Fix concurrent data race problem

[hilyjiang]

Data race test failed when in concurrent systems.

The test code can be found here: #74

[op]

Can you fix this without using locks? In most cases, these things are initialised first thing and doesn't require locks.

[Astarry]

Please fix this. We are using go-logging, and this issue keeps coming up for us. We use golang for the concurrency. There is a race condition flagged in the concurrent read/write access to the map. One module is trying to log a stmt(multi.go line 25 function Log, which calls IsEnabledFor), while another is initializing its logger (multi.go line 51, which calls SetLevel). There is a concurrent read/write to the map (level.go line 65, levels map[string]Level in type moduleLeveled struct). The library works awesomely, other than the intermittent failure it causes our application because of this race condition.

[ccl0326]

In implementation of glog includes(C++, Golang), the vmoudle is fixed in running time.In C++ version glog, they use macro to make static anonymous variable in every module to store the log level.So i think if you want to fix this, change the moudle usage and some tricky technology should be required.