view tests/test-subrepo-missing.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)

  $ hg init repo
  $ cd repo
  $ hg init subrepo
  $ echo a > subrepo/a
  $ hg -R subrepo ci -Am adda
  adding a
  $ echo 'subrepo = subrepo' > .hgsub
  $ hg ci -Am addsubrepo
  adding .hgsub
  $ echo b > subrepo/b
  $ hg -R subrepo ci -Am addb
  adding b
  $ hg ci -m updatedsub

ignore blanklines in .hgsubstate

  >>> open('.hgsubstate', 'wb').write(b'\n\n   \t \n   \n') and None
  $ hg st --subrepos
  M .hgsubstate
  $ hg revert -qC .hgsubstate

abort more gracefully on .hgsubstate parsing error

  $ cp .hgsubstate .hgsubstate.old
  >>> open('.hgsubstate', 'wb').write(b'\ninvalid') and None
  $ hg st --subrepos --cwd $TESTTMP -R $TESTTMP/repo
  abort: invalid subrepository revision specifier in 'repo/.hgsubstate' line 2
  [255]
  $ mv .hgsubstate.old .hgsubstate

delete .hgsub and revert it

  $ rm .hgsub
  $ hg revert .hgsub
  warning: subrepo spec file '.hgsub' not found
  warning: subrepo spec file '.hgsub' not found

delete .hgsubstate and revert it

  $ rm .hgsubstate
  $ hg revert .hgsubstate

delete .hgsub and update

  $ rm .hgsub
  $ hg up 0 --cwd $TESTTMP -R $TESTTMP/repo
  warning: subrepo spec file 'repo/.hgsub' not found
  warning: subrepo spec file 'repo/.hgsub' not found
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg st
  warning: subrepo spec file '.hgsub' not found
  ! .hgsub
  $ ls -A subrepo
  .hg
  a

delete .hgsubstate and update

  $ hg up -C
  warning: subrepo spec file '.hgsub' not found
  warning: subrepo spec file '.hgsub' not found
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm .hgsubstate
  $ hg up 0
  other [destination] changed .hgsubstate which local [working copy] deleted
  use (c)hanged version or leave (d)eleted? c
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg st
  $ ls -A subrepo
  .hg
  a

Enable obsolete

  $ cat >> $HGRCPATH << EOF
  > [ui]
  > logtemplate= {rev}:{node|short} {desc|firstline}
  > [phases]
  > publish=False
  > [experimental]
  > evolution.createmarkers=True
  > EOF

check that we can update parent repo with missing (amended) subrepo revision

  $ hg up --repository subrepo -r tip
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg ci -m "updated subrepo to tip"
  created new head
  $ cd subrepo
  $ hg update -r tip
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo foo > a
  $ hg commit --amend -m "addb (amended)"
  $ cd ..
  $ hg update --clean .
  revision 102a90ea7b4a in subrepository "subrepo" is hidden
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

check that --hidden is propagated to the subrepo

  $ hg -R subrepo up tip
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg ci -m 'commit with amended subrepo'
  $ echo bar > subrepo/a
  $ hg -R subrepo ci --amend -m "amend a (again)"
  $ hg --hidden cat subrepo/a
  foo

verify will warn if locked-in subrepo revisions are hidden or missing

  $ hg ci -m "amended subrepo (again)"
  $ hg --config extensions.strip= --hidden strip -R subrepo -qr 'tip' --config devel.strip-obsmarkers=no
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 5 changesets with 5 changes to 2 files
  checking subrepo links
  subrepo 'subrepo' is hidden in revision a66de08943b6
  subrepo 'subrepo' is hidden in revision 674d05939c1e
  subrepo 'subrepo' not found in revision a7d05d9055a4

verifying shouldn't init a new subrepo if the reference doesn't exist

  $ mv subrepo b
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 5 changesets with 5 changes to 2 files
  checking subrepo links
  0: repository $TESTTMP/repo/subrepo not found
  1: repository $TESTTMP/repo/subrepo not found
  3: repository $TESTTMP/repo/subrepo not found
  4: repository $TESTTMP/repo/subrepo not found
  $ ls -A
  .hg
  .hgsub
  .hgsubstate
  b
  $ mv b subrepo

  $ cd ..