hg: obtain lock when creating share from pooled repo (issue5104)
There are race conditions between clients performing a shared clone
to pooled storage:
1) Clients race to create the new shared repo in the pool directory
2) 1 client is seeding the repo in the pool directory and another goes
to share it before it is fully cloned
We prevent these race conditions by obtaining a lock in the pool
directory that is derived from the name of the repo we will be
accessing.
To test this, a simple generic "lockdelay" extension has been added.
The extension inserts an optional, configurable delay before or after
lock acquisition. In the test, we delay 2 seconds after lock acquisition
in the first process and 1 second before lock acquisition in the 2nd
process. This means the first process has 1s to obtain the lock. There
is a race condition here. If we encounter it in the wild, we could
change the dummy extension to wait on the lock file to appear instead
of relying on timing. But that's more complicated. Let's see what
happens first.
#
# tcsh completion for Mercurial
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# Copyright (C) 2005 TK Soh.
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complete hg \
'n/--cwd/d/' 'n/-R/d/' 'n/--repository/d/' \
'C/-/( -R --repository \
--cwd \
-y --noninteractive \
-q --quiet \
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--config \
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--encoding \
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--traceback \
--time \
--profile \
--version \
-h --help)/' \
'p/1/(add addremove annotate blame archive \
backout bisect bookmarks branch branches \
bundle cat clone commit ci \
copy cp debugancestor debugbuilddag debugcheckstate \
debugcommands debugcomplete debugdag debugdata debugdate \
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forget grep heads help identify \
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merge outgoing out parents paths \
pull push recover remove rm \
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rollback root serve showconfig debugconfig \
status st summary sum tag \
tags tip unbundle update up \
checkout co verify version)/'