MongoDB tracing error upon truncating for specs

[Azure7111]

I'm currently adding the datadog agent to an app which is truncating its database each time before any specs are run. Although tracing is supposed to be disabled in the test environment the gem still tries to trace the truncation. So trying to run the specs results in the following error:

NoMethodError: undefined method `delete' for nil:NilClass
  /home/redacted/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/ddtrace-0.18.2/lib/ddtrace/contrib/mongodb/subscribers.rb:53:in `failed'

It turns out that this very line was changed in the most recent version (0.18.2), and downgrading to version 0.18.1 makes the issue go away.

[delner]

Thanks for the report @Azure7111; do you have a code sample which we can reproduce the issue? Looks like somehow an operation called failed before ever calling started, or the failed event is being handled on a different thread than started, which is not something we anticipated.

Related to #658.

[delner]

Opened up #675 that might fix this. Can you give it a try @Azure7111?

[Azure7111]

First off let me say that I'm impressed by the quick response. Thanks!

Just gave #675 a try and it works for me! Awesome! :)

Do you still need a code sample in that case?

[delner]

@Azure7111 cool, glad to hear it's working.

If you could, it would still be helpful, because I can't say I understand how it called failed before calling started; the gem source code seemed to suggest it always happens in sequence, yet it appears that's not what happened in your application. Having a little extra insight there might help reassure us that the fix is robust enough to prevent this from happening again, or that this issue isn't symptomatic of something bigger.

I'm aiming to put this out with our next bugfix release, 0.18.3, which should hopefully roll today.

[delner]

Fix is merged to master, closing this.