AtomicInteger的实际用法 [英] Practical uses for AtomicInteger

问题描述

我理解AtomicInteger和其他Atomic变量允许并发访问。 AtomicInteger code>：

• 作为原子计数器（ incrementAndGet（）




• 作为支持 compare-and-swap 指令（ compareAndSet（））来实现非阻塞算法。

  
  
  

  下面是 Brian的非阻塞随机数生成器示例Göetz的Java并发实践：

    public class AtomicPseudoRandom extends PseudoRandom {
   private AtomicInteger seed; 
   AtomicPseudoRandom（int seed）{
   this.seed = new AtomicInteger（seed）; 
  } 
   
   public int nextInt（int n）{
   while（true）{
   int s = seed.get（）; 
   int nextSeed = calculateNext（s）; 
   if（seed.compareAndSet（s，nextSeed））{
   int remainder = s％n; 
   return remaining> 0？余数：余数+ n; 
  } 
  } 
  } 
   ... 
  } 
    

  
  b $ b

  可以看到，它基本上与 incrementAndGet（）几乎相同，但执行任意计算（ calculateNext




I sort of understand that AtomicInteger and other Atomic variables allow concurrent accesses. In what cases is this class typically used though?

解决方案

There are two main uses of AtomicInteger:

• As an atomic counter (incrementAndGet(), etc) that can be used by many threads concurrently

• As a primitive that supports compare-and-swap instruction (compareAndSet()) to implement non-blocking algorithms.

  Here is an example of non-blocking random number generator from Brian Göetz's Java Concurrency In Practice:

  public class AtomicPseudoRandom extends PseudoRandom {
      private AtomicInteger seed;
      AtomicPseudoRandom(int seed) {
          this.seed = new AtomicInteger(seed);
      }
  
      public int nextInt(int n) {
          while (true) {
              int s = seed.get();
              int nextSeed = calculateNext(s);
              if (seed.compareAndSet(s, nextSeed)) {
                  int remainder = s % n;
                  return remainder > 0 ? remainder : remainder + n;
              }
          }
      }
      ...
  }
  

  As you can see, it basically works almost the same way as incrementAndGet(), but performs arbitrary calculation (calculateNext()) instead of increment (and processes the result before return).

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