inject: Use a semaphore to prevent multiple runs of inject to interfere with each other.
inject: Use a semaphore to prevent multiple runs of inject to interfere with each other.

Most users would never hit this, but it enables me to run apitrace tests
in parallel reliably.

tuanthng/apitrace,EoD/apitrace,surround-io/apitrace,tuanthng/apitrace,apitrace/apitrace,swq0553/apitrace,tuanthng/apitrace,joshua5201/apitrace,joshua5201/apitrace,schulmar/apitrace,trtt/apitrace,trtt/apitrace,surround-io/apitrace,apitrace/apitrace,EoD/apitrace,joshua5201/apitrace,trtt/apitrace,EoD/apitrace,surround-io/apitrace,trtt/apitrace,EoD/apitrace,schulmar/apitrace,surround-io/apitrace,tuanthng/apitrace,schulmar/apitrace,schulmar/apitrace,trtt/apitrace,surround-io/apitrace,tuanthng/apitrace,joshua5201/apitrace,joshua5201/apitrace,swq0553/apitrace,swq0553/apitrace,schulmar/apitrace,EoD/apitrace,apitrace/apitrace,swq0553/apitrace,apitrace/apitrace,swq0553/apitrace