view tests/test-convert-cvs-synthetic.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 cvs112 no-root

This feature requires use of builtin cvsps!

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "convert = " >> $HGRCPATH

create cvs repository with one project

  $ mkdir cvsrepo
  $ cd cvsrepo
  $ CVSROOT=`pwd`
  $ export CVSROOT
  $ CVS_OPTIONS=-f
  $ export CVS_OPTIONS
  $ cd ..
  $ rmdir cvsrepo
  $ cvscall()
  > {
  >     cvs -f "$@"
  > }

output of 'cvs ci' varies unpredictably, so just discard it

  $ cvsci()
  > {
  >     sleep 1
  >     cvs -f ci "$@" >/dev/null
  > }
  $ cvscall -d "$CVSROOT" init
  $ mkdir cvsrepo/proj
  $ cvscall -q co proj

create file1 on the trunk

  $ cd proj
  $ touch file1
  $ cvscall -Q add file1
  $ cvsci -m"add file1 on trunk" file1

create two branches

  $ cvscall -q tag -b v1_0
  T file1
  $ cvscall -q tag -b v1_1
  T file1

create file2 on branch v1_0

  $ cvscall -Q up -rv1_0
  $ touch file2
  $ cvscall -Q add file2
  $ cvsci -m"add file2" file2

create file3, file4 on branch v1_1

  $ cvscall -Q up -rv1_1
  $ touch file3
  $ touch file4
  $ cvscall -Q add file3 file4
  $ cvsci -m"add file3, file4 on branch v1_1" file3 file4

merge file2 from v1_0 to v1_1

  $ cvscall -Q up -jv1_0
  $ cvsci -m"MERGE from v1_0: add file2"
  cvs commit: Examining .

Step things up a notch: now we make the history really hairy, with
changes bouncing back and forth between trunk and v1_2 and merges
going both ways.  (I.e., try to model the real world.)
create branch v1_2

  $ cvscall -Q up -A
  $ cvscall -q tag -b v1_2
  T file1

create file5 on branch v1_2

  $ cvscall -Q up -rv1_2
  $ touch file5
  $ cvs -Q add file5
  $ cvsci -m"add file5 on v1_2"
  cvs commit: Examining .

create file6 on trunk post-v1_2

  $ cvscall -Q up -A
  $ touch file6
  $ cvscall -Q add file6
  $ cvsci -m"add file6 on trunk post-v1_2"
  cvs commit: Examining .

merge file5 from v1_2 to trunk

  $ cvscall -Q up -A
  $ cvscall -Q up -jv1_2 file5
  $ cvsci -m"MERGE from v1_2: add file5"
  cvs commit: Examining .

merge file6 from trunk to v1_2

  $ cvscall -Q up -rv1_2
  $ cvscall up -jHEAD file6
  U file6
  $ cvsci -m"MERGE from HEAD: add file6"
  cvs commit: Examining .

cvs rlog output

  $ cvscall -q rlog proj | egrep '^(RCS file|revision)'
  RCS file: $TESTTMP/cvsrepo/proj/file1,v
  revision 1.1
  RCS file: $TESTTMP/cvsrepo/proj/Attic/file2,v
  revision 1.1
  revision 1.1.4.2
  revision 1.1.4.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/Attic/file3,v
  revision 1.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/Attic/file4,v
  revision 1.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/file5,v
  revision 1.2
  revision 1.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/file6,v
  revision 1.1
  revision 1.1.2.2
  revision 1.1.2.1

convert to hg (#1)

  $ cd ..
  $ hg convert --datesort proj proj.hg
  initializing destination proj.hg repository
  connecting to $TESTTMP/cvsrepo
  scanning source...
  collecting CVS rlog
  15 log entries
  creating changesets
  9 changeset entries
  sorting...
  converting...
  8 add file1 on trunk
  7 add file2
  6 MERGE from v1_0: add file2
  5 file file3 was initially added on branch v1_1.
  4 add file3, file4 on branch v1_1
  3 add file5 on v1_2
  2 add file6 on trunk post-v1_2
  1 MERGE from HEAD: add file6
  0 MERGE from v1_2: add file5

hg log -G output (#1)

  $ hg -R proj.hg log -G --template "{rev} {desc}\n"
  o  8 MERGE from v1_2: add file5
  |
  | o  7 MERGE from HEAD: add file6
  | |
  o |  6 add file6 on trunk post-v1_2
  | |
  | o  5 add file5 on v1_2
  | |
  | | o  4 add file3, file4 on branch v1_1
  | | |
  o | |  3 file file3 was initially added on branch v1_1.
  |/ /
  | o  2 MERGE from v1_0: add file2
  |/
  | o  1 add file2
  |/
  o  0 add file1 on trunk
  

convert to hg (#2: with merge detection)

  $ hg convert \
  >   --config convert.cvsps.mergefrom='"^MERGE from (\S+):"' \
  >   --datesort \
  >   proj proj.hg2
  initializing destination proj.hg2 repository
  connecting to $TESTTMP/cvsrepo
  scanning source...
  collecting CVS rlog
  15 log entries
  creating changesets
  9 changeset entries
  sorting...
  converting...
  8 add file1 on trunk
  7 add file2
  6 MERGE from v1_0: add file2
  5 file file3 was initially added on branch v1_1.
  4 add file3, file4 on branch v1_1
  3 add file5 on v1_2
  2 add file6 on trunk post-v1_2
  1 MERGE from HEAD: add file6
  0 MERGE from v1_2: add file5

hg log -G output (#2)

  $ hg -R proj.hg2 log -G --template "{rev} {desc}\n"
  o  8 MERGE from v1_2: add file5
  |
  | o  7 MERGE from HEAD: add file6
  | |
  o |  6 add file6 on trunk post-v1_2
  | |
  | o  5 add file5 on v1_2
  | |
  | | o  4 add file3, file4 on branch v1_1
  | | |
  o | |  3 file file3 was initially added on branch v1_1.
  |/ /
  | o  2 MERGE from v1_0: add file2
  |/
  | o  1 add file2
  |/
  o  0 add file1 on trunk