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115 lines
2.1 KiB
115 lines
2.1 KiB
package context
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import (
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"context"
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"sync"
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"sync/atomic"
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"time"
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)
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type mergeCtx struct {
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parent1, parent2 context.Context
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done chan struct{}
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doneMark uint32
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doneOnce sync.Once
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doneErr error
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cancelCh chan struct{}
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cancelOnce sync.Once
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}
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// Merge merges two contexts into one.
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func Merge(parent1, parent2 context.Context) (context.Context, context.CancelFunc) {
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mc := &mergeCtx{
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parent1: parent1,
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parent2: parent2,
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done: make(chan struct{}),
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cancelCh: make(chan struct{}),
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}
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select {
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case <-parent1.Done():
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_ = mc.finish(parent1.Err())
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case <-parent2.Done():
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_ = mc.finish(parent2.Err())
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default:
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go mc.wait()
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}
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return mc, mc.cancel
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}
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func (mc *mergeCtx) finish(err error) error {
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mc.doneOnce.Do(func() {
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mc.doneErr = err
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atomic.StoreUint32(&mc.doneMark, 1)
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close(mc.done)
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})
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return mc.doneErr
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}
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func (mc *mergeCtx) wait() {
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var err error
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select {
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case <-mc.parent1.Done():
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err = mc.parent1.Err()
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case <-mc.parent2.Done():
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err = mc.parent2.Err()
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case <-mc.cancelCh:
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err = context.Canceled
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}
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_ = mc.finish(err)
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}
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func (mc *mergeCtx) cancel() {
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mc.cancelOnce.Do(func() {
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close(mc.cancelCh)
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})
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}
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// Done implements context.Context.
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func (mc *mergeCtx) Done() <-chan struct{} {
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return mc.done
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}
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// Err implements context.Context.
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func (mc *mergeCtx) Err() error {
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if atomic.LoadUint32(&mc.doneMark) != 0 {
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return mc.doneErr
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}
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var err error
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select {
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case <-mc.parent1.Done():
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err = mc.parent1.Err()
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case <-mc.parent2.Done():
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err = mc.parent2.Err()
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case <-mc.cancelCh:
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err = context.Canceled
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default:
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return nil
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}
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return mc.finish(err)
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}
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// Deadline implements context.Context.
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func (mc *mergeCtx) Deadline() (time.Time, bool) {
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d1, ok1 := mc.parent1.Deadline()
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d2, ok2 := mc.parent2.Deadline()
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switch {
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case !ok1:
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return d2, ok2
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case !ok2:
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return d1, ok1
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case d1.Before(d2):
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return d1, true
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default:
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return d2, true
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}
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}
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// Value implements context.Context.
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func (mc *mergeCtx) Value(key interface{}) interface{} {
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if v := mc.parent1.Value(key); v != nil {
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return v
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}
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return mc.parent2.Value(key)
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}
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