From mboxrd@z Thu Jan  1 00:00:00 1970
From: ryx@gwmail.gwu.edu (Yuxin Ren)
Date: Wed, 27 Apr 2016 21:34:16 -0400
Subject: [lttng-dev] Question about lock in synchronize_rcu implementation
	of URCU
Message-ID: <CAAKbDrfmcqEE7_6p_J0DPVO85yDGJ0GCbi5k9Lm19g4VaLgOWw@mail.gmail.com>

Hi,

I am learning the URCU code.

Why do we need rcu_gp_lock in synchronize_rcu?
https://github.com/urcu/userspace-rcu/blob/master/urcu.c#L401

In the comment, it says this lock ensures mutual exclusion between
threads calling synchronize_rcu().
But only the first thread added to waiter queue can proceed to detect
grace period.
How can multiple threads currently perform the grace thread?

Thanks a lot!
Yuxin