helper/shadow: Value.Close
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3e7665db09
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@ -1,12 +1,24 @@
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package shadow
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import (
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"errors"
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"sync"
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)
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// ErrClosed is returned by any closed values.
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//
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// A "closed value" is when the shadow has been notified that the real
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// side is complete and any blocking values will _never_ be satisfied
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// in the future. In this case, this error is returned. If a value is already
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// available, that is still returned.
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var ErrClosed = errors.New("shadow closed")
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// Value is a struct that coordinates a value between two
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// parallel routines. It is similar to atomic.Value except that when
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// Value is called if it isn't set it will wait for it.
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//
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// The Value can be closed with Close, which will cause any future
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// blocking operations to return immediately with ErrClosed.
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type Value struct {
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lock sync.Mutex
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cond *sync.Cond
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@ -14,6 +26,22 @@ type Value struct {
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valueSet bool
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}
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// Close closes the value. This can never fail. For a definition of
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// "close" see the struct docs.
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func (w *Value) Close() error {
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w.lock.Lock()
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set := w.valueSet
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w.lock.Unlock()
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// If we haven't set the value, set it
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if !set {
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w.SetValue(ErrClosed)
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}
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// Done
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return nil
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}
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// Value returns the value that was set.
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func (w *Value) Value() interface{} {
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w.lock.Lock()
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@ -41,3 +41,32 @@ func TestValue(t *testing.T) {
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t.Fatalf("bad: %#v", val)
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}
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}
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func TestValueClose(t *testing.T) {
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var v Value
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// Close
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v.Close()
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// Verify
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val := v.Value()
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if val != ErrClosed {
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t.Fatalf("bad: %#v", val)
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}
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}
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func TestValueClose_existing(t *testing.T) {
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var v Value
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// Set the value
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v.SetValue(42)
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// Close
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v.Close()
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// Verify
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val := v.Value()
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if val != 42 {
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t.Fatalf("bad: %#v", val)
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}
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}
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