Corrupt an hg repo with two pulls.

create one repo with a long history

  $ hg init source1

  $ cd source1

  $ touch foo

  $ hg add foo

  $ for i in 1 2 3 4 5 6 7 8 9 10; do

  >     echo $i >> foo

  >     hg ci -m $i

  > done

  $ cd ..

create one repo with a shorter history

  $ hg clone -r 0 source1 source2

  adding changesets

  adding manifests

  adding file changes

  added 1 changesets with 1 changes to 1 files

  updating to branch default

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ cd source2

  $ echo a >> foo

  $ hg ci -m a

  $ cd ..

create a third repo to pull both other repos into it

  $ hg init corrupted

  $ cd corrupted

use a hook to make the second pull start while the first one is still running

  $ echo '[hooks]' >> .hg/hgrc

  $ echo 'prechangegroup = sleep 5' >> .hg/hgrc

start a pull...

... and start another pull before the first one has finished

  $ sleep 1

  $ hg pull ../source2 2>/dev/null

  pulling from ../source2

  searching for changes

  adding changesets

  adding manifests

  adding file changes

  added 1 changesets with 1 changes to 1 files (+1 heads)

  (run 'hg heads' to see heads, 'hg merge' to merge)

see the result

  $ wait

  $ hg verify

  checking changesets

  checking manifests

  crosschecking files in changesets and manifests

  checking files

  1 files, 11 changesets, 11 total revisions