THRIFT-4160: Fix use closed(freed) connections in non-blocking server

Client: cpp

When failing to add tasks into the thread manager, we close the
corresponding connections, then set the flags of these connections,
which have been already freed.

We should decrease the number of active processors.

This closes #1211

lib/cpp/src/thrift/server/TNonblockingServer.cpp

@@ -591,21 +591,24 @@ void TNonblockingServer::TConnection::transition() {
       // The application is now waiting on the task to finish
       appState_ = APP_WAIT_TASK;
 
+      // Set this connection idle so that libevent doesn't process more
+      // data on it while we're still waiting for the threadmanager to
+      // finish this task
+      setIdle();
+
       try {
         server_->addTask(task);
       } catch (IllegalStateException& ise) {
         // The ThreadManager is not ready to handle any more tasks (it's probably shutting down).
         GlobalOutput.printf("IllegalStateException: Server::process() %s", ise.what());
+        server_->decrementActiveProcessors();
         close();
       } catch (TimedOutException& to) {
         GlobalOutput.printf("[ERROR] TimedOutException: Server::process() %s", to.what());
+        server_->decrementActiveProcessors();
         close();
       }
 
-      // Set this connection idle so that libevent doesn't process more
-      // data on it while we're still waiting for the threadmanager to
-      // finish this task
-      setIdle();
       return;
     } else {
       try {