Opened 4 years ago

Closed 4 years ago

#18925 closed Bug (wontfix)

Exception information should be localized and passed to got_request_exception signal handlers

Reported by: Oliver Beattie Owned by: nobody
Component: HTTP handling Version: 1.4
Severity: Normal Keywords:
Cc: Triage Stage: Unreviewed
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no


It is possible, when Django is running under Gevent (ie. via Gunicorn), for traceback information for exceptions raised while processing a request to be lost. This is because Gunicorn will throw away traceback information (deliberately, though it doesn't necessarily sound as if this is "by design"), if a switch to another greenlet occurs during processing an exception.

The specific case where this has happened for me (and subsequently destroyed traceback information about errors happening in production), is when using a patched version of psycopg2 and a signal handler (like Sentry's) which accesses the database — causing a greenlet switch. It can be replicated by using the process described in a ticket on Gunicorn's tracker.

It seems the only way to solve this is for Django to localize sys.exc_info() before calling signal handlers (which may do who knows what with regard to greenlet switching), and to pass it explicitly to signal handlers. This shouldn't cause any issues with existing signal handlers since they all must accept **kwargs anyway. I've prepared a patch, which I'll submit via a Pull Request on GitHub referencing this ticket.

On my install, before applying the patch, Django error pages would appear without traceback information; after the change, they have a proper stack trace, as expected.

Change History (5)

comment:1 Changed 4 years ago by Oliver Beattie

Has patch: set
Needs documentation: unset
Needs tests: unset
Patch needs improvement: unset

I've sent a pull request on GitHub.

comment:2 Changed 4 years ago by Oliver Beattie

Should also add that this should not cause cyclical reference issues as mentioned that it may in the Python documentation, since the local reference is held in the handler, not the exception handlers.

comment:3 Changed 4 years ago by Claude Paroz

Needs tests: set

comment:4 Changed 4 years ago by Oliver Beattie

Needs tests: unset

I've now added a test for this, that doesn't require a dependency on Gunicorn to replicate

comment:5 Changed 4 years ago by Oliver Beattie

Resolution: wontfix
Status: newclosed

In response to my posts on the mailing list, this has actually been fixed in gevent, so closing this.

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