Signal Handling

signal_handle(signum, fn) registers a callback for an OS signal. signal_reset restores the default behavior. This recipe sends SIGUSR1 to itself and catches it.

Code

// Signal handling — reacting to OS signals
// Manejo de señales — reaccionar a señales del SO

var got_signal: int = 0

fn on_sigusr1() -> int {
    got_signal = 1
    return 0
}

fn main() -> int {
    // Register a handler for SIGUSR1 (signal 10)
    signal_handle(10, on_sigusr1)
    print("handler registered for SIGUSR1")

    // Send SIGUSR1 to ourselves
    let my_pid: int = getpid()
    print("my pid: " + int_to_string(my_pid))
    kill_process(my_pid, 10)

    // Give time for signal delivery
    sleep(10)

    if got_signal == 1 {
        print("signal received!")
    } else {
        print("no signal yet")
    }

    // Reset signal to default behavior
    signal_reset(10)
    print("handler reset to default")

    return 0
}

Output

handler registered for SIGUSR1
my pid: 12345
signal received!
handler reset to default

Explanation

signal_handle(signum, fn) installs a callback function for the given signal number. SIGUSR1 is signal 10 on Linux. The handler function must have the signature fn() -> int.

The program uses kill_process(pid, signal) to send SIGUSR1 to itself. After a brief sleep to allow delivery, it checks the global flag that the handler set.

signal_reset(signum) restores the default OS behavior for the signal. For SIGUSR1, the default action is to terminate the process, so you would not want to send it again after resetting.

Source: examples/by-example/66-signal-handling.nx