Traverse the container tree depth first and for each container find
the node in the subtree rooted at this container which comes first in
the descending sort order. Remember it as the subtree leader. Then,
while sorting siblings, compare their subtree leaders instead of the
sibling containers themselves.
IOW, make threads containing the newest message float to the top when
sorting by date in the descending order.
There is no significant performance degradation when sorting a
mailbox with ~16k messages:
$ mu find maildir:/INBOX | wc -l
16503
Current state:
$ perf stat --event=task-clock --repeat=10 -- \
mu find maildir:/INBOX -n 1 -t > /dev/null
Performance counter stats for 'mu find maildir:/INBOX -n 1 -t' (10 runs):
1231.761588 task-clock (msec) # 0.996 CPUs utilized ( +- 1.02% )
1.236209133 seconds time elapsed ( +- 1.08% )
With patch applied:
$ perf stat --event=task-clock --repeat=10 -- \
mu find maildir:/INBOX -n 1 -t > /dev/null
Performance counter stats for 'mu find maildir:/INBOX -n 1 -t' (10 runs):
1459.883316 task-clock (msec) # 0.998 CPUs utilized ( +- 0.72% )
1.462540088 seconds time elapsed ( +- 0.77% )
This implements https://github.com/djcb/mu/issues/164.
32f5c8b1f6