Make qps workers connect before even warmup stage begins

include/grpc++/impl/codegen/channel_interface.h

@@ -85,6 +85,15 @@ class ChannelInterface {
     return WaitForStateChangeImpl(last_observed, deadline_tp.raw_time());
   }
 
+  /// Wait for this channel to be connected
+  template <typename T>bool WaitForConnected(T deadline) {
+    grpc_connectivity_state state;
+    while ((state = GetState(true)) != GRPC_CHANNEL_READY) {
+      if (!WaitForStateChange(state, deadline)) return false;
+    }
+    return true;
+  }
+
  private:
   template <class R>
   friend class ::grpc::ClientReader;

test/cpp/qps/client.h

@@ -41,6 +41,7 @@
 #include <grpc++/support/byte_buffer.h>
 #include <grpc++/support/channel_arguments.h>
 #include <grpc++/support/slice.h>
+#include <grpc++/channel.h>
 #include <grpc/support/log.h>
 #include <grpc/support/time.h>
 
@@ -315,6 +316,8 @@ class ClientImpl : public Client {
           target, config.security_params().server_host_override(),
           config.has_security_params(), !config.security_params().use_test_ca(),
           std::shared_ptr<CallCredentials>(), args);
+      gpr_log(GPR_INFO, "Connecting to %s", target.c_str());
+      GPR_ASSERT(channel_->WaitForConnected(gpr_time_add(gpr_now(GPR_CLOCK_REALTIME), gpr_time_from_seconds(30, GPR_TIMESPAN))));
       stub_ = create_stub(channel_);
     }
     Channel* get_channel() { return channel_.get(); }