Fundamentals of concurrent programming (III)

The basis of concurrent programming （ 3、 ... and ）

The guardian thread User threads

The guardian thread ：daemon Threads , Background process that realizes general functions , Not necessary . for example Garbage collection

User threads ： for example ,main Method , After the user process completes execution, the daemon will automatically destroy ,JVM sign out .

Use

Set a thread as a guardian thread , Need to be in start() Before the method thread executes .

 t1.setDaemon(true);

After setting to daemon thread , Even if the execution is not completed , After the main thread finishes executing , Automatically destroy ,JVM I'll quit .

scene

It can be turned off at any time , There will be no adverse consequences . Generally, it serves user threads , Low priority , Garbage collection , Heartbeat monitoring , Temporary data cleaning, etc .

ThreadLocal

Thread local variable . When multithreading operates variables , The operation is local copy , To avoid thread safety problems .

Use

get() set() Method , Setting multiple values will be overwritten .

remove() Empty

   	ThreadLocal<String> threadLocal = new ThreadLocal<>();
    threadLocal.set("hello");
    threadLocal.set("work");
    System.out.println(threadLocal.get());
    threadLocal.remove();
    System.out.println(threadLocal.get());

Multithreading does not interfere with each other

public class Test {
    static ThreadLocal<String> threadLocal = new ThreadLocal<>();
    public static void main(String[] args) throws InterruptedException {
      Thread t1 = new Thread(new Runnable(){
          @Override
          public void run(){
              threadLocal.set("t1");
                  try {
                      Thread.sleep(5000);
                  } catch (InterruptedException e) {
                      e.printStackTrace();
                  }
                 System.out.println(threadLocal.get());
              }
      });
        Thread t2 = new Thread(new Runnable(){
            @Override
            public void run(){
                threadLocal.set("t2");
                System.out.println(threadLocal.get());
                threadLocal.remove();
            }
        });
        t1.start();
        t2.start();
    }
}