Use mutex to avoid concurrent write to metrics log file
Use mutex to avoid concurrent write to metrics log file

cloudfoundry-incubator/bits-service,cloudfoundry-incubator/bits-service,petergtz/bitsgo,petergtz/bitsgo,cloudfoundry-incubator/bits-service,cloudfoundry-incubator/bits-service,cloudfoundry-incubator/bits-service