wehub-resource-sync
498b235461
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109 lines
2.7 KiB
Go
109 lines
2.7 KiB
Go
package syncutil
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import (
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"context"
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"sync"
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)
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const (
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VersionedListenAtEarliest versionedListenAt = -1
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VersionedListenAtLatest versionedListenAt = -2
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)
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// versionedListenerAt is the position where the listener starts to listen.
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type versionedListenAt int
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// NewVersionedNotifier creates a new VersionedNotifier.
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func NewVersionedNotifier() *VersionedNotifier {
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return &VersionedNotifier{
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inner: &versionedSignal{
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version: 0,
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cond: NewContextCond(&sync.Mutex{}),
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},
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}
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}
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// versionedSignal is a signal with version.
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type versionedSignal struct {
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version int
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cond *ContextCond
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}
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// VersionedNotifier is a notifier with version.
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// A version-based notifier, any change of version could be seen by all listeners without lost.
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type VersionedNotifier struct {
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inner *versionedSignal
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}
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// NotifyAll notifies all listeners.
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func (vn *VersionedNotifier) NotifyAll() {
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vn.inner.cond.LockAndBroadcast()
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vn.inner.version++
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vn.inner.cond.L.Unlock()
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}
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// Listen creates a listener at given position.
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func (vn *VersionedNotifier) Listen(at versionedListenAt) *VersionedListener {
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var last int
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switch at {
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case VersionedListenAtEarliest:
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last = -1
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case VersionedListenAtLatest:
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vn.inner.cond.L.Lock()
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last = vn.inner.version
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vn.inner.cond.L.Unlock()
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}
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return &VersionedListener{
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lastNotifiedVersion: last,
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inner: vn.inner,
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}
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}
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// VersionedListener is a listener with version.
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type VersionedListener struct {
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lastNotifiedVersion int
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inner *versionedSignal
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}
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// Wait waits for the next notification.
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// If the context is canceled, it returns the error.
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// Otherwise it will block until the next notification.
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func (vl *VersionedListener) Wait(ctx context.Context) error {
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vl.inner.cond.L.Lock()
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for vl.lastNotifiedVersion >= vl.inner.version {
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if err := vl.inner.cond.Wait(ctx); err != nil {
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return err
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}
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}
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vl.lastNotifiedVersion = vl.inner.version
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vl.inner.cond.L.Unlock()
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return nil
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}
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// WaitChan returns a channel that will be closed when the next notification comes.
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// Use Sync to sync the listener to the latest version to avoid redundant notify.
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//
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// ch := vl.WaitChan()
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// <-ch
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// vl.Sync()
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// ... make use of the notification ...
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func (vl *VersionedListener) WaitChan() <-chan struct{} {
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vl.inner.cond.L.Lock()
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// Return a closed channel if the version is newer than the last notified version.
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if vl.lastNotifiedVersion < vl.inner.version {
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vl.lastNotifiedVersion = vl.inner.version
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vl.inner.cond.L.Unlock()
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ch := make(chan struct{})
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close(ch)
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return ch
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}
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return vl.inner.cond.WaitChan()
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}
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// Sync syncs the listener to the latest version.
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func (vl *VersionedListener) Sync() {
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vl.inner.cond.L.Lock()
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vl.lastNotifiedVersion = vl.inner.version
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vl.inner.cond.L.Unlock()
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}
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