哪些变量是java中多线程的accessbile？

Question

I am working on a simple message queue where I am creating separate thread for new connection. I want to know which variables are accessible and can be modified by multiple threads.

class RequestHandler implements Runnable {

    Socket socket;

    protected RequestHandler(Socket socket) {
        this.socket = socket;
    }

    public void run() { ..........

In above code is socket can be accessed by multiple threads, if yes then how do I protect it.

Complete code is available at. https://github.com/nakshay/JQueue

I am new to multithreading, please modify question if requried.

Answer 1

If the socket variable can be accessed by multiple threads you need synchronize access to the variable.

One of the ways is to create a wrapper, which basically will synchronize methods calls[1].

And then wrap your socket in the constructor:

class RequestHandler implements Runnable {

    Socket socket;

    protected RequestHandler(Socket socket) {
        this.socket = new SynchronizedSocket(socket);
    }

    public void run() { ..........

[1] - https://gist.github.com/Sammers21/a6635213276e9ea064a5a4f20dd53c11

Answer 2

Not shown in the post: You actually create a new RequestHandler and Socket for every thread, so since the socket is not static, you are fine. Each thread handles its own connection (represented by the Socket).