转载:
1.什么是thread
- 当我们提及多线程的时候会想到thread和threadpool,这都是异步操作,threadpool其实就是thread的集合,具有很多优势,不过在任务多的时候全局队列会存在竞争而消耗资源。thread默认为前台线程,主程序必须等线程跑完才会关闭,而threadpool相反。
- 总结:threadpool确实比thread性能优,但是两者都没有很好的api区控制,如果线程执行无响应就只能等待结束,从而诞生了task任务。
2.什么是task
3.创建一个task任务有两种模式:
1.使用factory创建会直接执行,使用new创建不会执行,必须等到start启动之后才执行。
var testTask = new Task(() => Console.WriteLine("task start"); var factoryTeak = Task.Factory.StartNew(() => Console.WriteLine("factory task start");
2.我们来看看task的生命周期
var testTask = new Task(() => Console.WriteLine("task start"); System.Threading.Thread.Sleep(2000); Console.WriteLine(testTask.Status); Console.WriteLine(testTask.Status); Console.WriteLine(testTask.Status); Console.WriteLine(testTask.Status); Console.WriteLine(testTask.Status);
输出结果:
Created
task start
Running
Running
RanToCompletion
RanToCompletion
可以看出task确实是异步执行,并且wait很好地控制了task。
3.下面演示几个控制task的方法
var testTask = new Task(() => Console.WriteLine("task start"); System.Threading.Thread.Sleep(2000);
var testTask = new Task(() => Console.WriteLine("task start"); System.Threading.Thread.Sleep(2000); var factoryTeak = Task.Factory.StartNew(() => Console.WriteLine("factory task start"); Task.WaitAll(testTask, factoryTeak); Console.WriteLine("end");
var testTask = new Task(() => Console.WriteLine("task start"); System.Threading.Thread.Sleep(2000); var factoryTeak = Task.Factory.StartNew(() => Console.WriteLine("factory task start"); Task.WaitAny(testTask, factoryTeak); Console.WriteLine("end");
通过wait()对单个task进行等待,Task.waitall()对多个task进行等待,waitany()执行任意一个task就往下继续执行。
4.task的回调执行
var testTask = new Task(() => Console.WriteLine("task start"); System.Threading.Thread.Sleep(2000); var resultTest = testTask.ContinueWith<string>((Task) => { Console.WriteLine("testTask end"); Console.WriteLine(resultTest.Result);
5.task的取消
首先创建一个取消task的令牌的实例,在不启动task直接取消:
var tokenSource = new CancellationTokenSource();//创建取消task实例 var testTask = new Task(() => for (int i = 0; i < 6; i++) { System.Threading.Thread.Sleep(1000); Console.WriteLine(testTask.Status); tokenSource.Token.Register(()=> { Console.WriteLine("task is to cancel"); Console.WriteLine(testTask.Status);
输出结果:
Created
task is to cancel
Canceled
如果task启动了真的取消了task?
var tokenSource = new CancellationTokenSource();//创建取消task实例 var testTask = new Task(() => for (int i = 0; i <6; i++) { System.Threading.Thread.Sleep(1000); Console.WriteLine(testTask.Status); Console.WriteLine(testTask.Status); tokenSource.Token.Register(()=> { Console.WriteLine("task is to cancel"); Console.WriteLine(testTask.Status); for (int i = 0; i < 10; i++) System.Threading.Thread.Sleep(1000); Console.WriteLine(testTask.Status);
输出结果:
Created
WaitingToRun
task is to cancel
Running
Running
Running
Running
Running
Running
RanToCompletion
RanToCompletion
RanToCompletion
RanToCompletion
RanToCompletion
可以看出其实并没有取消task,此时task还在继续跑。
6.task的嵌套
var parentTask = new Task(()=> { var childTask = new Task(() =>{ System.Threading.Thread.Sleep(2000); Console.WriteLine("childTask to start"); Console.WriteLine("parentTask to start"); Console.WriteLine("end");
此时为普通关联,父task和子task没影响
var parentTask = new Task(()=> { var childTask = new Task(() =>{ System.Threading.Thread.Sleep(2000); Console.WriteLine("childTask to start"); }, TaskCreationOptions.AttachedToParent); Console.WriteLine("parentTask to start"); Console.WriteLine("end");
此时为父task和子task关联,wait会一直等待父子task执行完。
6.task死锁的问题
我们可以设置最大等待时间,如果超过了等待时间,就不再等待,下面我们来修改代码,设置最大等待时间为5秒(项目中可以根据实际情况设置),如果超过5秒就输出哪个任务出错了
7.对Spinlock的使用
举例来说Parallel.for和Parallel.foreach是线程不安全的,有可能达不到你的预期,此时就需要加锁来解决此问题,我们可以加lock和spinlock(自旋锁)来解决
SpinLock slock = new SpinLock(false); var testLock= new object(); Parallel.For(0, 100000, i =>
Parallel.For(0, 100000, i => slock.Enter(ref lockTaken); Parallel.For(0, 100000, i => Console.WriteLine("Num1的值为:{0}", sum1); Console.WriteLine("Num2的值为:{0}", sum2); Console.WriteLine("Num3的值为:{0}", sum3);
输出结果:
Num1的值为:1660913202
Num2的值为:4999950000
Num3的值为:4999950000
Num1的值为:2754493646
Num2的值为:4999950000
Num3的值为:4999950000
Num1的值为:4999950000
Num2的值为:4999950000
Num3的值为:4999950000
最后看看threadpoll和task的结构图:
threadpool:
task:
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