mirror of
https://github.com/diamondburned/arikawa.git
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270 lines
6.6 KiB
Go
270 lines
6.6 KiB
Go
// Package handler handles incoming Gateway events. It reflects the function's
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// first argument and caches that for use in each event.
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//
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// Performance
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//
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// Each call to the event would take 167 ns/op for roughly each handler. Scaling
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// that up to 100 handlers is roughly the same as multiplying 167 ns by 100,
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// which gives 16700 ns or 0.0167 ms.
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//
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// BenchmarkReflect-8 7260909 167 ns/op
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//
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// Usage
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//
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// Handler's usage is mostly similar to Discordgo, in that AddHandler expects a
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// function with only one argument or an event channel. For more information,
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// refer to AddHandler.
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package handler
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import (
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"context"
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"fmt"
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"reflect"
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"sync"
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"github.com/pkg/errors"
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)
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// Handler is a container for command handlers. A zero-value instance is a valid
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// instance.
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type Handler struct {
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// Synchronous controls whether to spawn each event handler in its own
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// goroutine. Default false (meaning goroutines are spawned).
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Synchronous bool
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mutex sync.RWMutex
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slab slab
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}
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func New() *Handler {
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return &Handler{}
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}
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// Call calls all handlers with the given event. This is an internal method; use
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// with care.
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func (h *Handler) Call(ev interface{}) {
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var evV = reflect.ValueOf(ev)
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var evT = evV.Type()
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h.mutex.RLock()
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defer h.mutex.RUnlock()
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for _, entry := range h.slab.Entries {
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if entry.isInvalid() || entry.not(evT) {
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continue
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}
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if h.Synchronous {
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entry.call(evV)
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} else {
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go entry.call(evV)
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}
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}
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}
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// WaitFor blocks until there's an event. It's advised to use ChanFor instead,
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// as WaitFor may skip some events if it's not ran fast enough after the event
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// arrived.
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func (h *Handler) WaitFor(ctx context.Context, fn func(interface{}) bool) interface{} {
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var result = make(chan interface{})
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cancel := h.AddHandler(func(v interface{}) {
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if fn(v) {
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result <- v
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}
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})
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defer cancel()
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select {
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case r := <-result:
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return r
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case <-ctx.Done():
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return nil
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}
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}
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// ChanFor returns a channel that would receive all incoming events that match
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// the callback given. The cancel() function removes the handler and drops all
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// hanging goroutines.
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//
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// This method is more intended to be used as a filter. For a persistent event
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// channel, consider adding it directly as a handler with AddHandler.
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func (h *Handler) ChanFor(fn func(interface{}) bool) (out <-chan interface{}, cancel func()) {
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result := make(chan interface{})
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closer := make(chan struct{})
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removeHandler := h.AddHandler(func(v interface{}) {
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if fn(v) {
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select {
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case result <- v:
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case <-closer:
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}
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}
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})
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// Only allow cancel to be called once.
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var once sync.Once
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cancel = func() {
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once.Do(func() {
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removeHandler()
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close(closer)
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})
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}
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out = result
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return
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}
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// AddHandler adds the handler, returning a function that would remove this
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// handler when called. A handler type is either a single-argument no-return
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// function or a channel.
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//
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// Function
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//
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// A handler can be a function with a single argument that is the expected event
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// type. It must not have any returns or any other number of arguments.
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//
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// // An example of a valid function handler.
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// h.AddHandler(func(*gateway.MessageCreateEvent) {})
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//
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// Channel
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//
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// A handler can also be a channel. The underlying type that the channel wraps
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// around will be the event type. As such, the type rules are the same as
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// function handlers.
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//
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// Keep in mind that the user must NOT close the channel. In fact, the channel
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// should not be closed at all. The caller function WILL PANIC if the channel is
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// closed!
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//
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// When the rm callback that is returned is called, it will also guarantee that
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// all blocking sends will be cancelled. This helps prevent dangling goroutines.
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//
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// // An example of a valid channel handler.
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// ch := make(chan *gateway.MessageCreateEvent)
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// h.AddHandler(ch)
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//
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func (h *Handler) AddHandler(handler interface{}) (rm func()) {
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rm, err := h.addHandler(handler)
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if err != nil {
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panic(err)
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}
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return rm
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}
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// AddHandlerCheck adds the handler, but safe-guards reflect panics with a
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// recoverer, returning the error. Refer to AddHandler for more information.
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func (h *Handler) AddHandlerCheck(handler interface{}) (rm func(), err error) {
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// Reflect would actually panic if anything goes wrong, so this is just in
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// case.
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defer func() {
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if rec := recover(); rec != nil {
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if recErr, ok := rec.(error); ok {
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err = recErr
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} else {
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err = fmt.Errorf("%v", rec)
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}
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}
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}()
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return h.addHandler(handler)
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}
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func (h *Handler) addHandler(fn interface{}) (rm func(), err error) {
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// Reflect the handler
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r, err := newHandler(fn)
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if err != nil {
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return nil, errors.Wrap(err, "handler reflect failed")
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}
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h.mutex.Lock()
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id := h.slab.Put(r)
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h.mutex.Unlock()
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return func() {
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h.mutex.Lock()
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popped := h.slab.Pop(id)
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h.mutex.Unlock()
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popped.cleanup()
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}, nil
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}
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type handler struct {
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event reflect.Type // underlying type; arg0 or chan underlying type
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callback reflect.Value
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isIface bool
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chanclose reflect.Value // IsValid() if chan
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}
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// newHandler reflects either a channel or a function into a handler. A function
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// must only have a single argument being the event and no return, and a channel
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// must have the event type as the underlying type.
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func newHandler(unknown interface{}) (handler, error) {
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fnV := reflect.ValueOf(unknown)
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fnT := fnV.Type()
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// underlying event type
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var handler = handler{
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callback: fnV,
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}
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switch fnT.Kind() {
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case reflect.Func:
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if fnT.NumIn() != 1 {
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return handler, errors.New("function can only accept 1 event as argument")
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}
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if fnT.NumOut() > 0 {
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return handler, errors.New("function can't accept returns")
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}
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handler.event = fnT.In(0)
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case reflect.Chan:
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handler.event = fnT.Elem()
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handler.chanclose = reflect.ValueOf(make(chan struct{}))
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default:
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return handler, errors.New("given interface is not a function or channel")
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}
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var kind = handler.event.Kind()
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// Accept either pointer type or interface{} type
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if kind != reflect.Ptr && kind != reflect.Interface {
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return handler, errors.New("first argument is not pointer")
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}
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handler.isIface = kind == reflect.Interface
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return handler, nil
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}
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func (h handler) not(event reflect.Type) bool {
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if h.isIface {
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return !event.Implements(h.event)
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}
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return h.event != event
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}
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func (h handler) call(event reflect.Value) {
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if h.chanclose.IsValid() {
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reflect.Select([]reflect.SelectCase{
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{Dir: reflect.SelectSend, Chan: h.callback, Send: event},
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{Dir: reflect.SelectRecv, Chan: h.chanclose},
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})
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} else {
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h.callback.Call([]reflect.Value{event})
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}
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}
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func (h handler) cleanup() {
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if h.chanclose.IsValid() {
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// Closing this channel will force all ongoing selects to return
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// immediately.
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h.chanclose.Close()
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}
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}
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