Github user hanm commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/307#discussion_r128153360
  
    --- Diff: 
src/java/test/org/apache/zookeeper/server/ZooKeeperServerMainTest.java ---
    @@ -138,14 +145,56 @@ void delete(File f) throws IOException {
             ServerCnxnFactory getCnxnFactory() {
                 return main.getCnxnFactory();
             }
    +
         }
     
    -    public static  class TestZKSMain extends ZooKeeperServerMain {
    +    public static class TestZKSMain extends ZooKeeperServerMain {
    +
    +        private ServerStats serverStats;
    +
    +        @Override
    +        public ZooKeeperServer getZooKeeperServer(FileTxnSnapLog txnLog, 
ServerConfig config, ZKDatabase zkDb) {
    +            ZooKeeperServer zooKeeperServer = 
super.getZooKeeperServer(txnLog, config, zkDb);
    +            serverStats = zooKeeperServer.serverStats();
    +            return zooKeeperServer;
    +        }
    +
    +        @Override
             public void shutdown() {
                 super.shutdown();
             }
         }
     
    +    // Test for ZOOKEEPER-2770 ZooKeeper slow operation log
    +    @Test
    +    public void testRequestWarningThreshold() throws IOException, 
KeeperException, InterruptedException {
    +        ClientBase.setupTestEnv();
    +
    +        final int CLIENT_PORT = PortAssignment.unique();
    +
    +        MainThread main = new MainThread(CLIENT_PORT, true, null, 0);
    +        main.start();
    +
    +        Assert.assertTrue("waiting for server being up",
    +                ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT,
    +                        CONNECTION_TIMEOUT));
    +        // Get the stats object from the ZooKeeperServer to keep track of 
high latency requests.
    +        ServerStats stats = main.main.serverStats;
    +
    +        ZooKeeper zk = new ZooKeeper("127.0.0.1:" + CLIENT_PORT,
    +                ClientBase.CONNECTION_TIMEOUT, this);
    +
    +        zk.create("/foo1", "foobar".getBytes(), Ids.OPEN_ACL_UNSAFE,
    +                CreateMode.PERSISTENT);
    +
    +        Assert.assertEquals(new String(zk.getData("/foo1", null, null)), 
"foobar");
    +        // It takes a while for the counter to get updated sometimes, this 
is added to reduce flakyness
    +        Thread.sleep(1000);
    --- End diff --
    
    sync() will not help here because this specific counter is not part of any 
zab transactions. Two approaches to make test more robust:
    
    * We can always increase the counter before we send a response back to 
client in FinalRequestProcessor. This will make test deterministic, Or,
    
    * In test, implement retry polling with a timeout and a smaller sleep 
interval (e..g 10ms instead of 1000ms). We use this pattern a lot in our test. 
In general we'd like to make deterministic tests as much as possible (in other 
words, avoid sleep at all cost.) though sometimes that is hard to do due to 
various reasons.
    
    A side note on sync() - sync is not a quorum operation so it only works if 
the client connects to the leader. I think there is a jira trying to fix this.


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