knative.dev/pkg@v0.0.0-20260602142205-ac97e43f6622/configmap/informer/synced_callback.go (about)

     1  /*
     2  Copyright 2021 The Knative Authors
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package informer
    18  
    19  import (
    20  	"context"
    21  	"sync"
    22  
    23  	"k8s.io/apimachinery/pkg/util/sets"
    24  )
    25  
    26  // namedWaitGroup is used to increment and decrement a WaitGroup by name
    27  type namedWaitGroup struct {
    28  	waitGroup sync.WaitGroup
    29  	keys      sets.Set[string]
    30  	mu        sync.Mutex
    31  }
    32  
    33  // newNamedWaitGroup returns an instantiated namedWaitGroup.
    34  func newNamedWaitGroup() *namedWaitGroup {
    35  	return &namedWaitGroup{
    36  		keys: sets.New[string](),
    37  	}
    38  }
    39  
    40  // Add will add the key to the list of keys being tracked and increment the wait group.
    41  // If the key has already been added, the wait group will not be incremented again.
    42  func (n *namedWaitGroup) Add(key string) {
    43  	n.mu.Lock()
    44  	defer n.mu.Unlock()
    45  
    46  	if !n.keys.Has(key) {
    47  		n.keys.Insert(key)
    48  		n.waitGroup.Add(1)
    49  	}
    50  }
    51  
    52  // Done will decrement the counter if the key is present in the tracked keys. If it is not present
    53  // it will be ignored.
    54  func (n *namedWaitGroup) Done(key string) {
    55  	n.mu.Lock()
    56  	defer n.mu.Unlock()
    57  
    58  	if n.keys.Has(key) {
    59  		n.keys.Delete(key)
    60  		n.waitGroup.Done()
    61  	}
    62  }
    63  
    64  // Wait will wait for the underlying waitGroup to complete.
    65  func (n *namedWaitGroup) Wait() {
    66  	n.waitGroup.Wait()
    67  }
    68  
    69  // syncedCallback can be used to wait for a callback to be called at least once for a list of keys.
    70  type syncedCallback struct {
    71  	// namedWaitGroup will block until the callback has been called for all tracked entities
    72  	namedWaitGroup *namedWaitGroup
    73  
    74  	// callback is the callback that is intended to be called at least once for each key
    75  	// being tracked via WaitGroup
    76  	callback func(obj interface{})
    77  }
    78  
    79  // newSyncedCallback will return a syncedCallback that will track the provided keys.
    80  func newSyncedCallback(keys []string, callback func(obj interface{})) *syncedCallback {
    81  	s := &syncedCallback{
    82  		callback:       callback,
    83  		namedWaitGroup: newNamedWaitGroup(),
    84  	}
    85  	for _, key := range keys {
    86  		s.namedWaitGroup.Add(key)
    87  	}
    88  	return s
    89  }
    90  
    91  // Event is intended to be a wrapper for the actual event handler; this wrapper will signal via
    92  // the wait group that the event handler has been called at least once for the key.
    93  func (s *syncedCallback) Call(obj interface{}, key string) {
    94  	s.callback(obj)
    95  	s.namedWaitGroup.Done(key)
    96  }
    97  
    98  // WaitForAllKeys will block until s.Call has been called for all the keys we are tracking or the stop signal is
    99  // received.
   100  func (s *syncedCallback) WaitForAllKeys(stopCh <-chan struct{}) error {
   101  	c := make(chan struct{})
   102  	go func() {
   103  		defer close(c)
   104  		s.namedWaitGroup.Wait()
   105  	}()
   106  	select {
   107  	case <-c:
   108  		return nil
   109  	case <-stopCh:
   110  		return context.DeadlineExceeded
   111  	}
   112  }