view tests/test-rebase-base-flag.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 the "--base" flag of the rebase command. (Tests unrelated to the "--base"
flag should probably live in somewhere else)

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > drawdag=$TESTDIR/drawdag.py
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} {desc}"
  > EOF

  $ rebasewithdag() {
  >   N=`"$PYTHON" -c "print($N+1)"`
  >   hg init repo$N && cd repo$N
  >   hg debugdrawdag
  >   hg rebase "$@" > _rebasetmp
  >   r=$?
  >   grep -v 'saved backup bundle' _rebasetmp
  >   [ $r -eq 0 ] && hg tglog
  >   cd ..
  >   return $r
  > }

Single branching point, without merge:

  $ rebasewithdag -b D -d Z <<'EOS'
  >     D E
  >     |/
  > Z B C   # C: branching point, E should be picked
  >  \|/    # B should not be picked
  >   A
  >   |
  >   R
  > EOS
  rebasing 3:d6003a550c2c "C" (C)
  rebasing 5:4526cf523425 "D" (D)
  rebasing 6:b296604d9846 "E" (E tip)
  o  6: 4870f5e7df37 E
  |
  | o  5: dc999528138a D
  |/
  o  4: 6b3e11729672 C
  |
  o  3: 57e70bad1ea3 Z
  |
  | o  2: c1e6b162678d B
  |/
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Multiple branching points caused by selecting a single merge changeset:

  $ rebasewithdag -b E -d Z <<'EOS'
  >     E
  >    /|
  >   B C D  # B, C: multiple branching points
  >   | |/   # D should not be picked
  > Z | /
  >  \|/
  >   A
  >   |
  >   R
  > EOS
  rebasing 2:c1e6b162678d "B" (B)
  rebasing 3:d6003a550c2c "C" (C)
  rebasing 6:54c8f00cb91c "E" (E tip)
  o    6: 00598421b616 E
  |\
  | o  5: 6b3e11729672 C
  | |
  o |  4: 85260910e847 B
  |/
  o  3: 57e70bad1ea3 Z
  |
  | o  2: 8924700906fe D
  |/
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Rebase should not extend the "--base" revset using "descendants":

  $ rebasewithdag -b B -d Z <<'EOS'
  >     E
  >    /|
  > Z B C  # descendants(B) = B+E. With E, C will be included incorrectly
  >  \|/
  >   A
  >   |
  >   R
  > EOS
  rebasing 2:c1e6b162678d "B" (B)
  rebasing 5:54c8f00cb91c "E" (E tip)
  o    5: e583bf3ff54c E
  |\
  | o  4: 85260910e847 B
  | |
  | o  3: 57e70bad1ea3 Z
  | |
  o |  2: d6003a550c2c C
  |/
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Rebase should not simplify the "--base" revset using "roots":

  $ rebasewithdag -b B+E -d Z <<'EOS'
  >     E
  >    /|
  > Z B C  # roots(B+E) = B. Without E, C will be missed incorrectly
  >  \|/
  >   A
  >   |
  >   R
  > EOS
  rebasing 2:c1e6b162678d "B" (B)
  rebasing 3:d6003a550c2c "C" (C)
  rebasing 5:54c8f00cb91c "E" (E tip)
  o    5: 00598421b616 E
  |\
  | o  4: 6b3e11729672 C
  | |
  o |  3: 85260910e847 B
  |/
  o  2: 57e70bad1ea3 Z
  |
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
The destination is one of the two branching points of a merge:

  $ rebasewithdag -b F -d Z <<'EOS'
  >     F
  >    / \
  >   E   D
  >  /   /
  > Z   C
  >  \ /
  >   B
  >   |
  >   A
  > EOS
  nothing to rebase
  [1]

Multiple branching points caused by multiple bases (issue5420):

  $ rebasewithdag -b E1+E2+C2+B1 -d Z <<'EOS'
  >   Z    E2
  >   |   /
  >   F E1 C2
  >   |/  /
  >   E C1 B2
  >   |/  /
  >   C B1
  >   |/
  >   B
  >   |
  >   A
  >   |
  >   R
  > EOS
  rebasing 3:a113dbaa660a "B1" (B1)
  rebasing 5:06ce7b1cc8c2 "B2" (B2)
  rebasing 6:0ac98cce32d3 "C1" (C1)
  rebasing 8:781512f5e33d "C2" (C2)
  rebasing 9:428d8c18f641 "E1" (E1)
  rebasing 11:e1bf82f6b6df "E2" (E2)
  o  12: e4a37b6fdbd2 E2
  |
  o  11: 9675bea983df E1
  |
  | o  10: 4faf5d4c80dc C2
  | |
  | o  9: d4799b1ad57d C1
  |/
  | o  8: 772732dc64d6 B2
  | |
  | o  7: ad3ac528a49f B1
  |/
  o  6: 2cbdfca6b9d5 Z
  |
  o  5: fcdb3293ec13 F
  |
  o  4: a4652bb8ac54 E
  |
  o  3: bd5548558fcf C
  |
  o  2: c1e6b162678d B
  |
  o  1: 21a6c4502885 A
  |
  o  0: b41ce7760717 R
  
Multiple branching points with multiple merges:

  $ rebasewithdag -b G+P -d Z <<'EOS'
  > G   H   P
  > |\ /|   |\
  > F E D   M N
  >  \|/|  /| |\
  > Z C B I J K L
  >  \|/  |/  |/
  >   A   A   A
  > EOS
  rebasing 2:dc0947a82db8 "C" (C)
  rebasing 8:4e4f9194f9f1 "D" (D)
  rebasing 9:03ca77807e91 "E" (E)
  rebasing 10:afc707c82df0 "F" (F)
  rebasing 13:690dfff91e9e "G" (G)
  rebasing 14:2893b886bb10 "H" (H)
  rebasing 3:08ebfeb61bac "I" (I)
  rebasing 4:a0a5005cec67 "J" (J)
  rebasing 5:83780307a7e8 "K" (K)
  rebasing 6:e131637a1cb6 "L" (L)
  rebasing 11:d1f6d0c3c7e4 "M" (M)
  rebasing 12:7aaec6f81888 "N" (N)
  rebasing 15:325bc8f1760d "P" (P tip)
  o    15: 6ef6a0ea3b18 P
  |\
  | o    14: 20ba3610a7e5 N
  | |\
  o \ \    13: cd4f6c06d2ab M
  |\ \ \
  | | | o  12: bca872041455 L
  | | | |
  | | o |  11: 7bbb6c8a6ad7 K
  | | |/
  | o /  10: de0cbffe893e J
  | |/
  o /  9: 0e710f176a88 I
  |/
  | o    8: 52507bab39ca H
  | |\
  | | | o  7: bb5fe4652f0d G
  | | |/|
  | | | o  6: f4ad4b31daf4 F
  | | | |
  | | o |  5: b168f85f2e78 E
  | | |/
  | o |  4: 8d09fcdb5594 D
  | |\|
  +---o  3: ab70b4c5a9c9 C
  | |
  o |  2: 262e37e34f63 Z
  | |
  | o  1: 112478962961 B
  |/
  o  0: 426bada5c675 A
  
Slightly more complex merge case (mentioned in https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-November/091074.html):

  $ rebasewithdag -b A3+B3 -d Z <<'EOF'
  > Z     C1    A3     B3
  > |    /     / \    / \
  > M3 C0     A1  A2 B1  B2
  > | /       |   |  |   |
  > M2        M1  C1 C1  M3
  > |
  > M1
  > |
  > M0
  > EOF
  rebasing 4:8817fae53c94 "C0" (C0)
  rebasing 6:06ca5dfe3b5b "B2" (B2)
  rebasing 7:73508237b032 "C1" (C1)
  rebasing 9:fdb955e2faed "A2" (A2)
  rebasing 11:4e449bd1a643 "A3" (A3)
  rebasing 10:0a33b0519128 "B1" (B1)
  rebasing 12:209327807c3a "B3" (B3 tip)
  o    12: ceb984566332 B3
  |\
  | o  11: 19d93caac497 B1
  | |
  | | o    10: 058e73d3916b A3
  | | |\
  | +---o  9: 0ba13ad72234 A2
  | | |
  | o |  8: c122c2af10c6 C1
  | | |
  o | |  7: 74275896650e B2
  | | |
  | o |  6: 455ba9bd3ea2 C0
  |/ /
  o |  5: b3d7d2fda53b Z
  | |
  o |  4: 182ab6383dd7 M3
  | |
  o |  3: 6c3f73563d5f M2
  | |
  | o  2: 88c860fffcc2 A1
  |/
  o  1: bc852baa85dd M1
  |
  o  0: dbdfc5c9bcd5 M0
  
Disconnected graph:

  $ rebasewithdag -b B -d Z <<'EOS'
  >   B
  >   |
  > Z A
  > EOS
  nothing to rebase from 112478962961 to 48b9aae0607f
  [1]

Multiple roots. Roots are ancestors of dest:

  $ rebasewithdag -b B+D -d Z <<'EOF'
  > D Z B
  >  \|\|
  >   C A
  > EOF
  rebasing 2:112478962961 "B" (B)
  rebasing 3:b70f76719894 "D" (D)
  o  4: 511efad7bf13 D
  |
  | o  3: 25c4e279af62 B
  |/
  o    2: 3a49f54d7bb1 Z
  |\
  | o  1: 96cc3511f894 C
  |
  o  0: 426bada5c675 A
  
Multiple roots. One root is not an ancestor of dest:

  $ rebasewithdag -b B+D -d Z <<'EOF'
  > Z B D
  >  \|\|
  >   A C
  > EOF
  nothing to rebase from f675d5a1c6a4+b70f76719894 to 262e37e34f63
  [1]

Multiple roots. One root is not an ancestor of dest. Select using a merge:

  $ rebasewithdag -b E -d Z <<'EOF'
  >   E
  >   |\
  > Z B D
  >  \|\|
  >   A C
  > EOF
  rebasing 2:f675d5a1c6a4 "B" (B)
  rebasing 5:f68696fe6af8 "E" (E tip)
  o    5: f6e6f5081554 E
  |\
  | o    4: 30cabcba27be B
  | |\
  | | o  3: 262e37e34f63 Z
  | | |
  o | |  2: b70f76719894 D
  |/ /
  o /  1: 96cc3511f894 C
   /
  o  0: 426bada5c675 A
  
Multiple roots. Two children share two parents while dest has only one parent:

  $ rebasewithdag -b B+D -d Z <<'EOF'
  > Z B D
  >  \|\|\
  >   A C A
  > EOF
  rebasing 2:f675d5a1c6a4 "B" (B)
  rebasing 3:c2a779e13b56 "D" (D)
  o    4: 5eecd056b5f8 D
  |\
  +---o  3: 30cabcba27be B
  | |/
  | o  2: 262e37e34f63 Z
  | |
  o |  1: 96cc3511f894 C
   /
  o  0: 426bada5c675 A