c# - 多线程中的死锁

Question

我试图为死锁创建一个示例。我尝试了以下代码。但它并没有造成僵局，反而发挥了魅力。帮助我理解为什么它没有造成僵局。此代码中的哪些更改会造成死锁？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ReferenceTypes
{
    class DeadLockExample
    {
        static int a;
        static int b;

        public static void Main(string[] args)
        {
            DeadLockExample.a = 20;
            DeadLockExample.b = 30;

            DeadLockExample d = new DeadLockExample();

            Thread tA = new Thread(new ThreadStart(d.MethodA));
            Thread tB = new Thread(new ThreadStart(d.MethodB));

            tA.Start();
            tB.Start();

            Console.ReadLine();
        }

        private void MethodA()
        {
            lock (this)
            {
                Console.WriteLine(a);
                Thread.Sleep(1000);
                Console.WriteLine(b);
            }
        }

        private void MethodB()
        {
            lock (this)
            {
                Console.WriteLine(b);
                Thread.Sleep(1000);
                Console.WriteLine(a);
            }
        }
     }
}

Answer 1

正如其他人所说，两个锁以不同的顺序获取，因此每个锁都在等待另一个。我还更改了其中一个 sleep 长度，以确保发生死锁的可能性很高。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ReferenceTypes
{
    class DeadLockExample
    {
        static int a;
        static int b;

        static object lockedObjA = new object();
        static object lockedObjB = new object();

        public static void Main(string[] args)
        {
            DeadLockExample.a = 20;
            DeadLockExample.b = 30;

            DeadLockExample d = new DeadLockExample();

            Thread tA = new Thread(new ThreadStart(d.MethodA));
            Thread tB = new Thread(new ThreadStart(d.MethodB));

            tA.Start();
            tB.Start();

            Console.ReadLine();
        }

        private void MethodA()
        {
            lock (DeadLockExample.lockedObjA)
            {
                Console.WriteLine(a);
                Thread.Sleep(1200);

                lock (DeadLockExample.lockedObjB) {
                    Console.WriteLine(b);
                }
            }
        }

        private void MethodB()
        {
            lock (DeadLockExample.lockedObjB)
            {
                Console.WriteLine(b);
                Thread.Sleep(1000);

                lock (DeadLockExample.lockedObjA) {
                    Console.WriteLine(a);
                }
            }
        }
     }
}