lifecycle

lifecycle

Overview

lifecycle helps manage goroutines at the application level. context.Context has been great for propagating cancellation signals, but not for getting any feedback about when goroutines actually finish.

This package works with context.Context to ensure that applications don't quit before their goroutines do.

The semantics work similarly to the go (lifecycle.Go) and defer (lifecycle.Defer) keywords as well as sync.WaitGroup.Wait (lifecycle.Wait). Additionally, there are lifecycle.GoErr and lifecycle.DeferErr which only differ in that they take funcs that return errors.

lifecycle.Wait will block until one of the following happens:

• all funcs registered with Go complete successfully then all funcs registered with Defer complete successfully
• a func registered with Go returns an error, immediately canceling ctx and triggering Defer funcs to run. Once all Go and Defer funcs complete, Wait will return the error
• a signal (by default SIGINT and SIGTERM, but configurable with WithSignals) is received, immediately canceling ctx and triggering Defer funcs to run. Once all Go and Defer funcs complete, Wait will return ErrSignal
• a func registered with Go or Defer panics. the panic will be propagated to the goroutine that Wait runs in. there is no attempt, in case of a panic, to manage the state within the lifecycle package.

Example

Here is an example that shows how lifecycle could work with an http.Server:

// At the top of your application
ctx := lifecycle.New(
    context.Background(),
    lifecycle.WithTimeout(30*time.Second), // optional
)

helloHandler := func(w http.ResponseWriter, req *http.Request) {
    _, _ = io.WriteString(w, "Hello, world!\n")
}

mux := http.NewServeMux()
mux.HandleFunc("/hello", helloHandler)

srv := &http.Server{
    Addr:    ":8080",
    Handler: mux,
}

lifecycle.GoErr(ctx, srv.ListenAndServe)

lifecycle.DeferErr(ctx, func() error {
    // use a background context because we already have a timeout and when
    // Defer funcs run, ctx is necessarily canceled.
    return srv.Shutdown(context.Background())
})

// Any panics in Go or Defer funcs will be passed to the goroutine that Wait
// runs in, so it is possible to handle them like this
defer func() {
    if r := recover(); r != nil {
        panic(r) // example, you probably want to do something else
    }
}()

// Then at the end of main(), or run() or however your application operates
//
// The returned err is the first non-nil error returned by any func
// registered with Go or Defer, otherwise nil.
if err := lifecycle.Wait(ctx); err != nil {
    log.Fatal(err)
}