Hi All:
Use zookeeper to build distribute lock is main feature. now implement the lock 
function as below code:

Public void lock() throws InterruptedException{
    Do{
        If(path == null){
  Path = zk.create(lockPrefix,null,acl, CreateMode.EPHEMERAL_SEQUENTIAL)
}
       List<String> children = zk.getChildren(parentPath);
       If(isFirst(children,path)){
   Return;
}else{
     Final CowntDownLatch latch = new CountDownLatch(1);
    String nestestChild = findLastBefore(children,path);
       If(zk.exist(nestestChildPath,new Watcher(Event){
             Latch.countDown();
}) != null){
   Latch.await();
}else{
  //acquire lock success
   Return;
}
}
}while(true);
}

In high concurrent case, lock node may need to get a big ephemeral children 
nodes. So that the GetChildren may cause the package exceeding the 
limitation(4MB as default), and also this would cause the performance issue. To 
avoid the issue, I plan to add a new interface isFirst for zeekeeper. I don't 
know if it is useful as a common usage, but I do think it should help a little 
bit in the concurrent situation. Below is snippet of the code change, and the 
attachment is full list of it.

Public void lock() throws InterruptedException{
    Do{
        If(path == null){
  Path = zk.create(lockPrefix,null,acl, CreateMode.EPHEMERAL_SEQUENTIAL)
}
Final CowntDownLatch latch = new CountDownLatch(1);
If(!Zk.isFirst(parentPath,path,Type,new Watcher(Event){
         Latch.countDown();
})){
   Latch.countDown()
}else{
  //acquire success.
   Return;
}
}while(true);
}

As we know, only the first node can aquire the lock success, so when lock Type 
parent node remove child node, it need trigger the the wather to notify the 
first node.

the second lock requirement is:
in our current project, each save need require multiple lock. In distribute 
Env, it very maybe cause dead lock or lock starve. So we need a stateLock, in 
the lock node, it keep the multiple states to judge the node if acquire the 
lock or not. Example:
Client1:    lock( id1,id2,id3) ->zdnode---0000000001
Client2:    lock(id2,id3)    ->zdnode---0000000002
Client3:    lock(id4)       ->zdnode---0000000003

We need client2 need wait the lock until the client1 unlock lock. But client 3 
can acquire the lock at once. These judge logic in zookeeper server. We add a 
LockState interface:
public interface LockState{
    String PATH_SEPERATOR = "/";
    String PATH_DELIMIT = "|";
    boolean isConflict(LockState state);
    byte[] getBytes();
}

Any new lock strategy can be added by implement the interface.

Attached is my code diff from 3.2.2 and the use lock some case.


Best Regards
Joe Zou

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