[ZOOKEEPER-2037] ZooKeeper methods to wait on client connection (re)establishment.

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 3.5.0
• Component/s: java client
• Assignee: Hongchao Deng
• Reporter: Hongchao Deng
• Created: 15/Sep/14 21:00
• Updated: 28/Jan/15 04:32
• Resolved: 28/Jan/15 04:32

Description

When a ZooKeeper object is created and returned, it is not guaranteed that connection to a server is established.

Usually, a wait/signal pattern is used for the ZK watcher

latch = new CountDownLatch(1)
zk = new ZooKeeper(..., new Watcher() {
  override void process(WatchedEvent event) {
    if (event.type = SyncConnected) {
      latch.countDown()
    }
  }
},...)

latch.await();
// connection has been established. do something with zk.

There are two disadvantages:
1. The latch object isn't being garbage-collected. Because the watcher keeps monitoring all kinds of events.
2. With the introduction of dynamic reconfig, client move to other servers on needed and this latch method doesn't work so well.

Here I propose to add (both sync and async) wait methods to act as latch for connection establish such that it becomes much easier to manage and work around:

zk = new ZooKeeper(...)
zk.waitUntilConnected()