Fix: PostgreSQL prepared statement purge race condition

The fix ensures that when the purge checks ref_count_client under write lock, it sees the latest value from concurrent threads holding raw pointers, preventing reading stale data.

lib/PgSQL_PreparedStatement.cpp

@@ -291,24 +291,22 @@ void PgSQL_STMT_Manager::ref_count_client___purge_stmts_if_needed() noexcept {
 		// meaning there are no other references (from client or server) to this prepared statement.
 		// So we can safely remove this entry.
 		if (global_stmt_info.use_count() == 1) {
-
-			// ref_count_client and ref_count_server should both be 0 in this case
-			assert(global_stmt_info->ref_count_client.load(std::memory_order_relaxed) == 0);
-			assert(global_stmt_info->ref_count_server.load(std::memory_order_relaxed) == 0);
-
-			// Atomic counters
-			num_stmt_with_ref_client_count_zero.fetch_sub(1, std::memory_order_relaxed);
-			num_stmt_with_ref_server_count_zero.fetch_sub(1, std::memory_order_relaxed);
-
-			// Free ID
-			free_stmt_ids.push(global_stmt_info->statement_id);
-
-			// Update totals
-			//stat_totals.s_total -= global_stmt_info->ref_count_server.load(std::memory_order_relaxed);
-
-			// Safe erase from map while iterating
-			it = map_stmt_hash_to_info.erase(it);
-			remaining_removals--;
+			// Use memory_order_acquire to see latest refcount modifications
+			// Since write lock prevents NEW references, only existing raw pointers can race
+			if (global_stmt_info->ref_count_client.load(std::memory_order_acquire) == 0 &&
+				global_stmt_info->ref_count_server.load(std::memory_order_acquire) == 0) {
+
+				// Atomic counters
+				num_stmt_with_ref_client_count_zero.fetch_sub(1, std::memory_order_relaxed);
+				num_stmt_with_ref_server_count_zero.fetch_sub(1, std::memory_order_relaxed);
+
+				// Free ID
+				free_stmt_ids.push(global_stmt_info->statement_id);
+
+				// Safe erase from map while iterating
+				it = map_stmt_hash_to_info.erase(it);
+				remaining_removals--;
+			}
 		} else {
 			++it;
 		}