view tests/test-hgwebdir-paths.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

from __future__ import absolute_import

import os
from mercurial import (
    hg,
    ui as uimod,
)
from mercurial.hgweb import (
    hgwebdir_mod,
)
hgwebdir = hgwebdir_mod.hgwebdir

os.mkdir(b'webdir')
os.chdir(b'webdir')

webdir = os.path.realpath(b'.')

u = uimod.ui.load()
hg.repository(u, b'a', create=1)
hg.repository(u, b'b', create=1)
os.chdir(b'b')
hg.repository(u, b'd', create=1)
os.chdir(b'..')
hg.repository(u, b'c', create=1)
os.chdir(b'..')

paths = {b't/a/': b'%s/a' % webdir,
         b'b': b'%s/b' % webdir,
         b'coll': b'%s/*' % webdir,
         b'rcoll': b'%s/**' % webdir}

config = os.path.join(webdir, b'hgwebdir.conf')
configfile = open(config, 'wb')
configfile.write(b'[paths]\n')
for k, v in paths.items():
    configfile.write(b'%s = %s\n' % (k, v))
configfile.close()

confwd = hgwebdir(config)
dictwd = hgwebdir(paths)

assert len(confwd.repos) == len(dictwd.repos), 'different numbers'
assert len(confwd.repos) == 9, 'expected 9 repos, found %d' % len(confwd.repos)

found = dict(confwd.repos)
for key, path in dictwd.repos:
    assert key in found, 'repository %s was not found' % key
    assert found[key] == path, 'different paths for repo %s' % key