view tests/test-branch-option.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 branch selection options

  $ hg init branch
  $ cd branch
  $ hg branch a
  marked working directory as branch a
  (branches are permanent and global, did you want a bookmark?)
  $ echo a > foo
  $ hg ci -d '0 0' -Ama
  adding foo
  $ echo a2 > foo
  $ hg ci -d '0 0' -ma2
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch c
  marked working directory as branch c
  $ echo c > foo
  $ hg ci -d '0 0' -mc
  $ hg tag -l z
  $ cd ..
  $ hg clone -r 0 branch branch2
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 5b65ba7c951d
  updating to branch a
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd branch2
  $ hg up 0
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch b
  marked working directory as branch b
  $ echo b > foo
  $ hg ci -d '0 0' -mb
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg --encoding utf-8 branch æ
  marked working directory as branch \xc3\xa6 (esc)
  $ echo ae1 > foo
  $ hg ci -d '0 0' -mae1
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg --encoding utf-8 branch -f æ
  marked working directory as branch \xc3\xa6 (esc)
  $ echo ae2 > foo
  $ hg ci -d '0 0' -mae2
  created new head
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch -f b
  marked working directory as branch b
  $ echo b2 > foo
  $ hg ci -d '0 0' -mb2
  created new head

unknown branch and fallback

  $ hg in -qbz
  abort: unknown branch 'z'!
  [255]
  $ hg in -q ../branch#z
  2:f25d57ab0566
  $ hg out -qbz
  abort: unknown branch 'z'!
  [255]

in rev c branch a

  $ hg in -qr c ../branch#a
  1:dd6e60a716c6
  2:f25d57ab0566
  $ hg in -qr c -b a
  1:dd6e60a716c6
  2:f25d57ab0566

out branch .

  $ hg out -q ../branch#.
  1:b84708d77ab7
  4:65511d0e2b55
  $ hg out -q -b .
  1:b84708d77ab7
  4:65511d0e2b55

out branch . non-ascii

  $ hg --encoding utf-8 up æ
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg --encoding latin1 out -q ../branch#.
  2:df5a44224d4e
  3:4f4a5125ca10
  $ hg --encoding latin1 out -q -b .
  2:df5a44224d4e
  3:4f4a5125ca10

clone branch b

  $ cd ..
  $ hg clone branch2#b branch3
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 1 files (+1 heads)
  new changesets 5b65ba7c951d:65511d0e2b55
  updating to branch b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -q -R branch3 heads b
  2:65511d0e2b55
  1:b84708d77ab7
  $ hg -q -R branch3 parents
  2:65511d0e2b55
  $ rm -rf branch3

clone rev a branch b

  $ hg clone -r a branch2#b branch3
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 1 files (+1 heads)
  new changesets 5b65ba7c951d:65511d0e2b55
  updating to branch a
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -q -R branch3 heads b
  2:65511d0e2b55
  1:b84708d77ab7
  $ hg -q -R branch3 parents
  0:5b65ba7c951d
  $ rm -rf branch3