一个有趣的Unity多线程练习例子

这里将记录一些C#线程相关的信息，将持续更新，最总将形成一个工具类，方便在Unity中使用。

一些Tips：

1）Monitor VS. Mutex  

Difference between mutex and monitor. 

The biggest difference between the two is the scope: a mutex's scope is system-wide, whilst monitor's scope depends on the scope of the object you lock on. This means that with monitor, the widest scope you can get is generally application-wide.

So you would mostly use monitor to synchronise between threads running in an application, and use mutex to synchronise between different applications.

2）Monitor VS. lock

lock is just shortcut for Monitor.Enter with try + finally and Monitor.Exit. Use lock statement whenever it is enough - if you need something like TryEnter, you will have to use Monitor.

3）Semaphore VS. Monitors

Semaphore.WaitOne/Release vs Monitor.Pulse/Wait

Monitor.Wait and Monitor.Pulse are fundamental synchronization mechanisms that can be used to form pretty much any other synchronization device including semaphores.

结论，使用Monitor能够达到多线程的目的，lock可以简化这个过程。

4）Terminating a thread cleanly

5) Should a return statement be inside or outside a lock?

 At the IL level they are identical。

Only the current owner of the lock can signal a waiting object using Pulse.

The Pulse, PulseAll, and Wait methods must be invoked from within a synchronized block of code.

一个下载线程的例子：

 private class DownloadFactory {
        #region ===== 线程共享资源 =====
        private volatile bool isOpen;
        private Queue workingJobs = new Queue();
        private Queue finishedJobs = new Queue();
        #endregion

        const int WORK_NUM = 5; // 开启5个下载线程
        private Thread[] workers; // 工作线程，负责下载
        private Thread checker;  // 检测线程， 用来写磁盘或则重新下载

        public DownloadFactory() {
            isOpen = false;

            workers = new Thread[WORK_NUM];
            for (int i = 0; i < WORK_NUM; i++) { 
                workers[i] = new Thread(() => {
                    while (isOpen) {
                        var job = takeJob();
                        // do download affairs!
                        finJob(job);
                    }
                });
            }

            checker = new Thread(() => {
                while (isOpen) {
                    var job = checkJob();
                    if (!job.isOK) {  // 下载不成功，则重新下载
                        putJob(job);
                    } else { // 写文件操作

                    }
                }
            });
        }

        public bool isDone {
            get {
                return totalCount == 0;
            }
        }

        // 开始
        public void Open(Queue _allJobs) {
            workingJobs = _allJobs;
            isOpen = true;
            checker.Start();
            foreach (var w in workers) {
                w.Start();
            }
        }

        // 结束
        public void Close() {
            isOpen = false;
            checker.Interrupt();
            foreach (var w in workers) {
                w.Interrupt();
            }
            checker.Join();
            foreach (var w in workers) {
                w.Join();
            }
        }

        #region ========= 线程同步逻辑 ===========
        private int totalCount {
            get {
                lock (this) {
                    return workingJobs.Count + finishedJobs.Count;
                }
            }
        }

        private DownloadJob takeJob() {
            lock (this) {
                while (workingJobs.Count <= 0) {
                    Monitor.Wait(this);
                }
                var rt = workingJobs.Dequeue();
                Monitor.PulseAll(this);
                return rt;
            }
        }

        private void putJob(DownloadJob job) {
            lock (this) {
                workingJobs.Enqueue(job);
                Monitor.PulseAll(this);
            }
        }

        private void finJob(DownloadJob job) {
            lock (this) {
                finishedJobs.Enqueue(job);
                Monitor.PulseAll(this);
            }
        }

        private DownloadJob checkJob() {
            lock(this) {
                while (finishedJobs.Count <= 0) {
                    Monitor.Wait(this);
                }
                var job = finishedJobs.Dequeue();
                Monitor.PulseAll(this);
                return job;
            }
        }
        #endregion
    }

例子：生产消费者模式

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.Threading;
using UnityEngine.UI;

public class MultiThread : MonoBehaviour {
    private List threads = new List();
    public Text txtMessage;
    public Text txtMsg2;

    void Start() {
        var kitchen = new Kitchen();
        var table = new Table(10);
        var msgHandler = new TMsgHandler(this, msg => {
            txtMsg2.text = msg as string;
        });

        ThreadHelper.Run eater = env => {
            try {
                var random = new System.Random((int)env.param);
                while (env.alive) {
                    var cake = table.take();
                    Thread.Sleep(random.Next(100));
                    msgHandler.send(delegate {
                        txtMessage.text = env.name + "" + cake;
                    });
                }
            } catch (ThreadInterruptedException ex) {
                msgHandler.send(delegate {
                    txtMessage.text = string.Format("The {0} Interrupted!", env.name);
                });
            } finally {
                msgHandler.send(delegate {
                    txtMessage.text = string.Format("The {0} Ended!", env.name);
                });
            }
        };

        ThreadHelper.Run maker = env => {
            try {
                var param = env.param as object[];
                var random = new System.Random((int)param[1]);
                while (env.alive) {
                    Thread.Sleep(random.Next(100));
                    var cake = string.Format("[ Cake No.{0} by {1} ]", kitchen.nextCakeId, env.name);
                    table.put(cake);
                    msgHandler.send(env.name + "" + cake);
                }

            } catch (ThreadInterruptedException ex) {
                msgHandler.send(delegate {
                    txtMessage.text = string.Format("The {0} Interrupted!", env.name);
                });
            } finally {
                msgHandler.send(delegate {
                    txtMessage.text = string.Format("The {0} Ended!", env.name);
                });
            }
        };
        // 一些随机数种子：13821, 97535, 79593, 87481, 66158, 18199, 40915, 63093, 77880, 93602, 17603, 38327  
        threads.Add(new ThreadHelper("MakerThread-1", maker, new object[] { "111", 13821 }));
        threads.Add(new ThreadHelper("MakerThread-2", maker, new object[] { "222", 97535 }));
        threads.Add(new ThreadHelper("MakerThread-3", maker, new object[] { "111", 79593 }));
        threads.Add(new ThreadHelper("MakerThread-4", maker, new object[] { "222", 87481 }));
        threads.Add(new ThreadHelper("MakerThread-5", maker, new object[] { "111", 66158 }));
        threads.Add(new ThreadHelper("MakerThread-6", maker, new object[] { "222", 18199 }));
        threads.Add(new ThreadHelper("EaterThread-A", eater, 40915));
        threads.Add(new ThreadHelper("EaterThread-B", eater, 63093));
        threads.Add(new ThreadHelper("EaterThread-C", eater, 77880));
        threads.Add(new ThreadHelper("EaterThread-D", eater, 93602));
        threads.Add(new ThreadHelper("EaterThread-E", eater, 17603));
        threads.Add(new ThreadHelper("EaterThread-F", eater, 38327));

        // 开始线程    
        threads.ForEach(t => t.Start());
    }

    void OnDestroy() {
        threads.ForEach(m => m.Kill());
    }

    // 同步消息到主线程，模拟android.os.Handler的概念  
    public class TMsgHandler {
        public delegate void PostHandler();

        private System.Action