Merge pull request #289 from belugum/master

Add basic load balancing
CrowCpp · Dec 7, 2021 · 5037891 · 5037891
2 parents 120e1f3 + a997c2b
commit 5037891
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Showing 2 changed files with 32 additions and 13 deletions.
diff --git a/include/crow/http_connection.h b/include/crow/http_connection.h
@@ -186,15 +186,17 @@ namespace crow
           std::tuple<Middlewares...>* middlewares,
           std::function<std::string()>& get_cached_date_str_f,
           detail::task_timer& task_timer,
-          typename Adaptor::context* adaptor_ctx_):
+          typename Adaptor::context* adaptor_ctx_,
+          std::atomic<unsigned int>& queue_length):
           adaptor_(io_service, adaptor_ctx_),
           handler_(handler),
           parser_(this),
           server_name_(server_name),
           middlewares_(middlewares),
           get_cached_date_str(get_cached_date_str_f),
           task_timer_(task_timer),
-          res_stream_threshold_(handler->stream_threshold())
+          res_stream_threshold_(handler->stream_threshold()),
+          queue_length_(queue_length)
         {
 #ifdef CROW_ENABLE_DEBUG
             connectionCount++;
@@ -698,7 +700,8 @@ namespace crow
             CROW_LOG_DEBUG << this << " is_reading " << is_reading << " is_writing " << is_writing;
             if (!is_reading && !is_writing)
             {
-                CROW_LOG_DEBUG << this << " delete (idle) ";
+                queue_length_--;
+                CROW_LOG_DEBUG << this << " delete (idle) (queue length: " << queue_length_ << ')';
                 delete this;
             }
         }
@@ -758,6 +761,8 @@ namespace crow
         detail::task_timer& task_timer_;
 
         size_t res_stream_threshold_;
+
+        std::atomic<unsigned int>& queue_length_;
     };
 
 } // namespace crow
diff --git a/include/crow/http_server.h b/include/crow/http_server.h
@@ -36,6 +36,7 @@ namespace crow
           server_name_(server_name),
           port_(port),
           bindaddr_(bindaddr),
+          task_queue_length_pool_(concurrency_),
           middlewares_(middlewares),
           adaptor_ctx_(adaptor_ctx)
         {}
@@ -101,6 +102,7 @@ namespace crow
                         detail::task_timer task_timer(*io_service_pool_[i]);
                         task_timer.set_default_timeout(timeout_);
                         task_timer_pool_[i] = &task_timer;
+                        task_queue_length_pool_[i] = 0;
 
                         init_count++;
                         while (1)
@@ -175,24 +177,34 @@ namespace crow
         }
 
     private:
-        asio::io_service& pick_io_service()
+        uint16_t pick_io_service_idx()
         {
-            // TODO load balancing
-            roundrobin_index_++;
-            if (roundrobin_index_ >= io_service_pool_.size())
-                roundrobin_index_ = 0;
-            return *io_service_pool_[roundrobin_index_];
+            uint16_t min_queue_idx = 0;
+
+            // TODO improve load balancing
+            for (uint16_t i = 1; i < task_queue_length_pool_.size() && task_queue_length_pool_[min_queue_idx] > 0; i++)
+            // No need to check other io_services if the current one has no tasks
+            {
+                if (task_queue_length_pool_[i] < task_queue_length_pool_[min_queue_idx])
+                    min_queue_idx = i;
+            }
+            return min_queue_idx;
         }
 
         void do_accept()
         {
-            asio::io_service& is = pick_io_service();
+            uint16_t service_idx = pick_io_service_idx();
+            asio::io_service& is = *io_service_pool_[service_idx];
+            task_queue_length_pool_[service_idx]++;
+            CROW_LOG_DEBUG << &is << " {" << service_idx << "} queue length: " << task_queue_length_pool_[service_idx];
+
             auto p = new Connection<Adaptor, Handler, Middlewares...>(
               is, handler_, server_name_, middlewares_,
-              get_cached_date_str_pool_[roundrobin_index_], *task_timer_pool_[roundrobin_index_], adaptor_ctx_);
+              get_cached_date_str_pool_[service_idx], *task_timer_pool_[service_idx], adaptor_ctx_, task_queue_length_pool_[service_idx]);
+
             acceptor_.async_accept(
               p->socket(),
-              [this, p, &is](boost::system::error_code ec) {
+              [this, p, &is, service_idx](boost::system::error_code ec) {
                   if (!ec)
                   {
                       is.post(
@@ -202,6 +214,8 @@ namespace crow
                   }
                   else
                   {
+                      task_queue_length_pool_[service_idx]--;
+                      CROW_LOG_DEBUG << &is << " {" << service_idx << "} queue length: " << task_queue_length_pool_[service_idx];
                       delete p;
                   }
                   do_accept();
@@ -223,7 +237,7 @@ namespace crow
         std::string server_name_;
         uint16_t port_;
         std::string bindaddr_;
-        unsigned int roundrobin_index_{};
+        std::vector<std::atomic<unsigned int>> task_queue_length_pool_;
 
         std::chrono::milliseconds tick_interval_;
         std::function<void()> tick_function_;