view tests/test-issue3084.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)

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

Create the repository outside $HOME since largefiles write to
$HOME/.cache/largefiles.

  $ hg init test
  $ cd test
  $ echo "root" > root
  $ hg add root
  $ hg commit -m "Root commit" --config extensions.largefiles=!

Ensure that .hg/largefiles isn't created before largefiles are added
#if unix-permissions
  $ chmod 555 .hg
#endif
  $ hg status
#if unix-permissions
  $ chmod 755 .hg
#endif

  $ test -f .hg/largefiles
  [1]

  $ echo "large" > foo
  $ hg add --large foo
  $ hg commit -m "Add foo as a largefile"

  $ hg update -r 0
  getting changed largefiles
  0 largefiles updated, 1 removed
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo "normal" > foo
  $ hg add foo
  $ hg commit -m "Add foo as normal file"
  created new head

Normal file in the working copy, keeping the normal version:

  $ echo "n" | hg merge --config ui.interactive=Yes
  remote turned local normal file foo into a largefile
  use (l)argefile or keep (n)ormal file? n
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg status
  $ cat foo
  normal

Normal file in the working copy, keeping the largefile version:

  $ hg update -q -C
  $ echo "l" | hg merge --config ui.interactive=Yes
  remote turned local normal file foo into a largefile
  use (l)argefile or keep (n)ormal file? l
  getting changed largefiles
  1 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg status
  M foo

  $ hg diff --nodates
  diff -r fa129ab6b5a7 .hglf/foo
  --- /dev/null
  +++ b/.hglf/foo
  @@ -0,0 +1,1 @@
  +7f7097b041ccf68cc5561e9600da4655d21c6d18
  diff -r fa129ab6b5a7 foo
  --- a/foo
  +++ /dev/null
  @@ -1,1 +0,0 @@
  -normal

  $ cat foo
  large

Largefile in the working copy, keeping the normal version:

  $ hg update -q -C -r 1
  $ echo "n" | hg merge --config ui.interactive=Yes
  remote turned local largefile foo into a normal file
  keep (l)argefile or use (n)ormal file? n
  getting changed largefiles
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg status
  M foo

  $ hg diff --nodates
  diff -r ff521236428a .hglf/foo
  --- a/.hglf/foo
  +++ /dev/null
  @@ -1,1 +0,0 @@
  -7f7097b041ccf68cc5561e9600da4655d21c6d18
  diff -r ff521236428a foo
  --- /dev/null
  +++ b/foo
  @@ -0,0 +1,1 @@
  +normal

  $ cat foo
  normal

Largefile in the working copy, keeping the largefile version:

  $ hg update -q -C -r 1
  $ echo "l" | hg merge --config ui.interactive=Yes
  remote turned local largefile foo into a normal file
  keep (l)argefile or use (n)ormal file? l
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg status

  $ cat foo
  large

Whatever ... commit something so we can invoke merge when updating

  $ hg commit -m '3: Merge'

Updating from largefile to normal - no reason to prompt

  $ hg up -r 2
  getting changed largefiles
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ cat foo
  normal

(the update above used to leave the working dir in a very weird state - clean it
  $ hg up -qr null
  $ hg up -qr 2
)

Updating from normal to largefile - no reason to prompt

  $ hg up -r 3
  getting changed largefiles
  1 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ cat foo
  large

  $ cd ..


Systematic testing of merges involving largefiles:

Ancestor: normal  Parent: normal-id  Parent: large   result: large
Ancestor: normal  Parent: normal2    Parent: large   result: ?
Ancestor: large   Parent: large-id   Parent: normal  result: normal
Ancestor: large   Parent: large2     Parent: normal  result: ?

All cases should try merging both ways.

Prepare test repo:

  $ hg init merges
  $ cd merges

prepare cases with "normal" ancestor:

  $ hg up -qr null
  $ echo normal > f
  $ hg ci -Aqm "normal-ancestor"
  $ hg tag -l "normal-ancestor"
  $ touch f2
  $ hg ci -Aqm "normal-id"
  $ hg tag -l "normal-id"
  $ echo normal2 > f
  $ hg ci -m "normal2"
  $ hg tag -l "normal2"
  $ echo normal > f
  $ hg ci -Aqm "normal-same"
  $ hg tag -l "normal-same"
  $ hg up -qr "normal-ancestor"
  $ hg rm f
  $ echo large > f
  $ hg add --large f
  $ hg ci -qm "large"
  $ hg tag -l "large"

prepare cases with "large" ancestor:

  $ hg up -qr null
  $ echo large > f
  $ hg add --large f
  $ hg ci -qm "large-ancestor"
  $ hg tag -l "large-ancestor"
  $ touch f2
  $ hg ci -Aqm "large-id"
  $ hg tag -l "large-id"
  $ echo large2 > f
  $ hg ci -m "large2"
  $ hg tag -l "large2"
  $ echo large > f
  $ hg ci -Aqm "large-same"
  $ hg tag -l "large-same"
  $ hg up -qr "large-ancestor"
  $ hg rm f
  $ echo normal > f
  $ hg ci -qAm "normal"
  $ hg tag -l "normal"

  $ hg log -GT '{tags}'
  @  normal tip
  |
  | o  large-same
  | |
  | o  large2
  | |
  | o  large-id
  |/
  o  large-ancestor
  
  o  large
  |
  | o  normal-same
  | |
  | o  normal2
  | |
  | o  normal-id
  |/
  o  normal-ancestor
  


Ancestor: normal  Parent: normal-id  Parent: large   result: large

  $ hg up -Cqr normal-id
  $ hg merge -r large
  getting changed largefiles
  1 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large

swap

  $ hg up -Cqr large
  $ hg merge -r normal-id
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large

Ancestor: normal  Parent: normal-same  Parent: large   result: large

  $ hg up -Cqr normal-same
  $ hg merge -r large
  getting changed largefiles
  1 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large

swap

  $ hg up -Cqr large
  $ hg merge -r normal-same
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large

Ancestor: normal  Parent: normal2  Parent: large   result: ?
(annoying extra prompt ... but it do not do any serious harm)

  $ hg up -Cqr normal2
  $ hg merge -r large
  remote turned local normal file f into a largefile
  use (l)argefile or keep (n)ormal file? l
  getting changed largefiles
  1 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large

  $ hg up -Cqr normal2
  $ echo n | hg merge -r large --config ui.interactive=Yes
  remote turned local normal file f into a largefile
  use (l)argefile or keep (n)ormal file? n
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal2

swap

  $ hg up -Cqr large
  $ hg merge -r normal2
  remote turned local largefile f into a normal file
  keep (l)argefile or use (n)ormal file? l
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large

  $ hg up -Cqr large
  $ echo n | hg merge -r normal2 --config ui.interactive=Yes
  remote turned local largefile f into a normal file
  keep (l)argefile or use (n)ormal file? n
  getting changed largefiles
  0 largefiles updated, 0 removed
  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal2

Ancestor: large   Parent: large-id   Parent: normal  result: normal

  $ hg up -Cqr large-id
  $ hg merge -r normal
  getting changed largefiles
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal

swap

  $ hg up -Cqr normal
  $ hg merge -r large-id
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal

Ancestor: large   Parent: large-same   Parent: normal  result: normal

  $ hg up -Cqr large-same
  $ hg merge -r normal
  getting changed largefiles
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal

swap

  $ hg up -Cqr normal
  $ hg merge -r large-same
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal

Ancestor: large   Parent: large2   Parent: normal  result: ?
(annoying extra prompt ... but it do not do any serious harm)

  $ hg up -Cqr large2
  $ hg merge -r normal
  remote turned local largefile f into a normal file
  keep (l)argefile or use (n)ormal file? l
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large2

  $ hg up -Cqr large2
  $ echo n | hg merge -r normal --config ui.interactive=Yes
  remote turned local largefile f into a normal file
  keep (l)argefile or use (n)ormal file? n
  getting changed largefiles
  0 largefiles updated, 0 removed
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal

swap

  $ hg up -Cqr normal
  $ hg merge -r large2
  remote turned local normal file f into a largefile
  use (l)argefile or keep (n)ormal file? l
  getting changed largefiles
  1 largefiles updated, 0 removed
  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  large2

  $ hg up -Cqr normal
  $ echo n | hg merge -r large2 --config ui.interactive=Yes
  remote turned local normal file f into a largefile
  use (l)argefile or keep (n)ormal file? n
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ cat f
  normal

  $ cd ..