[CURATOR-527] Concurrency issue in LockInternals

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 2.12.0
• Component/s: Recipes
• Environment: Curator 2.12.0 ; zookeeper 3.4.14
• Assignee: Unassigned
• Reporter: Jaechang Kim
• Created: 05/Jun/19 11:52
• Updated: 05/Jun/19 17:43
• Resolved: 05/Jun/19 17:43

Description

I'm using InterProcessMutex and InterProcessMutex often failed to acquire lock.

In LockInternals.internalLockLoop(), watcher is registered to zookeeper and call wait() like below

client.getData().usingWatcher(watcher).forPath(previousSequencePath);
if ( millisToWait != null )
{
    millisToWait -= (System.currentTimeMillis() - startMillis);
    startMillis = System.currentTimeMillis();
    if ( millisToWait <= 0 )
    {
        doDelete = true;    // timed out - delete our node
        break;
    }

    wait(millisToWait);
}
else
{
    wait();
}

In my case, my program is waiting previousSequencePath=_c_f290140d-9856-42ad-b9bf-348ffc086062-lock-0000000759 to be deleted.

But _c_f290140d-9856-42ad-b9bf-348ffc086062-lock-0000000759 is deleted between client.getData() and wait().

if _c_f290140d-9856-42ad-b9bf-348ffc086062-lock-0000000759 is deleted when 
client.getData().usingWatcher(watcher).forPath(previousSequencePath) is called, it will throw Exception but it was exist at that time.

I'm using Curator 2.12.0 but latest version seems to have same issue.