Module crash_handler 

App-process crash handler.

In builds with "crash_handler" feature the crash handler takes over the first “app-process” turning it into the monitor-process, it spawns another process that is the monitored app-process. If the app-process crashes the monitor-process spawns a dialog-process that calls the dialog handler to show an error message, upload crash reports, etc.

The dialog handler can be set using crash_handler_config!.

Examples

The example below demonstrates an app setup to show a custom crash dialog.

use zng::prelude::*;

fn main() {
    // tracing applied to all processes.
    zng::app::print_tracing(tracing::Level::INFO, false, |_| true);

    // monitor-process spawns app-process and if needed dialog-process here.
    zng::env::init!();

    // app-process:
    app_main();
}

fn app_main() {
    APP.defaults().run_window("main", async {
        Window! {
            child_align = Align::CENTER;
            child = Stack! {
                direction = StackDirection::top_to_bottom();
                spacing = 5;
                children = ui_vec![
                    Button! {
                        child = Text!("Crash (panic)");
                        on_click = hn_once!(|_| {
                            panic!("Test panic!");
                        });
                    },
                    Button! {
                        child = Text!("Crash (access violation)");
                        on_click = hn_once!(|_| {
                            // SAFETY: deliberate access violation
                            #[expect(deref_nullptr)]
                            unsafe {
                                *std::ptr::null_mut() = true;
                            }
                        });
                    }
                ];
            };
        }
    });
}

zng::app::crash_handler::crash_handler_config!(|cfg| {
    // monitor-process and dialog-process

    cfg.dialog(|args| {
        // dialog-process
        APP.defaults().run_window("crash-dialog", async move {
            Window! {
                title = "App Crashed!";
                auto_size = true;
                min_size = (300, 100);
                start_position = window::StartPosition::CenterMonitor;
                on_load = hn_once!(|_| WINDOW.bring_to_top());
                padding = 10;
                child_spacing = 10;
                child = Text!(args.latest().message());
                child_bottom = Stack! {
                    direction = StackDirection::start_to_end();
                    layout::align = Align::BOTTOM_END;
                    spacing = 5;
                    children = ui_vec![
                        Button! {
                            child = Text!("Restart App");
                            on_click = hn_once!(args, |_| {
                                args.restart();
                            });
                        },
                        Button! {
                            child = Text!("Exit App");
                            on_click = hn_once!(|_| {
                                args.exit(0);
                            });
                        },
                    ];
                };
            }
        });
    });
});

Debugger

Note that because the crash handler spawns a different process for the app debuggers will not stop at break points in the app code. You can configure your debugger to set the NO_ZNG_CRASH_HANDLER environment variable to not use a crash handler in debug runs.

On VS Code with the CodeLLDB extension you can add this workspace configuration:

"lldb.launch.env": {
   "ZNG_NO_CRASH_HANDLER": ""
}

Full API

See zng_app::crash_handler and zng_wgt_inspector::crash_handler for the full API.

Macros

crash_handler_config

Register a FnOnce(&mut CrashConfig) closure to be called on process init to configure the crash handler.

Structs

CrashArgs

Arguments for the crash handler dialog function.

CrashConfig

Crash handler config.

CrashError

Info about an app-process crash.

Functions

debug_dialog

Debug dialog window.