Deadlock in SEQUENCER

I've just seen a deadlock in SEQUENCER, which I think occurs as follows:

• Start of day. coord=null, ack_mode=true, flushing=false.
• First view arrives. We call handleView(), and start a Flusher
• On the Flusher thread, flush() gets as far as waiting to acquire the send_lock, but doesn't yet have it.
• Meanwhile on Thread 2, the application tries broadcasting a message. This gets as far as the trace "forwarding my-address::1 to coord null", but does not yet enter forwardToCoord().
• Now on Thread 3, a second view arrives. handleViewChange() finds that coord_changed is true, and calls stopFlusher(). This sets flushing=false.
• Now Thread 2 picks up. flushing=false, ack_mode=true; so forwardToCoord() gets as far as acquiring the send_lock.
• Now Thread 2 loops around making no progress. forward() always drops the message, because coord is null. The send_lock is never relinquished
• So the Flusher thread can never acquire the send_lock, and the Flusher can't exit
• And so Thread 3 is stuck too, in stopFlusher().