view tests/test-remotefilelog-prefetch.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)

#require no-windows

  $ . "$TESTDIR/remotefilelog-library.sh"

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > EOF
  $ echo x > x
  $ echo z > z
  $ hg commit -qAm x
  $ echo x2 > x
  $ echo y > y
  $ hg commit -qAm y
  $ hg bookmark foo

  $ cd ..

# prefetch a revision

  $ hgcloneshallow ssh://user@dummy/master shallow --noupdate
  streaming all changes
  2 files to transfer, 528 bytes of data
  transferred 528 bytes in * seconds (*/sec) (glob)
  searching for changes
  no changes found
  $ cd shallow

  $ hg prefetch -r 0
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)

  $ hg cat -r 0 x
  x

# prefetch with base

  $ clearcache
  $ hg prefetch -r 0::1 -b 0
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)

  $ hg cat -r 1 x
  x2
  $ hg cat -r 1 y
  y

  $ hg cat -r 0 x
  x
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)

  $ hg cat -r 0 z
  z
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)

  $ hg prefetch -r 0::1 --base 0
  $ hg prefetch -r 0::1 -b 1
  $ hg prefetch -r 0::1

# prefetch a range of revisions

  $ clearcache
  $ hg prefetch -r 0::1
  4 files fetched over 1 fetches - (4 misses, 0.00% hit ratio) over *s (glob)

  $ hg cat -r 0 x
  x
  $ hg cat -r 1 x
  x2

# prefetch certain files

  $ clearcache
  $ hg prefetch -r 1 x
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)

  $ hg cat -r 1 x
  x2

  $ hg cat -r 1 y
  y
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)

# prefetch on pull when configured

  $ printf "[remotefilelog]\npullprefetch=bookmark()\n" >> .hg/hgrc
  $ hg strip tip
  saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/109c3a557a73-3f43405e-backup.hg (glob)

  $ clearcache
  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  updating bookmark foo
  added 1 changesets with 0 changes to 0 files
  new changesets 109c3a557a73
  (run 'hg update' to get a working copy)
  prefetching file contents
  3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over *s (glob)

  $ hg up tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

# prefetch only fetches changes not in working copy

  $ hg strip tip
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/109c3a557a73-3f43405e-backup.hg (glob)
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
  $ clearcache

  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  updating bookmark foo
  added 1 changesets with 0 changes to 0 files
  new changesets 109c3a557a73
  (run 'hg update' to get a working copy)
  prefetching file contents
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)

# Make some local commits that produce the same file versions as are on the
# server. To simulate a situation where we have local commits that were somehow
# pushed, and we will soon pull.

  $ hg prefetch -r 'all()'
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
  $ hg strip -q -r 0
  $ echo x > x
  $ echo z > z
  $ hg commit -qAm x
  $ echo x2 > x
  $ echo y > y
  $ hg commit -qAm y

# prefetch server versions, even if local versions are available

  $ clearcache
  $ hg strip -q tip
  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  updating bookmark foo
  added 1 changesets with 0 changes to 0 files
  new changesets 109c3a557a73
  1 local changesets published (?)
  (run 'hg update' to get a working copy)
  prefetching file contents
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)

  $ cd ..

# Prefetch unknown files during checkout

  $ hgcloneshallow ssh://user@dummy/master shallow2
  streaming all changes
  2 files to transfer, 528 bytes of data
  transferred 528 bytes in * seconds * (glob)
  searching for changes
  no changes found
  updating to branch default
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ cd shallow2
  $ hg up -q null
  $ echo x > x
  $ echo y > y
  $ echo z > z
  $ clearcache
  $ hg up tip
  x: untracked file differs
  3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over * (glob)
  abort: untracked files in working directory differ from files in requested revision
  [255]
  $ hg revert --all

# Test batch fetching of lookup files during hg status
  $ hg up --clean tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg debugrebuilddirstate
  $ clearcache
  $ hg status
  3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over * (glob)

# Prefetch during addrename detection
  $ hg up -q --clean tip
  $ hg revert --all
  $ mv x x2
  $ mv y y2
  $ mv z z2
  $ echo a > a
  $ hg add a
  $ rm a
  $ clearcache
  $ hg addremove -s 50 > /dev/null
  3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over * (glob)
  $ hg revert --all
  forgetting x2
  forgetting y2
  forgetting z2
  undeleting x
  undeleting y
  undeleting z


# Revert across double renames. Note: the scary "abort", error is because
# https://bz.mercurial-scm.org/5419 .

  $ cd ../master
  $ hg mv z z2
  $ hg commit -m 'move z -> z2'
  $ cd ../shallow2
  $ hg pull -q
  $ clearcache
  $ hg mv y y2
  y2: not overwriting - file exists
  ('hg rename --after' to record the rename)
  [1]
  $ hg mv x x2
  x2: not overwriting - file exists
  ('hg rename --after' to record the rename)
  [1]
  $ hg mv z2 z3
  z2: not copying - file is not managed
  abort: no files to copy
  [255]
  $ find $CACHEDIR -type f | sort
.. The following output line about files fetches is globed because it is
.. flaky, the core the test is checked when checking the cache dir, so
.. hopefully this flakyness is not hiding any actual bug.
  $ hg revert -a -r 1 || true
  ? files fetched over 1 fetches - (? misses, 0.00% hit ratio) over * (glob)
  abort: z2@109c3a557a73: not found in manifest! (?)
  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/11/f6ad8ec52a2984abaafd7c3b516503785c2072/ef95c5376f34698742fe34f315fd82136f8f68c0
  $TESTTMP/hgcache/master/39/5df8f7c51f007019cb30201c49e884b46b92fa/69a1b67522704ec122181c0890bd16e9d3e7516a
  $TESTTMP/hgcache/master/95/cb0bfd2977c761298d9624e4b4d4c72a39974a/076f5e2225b3ff0400b98c92aa6cdf403ee24cca
  $TESTTMP/hgcache/repos

# warning when we have excess remotefilelog fetching

  $ cat > repeated_fetch.py << EOF
  > import binascii
  > from mercurial import extensions, registrar
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > @command(b'repeated-fetch', [], b'', inferrepo=True)
  > def repeated_fetch(ui, repo, *args, **opts):
  >     for i in range(20):
  >         try:
  >             hexid = (b'%02x' % (i + 1)) * 20
  >             repo.fileservice.prefetch([(b'somefile.txt', hexid)])
  >         except Exception:
  >             pass
  > EOF

We should only output to the user once. We're ignoring most of the output
because we're not actually fetching anything real here, all the hashes are
bogus, so it's just going to be errors and a final summary of all the misses.
  $ hg --config extensions.repeated_fetch=repeated_fetch.py \
  >    --config remotefilelog.fetchwarning="fetch warning!" \
  >    --config extensions.blackbox= \
  >    repeated-fetch 2>&1 | grep 'fetch warning'
  fetch warning!

We should output to blackbox three times, with a stack trace on each (though
that isn't tested here).
  $ grep 'excess remotefilelog fetching' .hg/blackbox.log
  .* excess remotefilelog fetching: (re)
  .* excess remotefilelog fetching: (re)
  .* excess remotefilelog fetching: (re)