view tests/test-pathconflicts-merge.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

Path conflict checking is currently disabled by default because of issue5716.
Turn it on for this test.

  $ cat >> $HGRCPATH << EOF
  > [experimental]
  > merge.checkpathconflicts=True
  > EOF

  $ hg init repo
  $ cd repo
  $ echo base > base
  $ hg add base
  $ hg commit -m "base"
  $ hg bookmark -i base
  $ mkdir a
  $ echo 1 > a/b
  $ hg add a/b
  $ hg commit -m "file"
  $ hg bookmark -i file
  $ echo 2 > a/b
  $ hg commit -m "file2"
  $ hg bookmark -i file2
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

#if symlink
  $ mkdir a
  $ ln -s c a/b
  $ hg add a/b
  $ hg commit -m "link"
  created new head
#else
  $ hg import -q --bypass - <<EOF
  > # HG changeset patch
  > link
  > 
  > diff --git a/a/b b/a/b
  > new file mode 120000
  > --- /dev/null
  > +++ b/a/b
  > @@ -0,0 +1,1 @@
  > +c
  > \ No newline at end of file
  > EOF
  $ hg up -q
#endif

  $ hg bookmark -i link
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mkdir -p a/b/c
  $ echo 2 > a/b/c/d
  $ hg add a/b/c/d
  $ hg commit -m "dir"
  created new head
  $ hg bookmark -i dir

Merge - local file conflicts with remote directory

  $ hg up file
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (activating bookmark file)
  $ hg bookmark -i
  $ hg merge --verbose dir
  resolving manifests
  a/b: path conflict - a file or link has the same name as a directory
  the local file has been renamed to a/b~0ed027b96f31
  resolve manually then use 'hg resolve --mark a/b'
  moving a/b to a/b~0ed027b96f31
  getting a/b/c/d
  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
  $ hg status
  M a/b/c/d
  A a/b~0ed027b96f31
  R a/b
  $ hg resolve --all
  a/b: path conflict must be resolved manually
  $ hg forget a/b~0ed027b96f31 && rm a/b~0ed027b96f31
  $ hg resolve --mark a/b
  (no more unresolved files)
  $ hg commit -m "merge file and dir (deleted file)"

Merge - local symlink conflicts with remote directory

  $ hg up link
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (activating bookmark link)
  $ hg bookmark -i
  $ hg merge dir
  a/b: path conflict - a file or link has the same name as a directory
  the local file has been renamed to a/b~2ea68033e3be
  resolve manually then use 'hg resolve --mark a/b'
  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
  $ hg status
  M a/b/c/d
  A a/b~2ea68033e3be
  R a/b
  $ hg resolve --list
  P a/b
  $ hg resolve --all
  a/b: path conflict must be resolved manually
  $ hg mv a/b~2ea68033e3be a/b.old
  $ hg resolve --mark a/b
  (no more unresolved files)
  $ hg resolve --list
  R a/b
  $ hg commit -m "merge link and dir (renamed link)"

Merge - local directory conflicts with remote file or link

  $ hg up dir
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (activating bookmark dir)
  $ hg bookmark -i
  $ hg merge file
  a/b: path conflict - a file or link has the same name as a directory
  the remote file has been renamed to a/b~0ed027b96f31
  resolve manually then use 'hg resolve --mark a/b'
  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
  $ hg status
  A a/b~0ed027b96f31
  $ hg resolve --all
  a/b: path conflict must be resolved manually
  $ hg mv a/b~0ed027b96f31 a/b/old-b
  $ hg resolve --mark a/b
  (no more unresolved files)
  $ hg commit -m "merge dir and file (move file into dir)"
  created new head
  $ hg merge file2
  merging a/b/old-b and a/b to a/b/old-b
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat a/b/old-b
  2
  $ hg commit -m "merge file2 (copytrace tracked rename)"
  $ hg merge link
  a/b: path conflict - a file or link has the same name as a directory
  the remote file has been renamed to a/b~2ea68033e3be
  resolve manually then use 'hg resolve --mark a/b'
  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
  $ hg mv a/b~2ea68033e3be a/b.old

#if symlink
  $ readlink.py a/b.old
  a/b.old -> c
#else
  $ cat a/b.old
  c (no-eol)
#endif

  $ hg resolve --mark a/b
  (no more unresolved files)
  $ hg commit -m "merge link (rename link)"