Variable of multi-threaded concurrent programming

What you need to be interested in writing thread safety:

• Shared variables

• Variable variable

sharing means that multiple threads can be accessed at the same time, and mutable means that their values can change over the life cycle. For example, the following countvariables:

  
 

   
  

  
//线程不安全的类
  

   
  

  
public class UnsafeCount {
  

   
  

  
 private  int  =  0   //the variable is a shared   
  

   
  

  
 public     void   ()  { 
  

   
  

  
        count++;    //该变量是可变的
  

   
  

  
    }
  

   
  

  
 public     int   ()  {
  

   
  

  
        return count;
  

   
  

  
    } 
  

   
  

  
} 
  

  
 

There are 3 ways to fix this problem:
1. You can encapsulate a variable in a method without sharing the state variable in the thread (Stateless objects must be thread-safe)because the variables in the method are exclusive to each thread and are not shared with other threads. For example:

  
 

   
  

  
   public       add   (  >int    
  

   
  

  
return ++count;//这里也可以说无状态的对象一定是线程安全的
  

   
  

  
}
  

  
 

2.Modify the state variable to a variable that is immutable.

  
 

   
  
 
   
private final  int count = 0;
 
  
  
 

3. Use the synchronization policy in the Access state variable.

  
 

   
  

  
   public      void   ()  {
  

   
  

  
count++;
  

   
  

  
}
  

  
 

From for notes (Wiz)

Variable of multi-threaded concurrent programming