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package diodes
import (
"context"
"sync"
)
// Waiter will use a conditional mutex to alert the reader to when data is
// available.
type Waiter struct {
Diode
mu sync.Mutex
c *sync.Cond
ctx context.Context
}
// WaiterConfigOption can be used to setup the waiter.
type WaiterConfigOption func(*Waiter)
// WithWaiterContext sets the context to cancel any retrieval (Next()). It
// will not change any results for adding data (Set()). Default is
// context.Background().
func WithWaiterContext(ctx context.Context) WaiterConfigOption {
return func(c *Waiter) {
c.ctx = ctx
}
}
// NewWaiter returns a new Waiter that wraps the given diode.
func NewWaiter(d Diode, opts ...WaiterConfigOption) *Waiter {
w := new(Waiter)
w.Diode = d
w.c = sync.NewCond(&w.mu)
w.ctx = context.Background()
for _, opt := range opts {
opt(w)
}
go func() {
<-w.ctx.Done()
// Mutex is strictly necessary here to avoid a race in Next() (between
// w.isDone() and w.c.Wait()) and w.c.Broadcast() here.
w.mu.Lock()
w.c.Broadcast()
w.mu.Unlock()
}()
return w
}
// Set invokes the wrapped diode's Set with the given data and uses Broadcast
// to wake up any readers.
func (w *Waiter) Set(data GenericDataType) {
w.Diode.Set(data)
w.c.Broadcast()
}
// Next returns the next data point on the wrapped diode. If there is not any
// new data, it will Wait for set to be called or the context to be done.
// If the context is done, then nil will be returned.
func (w *Waiter) Next() GenericDataType {
w.mu.Lock()
defer w.mu.Unlock()
for {
data, ok := w.Diode.TryNext()
if !ok {
if w.isDone() {
return nil
}
w.c.Wait()
continue
}
return data
}
}
func (w *Waiter) isDone() bool {
select {
case <-w.ctx.Done():
return true
default:
return false
}
}
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