SecurityContextHolder 线程安全吗

SecurityContextHolder是Spring Security提供的一个用于管理当前用户安全上下文的工具类。它允许在应用程序中访问当前用户的身份验证信息，如用户名、权限和其他相关的安全上下文。然而，SecurityContextHolder是否线程安全是一个重要的问题。

java
public class SecurityContextThread implements Runnable {
    private String username;
    public SecurityContextThread(String username) {
        this.username = username;
    }
    @Override
    public void run() {
        SecurityContext securityContext = SecurityContextHolder.getContext();
        securityContext.setAuthentication(new UsernamePasswordAuthenticationToken(username, null));
        System.out.println("Thread: " + Thread.currentThread().getName() + ", User: " + securityContext.getAuthentication().getName());
    }
    public static void main(String[] args) {
        SecurityContextThread thread1 = new SecurityContextThread("user1");
        SecurityContextThread thread2 = new SecurityContextThread("user2");
        Thread t1 = new Thread(thread1);
        Thread t2 = new Thread(thread2);
        t1.start();
        t2.start();
    }
}