plainbox crashes while attempting to create session.next

[Zygmunt Krynicki]

I just looked up this crash from a comment in another bug:

2014-11-26 14:27:23 [pid:2392, thread:MainThread, reltime:13904ms] CRITICAL plainbox.crashes: Executable 'checkbox-launcher' invoked with Namespace(command=<checkbox_ng.commands.launcher.LauncherCommand object at 0x26cf650>, debug_console=False, debug_interrupt=False, dont_suppress_output=False, dry_run=False, launcher='/usr/bin/checkbox-cli', log_level=None, non_interactive=False, pdb=False, trace=[]) has crashed
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/plainbox/impl/clitools.py", line 529, in dispatch_and_catch_exceptions
    return self.dispatch_command(ns)
  File "/usr/lib/python3/dist-packages/plainbox/impl/clitools.py", line 525, in dispatch_command
    return ns.command.invoked(ns)
  File "/usr/lib/python3/dist-packages/checkbox_ng/commands/launcher.py", line 84, in invoked
    launcher).run()
  File "/usr/lib/python3/dist-packages/checkbox_ng/commands/newcli.py", line 113, in run
    return self.do_normal_sequence()
  File "/usr/lib/python3/dist-packages/checkbox_ng/commands/newcli.py", line 165, in do_normal_sequence
    self.run_all_selected_jobs()
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/inv_run.py", line 718, in run_all_selected_jobs
    self.run_single_job(job)
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/inv_run.py", line 722, in run_single_job
    self.run_single_job_with_ui(job, self.get_ui_for_job(job))
  File "/usr/lib/python3/dist-packages/plainbox/impl/commands/inv_run.py", line 739, in run_single_job_with_ui
    self.manager.checkpoint()
  File "/usr/lib/python3/dist-packages/plainbox/impl/session/manager.py", line 350, in checkpoint
    self.storage.save_checkpoint(data)
  File "/usr/lib/python3/dist-packages/plainbox/impl/session/storage.py", line 371, in save_checkpoint
    return self._save_checkpoint_unix_py32(data)
  File "/usr/lib/python3/dist-packages/plainbox/impl/session/storage.py", line 640, in _save_checkpoint_unix_py32
    os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o644)
OSError: [Errno 17] File exists: '/home/u/.cache/plainbox/sessions/pbox-54yfy1.session/session.next'

The full tarball is in
https://bugs.launchpad.net/plainbox/+bug/1393291/comments/8

[Zygmunt Krynicki (zyga)]

I'm demoting this to high because:
- this issue doesn't happen often
- it can always happen in principle (we need to handle this case, whatever that means)
- we have no idea why it happened (it _may_ happen though why is a big question)
- might (need to check) be possible to hit this if we open the same session twice somehow

[Zygmunt Krynicki (zyga)]

Somewhat related https://code.launchpad.net/~zkrynicki/checkbox/storage-fixes/+merge/243883

[Zygmunt Krynicki (zyga)]

09:02 <@spineau> zyga: did we merge a specific patch for https://bugs.launchpad.net/plainbox/+bug/1396532? I see a reference to https://code.launchpad.net/~zkrynicki/checkbox/storage-fixes/+merge/243883
09:02 <@spineau> zyga: it's all about session.next
09:03 <@spineau> zyga: I'll probably demote again the priority of this bug (High so far)
09:04 <@zyga> spineau: we did merge something that could cause that to happen
09:04 <@zyga> spineau: the error recovery path in session storage was wrong
09:05 <@spineau> zyga: does it mean that this bug can be closed?
09:05 <@zyga> spineau: the bug can be demoted low and left open as there's no recovery path to when that erorr (if ever) happens, we should think of some UI for that
09:05 <@zyga> spineau: I think that I'd leave it open as it can still (in theory) happen, I need to look at locking code in the storage class to be sure
09:05 <@spineau> zyga: ok to keep it open. Thanks
09:05 <@zyga> spineau: but let's demote it to low