原子引用相关

​ AtomicInteger和AtomicLong这类原子整数主要是针对整数类型的线程安全的，为了实现对原子引用的线程安全，引入了AtomicReference这个原子引用类

1. 还是拿1000个线程同时取10块钱的案例举例，代码如下所示：

   public interface Account {
   
      public BigDecimal getBalance();
   
      public void withdraw(BigDecimal amount);
   
      static void demo(Account account) {
          List<Thread> threads = new ArrayList<>();
          for (int i=0;i<1000;i++) {
              threads.add(new Thread(() -> {
                  account.withdraw(BigDecimal.TEN);
              }));
          }
   
          threads.forEach(Thread::start);
          long start = System.nanoTime();
          for (Thread thread : threads) {
              try {
                  thread.join();
              } catch (InterruptedException e) {
                  e.printStackTrace();
              }
          }
          long end = System.nanoTime();
          System.out.println("余额   " + account.getBalance() + "  ---" + "  cost  " + (end - start)/1000000 + "ms");
      }
   
   }
   

   具体实现类如下所示：

   class AccountReference implements Account {
   
      private AtomicReference<BigDecimal> balance;  // 通过AtomicReference 对结果进行包装
   
      public AccountReference(BigDecimal balance) {
          this.balance = new AtomicReference<>(balance);
      }
   
      @Override
      public BigDecimal getBalance() {
          return this.balance.get();
      }
   
      @Override
      public void withdraw(BigDecimal amount) {
          while (true) {
              BigDecimal prev = balance.get();
              BigDecimal next = prev.subtract(amount);
              if (balance.compareAndSet(prev, next)) { // 这条语句是原子性的
                  break;
              }
          }
      }
   }
   
   class Test {
      public static void main(String[] args) {
          Account.demo(new AccountReference(new BigDecimal(10000)));
      }
   }
   

2.运行结果