Question

如果有多个主题同时使用以下代码调用GetNextNumber，GetNextNumber将比其他任何数字多返回1次。

private class RoundRobbinNumber
{
    private int _maxNumbers = 10;
    private int _lastNumber;

    private RoundRobbinNumber(int maxNumbers)
    {
        _maxNumbers = maxNumbers;
    }

    public int GetNextNumber()
    {
        int nextNumber = Interlocked.Increment(ref _lastNumber);
        if (_lastNumber > _maxNumbers)
        {
            Interlocked.CompareExchange(ref _lastNumber, 1, _maxNumbers);
            nextNumber = 1;
        }
        return nextNumber;
    }
}

有没有办法将_lastNumber重置为1，并且可以为每个调用GetNextNumber()的线程可靠地返回递增的数字，而不必使用锁？

Answer 1

诀窍是在循环中执行操作，直到成功为止。我在答案here中为此方法提供了一般模板。

public int GetNextNumber()
{
  int initial, computed;
  do
  {
    initial = _lastNumber;
    computed = initial + 1;
    computed = computed > _maxNumbers ? computed = 1 : computed;
  } 
  while (Interlocked.CompareExchange(ref _lastNumber, computed, initial) != initial);
  return computed;
}

Answer 2

不确定是否可以帮助除此之外的任何人更简单：

class RoundRobinNumber
{
    private int _maxNumbers = 10;
    private int _lastNumber = 0;

    public RoundRobinNumber(int maxNumbers)
    {
        _maxNumbers = maxNumbers;
    }

    public int GetNextNumber()
    {
        int nextNumber = Interlocked.Increment(ref _lastNumber);

        int result = nextNumber % _maxNumbers;  

        return result >= 0 ? result : -result;
    }
}

Answer 3

安德烈没有条件陈述的回答：

using System;
namespace Utils
{
    public class RoundRobinCounter
    {
        private int _max;
        private int _currentNumber = 0;

        public RoundRobinCounter(int max)
        {
            _max = max;
        }

        public int GetNext()
        {
            uint nextNumber = unchecked((uint)System.Threading.Interlocked.Increment(ref _currentNumber));
            int result = (int)(nextNumber % _max);
            return result;
        }
    }
}

这是运行此代码的.net fiddle。

如何为具有最小争用的循环线程场景增加数字？

3 个答案: