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Threads(异步和多线程)

diezuo9326 2020-02-02 14:33 134 查看 https://blog.csdn.net/diezuo93

Task是.NET Framework3.0出现的,线程是基于线程池的,然后提供丰富的api,Thread方法很多很强大,但是太过强大,没有限制。

DoSomethingLong方法如下:

/// <summary>
/// 一个比较耗时耗资源的私有方法
/// </summary>
/// <param name="name"></param>
private void DoSomethingLong(string name)
{
Console.WriteLine($"****************DoSomethingLong Start  {name}  {Thread.CurrentThread.ManagedThreadId.ToString("00")} {DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fff")}***************");
long lResult = 0;
for (int i = 0; i < 1_000_000_000; i++)
{
lResult += i;
}
Thread.Sleep(2000);

Console.WriteLine($"****************DoSomethingLong   End  {name}  {Thread.CurrentThread.ManagedThreadId.ToString("00")} {DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fff")} {lResult}***************");
}
View Code

Task的使用:

{
Task task = new Task(() => this.DoSomethingLong("btnTask_Click_1"));
task.Start();
}
{
Task task = Task.Run(() => this.DoSomethingLong("btnTask_Click_2"));
}
{
TaskFactory taskFactory = Task.Factory;
Task task = taskFactory.StartNew(() => this.DoSomethingLong("btnTask_Click_3"));
}

 如果这样去调用:

ThreadPool.SetMaxThreads(8, 8);
for (int i = 0; i < 100; i++)
{
int k = i;
Task.Run(() =>
{
Console.WriteLine($"This is {k} running ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
Thread.Sleep(2000);
});
}

 

 

 

如果去掉设置最大线程的代码:

for (int i = 0; i < 100; i++)
{
int k = i;
Task.Run(() =>
{
Console.WriteLine($"This is {k} running ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
Thread.Sleep(2000);
});
}

运行结果如下:

 

 

 

 ThreadPool.SetMaxThreads(8, 8);

  线程池是单例的,全局唯一的,设置后,同时并发的Task只有8个,而且是复用的,Task的线程是源于线程池的,全局的,请不要这样设置。

假如我想控制下Task的并发数量,改怎么做?

{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Console.WriteLine("在Sleep之前");
Thread.Sleep(2000);//同步等待--当前线程等待2s 然后继续
Console.WriteLine("在Sleep之后");
stopwatch.Stop();
Console.WriteLine($"Sleep耗时{stopwatch.ElapsedMilliseconds}");
}
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Console.WriteLine("在Delay之前");
Task task = Task.Delay(2000)
.ContinueWith(t =>
{
stopwatch.Stop();
Console.WriteLine($"Delay耗时{stopwatch.ElapsedMilliseconds}");

Console.WriteLine($"This is ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
});//异步等待--等待2s后启动新任务
Console.WriteLine("在Delay之后");
stopwatch.Stop();
Console.WriteLine($"Delay耗时{stopwatch.ElapsedMilliseconds}");
}

运行结果如下:

  

 

 如果将最后一个stopwatch注释掉:

 

{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Console.WriteLine("在Sleep之前");
Thread.Sleep(2000);//同步等待--当前线程等待2s 然后继续
Console.WriteLine("在Sleep之后");
stopwatch.Stop();
Console.WriteLine($"Sleep耗时{stopwatch.ElapsedMilliseconds}");
}
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Console.WriteLine("在Delay之前");
Task task = Task.Delay(2000)
.ContinueWith(t =>
{
stopwatch.Stop();
Console.WriteLine($"Delay耗时{stopwatch.ElapsedMilliseconds}");

Console.WriteLine($"This is ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
});//异步等待--等待2s后启动新任务
Console.WriteLine("在Delay之后");
//stopwatch.Stop();
//Console.WriteLine($"Delay耗时{stopwatch.ElapsedMilliseconds}");
}

 

 

 

什么时候用多线程?

  任务并发是时候

多线程能干嘛?

  提升速度,优化用户体验。

 

比如,现在有一个场景,在公司开会,领导在分配任务,不能并发,因为只能有一个领导在讲话分配任务,当任务分配下去,开发们确实可以同时开始撸代码,这个是可以并发的。

TaskFactory taskFactory = new TaskFactory();
List<Task> taskList = new List<Task>();
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle1", "Portal")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle2", "  DBA ")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle3", "Client")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle4", "BackService")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle5", "Wechat")));

 

 现在要求,谁第一个完成,获得红包奖励(ContinueWhenAny);所有完成后,一起庆祝下(ContinueWhenAll),将其放入一个List<Task>里面去

TaskFactory taskFactory = new TaskFactory();
List<Task> taskList = new List<Task>();
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle1", "Portal")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle2", "  DBA ")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle3", "Client")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle4", "BackService")));
taskList.Add(taskFactory.StartNew(() => this.Coding("bingle5", "Wechat")));

//谁第一个完成,获取一个红包奖励
taskFactory.ContinueWhenAny(taskList.ToArray(), t => Console.WriteLine($"XXX开发完成,获取个红包奖励{Thread.CurrentThread.ManagedThreadId.ToString("00")}"));
//项目完成后,一起庆祝一下
taskList.Add(taskFactory.ContinueWhenAll(taskList.ToArray(), rArray => Console.WriteLine($"开发都完成,一起庆祝一下{Thread.CurrentThread.ManagedThreadId.ToString("00")}")));

ContinueWhenAny  ContinueWhenAll 非阻塞式的回调;而且使用的线程可能是新线程,也可能是刚完成任务的线程,唯一不可能是主线程

//阻塞当前线程,等着任意一个任务完成
Task.WaitAny(taskList.ToArray());//也可以限时等待
Console.WriteLine("准备环境开始部署");
//需要能够等待全部线程完成任务再继续  阻塞当前线程,等着全部任务完成
Task.WaitAll(taskList.ToArray());
Console.WriteLine("5个模块全部完成后,集中点评");

 

   Task.WaitAny  WaitAll都是阻塞当前线程,等任务完成后执行操作,阻塞卡界面,是为了并发以及顺序控制,网站首页:A数据库 B接口 C分布式服务 D搜索引擎,适合多线程并发,都完成后才能返回给用户,需要等待WaitAll,列表页:核心数据可能来自数据库/接口服务/分布式搜索引擎/缓存,多线程并发请求,哪个先完成就用哪个结果,其他的就不管了。

 假如说我想控制下Task的并发数量,该怎么做?  20个

List<Task> taskList = new List<Task>();
for (int i = 0; i < 10000; i++)
{
int k = i;
if (taskList.Count(t => t.Status != TaskStatus.RanToCompletion) >= 20)
{
Task.WaitAny(taskList.ToArray());
taskList = taskList.Where(t => t.Status != TaskStatus.RanToCompletion).ToList();
}
taskList.Add(Task.Run(() =>
{
Console.WriteLine($"This is {k} running ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
Thread.Sleep(2000);
}));
}

 

Parallel并发执行多个Action线程,主线程会参与计算---阻塞界面。等于TaskWaitAll+主线程计算

Parallel.Invoke(() => this.DoSomethingLong("btnParallel_Click_1"),
() => this.DoSomethingLong("btnParallel_Click_2"),
() => this.DoSomethingLong("btnParallel_Click_3"),
() => this.DoSomethingLong("btnParallel_Click_4"),
() => this.DoSomethingLong("btnParallel_Click_5"));
Parallel.For(0, 5, i => this.DoSomethingLong($"btnParallel_Click_{i}"));
Parallel.ForEach(new int[] { 0, 1, 2, 3, 4 }, i => this.DoSomethingLong($"btnParallel_Click_{i}"));

ParallelOptions options = new ParallelOptions();
options.MaxDegreeOfParallelism = 3;
Parallel.For(0, 10, options, i => this.DoSomethingLong($"btnParallel_Click_{i}"));

有没有办法不阻塞?

Task.Run(() =>
{
ParallelOptions options = new ParallelOptions();
options.MaxDegreeOfParallelism = 3;
Parallel.For(0, 10, options, i => this.DoSomethingLong($"btnParallel_Click_{i}"));
});

  几乎90%以上的多线程场景,以及顺序控制,以上的Task的方法就可以完成,如果你的多线程场景太复杂搞不定,那么请梳理一下你的流程,简化一下。建议最好不要线程嵌套线程,两三次勉强能懂,三层就hold不住了,更多的只能求神。

 

多线程异常:

try
{

List<Task> taskList = new List<Task>();
for (int i = 0; i < 100; i++)
{
string name = $"btnThreadCore_Click_{i}";
taskList.Add(Task.Run(() =>
{
if (name.Equals("btnThreadCore_Click_11"))
{
throw new Exception("btnThreadCore_Click_11异常");
}
else if (name.Equals("btnThreadCore_Click_12"))
{
throw new Exception("btnThreadCore_Click_12异常");
}
else if (name.Equals("btnThreadCore_Click_38"))
{
throw new Exception("btnThreadCore_Click_38异常");
}
Console.WriteLine($"This is {name}成功 ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
}));
}
//多线程里面抛出的异常,会终结当前线程;但是不会影响别的线程;
//那线程异常哪里去了? 被吞了,
//假如我想获取异常信息,还需要通知别的线程
Task.WaitAll(taskList.ToArray());//1 可以捕获到线程的异常
}
catch (AggregateException aex)//2 需要try-catch-AggregateException
{
foreach (var exception in aex.InnerExceptions)
{
Console.WriteLine(exception.Message);
}
}
catch (Exception ex)//可以多catch  先具体再全部
{
Console.WriteLine(ex);
}
//线程异常后经常是需要通知别的线程,而不是等到WaitAll,问题就是要线程取消
//工作中常规建议:多线程的委托里面不允许异常,包一层try-catch,然后记录下来异常信息,完成需要的操作

线程取消:

//多线程并发任务,某个失败后,希望通知别的线程,都停下来,how?
//Thread.Abort--终止线程;向当前线程抛一个异常然后终结任务;线程属于OS资源,可能不会立即停下来
//Task不能外部终止任务,只能自己终止自己(上帝才能打败自己)

//cts有个bool属性IsCancellationRequested 初始化是false
//调用Cancel方法后变成true(不能再变回去),可以重复cancel
try
{
CancellationTokenSource cts = new CancellationTokenSource();
List<Task> taskList = new List<Task>();
for (int i = 0; i < 50; i++)
{
string name = $"btnThreadCore_Click_{i}";
taskList.Add(Task.Run(() =>
{
try
{
if (!cts.IsCancellationRequested)
Console.WriteLine($"This is {name} 开始 ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");

Thread.Sleep(new Random().Next(50, 100));

if (name.Equals("btnThreadCore_Click_11"))
{
throw new Exception("btnThreadCore_Click_11异常");
}
else if (name.Equals("btnThreadCore_Click_12"))
{
throw new Exception("btnThreadCore_Click_12异常");
}
else if (name.Equals("btnThreadCore_Click_13"))
{
cts.Cancel();
}
if (!cts.IsCancellationRequested)
{
Console.WriteLine($"This is {name}成功结束 ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
}
else
{
Console.WriteLine($"This is {name}中途停止 ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
return;
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
cts.Cancel();
}
}, cts.Token));
}
//1 准备cts  2 try-catch-cancel  3 Action要随时判断IsCancellationRequested
//尽快停止,肯定有延迟,在判断环节才会结束

Task.WaitAll(taskList.ToArray());
//如果线程还没启动,能不能就别启动了?
//1 启动线程传递Token  2 异常抓取
//在Cancel时还没有启动的任务,就不启动了;也是抛异常,cts.Token.ThrowIfCancellationRequested
}
catch (AggregateException aex)
{
foreach (var exception in aex.InnerExceptions)
{
Console.WriteLine(exception.Message);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
View Code

临时变量:

for (int i = 0; i < 5; i++)
{
Task.Run(() =>
{
Console.WriteLine($"This is btnThreadCore_Click_{i} ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
});
}

 

 为什么运行结果后,都是5呢?

  临时变量问题,线程是非阻塞的,延迟启动的;线程执行的时候,i已经是5了

那么该如何解决呢?

  每次都声明一个变量k去接收,k是闭包里面的变量,每次循环都有一个独立的k,5个k变量  1个i变量

for (int i = 0; i < 5; i++)
{
int k = i;
Task.Run(() =>
{
Console.WriteLine($"This is btnThreadCore_Click_{i}_{k} ThreadId={Thread.CurrentThread.ManagedThreadId.ToString("00")}");
});
}

这样再运行,结果就正常了。

 

 线程安全&lock:

线程安全:如果你的代码在进程中有多个线程同时运行这一段,如果每次运行的结果都跟单线程运行时的结果一致,那么就是线程安全的

线程安全问题一般都是有全局变量/共享变量/静态变量/硬盘文件/数据库的值,只要多线程都能访问和修改

发生是因为多个线程相同操作,出现了覆盖,怎么解决?

1 Lock解决多线程冲突

Lock是语法糖,Monitor.Enter,占据一个引用,别的线程就只能等着

推荐锁是private static readonly object,

 A不能是Null,可以编译不能运行;

B 不推荐lock(this),外面如果也要用实例,就冲突了

//Test test = new Test();
//Task.Delay(1000).ContinueWith(t =>
//{
//    lock (test)
//    {
//        Console.WriteLine("*********Start**********");
//        Thread.Sleep(5000);
//        Console.WriteLine("*********End**********");
//    }
//});
//test.DoTest();

//C 不应该是string; string在内存分配上是重用的,会冲突
//D Lock里面的代码不要太多,这里是单线程的
Test test = new Test();
string student = "水煮鱼";
Task.Delay(1000).ContinueWith(t =>
{
lock (student)
{
Console.WriteLine("*********Start**********");
Thread.Sleep(5000);
Console.WriteLine("*********End**********");
}
});
test.DoTestString();
//2 线程安全集合
//System.Collections.Concurrent.ConcurrentQueue<int>

//3 数据分拆,避免多线程操作同一个数据;又安全又高效

for (int i = 0; i < 10000; i++)
{
this.iNumSync++;
}
for (int i = 0; i < 10000; i++)
{
Task.Run(() =>
{
lock (Form_Lock)//任意时刻只有一个线程能进入方法块儿,这不就变成了单线程
{
this.iNumAsync++;
}
});
}
for (int i = 0; i < 10000; i++)
{
int k = i;
Task.Run(() => this.iListAsync.Add(k));
}

Thread.Sleep(5 * 1000);
Console.WriteLine($"iNumSync={this.iNumSync} iNumAsync={this.iNumAsync} listNum={this.iListAsync.Count}");
//iNumSync 和  iNumAsync分别是多少   9981/9988  1到10000以内

 

转载于:https://www.cnblogs.com/taotaozhuanyong/p/11559834.html

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