tests/test-push-checkheads-superceed-A1.t

lock: block signal interrupt while making a lock file

On Windows where symlink isn't supported, util.makelock() could leave an empty
file if interrupted immediately after os.open(). This empty lock never dies
as it has no process id recorded.

    ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
    # an interrupt may occur here
    os.write(ld, info)
    os.close(ld)

This was a long-standing bug of TortoiseHg which runs a command-server and
kills it by CTRL_C_EVENT, reported by random Windows users.

https://bitbucket.org/tortoisehg/thg/issues/4873/#comment-43591129

At first, I tried to fix makelock() to clean up a stale lock file, which
turned out to be hard because any instructions may be interrupted by a
signal.

    ld = None
    try:
        # CALL_FUNCTION  # os.open(...)
        # an interrupt may occur here
        # STORE_FAST     # ld = ...
        ld = os.open(pathname, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
        os.write(ld, info)
        ...
        return True
    except:
        if ld:
            ...
            os.unlink(pathname)
        return False

So I decided to block signals by temporarily replacing the signal handlers
so makelcok() and held = 1 will never be interrupted.

Many thanks to Fernando Najera for investigating the issue.

====================================
Testing head checking code: Case A-1
====================================

Mercurial checks for the introduction of new heads on push. Evolution comes
into play to detect if existing branches on the server are being replaced by
some of the new one we push.

This case is part of a series of tests checking this behavior.

Category A: simple case involving a branch being superceeded by another.
TestCase 1: single-changeset branch

.. old-state:
..
.. * 1 changeset branch
..
.. new-state:
..
.. * 1 changeset branch succeeding to A
..
.. expected-result:
..
.. * push allowed
..
.. graph-summary:
..
..   A ø⇠◔ A'
..     |/
..     ●

  $ . $TESTDIR/testlib/push-checkheads-util.sh

Test setup
----------

  $ mkdir A1
  $ cd A1
  $ setuprepos
  creating basic server and client repo
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mkcommit A1
  created new head
  $ hg debugobsolete `getid "desc(A0)" ` `getid "desc(A1)"`
  obsoleted 1 changesets
  $ hg log -G --hidden
  @  f6082bc4ffef (draft): A1
  |
  | x  8aaa48160adc (draft): A0
  |/
  o  1e4be0697311 (public): root
  

Actual testing
--------------

  $ hg push
  pushing to $TESTTMP/A1/server
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  1 new obsolescence markers
  obsoleted 1 changesets

  $ cd ../..