Method: Etcd::Client#observe

Defined in:
lib/etcd/client/observing.rb

#observe(prefix, options = {}, &handler) ⇒ #cancel, #join

Sets up a continuous watch of a key or prefix.

This method works like #watch (which is used behind the scenes), but will re-watch the key or prefix after receiving a change notificiation.

When re-watching the index of the previous change notification is used, so no subsequent changes will be lost while a change is being processed.

Unlike #watch this method as asynchronous. The watch handler runs in a separate thread (currently a new thread is created for each invocation, keep this in mind if you need to watch many different keys), and can be cancelled by calling ‘#cancel` on the returned object.

Because of implementation details the watch handler thread will not be stopped directly when you call ‘#cancel`. The thread will be blocked until the next change notification (which will be ignored). This will have very little effect on performance since the thread will not be runnable. Unless you’re creating lots of observers it should not matter. If you want to make sure you wait for the thread to stop you can call ‘#join` on the returned object.

Examples:

Creating and cancelling an observer

observer = client.observe('/foo') do |value|
  # do something on changes
end
# ...
observer.cancel

Returns:

  • (#cancel, #join) —

    an observer object which you can call cancel and join on



34
35
36
37
38
 
# File 'lib/etcd/client/observing.rb', line 34

def observe(prefix, options = {}, &handler)
  ob = Observer.new(self, prefix, handler, options).tap(&:run)
  @observers[prefix] = ob
  ob
end