** Description changed:

  [Impact]
  apt acquires /var/lib/dpkg/lock but has to release it while running dpkg, 
offering a short window for other clients to acquire the lock. This implements 
/var/lib/dpkg/lock-frontend which will be acquired earlier and not released by 
apt for dpkg to run.
  
  dpkg will try to acquire the frontend lock as well, unless told not to
  do so via an environment variable, which apt does; hence concurrent runs
  of dpkg without other locking can't happen.
  
  [Test case]
  Run strace apt install $something and check that lock-frontend is acquired at 
the beginning and not released until the end.
  
  [Regression potential]
  Frontend locking failures are in English, as there are no translations yet. 
More locks also mean more potential for locking to go wrong across programs, 
but since we don't have any waiting locks we at least won't deadlock.
+ 
+ [Other info]
+ This is part of a wider series of SRUs for frontend locking
+ 
+ - dpkg (bug 1796081)
+ - apt (bug 1781169)
+ - python-apt (bug 1795407)
+ - packagekit (bug 1795614)
+ - unattended-upgrades
+ - aptdaemon (no bug filed yet)
+ 
+ Further details about frontend locking can be found in
+ https://lists.debian.org/debian-dpkg/2017/01/msg00044.html

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https://bugs.launchpad.net/bugs/1781169

Title:
  apt frontend locking

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