[ltt-dev] [PATCH 07/10] call_rcu: remove write-only qlen variable

[paulmck@linux.vnet.ibm.com (Paul E. McKenney)]

On Wed, Jun 08, 2011 at 06:46:20PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck at linux.vnet.ibm.com) wrote:
> > On Wed, Jun 08, 2011 at 06:15:30PM -0400, Mathieu Desnoyers wrote:
> > > * Paolo Bonzini (pbonzini at redhat.com) wrote:
> > > > The qlen variable is write-only, we can remove it easily.
> > > 
> > > I defer to Paul for this one: he likes keeping qlen there so the
> > > debugger can show the list state, which is useful for debugging. I'll
> > > let you two figure out how to come to an agreement. ;)
> > 
> > Indeed, I have often used gdb to read ->qlen.  ;-)
> 
> So maybe adding a comment besides qlen stating the reason why it's there
> (e.g. for debugging purposes) might be appropriate ?

Good point!  How about the following?

							Thanx, Paul

------------------------------------------------------------------------

Add comment to flag purpose of the ->qlen field

It is write-only, but is needed for debugging purposes.

Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>

diff --git a/urcu-call-rcu-impl.h b/urcu-call-rcu-impl.h
index cfe1cce..9beb58c 100644
--- a/urcu-call-rcu-impl.h
+++ b/urcu-call-rcu-impl.h
@@ -48,7 +48,7 @@ struct call_rcu_data {
 	unsigned long flags;
 	pthread_mutex_t mtx;
 	int futex;
-	unsigned long qlen;
+	unsigned long qlen; /* maintained for debugging. */
 	pthread_t tid;
 	int cpu_affinity;
 	struct cds_list_head list;