view tests/test-log-exthook.t @ 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 hg log changeset printer external hook
-------------------------------------------

  $ cat > $TESTTMP/logexthook.py <<EOF
  > from __future__ import absolute_import
  > from mercurial import (
  >   commands,
  >   logcmdutil,
  >   repair,
  > )
  > def rot13description(self, ctx):
  >     summary = "summary".encode('rot13')
  >     description = ctx.description().strip().splitlines()[0].encode('rot13')
  >     self.ui.write("%s:     %s\n" % (summary, description))
  > def reposetup(ui, repo):
  >     logcmdutil.changesetprinter._exthook = rot13description
  > EOF

Prepare the repository

  $ hg init empty
  $ cd empty
  $ touch ROOT
  $ hg commit -A -m "Root" ROOT

  $ touch a b c
  $ hg commit -A -m "Add A, B, C" a b c

Check the log

  $ hg log --config extensions.t=$TESTTMP/logexthook.py
  changeset:   1:70fc82b23320
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  fhzznel:     Nqq N, O, P
  summary:     Add A, B, C
  
  changeset:   0:b00443a54871
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  fhzznel:     Ebbg
  summary:     Root
  
Check that exthook is working with graph log too

  $ hg log -G --config extensions.t=$TESTTMP/logexthook.py
  @  changeset:   1:70fc82b23320
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  fhzznel:     Nqq N, O, P
  |  summary:     Add A, B, C
  |
  o  changeset:   0:b00443a54871
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     fhzznel:     Ebbg
     summary:     Root