procutil: always waiting on child processes to prevent zombies with 'hg serve'
When runbgcommand is invoked by an extension with ensurestart=False, we never
called waitpid - which is fine in most cases, except if that's happening on a
command server (e.g. chg), in which case the child defunct process will just
sit there for as long as the server is running.
The actual semantics of SIGCHLD signal handling is a lot more complex than
it seems, and the POSIX standard *seems* to read that it's ignored by default
and everything would just work without the waitpid if we're not listening for
it, but the truth is that it's only ignored if we *explicitly* set it to
SIG_IGN. We further cannot set it to SIG_IGN or to a catch-all handler across
all of 'hg serve', because Python's suprocess.Popen relies on that signal,
and a few specific parts of hg also set custom handlers, so instead we wait
for specific PIDs in dedicated threads.
I did a poor-man's benchmark of the thread creation and it seems to take
about 1ms, which is way better than the 20+ms from ensurestart=True.
Differential Revision: https://phab.mercurial-scm.org/D8497
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
# based on bundleheads extension by Gregory Szorc <gps@mozilla.com>
from __future__ import absolute_import
import abc
import os
import subprocess
import tempfile
from mercurial.pycompat import open
from mercurial import (
node,
pycompat,
)
from mercurial.utils import (
hashutil,
procutil,
)
NamedTemporaryFile = tempfile.NamedTemporaryFile
class BundleWriteException(Exception):
pass
class BundleReadException(Exception):
pass
class abstractbundlestore(object): # pytype: disable=ignored-metaclass
"""Defines the interface for bundle stores.
A bundle store is an entity that stores raw bundle data. It is a simple
key-value store. However, the keys are chosen by the store. The keys can
be any Python object understood by the corresponding bundle index (see
``abstractbundleindex`` below).
"""
__metaclass__ = abc.ABCMeta
@abc.abstractmethod
def write(self, data):
"""Write bundle data to the store.
This function receives the raw data to be written as a str.
Throws BundleWriteException
The key of the written data MUST be returned.
"""
@abc.abstractmethod
def read(self, key):
"""Obtain bundle data for a key.
Returns None if the bundle isn't known.
Throws BundleReadException
The returned object should be a file object supporting read()
and close().
"""
class filebundlestore(object):
"""bundle store in filesystem
meant for storing bundles somewhere on disk and on network filesystems
"""
def __init__(self, ui, repo):
self.ui = ui
self.repo = repo
self.storepath = ui.configpath(b'scratchbranch', b'storepath')
if not self.storepath:
self.storepath = self.repo.vfs.join(
b"scratchbranches", b"filebundlestore"
)
if not os.path.exists(self.storepath):
os.makedirs(self.storepath)
def _dirpath(self, hashvalue):
"""First two bytes of the hash are the name of the upper
level directory, next two bytes are the name of the
next level directory"""
return os.path.join(self.storepath, hashvalue[0:2], hashvalue[2:4])
def _filepath(self, filename):
return os.path.join(self._dirpath(filename), filename)
def write(self, data):
filename = node.hex(hashutil.sha1(data).digest())
dirpath = self._dirpath(filename)
if not os.path.exists(dirpath):
os.makedirs(dirpath)
with open(self._filepath(filename), b'wb') as f:
f.write(data)
return filename
def read(self, key):
try:
with open(self._filepath(key), b'rb') as f:
return f.read()
except IOError:
return None
class externalbundlestore(abstractbundlestore):
def __init__(self, put_binary, put_args, get_binary, get_args):
"""
`put_binary` - path to binary file which uploads bundle to external
storage and prints key to stdout
`put_args` - format string with additional args to `put_binary`
{filename} replacement field can be used.
`get_binary` - path to binary file which accepts filename and key
(in that order), downloads bundle from store and saves it to file
`get_args` - format string with additional args to `get_binary`.
{filename} and {handle} replacement field can be used.
"""
self.put_args = put_args
self.get_args = get_args
self.put_binary = put_binary
self.get_binary = get_binary
def _call_binary(self, args):
p = subprocess.Popen(
pycompat.rapply(procutil.tonativestr, args),
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
close_fds=True,
)
stdout, stderr = p.communicate()
returncode = p.returncode
return returncode, stdout, stderr
def write(self, data):
# Won't work on windows because you can't open file second time without
# closing it
# TODO: rewrite without str.format() and replace NamedTemporaryFile()
# with pycompat.namedtempfile()
with NamedTemporaryFile() as temp:
temp.write(data)
temp.flush()
temp.seek(0)
formatted_args = [
arg.format(filename=temp.name) for arg in self.put_args
]
returncode, stdout, stderr = self._call_binary(
[self.put_binary] + formatted_args
)
if returncode != 0:
raise BundleWriteException(
b'Failed to upload to external store: %s' % stderr
)
stdout_lines = stdout.splitlines()
if len(stdout_lines) == 1:
return stdout_lines[0]
else:
raise BundleWriteException(
b'Bad output from %s: %s' % (self.put_binary, stdout)
)
def read(self, handle):
# Won't work on windows because you can't open file second time without
# closing it
# TODO: rewrite without str.format() and replace NamedTemporaryFile()
# with pycompat.namedtempfile()
with NamedTemporaryFile() as temp:
formatted_args = [
arg.format(filename=temp.name, handle=handle)
for arg in self.get_args
]
returncode, stdout, stderr = self._call_binary(
[self.get_binary] + formatted_args
)
if returncode != 0:
raise BundleReadException(
b'Failed to download from external store: %s' % stderr
)
return temp.read()