144 lines
2.9 KiB
Go
144 lines
2.9 KiB
Go
package gubgub
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import (
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"context"
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"fmt"
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"sync"
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)
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// AsyncTopic allows any message T to be broadcast to subscribers. Publishing as well as
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// subscribing happens asynchronously.
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// This guarantees that every published message will be delivered but does NOT guarantee delivery
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// order.
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// In the unlikely scenario where subscribers are being queued very aggressively it is possible
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// that some might never actually receive any message. Subscriber registration order is also not
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// guaranteed.
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type AsyncTopic[T any] struct {
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options AsyncTopicOptions
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mu sync.RWMutex
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closed bool
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publishCh chan T
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subscribeCh chan Subscriber[T]
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}
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// NewAsyncTopic creates an AsyncTopic that will be closed when the given context is cancelled.
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// After closed calls to Publish or Subscribe will return an error.
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func NewAsyncTopic[T any](ctx context.Context, opts ...AsyncTopicOption) *AsyncTopic[T] {
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options := AsyncTopicOptions{
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onClose: func() {},
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onSubscribe: func(count int) {},
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}
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for _, opt := range opts {
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opt(&options)
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}
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t := AsyncTopic[T]{
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options: options,
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publishCh: make(chan T, 1),
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subscribeCh: make(chan Subscriber[T], 1),
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}
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go t.closer(ctx)
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go t.run()
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return &t
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}
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func (t *AsyncTopic[T]) closer(ctx context.Context) {
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<-ctx.Done()
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t.mu.Lock()
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t.closed = true // no more subscribing or publishing
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t.mu.Unlock()
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close(t.publishCh)
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close(t.subscribeCh)
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t.options.onClose()
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}
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func (t *AsyncTopic[T]) run() {
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var subscribers []Subscriber[T]
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for {
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select {
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case newCallback := <-t.subscribeCh:
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subscribers = append(subscribers, newCallback)
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t.options.onSubscribe(len(subscribers))
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case msg, more := <-t.publishCh:
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if !more {
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// No more published messages, promise was fulfilled and we can return
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return
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}
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keepers := make([]Subscriber[T], 0, len(subscribers))
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for _, callback := range subscribers {
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keep := callback(msg)
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if keep {
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keepers = append(keepers, callback)
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}
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}
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subscribers = keepers
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}
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}
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}
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// Publish broadcasts a msg to all subscribers.
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func (t *AsyncTopic[T]) Publish(msg T) error {
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t.mu.RLock()
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if t.closed {
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t.mu.RUnlock()
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return fmt.Errorf("async topic publish: %w", ErrTopicClosed)
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}
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go func() {
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t.publishCh <- msg
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t.mu.RUnlock()
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}()
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return nil
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}
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// Subscribe adds a Subscriber func that will consume future published messages.
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func (t *AsyncTopic[T]) Subscribe(fn Subscriber[T]) error {
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t.mu.RLock()
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if t.closed {
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t.mu.RUnlock()
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return fmt.Errorf("async topic subscribe: %w", ErrTopicClosed)
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}
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go func() {
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t.subscribeCh <- fn
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t.mu.RUnlock()
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}()
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return nil
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}
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type AsyncTopicOptions struct {
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onClose func()
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onSubscribe func(count int)
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}
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type AsyncTopicOption func(*AsyncTopicOptions)
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func WithOnClose(fn func()) AsyncTopicOption {
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return func(opts *AsyncTopicOptions) {
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opts.onClose = fn
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}
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}
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func WithOnSubscribe(fn func(count int)) AsyncTopicOption {
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return func(opts *AsyncTopicOptions) {
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opts.onSubscribe = fn
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}
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}
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