67 lines
1.3 KiB
Go
67 lines
1.3 KiB
Go
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package shadow
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import (
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"container/list"
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"sync"
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)
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// OrderedValue is a struct that keeps track of a value in the order
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// it is set. Each time Value() is called, it will return the most recent
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// calls value then discard it.
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//
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// This is unlike Value that returns the same value once it is set.
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type OrderedValue struct {
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lock sync.Mutex
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values *list.List
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waiters *list.List
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}
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// Value returns the last value that was set, or blocks until one
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// is received.
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func (w *OrderedValue) Value() interface{} {
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w.lock.Lock()
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// If we have a pending value already, use it
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if w.values != nil && w.values.Len() > 0 {
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front := w.values.Front()
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w.values.Remove(front)
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w.lock.Unlock()
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return front.Value
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}
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// No pending value, create a waiter
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if w.waiters == nil {
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w.waiters = list.New()
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}
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var val Value
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w.waiters.PushBack(&val)
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w.lock.Unlock()
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// Return the value once we have it
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return val.Value()
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}
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// SetValue sets the latest value.
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func (w *OrderedValue) SetValue(v interface{}) {
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w.lock.Lock()
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defer w.lock.Unlock()
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// If we have a waiter, notify it
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if w.waiters != nil && w.waiters.Len() > 0 {
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front := w.waiters.Front()
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w.waiters.Remove(front)
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val := front.Value.(*Value)
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val.SetValue(v)
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return
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}
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// Add it to the list of values
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if w.values == nil {
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w.values = list.New()
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}
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w.values.PushBack(v)
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}
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