[Bug 1652641] Re: crash in indexer.py, AttributeError: 'NoneType' object has no attribute 'unlink'

[Carlo Vanini]

** Description changed:

- While installing Muon the following exception was raised.
+ [Impact]
  
- Ophalen:1 http://nl.archive.ubuntu.com/ubuntu zesty/universe amd64 muon amd64
- 4:5.6.0-0ubuntu2 [332 kB]
- Ophalen:2 http://nl.archive.ubuntu.com/ubuntu zesty/universe amd64 muon-updater
- all 4:5.8.4-0ubuntu1 [3268 B]
- 335 kB opgehaald in 0s (861 kB/s)
- Voorheen niet geselecteerd pakket muon wordt geselecteerd.
- (Database wordt ingelezen ... 238429 bestanden en mappen momenteel
- geïnstalleerd.)
- Uitpakken van .../0-muon_4%3a5.6.0-0ubuntu2_amd64.deb wordt voorbereid...
- Bezig met uitpakken van muon (4:5.6.0-0ubuntu2) ...
- Voorheen niet geselecteerd pakket muon-updater wordt geselecteerd.
- Uitpakken van .../1-muon-updater_4%3a5.8.4-0ubuntu1_all.deb wordt voorbereid...
- Bezig met uitpakken van muon-updater (4:5.8.4-0ubuntu1) ...
- Bezig met afhandelen van triggers voor mime-support (3.60ubuntu1) ...
- Instellen van muon-updater (4:5.8.4-0ubuntu1) ...
- Instellen van muon (4:5.6.0-0ubuntu2) ...
+ When the apt-xapian-index is already up to date, and under certain
+ conditions, update-apt-xapian-index throws an exception.
  
  The index /var/lib/apt-xapian-index is up to date
  Exception ignored in: <bound method ServerProgress.__del__ of
  <axi.indexer.ServerProgress object at 0x7f04a5ae4c18>>
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/axi/indexer.py", line 306, in __del__
  AttributeError: 'NoneType' object has no attribute 'unlink'
  
+ This happens more frequently when it is run with nice and ionice, which
+ is the case in the cron.weekly/apt-xapian-index cron job.
  
- Bezig met afhandelen van triggers voor hicolor-icon-theme (0.15-1) ...
- done..
+ This is not severe, since the exception is thrown on exit, and depends
+ on the way python3 cleans up the environment. Anyway, this leaves a
+ socket file behind, and creates noise in cron logs (see comment #2).
  
+ The patch keeps a reference to the os.unlink function in the
+ ServerProgress instance, such that it has the same lifespan.
  
- This bug was originally reported against Muon as https://bugs.kde.org/show_bug.cgi?id=374084 but the crash actually happens in a-x-i.
+ [Test Case]
+ 
+ * `sudo nice -n 19 ionice -c 3 update-apt-xapian-index --quiet`
+ * may need to run 4 times or more
+ * no exception is thrown
+ 
+ [Regression Potential]
+ 
+ * If the os module is unloaded anyway and self.os_unlink becomes
+ unreachable, we get the same exception again.
+ 
+ [Other Info]
+ 
+ * There is probably a more "pythonic" way to fix this. For instance,
+ avoiding __del__. That requires a larger change.

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https://bugs.launchpad.net/bugs/1652641

Title:
  crash in indexer.py, AttributeError: 'NoneType' object has no
  attribute 'unlink'

Status in apt-xapian-index package in Ubuntu:
  Confirmed

Bug description:
  [Impact]

  When the apt-xapian-index is already up to date, and under certain
  conditions, update-apt-xapian-index throws an exception.

  The index /var/lib/apt-xapian-index is up to date
  Exception ignored in: <bound method ServerProgress.__del__ of
  <axi.indexer.ServerProgress object at 0x7f04a5ae4c18>>
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/axi/indexer.py", line 306, in __del__
  AttributeError: 'NoneType' object has no attribute 'unlink'

  This happens more frequently when it is run with nice and ionice,
  which is the case in the cron.weekly/apt-xapian-index cron job.

  This is not severe, since the exception is thrown on exit, and depends
  on the way python3 cleans up the environment. Anyway, this leaves a
  socket file behind, and creates noise in cron logs (see comment #2).

  The patch keeps a reference to the os.unlink function in the
  ServerProgress instance, such that it has the same lifespan.

  [Test Case]

  * `sudo nice -n 19 ionice -c 3 update-apt-xapian-index --quiet`
  * may need to run 4 times or more
  * no exception is thrown

  [Regression Potential]

  * If the os module is unloaded anyway and self.os_unlink becomes
  unreachable, we get the same exception again.

  [Other Info]

  * There is probably a more "pythonic" way to fix this. For instance,
  avoiding __del__. That requires a larger change.

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