view tests/test-commit-unresolved.t @ 44950:f9734b2d59cc

py3: make stdout line-buffered if connected to a TTY

Status messages that are to be shown on the terminal should be written to the
file descriptor before anything further is done, to keep the user updated.

One common way to achieve this is to make stdout line-buffered if it is
connected to a TTY. This is done on Python 2 (except on Windows, where libc,
which the CPython 2 streams depend on, does not properly support this).

Python 3 rolls it own I/O streams. On Python 3, buffered binary streams can't be
set line-buffered. The previous code (added in 227ba1afcb65) incorrectly
assumed that on Python 3, pycompat.stdout (sys.stdout.buffer) is already
line-buffered. However the interpreter initializes it with a block-buffered
stream or an unbuffered stream (when the -u option or the PYTHONUNBUFFERED
environment variable is set), never with a line-buffered stream.

One example where the current behavior is unacceptable is when running
`hg pull https://www.mercurial-scm.org/repo/hg` on Python 3, where the line
"pulling from https://www.mercurial-scm.org/repo/hg" does not appear on the
terminal before the hg process blocks while waiting for the server.

Various approaches to fix this problem are possible, including:

1. Weaken the contract of procutil.stdout to not give any guarantees about
   buffering behavior. In this case, users of procutil.stdout need to be
   changed to do enough flushes. In particular,
  1. either ui must insert enough flushes for ui.write() and friends, or
  2. ui.write() and friends get split into flushing and fully buffered
     methods, or
  3. users of ui.write() and friends must flush explicitly.
2. Make stdout unbuffered.
3. Make stdout line-buffered. Since Python 3 does not natively support that for
   binary streams, we must implement it ourselves.

(2.) is problematic because using unbuffered I/O changes the performance
characteristics significantly compared to line-buffered (which is used on
Python 2) and this would be a regression.

(1.2.) and (1.3) are a substantial amount of work. It’s unclear whether the
added complexity would be justified, given that raw performance doesn’t matter
that much when writing to a terminal much faster than the user could read it.

(1.1.) pushes complexity into the ui class instead of separating the concern of
how stdout is buffered. Other users of procutil.stdout would still need to take
care of the flushes.

This patch implements (3.). The general performance considerations are very
similar to (1.1.). The extra method invocation and method forwarding add a
little more overhead if the class is used. In exchange, it doesn’t add overhead
if not used.


For the benchmarks, I compared the previous implementation (incorrect on Python
3), (1.1.), (3.) and (2.). The command was chosen so that the streams were
configured as if they were writing to a TTY, but actually write to a pager,
which is also the default:
HGRCPATH=/dev/null python3 ./hg --cwd ~/vcs/mozilla-central --time --pager yes --config pager.pager='cat > /dev/null' status --all

previous:
time: real 7.880 secs (user 7.290+0.050 sys 0.580+0.170)
time: real 7.830 secs (user 7.220+0.070 sys 0.590+0.140)
time: real 7.800 secs (user 7.210+0.050 sys 0.570+0.170)

(1.1.) using Yuya Nishihara’s patch:
time: real 9.860 secs (user 8.670+0.350 sys 1.160+0.830)
time: real 9.540 secs (user 8.430+0.370 sys 1.100+0.770)
time: real 9.830 secs (user 8.630+0.370 sys 1.180+0.840)

(3.) using this patch:
time: real 9.580 secs (user 8.480+0.350 sys 1.090+0.770)
time: real 9.670 secs (user 8.480+0.330 sys 1.170+0.860)
time: real 9.640 secs (user 8.500+0.350 sys 1.130+0.810)

(2.) using a previous patch by me:
time: real 10.480 secs (user 8.850+0.720 sys 1.590+1.500)
time: real 10.490 secs (user 8.750+0.750 sys 1.710+1.470)
time: real 10.240 secs (user 8.600+0.700 sys 1.590+1.510)


As expected, there’s no difference on Python 2, as exactly the same code paths
are used:

previous:
time: real 6.950 secs (user 5.870+0.330 sys 1.070+0.770)
time: real 7.040 secs (user 6.040+0.360 sys 0.980+0.750)
time: real 7.070 secs (user 5.950+0.360 sys 1.100+0.760)

this patch:
time: real 7.010 secs (user 5.900+0.390 sys 1.070+0.730)
time: real 7.000 secs (user 5.850+0.350 sys 1.120+0.760)
time: real 7.000 secs (user 5.790+0.380 sys 1.170+0.710)

#testcases abortcommand abortflag
#if abortflag
  $ cat >> $HGRCPATH <<EOF
  > [alias]
  > abort = merge --abort
  > EOF
#endif

  $ addcommit () {
  >     echo $1 > $1
  >     hg add $1
  >     hg commit -d "${2} 0" -m $1
  > }

  $ commit () {
  >     hg commit -d "${2} 0" -m $1
  > }

  $ hg init a
  $ cd a
  $ addcommit "A" 0
  $ addcommit "B" 1
  $ echo "C" >> A
  $ commit "C" 2

  $ hg update -C 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo "D" >> A
  $ commit "D" 3
  created new head

State before the merge

  $ hg status
  $ hg id
  e45016d2b3d3 tip
  $ hg summary
  parent: 3:e45016d2b3d3 tip
   D
  branch: default
  commit: (clean)
  update: 2 new changesets, 2 branch heads (merge)
  phases: 4 draft

Testing the abort functionality first in case of conflicts

  $ hg abort
  abort: no merge in progress (abortflag !)
  abort: no operation in progress (abortcommand !)
  [255]

  $ hg merge
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  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 merge --abort e4501
  abort: cannot specify a node with --abort
  [255]
  $ hg merge --abort --rev e4501
  abort: cannot specify both --abort and --rev
  [255]

#if abortcommand
when in dry-run mode
  $ hg abort --dry-run
  merge in progress, will be aborted
#endif

  $ hg abort
  aborting the merge, updating back to e45016d2b3d3
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

Checking that we got back in the same state

  $ hg status
  ? A.orig
  $ hg id
  e45016d2b3d3 tip
  $ hg summary
  parent: 3:e45016d2b3d3 tip
   D
  branch: default
  commit: 1 unknown (clean)
  update: 2 new changesets, 2 branch heads (merge)
  phases: 4 draft

Merging a conflict araises

  $ hg merge
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  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]

Correct the conflict without marking the file as resolved

  $ echo "ABCD" > A
  $ hg commit -m "Merged"
  abort: unresolved merge conflicts (see 'hg help resolve')
  [255]

Mark the conflict as resolved and commit

  $ hg resolve -m A
  (no more unresolved files)
  $ hg commit -m "Merged"

Test that if a file is removed but not marked resolved, the commit still fails
(issue4972)

  $ hg up ".^"
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge 2
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  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 rm --force A
  $ hg commit -m merged
  abort: unresolved merge conflicts (see 'hg help resolve')
  [255]

  $ hg resolve -ma
  (no more unresolved files)
  $ hg commit -m merged
  created new head

Testing the abort functionality in case of no conflicts

  $ hg update -C 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ addcommit "E" 4
  created new head
  $ hg id
  68352a18a7c4 tip

  $ hg merge -r 4
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg merge --preview --abort
  abort: cannot specify both --abort and --preview
  [255]

  $ hg abort
  aborting the merge, updating back to 68352a18a7c4
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg id
  68352a18a7c4 tip

  $ cd ..