Every thread intitiates multiple RPCs. The Callback of the unary RPC then issues a new RPC and this goes until the benchmark shuts down. For shutdown the main thread waits on a conditional variable. After shutdown the callbacks increment a rpcs done variable and once the the rpcs done equate the the total number of outstanding rpcs, the last callback performing the increment operation also issues a signal to wake up the main thread. The mainthread process to join the other threads and perform cleanup