Process Lifecycle

The on shutdown reason hook is registered before process.exit(0). Run locally with DEMO_MODE=fail to see the exit with code 1.

// Feature: controlled exit — `process.exit(code)`

// Syntax: `process.exit(0)` for success, `!= 0` for failure.

// When to use: a CLI script signaling a code to the shell; pre-flight

// checks that need to abort early. `on shutdown` hooks still run before

// the process exits.


use std::process
use std::env

on shutdown reason {
  print("[shutdown] reason: {reason}")
}

let mode = env.get("DEMO_MODE") ?? "ok"

if mode == "fail" {
  print("failure mode - exiting with 1")
  process.exit(1)
}

print("success mode - exiting with 0")
process.exit(0)
print("unreachable")
// expected:

//   success mode - exiting with 0

//   [shutdown] reason: exit

Requires the Zolo CLI/host — open in the playground or run locally.

Three on shutdown blocks — hook 3 runs before 2, which runs before 1. The reason parameter is optional: omitting it is valid.

// Feature: lifecycle — `on shutdown` (composes in LIFO order)
// Syntax: `on shutdown { ... }` or `on shutdown reason { ... }`
// When to use: clean up resources (close files, flush logs, drop
// connections) regardless of the exit path (normal, exit, panic, signal).

// Multiple blocks compose in LIFO order — the last one declared runs first.
on shutdown {
  print("[hook 1] outermost cleanup (declared first, runs LAST)")
}

on shutdown reason {
  print("[hook 2] exit reason: {reason}")
}

on shutdown {
  print("[hook 3] innermost cleanup (declared last, runs FIRST)")
}

print("main work")
print("done")
// expected:
//   main work
//   done
//   [hook 3] innermost cleanup (declared last, runs FIRST)
//   [hook 2] exit reason: normal
//   [hook 1] outermost cleanup (declared first, runs LAST)

Requires the Zolo CLI/host — open in the playground or run locally.

The panic(...) call is commented out to keep the exit code 0 in the sandbox; read the comments and uncomment locally to see the full sequence.

// Feature: lifecycle — `on panic` catches uncaught panics
// Syntax: `on panic e { ... }` receives the message; runs BEFORE
// `on shutdown` — last chance to log / dump diagnostics.
// When to use: catch crashes in production (telemetry, dump file),
// turn a panic into a structured log entry.
//
// NOTE: an uncaught panic exits the process with a non-zero status
// AFTER the `on panic` / `on shutdown` hooks fire. To keep this
// example green in test harnesses (which expect exit code 0), the
// `panic(...)` call below is left commented out and only documented.

on panic e {
  print("[panic] caught: {e}")
}

on shutdown reason {
  print("[shutdown] reason: {reason}")
}

print("before crash")
// panic("something went very wrong")
//
// expected (when the panic line is uncommented):
//   before crash
//   [panic] caught: something went very wrong
//   [shutdown] reason: panic
//   (process exits with non-zero status)
print("(panic skipped to keep exit code 0; see comment above)")

Requires the Zolo CLI/host — open in the playground or run locally.

process.raise("SIGINT") delivers the signal; process.sleep(50) waits for the signal thread to drain the event before main execution continues.

// Feature: lifecycle — `on signal` for SIGINT / SIGTERM

// Syntax: `on signal SIGINT { ... }`. On Windows, only SIGINT (Ctrl+C)

// and SIGTERM (Ctrl+Break) are delivered.

// When to use: graceful shutdown — interrupt server loops, save

// state, close connections before dying.


use std::process

var fired = 0

on signal SIGINT {
  fired = fired + 1
  print("SIGINT received (time #{fired})")
}

on shutdown reason {
  print("shutdown reason: {reason}")
}

// `process.raise` injects a synthetic signal — useful for testing

// without needing a shell to send Ctrl+C from outside.

print("raising SIGINT...")
process.raise("SIGINT")

// Give the lifecycle thread time to drain the signal.

process.sleep(50)

print("after sleep, fired={fired}")
print("done")
// expected:

//   raising SIGINT...

//   SIGINT received (time #1)

//   after sleep, fired=1

//   done

//   shutdown reason: normal

Requires the Zolo CLI/host — open in the playground or run locally.