procutil: make stream detection in make_line_buffered more correct and strict
In make_line_buffered(), we don’t want to wrap the stream if we know that lines
get flushed to the underlying raw stream already.
Previously, the heuristic was too optimistic. It assumed that any stream which
is not an instance of io.BufferedIOBase doesn’t need wrapping. However, there
are buffered streams that aren’t instances of io.BufferedIOBase, like
Mercurial’s own winstdout.
The new logic is different in two ways:
First, only for the check, if unwraps any combination of WriteAllWrapper and
winstdout.
Second, it skips wrapping the stream only if it is an instance of io.RawIOBase
(or already wrapped). If it is an instance of io.BufferedIOBase, it gets
wrapped. In any other case, the function raises an exception. This ensures
that, if an unknown stream is passed or we add another wrapper in the future,
we don’t wrap the stream if it’s already line buffered or not wrap the stream
if it’s not line buffered. In fact, this was already helpful during development
of this change. Without it, I possibly would have forgot that WriteAllWrapper
needs to be ignored for the check, leading to unnecessary wrapping if stdout is
unbuffered.
The alternative would have been to always wrap unknown streams. However, I
don’t think that anyone would benefit from being less strict. We can expect
streams from the standard library to be subclassing either io.RawIOBase or
io.BufferedIOBase, so running Mercurial in the standard way should not regress
by this change. Py2exe might replace sys.stdout and sys.stderr, but that
currently breaks Mercurial anyway and also these streams don’t claim to be
interactive, so this function is not called for them.
#!/usr/bin/env python3
#
# Copyright 2018 Google LLC.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
"""Tool read primitive events from a pipe to produce a catapult trace.
Usage:
Terminal 1: $ catapipe.py /tmp/mypipe /tmp/trace.json
Terminal 2: $ HGCATAPULTSERVERPIPE=/tmp/mypipe hg root
<ctrl-c catapipe.py in Terminal 1>
$ catapult/tracing/bin/trace2html /tmp/trace.json # produce /tmp/trace.html
<open trace.html in your browser of choice; the WASD keys are very useful>
(catapult is located at https://github.com/catapult-project/catapult)
For now the event stream supports
START $SESSIONID ...
and
END $SESSIONID ...
events. Everything after the SESSIONID (which must not contain spaces)
is used as a label for the event. Events are timestamped as of when
they arrive in this process and are then used to produce catapult
traces that can be loaded in Chrome's about:tracing utility. It's
important that the event stream *into* this process stay simple,
because we have to emit it from the shell scripts produced by
run-tests.py.
Typically you'll want to place the path to the named pipe in the
HGCATAPULTSERVERPIPE environment variable, which both run-tests and hg
understand. To trace *only* run-tests, use HGTESTCATAPULTSERVERPIPE instead.
"""
import argparse
import json
import os
import timeit
_TYPEMAP = {
'START': 'B',
'END': 'E',
'COUNTER': 'C',
}
_threadmap = {}
# Timeit already contains the whole logic about which timer to use based on
# Python version and OS
timer = timeit.default_timer
def main():
parser = argparse.ArgumentParser()
parser.add_argument(
'pipe',
type=str,
nargs=1,
help='Path of named pipe to create and listen on.',
)
parser.add_argument(
'output',
default='trace.json',
type=str,
nargs='?',
help='Path of json file to create where the traces ' 'will be stored.',
)
parser.add_argument(
'--debug',
default=False,
action='store_true',
help='Print useful debug messages',
)
args = parser.parse_args()
fn = args.pipe[0]
os.mkfifo(fn)
try:
with open(fn) as f, open(args.output, 'w') as out:
out.write('[\n')
start = timer()
while True:
ev = f.readline().strip()
if not ev:
continue
now = timer()
if args.debug:
print(ev)
verb, session, label = ev.split(' ', 2)
if session not in _threadmap:
_threadmap[session] = len(_threadmap)
if verb == 'COUNTER':
amount, label = label.split(' ', 1)
payload_args = {'value': int(amount)}
else:
payload_args = {}
pid = _threadmap[session]
ts_micros = (now - start) * 1000000
out.write(
json.dumps(
{
"name": label,
"cat": "misc",
"ph": _TYPEMAP[verb],
"ts": ts_micros,
"pid": pid,
"tid": 1,
"args": payload_args,
}
)
)
out.write(',\n')
finally:
os.unlink(fn)
if __name__ == '__main__':
main()