[Bug 1781169] Update Released

[Łukasz Zemczak]

The verification of the Stable Release Update for apt has completed
successfully and the package has now been released to -updates.
Subsequently, the Ubuntu Stable Release Updates Team is being
unsubscribed and will not receive messages about this bug report.  In
the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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

Title:
  apt frontend locking

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Xenial:
  Fix Released
Status in apt source package in Bionic:
  Fix Released

Bug description:
  [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 (bug 1789637)
  - 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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