entry__delete() might be called from display thread.

Reference counting is a step in that direction, as to if the integer
inc/dec is enough or is already surrounded by existing serialization
needs to be checked.

- Arnaldo