[ZOOKEEPER-1739] thread safe bug in FastLeaderElection: instance of WorkerSender is not safe published, WorkerSender thread may see that WorkerSender.manager is the default value null

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 3.4.5
• Component/s: leaderElection
• Assignee: qingjie qiao
• Reporter: qingjie qiao
• Created: 09/Aug/13 04:29
• Updated: 11/Aug/13 03:01

Description

I am reading the trunk source code recently and find a thread-safe problem, but i'm not quite sure.

in FastLeaderElection:

class WorkerSender implements Runnable { 
    volatile boolean stop; 
    QuorumCnxManager manager; 

    WorkerSender(QuorumCnxManager manager){ 
        this.stop = false; 
        this.manager = manager; 
    } 

    public void run() {
 ...
    }
}

...

Messenger(QuorumCnxManager manager) {

    this.ws = new WorkerSender(manager);

    Thread t = new Thread(this.ws,
            "WorkerSender[myid=" + self.getId() + "]");
    t.setDaemon(true);
    t.start();

    this.wr = new WorkerReceiver(manager);

    t = new Thread(this.wr,
            "WorkerReceiver[myid=" + self.getId() + "]");
    t.setDaemon(true);
    t.start();
}
...

The instance of WorkerSender is constructed in main thread, and its field manager is assigned , and it is used in another thread. The later thread may see that WorkerSender.manager is the default value null. The solution may be:
(1) change

 
WorkerSender(QuorumCnxManager manager){ 
        this.stop = false; 
        this.manager = manager; 
} 

to

WorkerSender(QuorumCnxManager manager){ 
	this.manager = manager; 
	this.stop = false; 
} 

or(2)
change

QuorumCnxManager manager; 

to

final QuorumCnxManager manager;