view tests/test-dirstate.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 dirstate._dirs refcounting

  $ hg init t
  $ cd t
  $ mkdir -p a/b/c/d
  $ touch a/b/c/d/x
  $ touch a/b/c/d/y
  $ touch a/b/c/d/z
  $ hg ci -Am m
  adding a/b/c/d/x
  adding a/b/c/d/y
  adding a/b/c/d/z
  $ hg mv a z
  moving a/b/c/d/x to z/b/c/d/x
  moving a/b/c/d/y to z/b/c/d/y
  moving a/b/c/d/z to z/b/c/d/z

Test name collisions

  $ rm z/b/c/d/x
  $ mkdir z/b/c/d/x
  $ touch z/b/c/d/x/y
  $ hg add z/b/c/d/x/y
  abort: file 'z/b/c/d/x' in dirstate clashes with 'z/b/c/d/x/y'
  [255]
  $ rm -rf z/b/c/d
  $ touch z/b/c/d
  $ hg add z/b/c/d
  abort: directory 'z/b/c/d' already in dirstate
  [255]

  $ cd ..

Issue1790: dirstate entry locked into unset if file mtime is set into
the future

Prepare test repo:

  $ hg init u
  $ cd u
  $ echo a > a
  $ hg add
  adding a
  $ hg ci -m1

Set mtime of a into the future:

  $ touch -t 202101011200 a

Status must not set a's entry to unset (issue1790):

  $ hg status
  $ hg debugstate
  n 644          2 2021-01-01 12:00:00 a

Test modulo storage/comparison of absurd dates:

#if no-aix
  $ touch -t 195001011200 a
  $ hg st
  $ hg debugstate
  n 644          2 2018-01-19 15:14:08 a
#endif

Verify that exceptions during a dirstate change leave the dirstate
coherent (issue4353)

  $ cat > ../dirstateexception.py <<EOF
  > from __future__ import absolute_import
  > from mercurial import (
  >   error,
  >   extensions,
  >   merge,
  > )
  > 
  > def wraprecordupdates(orig, repo, actions, branchmerge):
  >     raise error.Abort("simulated error while recording dirstateupdates")
  > 
  > def reposetup(ui, repo):
  >     extensions.wrapfunction(merge, 'recordupdates', wraprecordupdates)
  > EOF

  $ hg rm a
  $ hg commit -m 'rm a'
  $ echo "[extensions]" >> .hg/hgrc
  $ echo "dirstateex=../dirstateexception.py" >> .hg/hgrc
  $ hg up 0
  abort: simulated error while recording dirstateupdates
  [255]
  $ hg log -r . -T '{rev}\n'
  1
  $ hg status
  ? a