view tests/test-issue2137.t @ 32783:4483696dacee

profile: upgrade the "profile" context manager to a full class

So far we have been able to use a simple decorator for this. However using the
current context manager makes the scope of the profiling in dispatch
constrainted and the time frame to decide to enable profiling quite limited
(using "maybeprofile")

This is the first step toward the ability to enable the profiling from within
the profiling scope. eg::

  with maybeprofiling(ui) as profiler:
      ...
      bar.foo():
      ...
      if options['profile']:
          profiler.start()
      ...
      fooz()
      ...

My target usecase is adding support for  "--profile" to alias definitions with
effect.  These are to be used with "profiling.output=blackbox" to gather data
about operation that get slow from time to time (eg: pull being minutes instead
of seconds from time to time).

Of course, in such case, the scope of the profiling would be smaller since
profiler would be started after running extensions 'reposetup' (and other
potentially costly logic), but these are not relevant for my target usecase
(multiple second commits, multiple tens of seconds pull).

Currently adding '--profile' to a command through alias requires to re-spin a
Mercurial binary (using "!$HG" in alias), which as a significant performance
impact, especially in context where startup performance is being worked on...

An alternative approach would be to stop using the context manager in dispatch
and move back to a try/finally setup.

https://bz.mercurial-scm.org/2137

Setup:

create a little extension that has 3 side-effects:
1) ensure changelog data is not inlined
2) make revlog to use lazyparser
3) test that repo.lookup() works
1 and 2 are preconditions for the bug; 3 is the bug.

  $ cat > commitwrapper.py <<EOF
  > from mercurial import extensions, node, revlog
  > 
  > def reposetup(ui, repo):
  >     class wraprepo(repo.__class__):
  >         def commit(self, *args, **kwargs):
  >             result = super(wraprepo, self).commit(*args, **kwargs)
  >             tip1 = node.short(repo.changelog.tip())
  >             tip2 = node.short(repo.lookup(tip1))
  >             assert tip1 == tip2
  >             ui.write('new tip: %s\n' % tip1)
  >             return result
  >     repo.__class__ = wraprepo
  > 
  > def extsetup(ui):
  >     revlog._maxinline = 8             # split out 00changelog.d early
  >     revlog._prereadsize = 8           # use revlog.lazyparser
  > EOF

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > commitwrapper = `pwd`/commitwrapper.py
  > EOF

  $ hg init repo1
  $ cd repo1
  $ echo a > a
  $ hg commit -A -m'add a with a long commit message to make the changelog a bit bigger'
  adding a
  new tip: 553596fad57b

Test that new changesets are visible to repo.lookup():

  $ echo a >> a
  $ hg commit -m'one more commit to demonstrate the bug'
  new tip: 799ae3599e0e

  $ hg tip
  changeset:   1:799ae3599e0e
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     one more commit to demonstrate the bug
  

  $ cd ..