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