gtklock is a GTK-based lockscreen for Wayland compositors. It locks the screen using the ext-session-lock protocol and authenticates users via PAM. The application creates a window for each monitor displaying a clock, date, and password entry. It supports features like idle hiding, multi-monitor focus following, and running custom commands on lock/unlock events. The architecture is modular, with a core GTK application loop, pluggable modules for extensibility, and isolated subsystems for authentication and configuration. The main entry point is in src/source.c, which initializes the GTK application, loads configuration and modules, and sets up event handlers for screen locking and unlocking.