view tests/test-directaccess.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)

Tests for access level on hidden commits by various commands on based of their
type.

Setting the required config to start this

  $ cat >> $HGRCPATH <<EOF
  > [experimental]
  > evolution=createmarkers, allowunstable
  > directaccess=True
  > directaccess.revnums=True
  > [extensions]
  > amend =
  > EOF

  $ hg init repo
  $ cd repo
  $ for ch in a b c; do touch $ch; echo "foo" >> $ch; hg ci -Aqm "Added "$ch; done

  $ hg log -G -T '{rev}:{node} {desc}' --hidden
  @  2:28ad74487de9599d00d81085be739c61fc340652 Added c
  |
  o  1:29becc82797a4bc11ec8880b58eaecd2ab3e7760 Added b
  |
  o  0:18d04c59bb5d2d4090ad9a5b59bd6274adb63add Added a
  
  $ echo "bar" >> c
  $ hg amend

  $ hg log -G -T '{rev}:{node} {desc}' --hidden
  @  3:2443a0e664694756d8b435d06b6ad84f941b6fc0 Added c
  |
  | x  2:28ad74487de9599d00d81085be739c61fc340652 Added c
  |/
  o  1:29becc82797a4bc11ec8880b58eaecd2ab3e7760 Added b
  |
  o  0:18d04c59bb5d2d4090ad9a5b59bd6274adb63add Added a
  
Testing read only commands on the hidden revision

Testing with rev number

  $ hg exp 2 --config experimental.directaccess.revnums=False
  abort: hidden revision '2' was rewritten as: 2443a0e66469!
  (use --hidden to access hidden revisions)
  [255]

  $ hg exp 2
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 28ad74487de9599d00d81085be739c61fc340652
  # Parent  29becc82797a4bc11ec8880b58eaecd2ab3e7760
  Added c
  
  diff -r 29becc82797a -r 28ad74487de9 c
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/c	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

  $ hg log -r 2
  changeset:   2:28ad74487de9
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  obsolete:    rewritten using amend as 3:2443a0e66469
  summary:     Added c
  
  $ hg identify -r 2
  28ad74487de9

  $ hg status --change 2
  A c

  $ hg status --change 2 --config experimental.directaccess.revnums=False
  abort: hidden revision '2' was rewritten as: 2443a0e66469!
  (use --hidden to access hidden revisions)
  [255]

  $ hg diff -c 2
  diff -r 29becc82797a -r 28ad74487de9 c
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/c	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

Testing with hash

`hg export`

  $ hg exp 28ad74
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 28ad74487de9599d00d81085be739c61fc340652
  # Parent  29becc82797a4bc11ec8880b58eaecd2ab3e7760
  Added c
  
  diff -r 29becc82797a -r 28ad74487de9 c
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/c	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

`hg log`

  $ hg log -r 28ad74
  changeset:   2:28ad74487de9
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  obsolete:    rewritten using amend as 3:2443a0e66469
  summary:     Added c
  
`hg cat`

  $ hg cat -r 28ad74 c
  foo

`hg diff`

  $ hg diff -c 28ad74
  diff -r 29becc82797a -r 28ad74487de9 c
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/c	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

`hg files`

  $ hg files -r 28ad74
  a
  b
  c

`hg identify`

  $ hg identify -r 28ad74
  28ad74487de9

`hg annotate`

  $ hg annotate -r 28ad74 a
  0: foo

`hg status`

  $ hg status --change 28ad74
  A c

`hg archive`

This should not throw error
  $ hg archive -r 28ad74 foo

`hg update`

  $ hg up 28ad74
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to hidden changeset 28ad74487de9
  (hidden revision '28ad74487de9' was rewritten as: 2443a0e66469)

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

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

`hg revert`

  $ hg revert -r 28ad74 --all
  reverting c

  $ hg diff
  diff -r 2443a0e66469 c
  --- a/c	Thu Jan 01 00:00:00 1970 +0000
  +++ b/c	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,2 +1,1 @@
   foo
  -bar

Test special hash/rev

  $ hg log -qr 'null:wdir() & 000000000000'
  -1:000000000000
  $ hg log -qr 'null:wdir() & ffffffffffff'
  2147483647:ffffffffffff
  $ hg log -qr 'null:wdir() & rev(-1)'
  -1:000000000000
  $ hg log -qr 'null:wdir() & rev(2147483647)'
  2147483647:ffffffffffff
  $ hg log -qr 'null:wdir() & 2147483647'
  2147483647:ffffffffffff

Commands with undefined intent should not work right now

  $ hg phase -r 28ad74
  abort: hidden revision '28ad74' was rewritten as: 2443a0e66469!
  (use --hidden to access hidden revisions)
  [255]

  $ hg phase -r 2
  abort: hidden revision '2' was rewritten as: 2443a0e66469!
  (use --hidden to access hidden revisions)
  [255]

Setting a bookmark will make that changeset unhidden, so this should come in end

  $ hg bookmarks -r 28ad74 book
  bookmarking hidden changeset 28ad74487de9
  (hidden revision '28ad74487de9' was rewritten as: 2443a0e66469)

  $ hg bookmarks
     book                      2:28ad74487de9