On "waiting for awakening mechanism"

Wait for the wake-up mechanism

Inter thread communication ：

  Multiple threads are processing the same resource , But the action of handling （ Thread tasks ） But not the same 

Why handle inter thread communication ？

When multiple threads execute concurrently , By default CPU It's random thread switching , When we need multiple threads to complete a task together , And I hope they will implement it regularly , So many threads need some coordinated communication , In order to help us achieve multi-threaded common operation of a piece of data
How to ensure inter thread communication and make effective use of resources ？

Multiple threads are processing the same resource , And the tasks are different , Thread communication is needed to help solve the problem between threads
The use or operation of the same variable . When multiple threads operate on the same data , Avoid contention for the same shared variable . That is, we need to use certain means to make each thread make effective use of resources , And that means ---- Wait for the wake-up mechanism

Wait for the wake-up mechanism

Waiting for wake-up mechanism is actually a classic “ Producers and consumers ” The problem of

Understand the waiting wake-up mechanism with buying and selling steamed stuffed buns

Waiting for wake-up cases ： Communication between threads

Create a customer thread （ consumer ）： Tell the boss the type and quantity of steamed buns to buy , call wait Method , give up cpu Implementation , Enter into WAITING state （ Wait indefinitely ）

Create a boss thread （ producer ）： Spend some time making steamed stuffed buns , After making the steamed stuffed bun , call notify Method , Wake up customers to eat steamed stuffed buns

Be careful ：

Customer and boss threads must be wrapped in synchronized code blocks , Ensure that only one of the wait and wake-up can be performed
The lock object used in synchronization must be unique
Only lock objects can call wait and notify Method

Object Methods in class

void wait() This object is called in another thread notify() Method or notifyAll() Before the method , Causes the current thread to wait
void notify() Wake up a single thread waiting on this object monitor , Will continue to execute wait The code after the method

 public static void main(String[] args) {
    
        // Create lock object , Ensure that the only 
       Object obj=new Object();
       // Create a customer thread （ consumer ）
       new Thread(){
    
           @Override
           public void run(){
    
               // Ensure that only one thread waiting and waking up can execute , Need to use synchronization technology 
               //synchronized    Synchronization means 
             //  while(true)  loop   I've been waiting to buy steamed stuffed buns 
             //  {
    
                   synchronized (obj){
    
                       System.out.println(" Tell the boss the type and quantity of steamed buns you want ");
                       // call wait Method , give up cpu Implementation , Enter into WAITING state （ Wait indefinitely ）
                       try
                       {
    
                           obj.wait();
                       }catch(InterruptedException e){
    
                           e.printStackTrace();
                       }
                       // Code executed after wake-up 
                       System.out.println(" The steamed stuffed bun has been made , You can eat ");
                   }
             //  }

           }
       }.start();
       // Create a boss thread （ producer ）
        new Thread(){
    
            @Override
            public void run(){
    
                // Ensure that only one thread waiting and waking up can execute , Need to use synchronization technology 
                    // call wait Method , give up cpu Implementation , Enter into WAITING state （ Wait indefinitely ）
                    try
                    {
    
                        Thread.sleep(5000);// cost 5 Make steamed stuffed bun in seconds 
                    }catch(InterruptedException e){
    
                        e.printStackTrace();
                    }
                   synchronized (obj){
    
                    System.out.println(" Boss 5 Make steamed stuffed buns in seconds , Tell the customer ");
                    // After making the steamed stuffed bun , call notify() Method , Wake up customers to eat steamed stuffed buns 
                       obj.notify();
                }
            }
        }.start();
    }