Pessimistic lock and optimistic lock of multithreading

process : The smallest unit of resource allocation

No one will wait for anyone between threads . Who is the first to get cpu Whoever calculates first

 

Time slice rotation algorithm :cpu The time allocated to each thread that it can execute . Writing memory needs to occupy the bus 64bit

Multithreaded code

package wangyi0820;
//z Main method 
public class MultiDemo {
    public static void main(String[] args) {
        ThreadNew tn1 = new ThreadNew(1);
        ThreadNew tn2 = new ThreadNew(2);
        tn1.start();
        tn2.start();
    }
}
​
​
package wangyi0820;
​
public class ThreadNew extends Thread {
​
    private int falge;
​
    public ThreadNew(int falge) {
        this.falge = falge;
    }
​
    public void run() {
        if (falge == 1) {
            System.out.println("run1() Method execution ");
        } else {
            System.out.println("run2() Method execution ");
        }
    }
}
​

lock

• Pessimistic locking ( Also known as locking )

  • Don't let users read , Don't let users write , Only when one thread finishes writing can another thread read and write

• 

   

• Optimism lock ( Also known as semaphore )

  • Let users read , But don't let users write , Yes Version number , Wrong version , Just redo the calculation . amount to Gitee Branches and mainlines

•