phases: avoid N² behavior in `advanceboundary`
We allowed duplicated entries in the deque, which each entry could potentially
insert all its ancestors. So advancing boundary for the full repository would
mean each revision would walk all its ancestors, resulting in O(N²) iteration.
For repository of any decent size, N² is quickly insane.
We introduce a simple set to avoid this and get back to reasonable performance.
#!/usr/bin/env python3
#
# This is literally `cat` but in python, one char at a time.
#
# see sigpipe-remote.py for details.
import io
import os
import sys
if isinstance(sys.stdout.buffer, io.BufferedWriter):
print('SIGPIPE-WORKER: script need unbuffered output', file=sys.stderr)
sys.exit(255)
while True:
c = os.read(sys.stdin.fileno(), 1)
os.write(sys.stdout.fileno(), c)