[Bug 1781169] Re: apt frontend locking

[Brian Murray]

Hello Julian, or anyone else affected,

Accepted apt into xenial-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/apt/1.2.29 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-xenial to verification-done-xenial. If it does not
fix the bug for you, please add a comment stating that, and change the
tag to verification-failed-xenial. In either case, without details of
your testing we will not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Tags removed: verification-failed verification-failed-xenial
** Tags added: verification-needed verification-needed-xenial

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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 Committed
Status in apt source package in Bionic:
  Fix Committed

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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