added multi threaded pool test

include/matador/sql/connection_pool.hpp

@@ -86,19 +86,21 @@ public:
   }
 
   connection_pointer acquire() {
+    std::unique_lock<std::mutex> lock(mutex_);
+    while (idle_connections_.empty()) {
+      cv.wait(lock);
+    }
+
+    return get_next_connection();
+  }
+
+  connection_pointer try_acquire() {
     std::unique_lock<std::mutex> lock(mutex_);
     if (idle_connections_.empty()) {
       return {nullptr, this};
     }
 
-    pointer next_connection{nullptr};
-    for (auto &item : idle_connections_) {
-      next_connection = item.second;
-      auto node = idle_connections_.extract(item.first);
-      inuse_connections_.insert(std::move(node));
-      break;
-    }
-    return {next_connection, this};
+    return get_next_connection();
   }
 
   connection_pointer acquire(size_t id) {
@@ -151,8 +153,21 @@ public:
   const connection_info &info() const {
     return info_;
   }
+
+private:
+  connection_pointer get_next_connection() {
+    pointer next_connection{nullptr};
+    for (auto &item : idle_connections_) {
+      next_connection = item.second;
+      auto node = idle_connections_.extract(item.first);
+      inuse_connections_.insert(std::move(node));
+      break;
+    }
+    return {next_connection, this};
+  }
 private:
   mutable std::mutex mutex_;
+  std::condition_variable cv;
   std::vector<IdConnection<Connection>> connection_repo_;
   using pointer = IdConnection<Connection>*;
   using connection_map = std::unordered_map<size_t, pointer>;