view tests/test-obsolete-changeset-exchange.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)

Test changesets filtering during exchanges (some tests are still in
test-obsolete.t)

  $ cat >> $HGRCPATH << EOF
  > [experimental]
  > evolution.createmarkers=True
  > EOF

Push does not corrupt remote
----------------------------

Create a DAG where a changeset reuses a revision from a file first used in an
extinct changeset.

  $ hg init local
  $ cd local
  $ echo 'base' > base
  $ hg commit -Am base
  adding base
  $ echo 'A' > A
  $ hg commit -Am A
  adding A
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg revert -ar 1
  adding A
  $ hg commit -Am "A'"
  created new head
  $ hg log -G --template='{desc} {node}'
  @  A' f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  |
  | o  A 9d73aac1b2ed7d53835eaeec212ed41ea47da53a
  |/
  o  base d20a80d4def38df63a4b330b7fb688f3d4cae1e3
  
  $ hg debugobsolete 9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  1 new obsolescence markers
  obsoleted 1 changesets

Push it. The bundle should not refer to the extinct changeset.

  $ hg init ../other
  $ hg push ../other
  pushing to ../other
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files
  $ hg -R ../other verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 2 changes to 2 files

Adding a changeset going extinct locally
------------------------------------------

Pull a changeset that will immediatly goes extinct (because you already have a
marker to obsolete him)
(test resolution of issue3788)

  $ hg phase --draft --force f89bcc95eba5
  $ hg phase -R ../other --draft --force f89bcc95eba5
  $ hg commit --amend -m "A''"
  $ hg --hidden --config extensions.mq= strip  --no-backup f89bcc95eba5
  $ hg pull ../other
  pulling from ../other
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 1 files (+1 heads)
  1 new phase-divergent changesets
  new changesets f89bcc95eba5
  (run 'hg heads' to see heads, 'hg merge' to merge)

check that bundle is not affected

  $ hg bundle --hidden --rev f89bcc95eba5 --base "f89bcc95eba5^" ../f89bcc95eba5.hg
  1 changesets found
  $ hg --hidden --config extensions.mq= strip --no-backup f89bcc95eba5
  $ hg unbundle ../f89bcc95eba5.hg
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 1 files (+1 heads)
  (1 other changesets obsolete on arrival)
  (run 'hg heads' to see heads)

check-that bundle can contain markers:

  $ hg bundle --hidden --rev f89bcc95eba5 --base "f89bcc95eba5^" ../f89bcc95eba5-obs.hg --config experimental.evolution.bundle-obsmarker=1
  1 changesets found
  $ hg debugbundle ../f89bcc95eba5.hg
  Stream params: {Compression: BZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  cache:rev-branch-cache -- {} (mandatory: False)
  $ hg debugbundle ../f89bcc95eba5-obs.hg
  Stream params: {Compression: BZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  cache:rev-branch-cache -- {} (mandatory: False)
  obsmarkers -- {} (mandatory: True)
      version: 1 (70 bytes)
      9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}

  $ cd ..

pull does not fetch excessive changesets when common node is hidden (issue4982)
-------------------------------------------------------------------------------

initial repo with server and client matching

  $ hg init pull-hidden-common
  $ cd pull-hidden-common
  $ touch foo
  $ hg -q commit -A -m initial
  $ echo 1 > foo
  $ hg commit -m 1
  $ echo 2a > foo
  $ hg commit -m 2a
  $ cd ..
  $ hg clone --pull pull-hidden-common pull-hidden-common-client
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 1 files
  new changesets 96ee1d7354c4:6a29ed9c68de
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

server obsoletes the old head

  $ cd pull-hidden-common
  $ hg -q up -r 1
  $ echo 2b > foo
  $ hg -q commit -m 2b
  $ hg debugobsolete 6a29ed9c68defff1a139e5c6fa9696fb1a75783d bec0734cd68e84477ba7fc1d13e6cff53ab70129
  1 new obsolescence markers
  obsoleted 1 changesets
  $ cd ..

client only pulls down 1 changeset

  $ cd pull-hidden-common-client
  $ hg pull --debug
  pulling from $TESTTMP/pull-hidden-common
  query 1; heads
  searching for changes
  taking quick initial sample
  query 2; still undecided: 2, sample size is: 2
  2 total queries in *.????s (glob)
  1 changesets found
  list of changesets:
  bec0734cd68e84477ba7fc1d13e6cff53ab70129
  listing keys for "bookmarks"
  bundle2-output-bundle: "HG20", 4 parts total
  bundle2-output-part: "changegroup" (params: 1 mandatory 1 advisory) streamed payload
  bundle2-output-part: "listkeys" (params: 1 mandatory) empty payload
  bundle2-output-part: "phase-heads" 24 bytes payload
  bundle2-output-part: "cache:rev-branch-cache" (advisory) streamed payload
  bundle2-input-bundle: with-transaction
  bundle2-input-part: "changegroup" (params: 1 mandatory 1 advisory) supported
  adding changesets
  add changeset bec0734cd68e
  adding manifests
  adding file changes
  adding foo revisions
  bundle2-input-part: total payload size 476
  bundle2-input-part: "listkeys" (params: 1 mandatory) supported
  bundle2-input-part: "phase-heads" supported
  bundle2-input-part: total payload size 24
  bundle2-input-part: "cache:rev-branch-cache" (advisory) supported
  bundle2-input-part: total payload size 39
  bundle2-input-bundle: 4 parts total
  checking for updated bookmarks
  updating the branch cache
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets bec0734cd68e
  (run 'hg heads' to see heads, 'hg merge' to merge)