hgdemandimport: apply lazy module loading to sys.meta_path finders
Python's `sys.meta_path` finders are the primary objects whose job it
is to find a module at import time. When `import` is called, Python
iterates objects in this list and calls `o.find_spec(...)` to find
a `ModuleSpec` (or None if the module couldn't be found by that
finder). If no meta path finder can find a module, import fails.
One of the default meta path finders is `PathFinder`. Its job is to
import modules from the filesystem and is probably the most important
importer. This finder looks at `sys.path` and `sys.path_hooks` to do
its job.
The `ModuleSpec` returned by `MetaPathImporter.find_spec()` has a
`loader` attribute, which defines the concrete module loader to use.
`sys.path_hooks` is a hook point for teaching `PathFinder` to
instantiate custom loader types.
Previously, we injected a custom `sys.path_hook` that told `PathFinder`
to wrap the default loaders with a loader that creates a module object
that is lazy.
This approach worked. But its main limitation was that it only applied
to the `PathFinder` meta path importer. There are other meta path
importers that are registered. And in the case of PyOxidizer loading
modules from memory, `PathFinder` doesn't come into play since
PyOxidizer's own meta path importer was handling all imports.
This commit changes our approach to lazy module loading by proxying
all meta path importers. Specifically, we overload the `find_spec()`
method to swap in a wrapped loader on the `ModuleSpec` before it
is returned. The end result of this is all meta path importers should
be lazy.
As much as I would have loved to utilize .__class__ manipulation to
achieve this, some meta path importers are implemented in C/Rust
in such a way that they cannot be monkeypatched. This is why we
use __getattribute__ to define a proxy.
Also, this change could theoretically open us up to regressions in
meta path importers whose loader is creating module objects which
can't be monkeypatched. But I'm not aware of any of these in the
wild. So I think we'll be safe.
According to hyperfine, this change yields a decent startup time win of
5-6ms:
```
Benchmark #1: ~/.pyenv/versions/3.6.10/bin/python ./hg version
Time (mean ± σ): 86.8 ms ± 0.5 ms [User: 78.0 ms, System: 8.7 ms]
Range (min … max): 86.0 ms … 89.1 ms 50 runs
Time (mean ± σ): 81.1 ms ± 2.7 ms [User: 74.5 ms, System: 6.5 ms]
Range (min … max): 77.8 ms … 90.5 ms 50 runs
Benchmark #2: ~/.pyenv/versions/3.7.6/bin/python ./hg version
Time (mean ± σ): 78.9 ms ± 0.6 ms [User: 70.2 ms, System: 8.7 ms]
Range (min … max): 78.1 ms … 81.2 ms 50 runs
Time (mean ± σ): 73.4 ms ± 0.6 ms [User: 65.3 ms, System: 8.0 ms]
Range (min … max): 72.4 ms … 75.7 ms 50 runs
Benchmark #3: ~/.pyenv/versions/3.8.1/bin/python ./hg version
Time (mean ± σ): 78.1 ms ± 0.6 ms [User: 70.2 ms, System: 7.9 ms]
Range (min … max): 77.4 ms … 80.9 ms 50 runs
Time (mean ± σ): 72.1 ms ± 0.4 ms [User: 64.4 ms, System: 7.6 ms]
Range (min … max): 71.4 ms … 74.1 ms 50 runs
```
Differential Revision: https://phab.mercurial-scm.org/D7954
# server.py - utility and factory of server
#
# Copyright 2005-2007 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import
import os
from .i18n import _
from .pycompat import open
from . import (
chgserver,
cmdutil,
commandserver,
error,
hgweb,
pycompat,
util,
)
from .utils import procutil
def runservice(
opts,
parentfn=None,
initfn=None,
runfn=None,
logfile=None,
runargs=None,
appendpid=False,
):
'''Run a command as a service.'''
postexecargs = {}
if opts[b'daemon_postexec']:
for inst in opts[b'daemon_postexec']:
if inst.startswith(b'unlink:'):
postexecargs[b'unlink'] = inst[7:]
elif inst.startswith(b'chdir:'):
postexecargs[b'chdir'] = inst[6:]
elif inst != b'none':
raise error.Abort(
_(b'invalid value for --daemon-postexec: %s') % inst
)
# When daemonized on Windows, redirect stdout/stderr to the lockfile (which
# gets cleaned up after the child is up and running), so that the parent can
# read and print the error if this child dies early. See 594dd384803c. On
# other platforms, the child can write to the parent's stdio directly, until
# it is redirected prior to runfn().
if pycompat.iswindows and opts[b'daemon_postexec']:
if b'unlink' in postexecargs and os.path.exists(
postexecargs[b'unlink']
):
procutil.stdout.flush()
procutil.stderr.flush()
fd = os.open(
postexecargs[b'unlink'], os.O_WRONLY | os.O_APPEND | os.O_BINARY
)
try:
os.dup2(fd, procutil.stdout.fileno())
os.dup2(fd, procutil.stderr.fileno())
finally:
os.close(fd)
def writepid(pid):
if opts[b'pid_file']:
if appendpid:
mode = b'ab'
else:
mode = b'wb'
fp = open(opts[b'pid_file'], mode)
fp.write(b'%d\n' % pid)
fp.close()
if opts[b'daemon'] and not opts[b'daemon_postexec']:
# Signal child process startup with file removal
lockfd, lockpath = pycompat.mkstemp(prefix=b'hg-service-')
os.close(lockfd)
try:
if not runargs:
runargs = procutil.hgcmd() + pycompat.sysargv[1:]
runargs.append(b'--daemon-postexec=unlink:%s' % lockpath)
# Don't pass --cwd to the child process, because we've already
# changed directory.
for i in pycompat.xrange(1, len(runargs)):
if runargs[i].startswith(b'--cwd='):
del runargs[i]
break
elif runargs[i].startswith(b'--cwd'):
del runargs[i : i + 2]
break
def condfn():
return not os.path.exists(lockpath)
pid = procutil.rundetached(runargs, condfn)
if pid < 0:
# If the daemonized process managed to write out an error msg,
# report it.
if pycompat.iswindows and os.path.exists(lockpath):
with open(lockpath, b'rb') as log:
for line in log:
procutil.stderr.write(line)
raise error.Abort(_(b'child process failed to start'))
writepid(pid)
finally:
util.tryunlink(lockpath)
if parentfn:
return parentfn(pid)
else:
return
if initfn:
initfn()
if not opts[b'daemon']:
writepid(procutil.getpid())
if opts[b'daemon_postexec']:
try:
os.setsid()
except AttributeError:
pass
if b'chdir' in postexecargs:
os.chdir(postexecargs[b'chdir'])
procutil.hidewindow()
procutil.stdout.flush()
procutil.stderr.flush()
nullfd = os.open(os.devnull, os.O_RDWR)
logfilefd = nullfd
if logfile:
logfilefd = os.open(
logfile, os.O_RDWR | os.O_CREAT | os.O_APPEND, 0o666
)
os.dup2(nullfd, procutil.stdin.fileno())
os.dup2(logfilefd, procutil.stdout.fileno())
os.dup2(logfilefd, procutil.stderr.fileno())
stdio = (
procutil.stdin.fileno(),
procutil.stdout.fileno(),
procutil.stderr.fileno(),
)
if nullfd not in stdio:
os.close(nullfd)
if logfile and logfilefd not in stdio:
os.close(logfilefd)
# Only unlink after redirecting stdout/stderr, so Windows doesn't
# complain about a sharing violation.
if b'unlink' in postexecargs:
os.unlink(postexecargs[b'unlink'])
if runfn:
return runfn()
_cmdservicemap = {
b'chgunix': chgserver.chgunixservice,
b'pipe': commandserver.pipeservice,
b'unix': commandserver.unixforkingservice,
}
def _createcmdservice(ui, repo, opts):
mode = opts[b'cmdserver']
try:
servicefn = _cmdservicemap[mode]
except KeyError:
raise error.Abort(_(b'unknown mode %s') % mode)
commandserver.setuplogging(ui, repo)
return servicefn(ui, repo, opts)
def _createhgwebservice(ui, repo, opts):
# this way we can check if something was given in the command-line
if opts.get(b'port'):
opts[b'port'] = util.getport(opts.get(b'port'))
alluis = {ui}
if repo:
baseui = repo.baseui
alluis.update([repo.baseui, repo.ui])
else:
baseui = ui
webconf = opts.get(b'web_conf') or opts.get(b'webdir_conf')
if webconf:
if opts.get(b'subrepos'):
raise error.Abort(_(b'--web-conf cannot be used with --subrepos'))
# load server settings (e.g. web.port) to "copied" ui, which allows
# hgwebdir to reload webconf cleanly
servui = ui.copy()
servui.readconfig(webconf, sections=[b'web'])
alluis.add(servui)
elif opts.get(b'subrepos'):
servui = ui
# If repo is None, hgweb.createapp() already raises a proper abort
# message as long as webconf is None.
if repo:
webconf = dict()
cmdutil.addwebdirpath(repo, b"", webconf)
else:
servui = ui
optlist = (
b"name templates style address port prefix ipv6"
b" accesslog errorlog certificate encoding"
)
for o in optlist.split():
val = opts.get(o, b'')
if val in (None, b''): # should check against default options instead
continue
for u in alluis:
u.setconfig(b"web", o, val, b'serve')
app = hgweb.createapp(baseui, repo, webconf)
return hgweb.httpservice(servui, app, opts)
def createservice(ui, repo, opts):
if opts[b"cmdserver"]:
return _createcmdservice(ui, repo, opts)
else:
return _createhgwebservice(ui, repo, opts)