nghttpx: Use dedicated worker for API processing

Some API processing is very slow (e.g., getaddrinfo).  To avoid to
slow down regular request handling, if multi threaded configuration is
enabled, we allocate dedicated worker for API.

src/shrpx_config.cc

@@ -1738,6 +1738,10 @@ int parse_config(Config *config, int optid, const StringRef &opt,
     addr.tls = params.tls;
     addr.api = params.api;
 
+    if (addr.api) {
+      listenerconf.api = true;
+    }
+
     if (util::istarts_with(optarg, SHRPX_UNIX_PATH_PREFIX)) {
       auto path = std::begin(optarg) + SHRPX_UNIX_PATH_PREFIX.size();
       addr.host = ImmutableString{path, addr_end};

src/shrpx_config.h

@@ -652,6 +652,8 @@ struct ConnectionConfig {
     // TCP fastopen.  If this is positive, it is passed to
     // setsockopt() along with TCP_FASTOPEN.
     int fastopen;
+    // true if at least one of UpstreamAddr has api enabled
+    bool api;
   } listener;
 
   struct {

src/shrpx_connection_handler.cc

@@ -120,7 +120,7 @@ ConnectionHandler::ConnectionHandler(struct ev_loop *loop)
       loop_(loop),
       tls_ticket_key_memcached_get_retry_count_(0),
       tls_ticket_key_memcached_fail_count_(0),
-      worker_round_robin_cnt_(0),
+      worker_round_robin_cnt_(get_config()->conn.listener.api ? 1 : 0),
       graceful_shutdown_(false) {
   ev_timer_init(&disable_acceptor_timer_, acceptor_disable_cb, 0., 0.);
   disable_acceptor_timer_.data = this;
@@ -268,6 +268,12 @@ int ConnectionHandler::create_worker_thread(size_t num) {
 
   auto &tlsconf = get_config()->tls;
   auto &memcachedconf = get_config()->tls.session_cache.memcached;
+  auto &listenerconf = get_config()->conn.listener;
+
+  // We have dedicated worker for API request processing.
+  if (listenerconf.api) {
+    ++num;
+  }
 
   for (size_t i = 0; i < num; ++i) {
     auto loop = ev_loop_new(get_config()->ev_loop_flags);
@@ -300,6 +306,7 @@ int ConnectionHandler::create_worker_thread(size_t num) {
   for (auto &worker : workers_) {
     worker->run_async();
   }
+
 #endif // NOTHREADS
 
   return 0;
@@ -384,11 +391,32 @@ int ConnectionHandler::handle_connection(int fd, sockaddr *addr, int addrlen,
     return 0;
   }
 
-  size_t idx = worker_round_robin_cnt_ % workers_.size();
-  if (LOG_ENABLED(INFO)) {
-    LOG(INFO) << "Dispatch connection to worker #" << idx;
+  Worker *worker;
+
+  if (faddr->api) {
+    worker = workers_[0].get();
+
+    if (LOG_ENABLED(INFO)) {
+      LOG(INFO) << "Dispatch connection to API worker #0";
+    }
+  } else {
+    worker = workers_[worker_round_robin_cnt_].get();
+
+    if (LOG_ENABLED(INFO)) {
+      LOG(INFO) << "Dispatch connection to worker #" << worker_round_robin_cnt_;
+    }
+
+    if (++worker_round_robin_cnt_ == workers_.size()) {
+      auto &listenerconf = get_config()->conn.listener;
+
+      if (listenerconf.api) {
+        worker_round_robin_cnt_ = 1;
+      } else {
+        worker_round_robin_cnt_ = 0;
+      }
+    }
   }
-  ++worker_round_robin_cnt_;
+
   WorkerEvent wev{};
   wev.type = NEW_CONNECTION;
   wev.client_fd = fd;
@@ -396,7 +424,7 @@ int ConnectionHandler::handle_connection(int fd, sockaddr *addr, int addrlen,
   wev.client_addrlen = addrlen;
   wev.faddr = faddr;
 
-  workers_[idx]->send(wev);
+  worker->send(wev);
 
   return 0;
 }

src/shrpx_connection_handler.h

@@ -171,6 +171,8 @@ private:
   // ev_loop for each worker
   std::vector<struct ev_loop *> worker_loops_;
   // Worker instances when multi threaded mode (-nN, N >= 2) is used.
+  // If at least one frontend enables API request, we allocate 1
+  // additional worker dedicated to API request .
   std::vector<std::unique_ptr<Worker>> workers_;
   // mutex for serial event resive buffer handling
   std::mutex serial_event_mu_;