view tests/test-config-env.py @ 38732:be4984261611

merge: mark file gets as not thread safe (issue5933)

In default installs, this has the effect of disabling the thread-based
worker on Windows when manifesting files in the working directory. My
measurements have shown that with revlog-based repositories, Mercurial
spends a lot of CPU time in revlog code resolving file data. This ends
up incurring a lot of context switching across threads and slows down
`hg update` operations when going from an empty working directory to
the tip of the repo.

On mozilla-unified (246,351 files) on an i7-6700K (4+4 CPUs):

before: 487s wall
after:  360s wall (equivalent to worker.enabled=false)
cpus=2: 379s wall

Even with only 2 threads, the thread pool is still slower.

The introduction of the thread-based worker (02b36e860e0b) states that
it resulted in a "~50%" speedup for `hg sparse --enable-profile` and
`hg sparse --disable-profile`. This disagrees with my measurement
above. I theorize a few reasons for this:

1) Removal of files from the working directory is I/O - not CPU - bound
   and should benefit from a thread pool (unless I/O is insanely fast
   and the GIL release is near instantaneous). So tests like `hg sparse
   --enable-profile` may exercise deletion throughput and aren't good
   benchmarks for worker tasks that are CPU heavy.
2) The patch was authored by someone at Facebook. The results were
   likely measured against a repository using remotefilelog. And I
   believe that revision retrieval during working directory updates with
   remotefilelog will often use a remote store, thus being I/O and not
   CPU bound. This probably resulted in an overstated performance gain.

Since there appears to be a need to enable the thread-based worker with
some stores, I've made the flagging of file gets as thread safe
configurable. I've made it experimental because I don't want to formalize
a boolean flag for this option and because this attribute is best
captured against the store implementation. But we don't have a proper
store API for this yet. I'd rather cross this bridge later.

It is possible there are revlog-based repositories that do benefit from
a thread-based worker. I didn't do very comprehensive testing. If there
are, we may want to devise a more proper algorithm for whether to use
the thread-based worker, including possibly config options to limit the
number of threads to use. But until I see evidence that justifies
complexity, simplicity wins.

Differential Revision: https://phab.mercurial-scm.org/D3963

# Test the config layer generated by environment variables

from __future__ import absolute_import, print_function

import os

from mercurial import (
    encoding,
    rcutil,
    ui as uimod,
    util,
)

from mercurial.utils import (
    procutil,
)

testtmp = encoding.environ[b'TESTTMP']

# prepare hgrc files
def join(name):
    return os.path.join(testtmp, name)

with open(join(b'sysrc'), 'wb') as f:
    f.write(b'[ui]\neditor=e0\n[pager]\npager=p0\n')

with open(join(b'userrc'), 'wb') as f:
    f.write(b'[ui]\neditor=e1')

# replace rcpath functions so they point to the files above
def systemrcpath():
    return [join(b'sysrc')]

def userrcpath():
    return [join(b'userrc')]

rcutil.systemrcpath = systemrcpath
rcutil.userrcpath = userrcpath
os.path.isdir = lambda x: False # hack: do not load default.d/*.rc

# utility to print configs
def printconfigs(env):
    encoding.environ = env
    rcutil._rccomponents = None # reset cache
    ui = uimod.ui.load()
    for section, name, value in ui.walkconfig():
        source = ui.configsource(section, name)
        procutil.stdout.write(b'%s.%s=%s # %s\n'
                              % (section, name, value, util.pconvert(source)))
    procutil.stdout.write(b'\n')

# environment variable overrides
printconfigs({})
printconfigs({b'EDITOR': b'e2', b'PAGER': b'p2'})