Thanks for the info, Dimiter. That is almost certainly going to bite someone else at some point.
On Thu, Jul 16, 2015 at 6:35 AM Dimiter Naydenov < dimiter.nayde...@canonical.com> wrote: > -----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: > http://herman.asia/running-the-go-race-detector-with-cover > > 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 <dimiter.nayde...@canonical.com> > Juju Core Sapphire team <http://juju.ubuntu.com> > -----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 > Juju-dev@lists.ubuntu.com > Modify settings or unsubscribe at: > https://lists.ubuntu.com/mailman/listinfo/juju-dev >
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