C# Spinlock 구현

방법1.

using System;
using System.Threading;
using System.Threading.Tasks;

namespace GameServerCore
{
    class SpinLock
    {
        volatile int _locked = 0;
        public void Acquire()
        {
            while (true)
            {
                int original = Interlocked.Exchange(ref _locked, 1);
                if (original == 0)
                    break;
            }
        }

        public void Release()
        {
            _locked = 0;
        }
    }

    class Program
    {
        static int _num = 0;
        static SpinLock _lock = new SpinLock();
        static void Main(string[] args)
        {
            Task t1 = new Task(Thread1);
            Task t2 = new Task(Thread2);
            t1.Start();
            t2.Start();

            Task.WaitAll(t1, t2);

            Console.WriteLine(_num);
        }

        static void Thread1()
        {
            for (int i = 0; i < 100000; i++)
            {
                _lock.Acquire();
                _num++;
                _lock.Release();
            }
        }

        static void Thread2()
        {
            for (int i = 0; i < 100000; i++)
            {
                _lock.Acquire();
                _num--;
                _lock.Release();
            }
        }
    }
}

 

방법2. (권장되는 방법)

 

.CompareExchange()처럼 두 값을 비교해 같을 경우 어떤 값을 대입하는 연산을

CAS 혹은 Compare and Swap연산이라고 하며 C++에서도 함수로 존재한다.

using System;
using System.Threading;
using System.Threading.Tasks;

namespace GameServerCore
{
    class SpinLock
    {
        volatile int _locked = 0;
        public void Acquire()
        {
            while (true)
            {
                int expected = 0;
                int desired = 1;
                // _locked == 0이면 _locked 에 1을 넣음.
                // CompareExchange의 반환값은 _locked의 대입 전 값, 즉  원본값이라는 것에 유의
                if (Interlocked.CompareExchange(ref _locked, desired, 0) == expected)
                {
                    break;
                }
            }
        }

        public void Release()
        {
            _locked = 0;
        }
    }

    class Program
    {
        static int _num = 0;
        static SpinLock _lock = new SpinLock();
        static void Main(string[] args)
        {
            Task t1 = new Task(Thread1);
            Task t2 = new Task(Thread2);
            t1.Start();
            t2.Start();

            Task.WaitAll(t1, t2);

            Console.WriteLine(_num);
        }

        static void Thread1()
        {
            for (int i = 0; i < 100000; i++)
            {
                _lock.Acquire();
                _num++;
                _lock.Release();
            }
        }

        static void Thread2()
        {
            for (int i = 0; i < 100000; i++)
            {
                _lock.Acquire();
                _num--;
                _lock.Release();
            }
        }
    }
}