137 lines
3.0 KiB
Go
137 lines
3.0 KiB
Go
package gubgub
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import (
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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 (as non-blocking as possible).
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// Closing the topic guarantees that published message will be delivered and no further messages
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// nor subscribers will be accepted.
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// Delivery order is NOT guaranteed.
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type AsyncTopic[T any] struct {
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options TopicOptions
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mu sync.RWMutex
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closing bool
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closed chan struct{}
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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.
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func NewAsyncTopic[T any](opts ...TopicOption) *AsyncTopic[T] {
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t := AsyncTopic[T]{
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closed: make(chan struct{}),
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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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t.SetOptions(opts...)
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go t.run()
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return &t
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}
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// Close terminates background go routines and prevents further publishing and subscribing. All
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// published messages are guaranteed to be delivered once Close returns. This is idempotent and
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// thread safe.
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func (t *AsyncTopic[T]) Close() {
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t.mu.Lock()
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if t.closing {
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// Multiple go routines attempted to close this topic. All should wait for the topic to be
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// closed before returning.
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t.mu.Unlock()
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<-t.closed
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return
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}
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t.closing = 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.closed
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}
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func (t *AsyncTopic[T]) run() {
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defer close(t.closed)
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defer t.options.TriggerClose()
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var subscribers []Subscriber[T]
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defer func() {
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// There is only one way to get here: the topic is now closing!
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// Because both `subscribeCh` and `publishCh` channels are closed when the topic is closed
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// we can assume this will always eventually return.
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// This will deliver any potential queued message thus fulfilling the message delivery
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// promise.
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for msg := range t.publishCh {
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subscribers = sequentialDelivery(msg, subscribers)
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}
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}()
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for {
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select {
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case newCallback, more := <-t.subscribeCh:
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if !more {
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return
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}
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subscribers = append(subscribers, newCallback)
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t.options.TriggerSubscribe()
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case msg, more := <-t.publishCh:
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if !more {
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return
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}
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subscribers = sequentialDelivery(msg, subscribers)
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}
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}
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}
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// Publish broadcasts a msg to all subscribers asynchronously.
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func (t *AsyncTopic[T]) Publish(msg T) error {
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t.mu.RLock()
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// We hold the Read lock until we are done with publishing to avoid panic due to a closed channel.
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if t.closing {
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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 registers a Subscriber func asynchronously.
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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.closing {
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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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func (t *AsyncTopic[T]) SetOptions(opts ...TopicOption) {
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t.options.Apply(opts...)
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}
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