horus: Work around race in cover:is_compiled/1
#28
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[Why]
The `cover:call/1` internal checks if the cover server is running and
starts it if it's not:
Ref = erlang:monitor(process,?SERVER),
receive {'DOWN', Ref, _Type, _Object, noproc} ->
erlang:demonitor(Ref),
{ok,_} = start(),
...
However, there is no lock between the check and
the start. Therefore, any concurrent uses of this code may cause a
`badmatch` crash on `{ok,_} = start()` because it might have been
started in parallel and the function returns the `already_started`
error.
[How]
To work around the problem, we catch the `badmatch` and retry once after
a sleep of 100 ms. We don't try to catch any exception from that second
attempt.
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #28 +/- ##
==========================================
- Coverage 84.41% 84.26% -0.15%
==========================================
Files 3 3
Lines 943 947 +4
==========================================
+ Hits 796 798 +2
- Misses 147 149 +2
Flags with carried forward coverage won't be shown. Click here to find out more. ☔ View full report in Codecov by Sentry. |
|
A patch to fix the root problem was submitted upstream in erlang/otp#9124. |
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Why
The
cover:call/1internal checks if the cover server is running and starts it if it's not:However, there is no lock between the check and
the start. Therefore, any concurrent uses of this code may cause a
badmatchcrash on{ok,_} = start()because it might have been started in parallel and the function returns thealready_startederror.How
To work around the problem, we catch the
badmatchand retry once after a sleep of 100 ms. We don't try to catch any exception from that second attempt.