Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
-+-
 Reporter:  Aymeric Augustin |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  master
 Severity:  Normal   |   Resolution:  fixed
 Keywords:  app-loading  | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham ):

 * status:  new => closed
 * resolution:   => fixed


Comment:

 In [changeset:"fba4f831bc75369c975a95c9b7774e9e89f8a2f9" fba4f83]:
 {{{
 #!CommitTicketReference repository=""
 revision="fba4f831bc75369c975a95c9b7774e9e89f8a2f9"
 Fixed #27176 -- Raised an exception for reentrant calls to
 apps.populate().

 Thanks to Aymeric Augustin, Harry Percival, and Tim Graham.
 }}}

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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
-+-
 Reporter:  Aymeric Augustin |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Core (Other) |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  app-loading  | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham):

 * stage:  Accepted => Ready for checkin


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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+
 Reporter:  Aymeric Augustin  |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Accepted
Has patch:  1 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+
Changes (by François Freitag):

 * needs_better_patch:  1 => 0


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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+
 Reporter:  Aymeric Augustin  |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Accepted
Has patch:  1 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  1
Easy pickings:  0 |UI/UX:  0
--+
Changes (by Tim Graham):

 * needs_better_patch:  0 => 1


--
Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+
 Reporter:  Aymeric Augustin  |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Accepted
Has patch:  1 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+
Changes (by François Freitag):

 * needs_better_patch:  1 => 0


--
Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+
 Reporter:  Aymeric Augustin  |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Accepted
Has patch:  1 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  1
Easy pickings:  0 |UI/UX:  0
--+
Changes (by Tim Graham):

 * needs_better_patch:  0 => 1


Comment:

 Comments for improvement are on the PR.

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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+
 Reporter:  Aymeric Augustin  |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Accepted
Has patch:  1 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+
Changes (by François Freitag):

 * has_patch:  0 => 1


Comment:

 PR: https://github.com/django/django/pull/7682

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Ticket URL: 
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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+
 Reporter:  aaugustin |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Accepted
Has patch:  0 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+
Changes (by timgraham):

 * stage:  Unreviewed => Accepted


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Re: [Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
--+--
 Reporter:  aaugustin |Owner:  nobody
 Type:  Bug   |   Status:  new
Component:  Core (Other)  |  Version:  master
 Severity:  Normal|   Resolution:
 Keywords:  app-loading   | Triage Stage:  Unreviewed
Has patch:  0 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+--

Comment (by aaugustin):

 The ticket description is purely based #26152 and on code analysis. I
 didn't test my theory.

 I'd like to investigate further and submit a patch, but I'm not sure when
 I'll have time for that, so feel free to assign the ticket and work on it
 if you're interested.

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[Django] #27176: django.setup() should raise an exception instead of hanging on re-entrant calls

[Django]

#27176: django.setup() should raise an exception instead of hanging on 
re-entrant
calls
+-
   Reporter:  aaugustin |  Owner:  nobody
   Type:  Bug   | Status:  new
  Component:  Core (Other)  |Version:  master
   Severity:  Normal|   Keywords:  app-loading
   Triage Stage:  Unreviewed|  Has patch:  0
Needs documentation:  0 |Needs tests:  0
Patch needs improvement:  0 |  Easy pickings:  0
  UI/UX:  0 |
+-
 #25864 and #26152 discuss issues with calling `django.setup()` in a file
 that is imported during the app-loading process. This is actually about
 `apps.populate()` -- I wrote `django.setup()` in the title because it's
 the public API people are familiar with.

 Actually there are three cases.

 1. If `django.setup()` has already completed successfully, calling it
 again returns immediately.

 {{{
 if self.ready:
 return
 }}}

 2. If `django.setup()` is running in another thread, calling it again
 returns as soon as that other thread has completed the process.

 {{{
 # populate() might be called by two threads in parallel on servers
 # that create threads before initializing the WSGI callable.
 with self._lock:
 if self.ready:
 return
 }}}

 3. If `django.setup()` is running in the same thread, calling it must
 crash. Indeed, `django.setup()` isn't allowed to return until app-loading
 has completed. The first call cannot complete without going through the
 second one, which cannot return, so there's a deadlock. The code tries to
 detect this condition:

 {{{
 # app_config should be pristine, otherwise the code below
 won't
 # guarantee that the order matches the order in
 INSTALLED_APPS.
 if self.app_configs:
 raise RuntimeError("populate() isn't reentrant")
 }}}

 #26152 suggest that the code hangs instead of raising an exception.
 Indeed, the second call must block on `with self._lock:`, since
 `self._lock` isn't reentrant. Making it a `RLock` instead of a `Lock`
 should allow the second thread to proceed and to hit that exception.

 Also the error condition is incorrect: it won't trigger if the reentrant
 call happens while importing the first app. (We're reasoning in the single
 threaded case, which is easy.) Instead `populate()` should set a private
 attribute before it starts importing apps and raise the exception if that
 attribute is set. Alternatively it could check if the `RLock` is being
 taken for the second time, but no public API for this appears to exist.

--
Ticket URL: 
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