should be it

external/duckdb/test/appender/test_concurrent_append.cpp

@@ -0,0 +1,55 @@
+#include "catch.hpp"
+#include "duckdb/main/appender.hpp"
+#include "test_helpers.hpp"
+
+#include <atomic>
+#include <thread>
+#include <vector>
+
+using namespace duckdb;
+using namespace std;
+
+atomic<int> finished_threads;
+
+#define THREAD_COUNT    8
+#define INSERT_ELEMENTS 2000
+
+static void append_to_integers(DuckDB *db, size_t threadnr) {
+	Connection con(*db);
+
+	Appender appender(con, "integers");
+	for (size_t i = 0; i < INSERT_ELEMENTS; i++) {
+		appender.BeginRow();
+		appender.Append<int32_t>(1);
+		appender.EndRow();
+	}
+	finished_threads++;
+	while (finished_threads != THREAD_COUNT)
+		;
+	appender.Close();
+}
+
+TEST_CASE("Test concurrent appends", "[appender][.]") {
+	duckdb::unique_ptr<QueryResult> result;
+	DBConfig config;
+	config.options.maximum_threads = 1;
+	DuckDB db(nullptr, &config);
+	Connection con(db);
+
+	// create a single table to append to
+	REQUIRE_NO_FAIL(con.Query("CREATE TABLE integers(i INTEGER)"));
+
+	finished_threads = 0;
+
+	thread threads[THREAD_COUNT];
+	for (size_t i = 0; i < THREAD_COUNT; i++) {
+		threads[i] = thread(append_to_integers, &db, i);
+	}
+
+	for (size_t i = 0; i < THREAD_COUNT; i++) {
+		threads[i].join();
+	}
+	// check how many entries we have
+	result = con.Query("SELECT COUNT(*) FROM integers");
+	REQUIRE(CHECK_COLUMN(result, 0, {THREAD_COUNT * INSERT_ELEMENTS}));
+}