adapter.StopScan() not thread-safe

[okvorb]

According to examples StopScan() must be called from Scan() callback but it is not always convinient way to stop a scanner. It will be nice to have an option to call StopScan() method from another goroutine thread safely. Current implementation leads to data race warning on MacOS (but not on Ubuntu/Linux) on next line inside StopScan() method :

if a.scanChan == nil {

a.scanChan variable is not synchronized for reading and writing from different goroutines what leads to the data race.

[alexander-eroma]

Do you plan any activity regarding this issue?

[aykevl]

@okvorb @alexander-eroma would any of you like to make a PR to fix this issue? (I'm not using macOS that often).