Attempt to set max concurrent connections manually

cpp/db_common.cpp

@@ -17,6 +17,7 @@
 
 #include <atomic>
 #include <chrono>
+#include <condition_variable>
 #include <mutex>
 #include <thread>
 
@@ -26,8 +27,11 @@
 #include <QString>
 
 // get_thread_connection and init_database
+constexpr int MAX_CONNECTIONS = 5;
 static std::mutex connection_mutex_;
+static std::condition_variable connection_cv_;
 static std::atomic<unsigned int> thread_id_counter{1};
+static int active_connections = 0;
 static QString shared_database_path;
 
 static int get_delay(int attempt) {
@@ -40,7 +44,13 @@ QSqlDatabase get_thread_connection() {
     bool passed = false;
     int attempt = 0;
     while (!passed) {
-        std::lock_guard<std::mutex> lock(connection_mutex_);
+        {
+            std::unique_lock<std::mutex> lock(connection_mutex_);
+            connection_cv_.wait(lock, [] { return active_connections < MAX_CONNECTIONS; });
+            active_connections++;
+        }
+
+        try {
             thread_local unsigned int thread_unique_id = thread_id_counter.fetch_add(1);
             connection_name = QString("CIConn_%1").arg(thread_unique_id);
 
@@ -66,7 +76,21 @@ QSqlDatabase get_thread_connection() {
 
             if (!thread_db.open()) throw std::runtime_error("Failed to open new database connection for thread: " + thread_db.lastError().text().toStdString());
             passed = true;
+        } catch (...) {
+            {
+                std::lock_guard<std::mutex> lock(connection_mutex_);
+                active_connections--;
             }
+            connection_cv_.notify_one();
+            throw;
+        }
+    }
+
+    {
+        std::lock_guard<std::mutex> lock(connection_mutex_);
+        active_connections--;
+    }
+    connection_cv_.notify_one();
 
     return thread_db;
 }