cborutil: change buffering strategy
Profiling revealed that we were spending a lot of time on the
line that was concatenating the old buffer with the incoming data
when attempting to decode long byte strings, such as manifest
revisions.
Essentially, we were feeding N chunks of size len(X) << len(Y) into
decode() and continuously allocating a new, larger buffer to hold
the undecoded input. This created substantial memory churn and
slowed down execution.
Changing the code to aggregate pending chunks in a list until we
have enough data to fully decode the next atom makes things much
more efficient.
I don't have exact data, but I recall the old code spending >1s
on manifest fulltexts from the mozilla-unified repo. The new code
doesn't significantly appear in profile output.
Differential Revision: https://phab.mercurial-scm.org/D4854
#!/usr/bin/env python
# Filter output by pyflakes to control which warnings we check
from __future__ import absolute_import, print_function
import re
import sys
lines = []
for line in sys.stdin:
# We blacklist tests that are too noisy for us
pats = [
r"undefined name 'WindowsError'",
r"redefinition of unused '[^']+' from line",
# for cffi, allow re-exports from pure.*
r"cffi/[^:]*:.*\bimport \*' used",
r"cffi/[^:]*:.*\*' imported but unused",
]
keep = True
for pat in pats:
if re.search(pat, line):
keep = False
break # pattern matches
if keep:
fn = line.split(':', 1)[0]
f = open(fn)
data = f.read()
f.close()
if 'no-' 'check-code' in data:
continue
lines.append(line)
for line in lines:
sys.stdout.write(line)
print()