goroutine

Results 2 issues of goroutine

Excellent work! @stepancheg What's the status of the project ? We want to use gRPC in our project [TiKV](https://github.com/pingcap/tikv), and we can help you to test the project.

Currently, the only component of goleveldb that tidb depends on is memdb, and tidb is using it in a single thread/goroutine, there is no need to use mutex. Not sure...