github.com/m3db/m3@v1.5.0/src/query/storage/m3/cluster_namespaces_watcher.go (about)

     1  // Copyright (c) 2020  Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  package m3
    22  
    23  import (
    24  	xresource "github.com/m3db/m3/src/x/resource"
    25  	xwatch "github.com/m3db/m3/src/x/watch"
    26  )
    27  
    28  type clusterNamespacesWatcher struct {
    29  	watchable xwatch.Watchable
    30  }
    31  
    32  // NewClusterNamespacesWatcher creates a new ClusterNamespacesWatcher.
    33  func NewClusterNamespacesWatcher() ClusterNamespacesWatcher {
    34  	watchable := xwatch.NewWatchable()
    35  	return &clusterNamespacesWatcher{watchable: watchable}
    36  }
    37  
    38  func (n *clusterNamespacesWatcher) Update(namespaces ClusterNamespaces) error {
    39  	return n.watchable.Update(namespaces)
    40  }
    41  
    42  func (n *clusterNamespacesWatcher) Get() ClusterNamespaces {
    43  	value := n.watchable.Get()
    44  	if value == nil {
    45  		return nil
    46  	}
    47  
    48  	return value.(ClusterNamespaces)
    49  }
    50  
    51  // RegisterListener registers the provided listener and returns a closer to clean up the watch.
    52  // If the watcher is already closed, nothing is registered.
    53  func (n *clusterNamespacesWatcher) RegisterListener(
    54  	listener ClusterNamespacesListener,
    55  ) xresource.SimpleCloser {
    56  	if n.watchable.IsClosed() {
    57  		return xresource.SimpleCloserFn(func() {})
    58  	}
    59  	_, watch, _ := n.watchable.Watch()
    60  
    61  	namespaces := watch.Get()
    62  
    63  	// Deliver the current cluster namespaces, synchronously, if already set.
    64  	if namespaces != nil {
    65  		<-watch.C() // Consume initial notification
    66  		listener.OnUpdate(namespaces.(ClusterNamespaces))
    67  	}
    68  
    69  	// Spawn a new goroutine to listen for updates.
    70  	go func() {
    71  		for range watch.C() {
    72  			listener.OnUpdate(watch.Get().(ClusterNamespaces))
    73  		}
    74  	}()
    75  
    76  	return watch
    77  }
    78  
    79  func (n *clusterNamespacesWatcher) Close() {
    80  	n.watchable.Close()
    81  }