The InterProcessMutex is essentially a distributed lock. In each of your
clients you just create an InterProcessMutex instance referring to the same
ZK path
CuratorFramework curator = ...
String lockPath = "/lockPath";
InterProcessMutex mutex = new InterProcessMutex(curator, lockPath);
try {
//This will block until the mutex is acquire.
mutex.acquire();
//Do your critical stuff
} finally {
//Release the mutex
mutex.release();
}
On Fri, Jan 16, 2015 at 12:05 PM, Check Peck <[email protected]>
wrote:
> What is the benefit I will have with InterProcessMutex? I have never use
> this before. Is there any example which I can take a look?
>
> On Thu, Jan 15, 2015 at 4:07 PM, Cameron McKenzie <[email protected]>
> wrote:
>
>> Yes, good point.
>>
>> On Fri, Jan 16, 2015 at 10:57 AM, Jordan Zimmerman <
>> [email protected]> wrote:
>>
>>> But if you go through that much trouble you might as well just use
>>> InterProcessMutex.
>>>
>>> -JZ
>>>
>>>
>>>
>>> On January 15, 2015 at 6:54:30 PM, Cameron McKenzie (
>>> [email protected]) wrote:
>>>
>>> If you use the callback as Jordan suggested, then you can just block
>>> on a latch, and then get this latch to be updated by the callback when it
>>> is notified that it's leader. Then you won't have to wait for some fixed
>>> amount of time, it will just block until it's leader.
>>>
>>>
>>> On Fri, Jan 16, 2015 at 10:48 AM, Check Peck <[email protected]>
>>> wrote:
>>>
>>>> As of now, I am adding a sleep of 1 minute and it works fine before I
>>>> check whether I am a leader or not.
>>>>
>>>> On Thu, Jan 15, 2015 at 3:43 PM, Check Peck <[email protected]>
>>>> wrote:
>>>>
>>>>> Yes that makes sense that 1 client will be leader. But suppose I
>>>>> have 5 background threads running in 5 different machines and each
>>>>> background thread is in different classes and I want to make sure that
>>>>> those 5 background threads are running from a single machine who is the
>>>>> leader so that's why we are doing that check whether I am the leader then
>>>>> do this.
>>>>>
>>>>> Will this work if we add a Listener to leaderlatch?
>>>>>
>>>>> On Thu, Jan 15, 2015 at 3:30 PM, Jordan Zimmerman <
>>>>> [email protected]> wrote:
>>>>>
>>>>>> The problem with that is you have to wait until you are the leader.
>>>>>> The benefit of LeaderSelector is that it has a callback that is invoked
>>>>>> when you are the leader. Remember, you are in a multithreaded, multi
>>>>>> client
>>>>>> environment. Only 1 client is going to be the leader. Maybe what you are
>>>>>> after is an InterProcessMutex?
>>>>>>
>>>>>> -JZ
>>>>>>
>>>>>>
>>>>>>
>>>>>> On January 15, 2015 at 6:24:06 PM, Check Peck (
>>>>>> [email protected]) wrote:
>>>>>>
>>>>>> I saw the leader election code here -
>>>>>> https://git-wip-us.apache.org/repos/asf?p=curator.git;a=tree;f=curator-examples/src/main/java/leader;h=73b547eadb98995c0ccbd06a5b76d0741ffef263;hb=HEAD
>>>>>>
>>>>>> But didn't understand few things - How can I call something like this
>>>>>> in my code - I want to do stuff in my code by just checking whether I am
>>>>>> the leader or not. And from the LeaderSelectorExample, I am not able to
>>>>>> understand this.
>>>>>>
>>>>>> if (zookClient.isLeader()) {
>>>>>>
>>>>>> // then do stuff
>>>>>>
>>>>>> }
>>>>>>
>>>>>>
>>>>>> On Thu, Jan 15, 2015 at 3:17 PM, Jordan Zimmerman <
>>>>>> [email protected]> wrote:
>>>>>>
>>>>>>> Oh - maybe I read the code too fast. I guess it doesn’t make more
>>>>>>> than one…
>>>>>>>
>>>>>>> There’s an example of LeaderSelector here:
>>>>>>> http://curator.apache.org/curator-examples/index.html
>>>>>>>
>>>>>>>
>>>>>>> On January 15, 2015 at 6:00:03 PM, Check Peck (
>>>>>>> [email protected]) wrote:
>>>>>>>
>>>>>>> Thanks Jordan for the input.
>>>>>>>
>>>>>>> * Where do you see that I am creating new Curator instance for each
>>>>>>> Leader? I guess I am using one Curator instance for my application?
>>>>>>> * Ok, I have commented out this line in ZookeeperClient class
>>>>>>> * That's a good point, how would I use the listener or the
>>>>>>> leaderselector in my code base? If possible, can you provide an example?
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Jan 15, 2015 at 2:38 PM, Jordan Zimmerman <
>>>>>>> [email protected]> wrote:
>>>>>>>
>>>>>>>> A few things:
>>>>>>>>
>>>>>>>> * You don’t need to create a new Curator instance for each Leader.
>>>>>>>> One Curator instance can be used for an application.
>>>>>>>> * Calling
>>>>>>>> client.getZookeeperClient().blockUntilConnectedOrTimedOut(); is
>>>>>>>> unnecessary
>>>>>>>> * Calling isLeader() immediately after starting the latch may not
>>>>>>>> work. It takes time for the leader to get selected. LeaderLatch has a
>>>>>>>> listener if you want to get notified. Alternatively, you can use
>>>>>>>> LeaderSelector.
>>>>>>>>
>>>>>>>> Hope this helps.
>>>>>>>>
>>>>>>>> -Jordan
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On January 15, 2015 at 5:25:26 PM, Check Peck (
>>>>>>>> [email protected]) wrote:
>>>>>>>>
>>>>>>>> I am using Zookeeper for the leadership election process. I have
>>>>>>>> three nodes zookeeper ensemble.
>>>>>>>>
>>>>>>>> We have a node like this "/test/msn" on which we are doing the
>>>>>>>> leadership election and it works fine and we have application servers
>>>>>>>> running it in production and using "/test/msn" node for leadership. And
>>>>>>>> this program is always running.
>>>>>>>>
>>>>>>>> Now we created another node like this "/testpnl" in the same
>>>>>>>> zookeeper servers. And we have another set of machines which is trying
>>>>>>>> to
>>>>>>>> do the leadership election on that node and whenever I run my program
>>>>>>>> in
>>>>>>>> production from one servers, it always returns back that the node is
>>>>>>>> not
>>>>>>>> leader? And I can see only one node inside "/testpnl" and it is the
>>>>>>>> same
>>>>>>>> node from which I am running my program?
>>>>>>>>
>>>>>>>> I am using Curator 2.7.0 and the zookeeper version is 3.4.5 Is
>>>>>>>> there anything wrong with my setup or zookeeper has some bug which I
>>>>>>>> am not
>>>>>>>> aware?
>>>>>>>>
>>>>>>>> Is anything
>>>>>>>>
>>>>>>>> public class ZookeeperLeaderTester {
>>>>>>>>
>>>>>>>> private ZookeeperClient zookClient;
>>>>>>>>
>>>>>>>> private static final String ZOOK_PRODUCTION =
>>>>>>>> "host1:2181,host2:2181,host3:2181";
>>>>>>>> private static final String LEADERSHIP_NODE = "/testpnl";
>>>>>>>>
>>>>>>>> private static class Holder {
>>>>>>>> static final ZookeeperLeaderTester INSTANCE = new
>>>>>>>> ZookeeperLeaderTester();
>>>>>>>> }
>>>>>>>>
>>>>>>>> public static ZookeeperLeaderTester getInstance() {
>>>>>>>> return Holder.INSTANCE;
>>>>>>>> }
>>>>>>>>
>>>>>>>> private ZookeeperLeaderTester() {
>>>>>>>> try {
>>>>>>>> String hostname = getHostName();
>>>>>>>>
>>>>>>>> zookClient = new ZookeeperClient(nodes,
>>>>>>>> LEADERSHIP_NODE, hostname);
>>>>>>>> zookClient.start();
>>>>>>>>
>>>>>>>> } catch (Exception ex) {
>>>>>>>> System.out.println (ex);
>>>>>>>> System.exit(1);
>>>>>>>> }
>>>>>>>> }
>>>>>>>>
>>>>>>>> public ZookeeperClient getZookClient() {
>>>>>>>> return zookClient;
>>>>>>>> }
>>>>>>>> }
>>>>>>>>
>>>>>>>> And here is my ZookeeperClient code -
>>>>>>>>
>>>>>>>> public class ZookeeperClient {
>>>>>>>>
>>>>>>>> private CuratorFramework client;
>>>>>>>> private String latchPath;
>>>>>>>> private String id;
>>>>>>>> private LeaderLatch leaderLatch;
>>>>>>>>
>>>>>>>> public ZookeeperClient(String connString, String latchPath,
>>>>>>>> String id) {
>>>>>>>> client = CuratorFrameworkFactory.newClient(connString,
>>>>>>>> new ExponentialBackoffRetry(1000, Integer.MAX_VALUE));
>>>>>>>> this.id = id;
>>>>>>>> this.latchPath = latchPath;
>>>>>>>> }
>>>>>>>>
>>>>>>>> public void start() throws Exception {
>>>>>>>> client.start();
>>>>>>>>
>>>>>>>> client.getZookeeperClient().blockUntilConnectedOrTimedOut();
>>>>>>>> leaderLatch = new LeaderLatch(client, latchPath, id);
>>>>>>>> leaderLatch.start();
>>>>>>>> }
>>>>>>>>
>>>>>>>> public boolean isLeader() {
>>>>>>>> return leaderLatch.hasLeadership();
>>>>>>>> }
>>>>>>>>
>>>>>>>> public Participant currentLeader() throws Exception {
>>>>>>>> return leaderLatch.getLeader();
>>>>>>>> }
>>>>>>>>
>>>>>>>> public void close() throws IOException {
>>>>>>>> leaderLatch.close();
>>>>>>>> client.close();
>>>>>>>> }
>>>>>>>>
>>>>>>>> public CuratorFramework getClient() {
>>>>>>>> return client;
>>>>>>>> }
>>>>>>>>
>>>>>>>> public String getLatchPath() {
>>>>>>>> return latchPath;
>>>>>>>> }
>>>>>>>>
>>>>>>>> public String getId() {
>>>>>>>> return id;
>>>>>>>> }
>>>>>>>>
>>>>>>>> public LeaderLatch getLeaderLatch() {
>>>>>>>> return leaderLatch;
>>>>>>>> }
>>>>>>>> }
>>>>>>>>
>>>>>>>> And this is the way I am using it -
>>>>>>>>
>>>>>>>> ZookeeperLeaderTester zookClient =
>>>>>>>> ZookeeperLeaderTester.getInstance().getZookClient();
>>>>>>>> if (zookClient.isLeader()) {
>>>>>>>> // then do stuff
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
