<div dir="ltr">Thanks for the info, Dimiter. That is almost certainly going to bite someone else at some point.</div> <div class="gmail_quote"><div dir="ltr">On Thu, Jul 16, 2015 at 6:35 AM Dimiter Naydenov <<a href="mailto:dimiter.naydenov@canonical.com">dimiter.naydenov@canonical.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hey all, tl;dr; When running $ go test -race -cover with go < 1.3, and you get data races, try adding "-covermode=atomic" as well to see if they are caused by the go coverage tool itself. In go 1.3+ -covermode defaults to atomic, so yet another reason to really move quickly to 1.5 across the board ASAP. I've discovered the hard way the go race detector doesn't play well with the go coverage tool in golang versions prior to 1.3. With -cover (and/or -coverprofile=filename, which assumes -cover), the code instrumentation generated by the coverage tool uses global variables to track which lines are covered and how many times. This causes the race detector to report data races in confusing locations (e.g. I had a whole bunch of them in the provider/ec2 pacakge), which are not happening without -cover enabled. I've discovered the issue very easily by adding -test.work argument to "go test". This causes "go test" to print the temporary work dir used and also keep it after "go test" completes. Then it's a simple matter of inspecting the work dir and the actual source files in there, which include race and coverage instrumentation code added. The DATA RACE output includes paths in that work dir and line numbers exactly matching the code generated by - -cover. Apparently, adding -covermode=atomic along with -cover and -race, works around the problem in both golang versions < 1.3 and 1.3+, by using atomic inc ops rather than global non-goroutine-safe vars. An interesting article describing the issue with examples: <a href="http://herman.asia/running-the-go-race-detector-with-cover" rel="noreferrer" target="_blank">http://herman.asia/running-the-go-race-detector-with-cover</a> Hopefully this will be helpful to somebody else and save them a few wasted hours trying to figure out why the result of "go test -race - -cover" has data races reported, while "go test -race" or "go test - -cover" for the same tests shows no races at all. - -- Dimiter Naydenov <<a href="mailto:dimiter.naydenov@canonical.com" target="_blank">dimiter.naydenov@canonical.com</a>> Juju Core Sapphire team <<a href="http://juju.ubuntu.com" rel="noreferrer" target="_blank">http://juju.ubuntu.com</a>> -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQEcBAEBAgAGBQJVp4kCAAoJENzxV2TbLzHwyJQIALb3MuDz9qSuLwhNNL7DfIjq DsEV14F82qDbdXcjS42f8I3ZIaq3ii8DQZWyR3dNoTtMOhc4thxIVs6LzHdzUR88 GxFLWZeSgsRzeGj0OVvVGeelwIkqUPORt2Q4m2uziPgVkiczniVwkM9FAC1kdu21 l54ibsIu1TsPwDUQzp6LPSEzP7zhv3pB9h8Qhq4sxoqSUjtQXt6ysgKn88Br/Cjl 7EBkcI0sDkm6bglklztNBh8fQqLUXLHW+cUXhdr/7psnhsAaGXHDEC3u3hPi16X+ Mc0yOrsyOHBNdsTV3J8aWiOI9AJFZWjwEWo1LbUc6vL1znX40LF2Uxq7tTuTJ6g= =DXZL -----END PGP SIGNATURE----- -- Juju-dev mailing list <a href="mailto:Juju-dev@lists.ubuntu.com" target="_blank">Juju-dev@lists.ubuntu.com</a> Modify settings or unsubscribe at: <a href="https://lists.ubuntu.com/mailman/listinfo/juju-dev" rel="noreferrer" target="_blank">https://lists.ubuntu.com/mailman/listinfo/juju-dev</a> </blockquote></div>