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package structr
import (
"context"
)
// QueueCtx is a context-aware form of Queue{}.
type QueueCtx[StructType any] struct {
Queue[StructType]
ch chan struct{}
}
// PopFront pops the current value at front of the queue, else blocking on ctx.
func (q *QueueCtx[T]) PopFront(ctx context.Context) (T, bool) {
return q.pop(ctx, func() *list_elem {
return q.queue.head
})
}
// PopBack pops the current value at back of the queue, else blocking on ctx.
func (q *QueueCtx[T]) PopBack(ctx context.Context) (T, bool) {
return q.pop(ctx, func() *list_elem {
return q.queue.tail
})
}
// PushFront pushes values to front of queue.
func (q *QueueCtx[T]) PushFront(values ...T) {
q.mutex.Lock()
for i := range values {
item := q.index(values[i])
q.queue.push_front(&item.elem)
}
if q.ch != nil {
close(q.ch)
q.ch = nil
}
q.mutex.Unlock()
}
// PushBack pushes values to back of queue.
func (q *QueueCtx[T]) PushBack(values ...T) {
q.mutex.Lock()
for i := range values {
item := q.index(values[i])
q.queue.push_back(&item.elem)
}
if q.ch != nil {
close(q.ch)
q.ch = nil
}
q.mutex.Unlock()
}
// Wait returns a ptr to the current ctx channel,
// this will block until next push to the queue.
func (q *QueueCtx[T]) Wait() <-chan struct{} {
q.mutex.Lock()
if q.ch == nil {
q.ch = make(chan struct{})
}
ctx := q.ch
q.mutex.Unlock()
return ctx
}
// Debug returns debug stats about queue.
func (q *QueueCtx[T]) Debug() map[string]any {
m := make(map[string]any)
q.mutex.Lock()
m["queue"] = q.queue.len
indices := make(map[string]any)
m["indices"] = indices
for i := range q.indices {
var n uint64
q.indices[i].data.Iter(func(_ string, l *list) (stop bool) {
n += uint64(l.len)
return
})
indices[q.indices[i].name] = n
}
q.mutex.Unlock()
return m
}
func (q *QueueCtx[T]) pop(ctx context.Context, next func() *list_elem) (T, bool) {
if next == nil {
panic("nil fn")
} else if ctx == nil {
panic("nil ctx")
}
// Acquire lock.
q.mutex.Lock()
var elem *list_elem
for {
// Get element.
elem = next()
if elem != nil {
break
}
if q.ch == nil {
// Allocate new ctx channel.
q.ch = make(chan struct{})
}
// Get current
// ch pointer.
ch := q.ch
// Unlock queue.
q.mutex.Unlock()
select {
// Ctx cancelled.
case <-ctx.Done():
var z T
return z, false
// Pushed!
case <-ch:
}
// Relock queue.
q.mutex.Lock()
}
// Cast the indexed item from elem.
item := (*indexed_item)(elem.data)
// Extract item value.
value := item.data.(T)
// Delete queued.
q.delete(item)
// Get func ptrs.
pop := q.Queue.pop
// Done with lock.
q.mutex.Unlock()
if pop != nil {
// Pass to
// user hook.
pop(value)
}
return value, true
}
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