added a lock mechanism to statement_proxy

include/matador/sql/error_code.hpp

@@ -21,6 +21,7 @@ enum class error_code : uint8_t {
   RESET_FAILED,
   OPEN_ERROR,
   CLOSE_ERROR,
+  STATEMENT_LOCKED,
   FAILURE
 };
 

source/orm/sql/statement_cache.cpp

@@ -3,6 +3,8 @@
 #include "matador/sql/error_code.hpp"
 #include "matador/sql/connection_pool.hpp"
 
+#include <atomic>
+
 namespace matador::sql {
 namespace internal {
 class statement_cache_proxy final : public statement_proxy {
@@ -11,11 +13,49 @@ public:
   : statement_proxy(std::move(stmt)) {}
 
   utils::result<size_t, utils::error> execute(interface::parameter_binder& bindings) override {
+    if (!try_lock()) {
+      return utils::failure(utils::error{
+        error_code::STATEMENT_LOCKED,
+        "Failed to execute statement because it is already in use"
+      });
+    }
+
+    auto guard = statement_guard(*this);
     return statement_->execute(bindings);
   }
   utils::result<std::unique_ptr<query_result_impl>, utils::error> fetch(interface::parameter_binder& bindings) override {
+    if (!try_lock()) {
+      return utils::failure(utils::error{
+        error_code::STATEMENT_LOCKED,
+        "Failed to execute statement because it is already in use"
+      });
+    }
+
+    auto guard = statement_guard(*this);
     return statement_->fetch(bindings);
   }
+
+protected:
+  [[nodiscard]] bool try_lock() {
+    bool expected = false;
+    return locked_.compare_exchange_strong(expected, true);
+  }
+
+  void unlock() {
+    locked_.store(false);
+  }
+
+private:
+  struct statement_guard {
+    explicit statement_guard(statement_cache_proxy &statement_proxy)
+    : proxy(statement_proxy) {}
+    ~statement_guard() { proxy.unlock(); }
+
+    statement_cache_proxy &proxy;
+  };
+
+private:
+  std::atomic_bool locked_{false};
 };
 
 }

test/orm/backend/test_connection.cpp

@@ -3,7 +3,6 @@
 #include "test_result_reader.hpp"
 
 #include "matador/sql/query_context.hpp"
-#include "matador/sql/record.hpp"
 
 #include "matador/sql/internal/query_result_impl.hpp"