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121 lines
4.2 KiB
Go
121 lines
4.2 KiB
Go
/*
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Copyright 2022 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package synctrack contains utilities for helping controllers track whether
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// they are "synced" or not, that is, whether they have processed all items
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// from the informer's initial list.
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package synctrack
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import (
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"sync"
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"sync/atomic"
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"k8s.io/apimachinery/pkg/util/sets"
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)
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// AsyncTracker helps propagate HasSynced in the face of multiple worker threads.
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type AsyncTracker[T comparable] struct {
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UpstreamHasSynced func() bool
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lock sync.Mutex
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waiting sets.Set[T]
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}
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// Start should be called prior to processing each key which is part of the
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// initial list.
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func (t *AsyncTracker[T]) Start(key T) {
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t.lock.Lock()
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defer t.lock.Unlock()
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if t.waiting == nil {
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t.waiting = sets.New[T](key)
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} else {
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t.waiting.Insert(key)
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}
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}
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// Finished should be called when finished processing a key which was part of
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// the initial list. Since keys are tracked individually, nothing bad happens
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// if you call Finished without a corresponding call to Start. This makes it
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// easier to use this in combination with e.g. queues which don't make it easy
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// to plumb through the isInInitialList boolean.
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func (t *AsyncTracker[T]) Finished(key T) {
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t.lock.Lock()
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defer t.lock.Unlock()
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if t.waiting != nil {
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t.waiting.Delete(key)
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}
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}
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// HasSynced returns true if the source is synced and every key present in the
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// initial list has been processed. This relies on the source not considering
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// itself synced until *after* it has delivered the notification for the last
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// key, and that notification handler must have called Start.
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func (t *AsyncTracker[T]) HasSynced() bool {
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// Call UpstreamHasSynced first: it might take a lock, which might take
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// a significant amount of time, and we can't hold our lock while
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// waiting on that or a user is likely to get a deadlock.
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if !t.UpstreamHasSynced() {
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return false
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}
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t.lock.Lock()
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defer t.lock.Unlock()
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return t.waiting.Len() == 0
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}
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// SingleFileTracker helps propagate HasSynced when events are processed in
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// order (i.e. via a queue).
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type SingleFileTracker struct {
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// Important: count is used with atomic operations so it must be 64-bit
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// aligned, otherwise atomic operations will panic. Having it at the top of
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// the struct will guarantee that, even on 32-bit arches.
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// See https://pkg.go.dev/sync/atomic#pkg-note-BUG for more information.
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count int64
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UpstreamHasSynced func() bool
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}
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// Start should be called prior to processing each key which is part of the
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// initial list.
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func (t *SingleFileTracker) Start() {
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atomic.AddInt64(&t.count, 1)
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}
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// Finished should be called when finished processing a key which was part of
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// the initial list. You must never call Finished() before (or without) its
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// corresponding Start(), that is a logic error that could cause HasSynced to
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// return a wrong value. To help you notice this should it happen, Finished()
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// will panic if the internal counter goes negative.
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func (t *SingleFileTracker) Finished() {
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result := atomic.AddInt64(&t.count, -1)
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if result < 0 {
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panic("synctrack: negative counter; this logic error means HasSynced may return incorrect value")
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}
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}
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// HasSynced returns true if the source is synced and every key present in the
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// initial list has been processed. This relies on the source not considering
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// itself synced until *after* it has delivered the notification for the last
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// key, and that notification handler must have called Start.
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func (t *SingleFileTracker) HasSynced() bool {
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// Call UpstreamHasSynced first: it might take a lock, which might take
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// a significant amount of time, and we don't want to then act on a
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// stale count value.
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if !t.UpstreamHasSynced() {
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return false
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}
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return atomic.LoadInt64(&t.count) <= 0
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}
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