<em>Mac</em>Book项目 2009年学校开始实施<em>Mac</em>Book项目,所有师生配备一本<em>Mac</em>Book,并同步更新了校园无线网络。学校每周进行电脑技术更新,每月发送技术支持资料,极大改变了教学及学习方式。因此2011
2021-06-01 09:32:01
c#多執行緒之執行緒基礎
2022-04-18 19:00:25
一、簡介
1.為了防止一個應用程式控制CPU而導致其他應用程式和作業系統本身永遠被掛起這一可能情況，作業系統不得不使用某種方式將物理計算分割為一些虛擬的程序，並給予每個執行程式一定量的計算能力。此外作業系統必須始終能夠優先存取CPU，並能調整不同程式存取CPU的優先順序。執行緒正式這一慨唸的實現。
2.多執行緒優缺點：
多執行緒優點：可以同時執行多個計算任務，有可能提高計算機的處理能力，使得計算機每秒能執行越來越多的命令
多執行緒缺點：消耗大量的作業系統資源。多個執行緒共用一個處理器將導致作業系統忙於管理這些執行緒，而無法執行程式。
二、建立執行緒
class Program
{
static void Main(string[] args)
{
Thread t1 = new Thread(new ThreadStart(PrintNumbers));//無引數的委託，把方法的參照當做引數
t1.Start();
Thread t2 = new Thread(new ParameterizedThreadStart(PrintNumbers));//有引數的委託，把方法的參照當做引數
t2.Start(10);
Console.ReadLine();
}
static void PrintNumbers()
{
Console.WriteLine("1.Starting...");
for (int i = 0; i < 10; i++)
{
Console.WriteLine(i);
}
}
//注意：要使用ParameterizedThreadStart，定義的引數必須為object
static void PrintNumbers(object count)
{
Console.WriteLine("2.Starting...");
for (int i = 0; i < Convert.ToInt32(count); i++)
{
Console.WriteLine(i);
}
}
}
}註釋：
1.我們只需指定在不同執行緒執行的方法名，而C#編譯器會在後臺建立這些物件。
2.要使用ParameterizedThreadStart，定義的引數必須為object型別。
三、暫停執行緒
class Program
{
static void Main(string[] args)
{
Thread t1 = new Thread(PrintNumbersWithDelay);
t1.Start();
PrintNumbers();
Console.ReadLine();
}
static void PrintNumbers()
{
Console.WriteLine("1.Starting...");
for (int i = 0; i < 10; i++)
{
Console.WriteLine("In 1.Starting: " + i);
}
}
static void PrintNumbersWithDelay()
{
Console.WriteLine("2.Starting...");
for (int i = 0; i < 10; i++)
{
//var a = TimeSpan.FromSeconds(2);
Thread.Sleep(TimeSpan.FromSeconds(2));//暫停兩秒
Console.WriteLine("In 2.Starting: " + i);
}
}
}註釋：使用Thread.Sleep(TimeSpan.FromSeconds(2));暫停執行緒一段時間
四、執行緒等待
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Starting...");
Thread t = new Thread(PrintNumbersWithDelay);
t.Start();
t.Join(); //使用Join等待t完成後，再向下執行PrintNumbers，如果註釋掉輸出明顯不同
PrintNumbers();
Console.WriteLine("Thread Complete");
Console.ReadLine();
}
static void PrintNumbers()
{
Console.WriteLine("1.Starting...");
for (int i = 0; i < 10; i++)
{
Console.WriteLine("In 1.Starting:" + i);
}
}
static void PrintNumbersWithDelay()
{
Console.WriteLine("2.Starting...");
for (int i = 0; i < 10; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(2));
Console.WriteLine("In 2.Starting:" + i);
}
}
}註釋：使用t.Join(); 等待t完成。
五、終止執行緒
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Starting Program...");
Thread t1 = new Thread(PrintNumbersWithDelay);
t1.Start();
Thread.Sleep(TimeSpan.FromSeconds(7));//此時t1執行緒會執行7秒
t1.Abort(); //使用Abort()終止執行緒
Console.WriteLine("Thread t1 has been aborted");
Thread t2 = new Thread(PrintNumbers);
t2.Start();
Console.ReadLine();
}
static void PrintNumbers()
{
Console.WriteLine("1.Starting...");
for (int i = 0; i < 10; i++)
{
Console.WriteLine("In 1.Starting:" + i);
}
}
static void PrintNumbersWithDelay()
{
Console.WriteLine("2.Starting...");
for (int i = 0; i < 10; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(2));
Console.WriteLine("In 2.Starting:" + i);
}
}
}註釋：使用Thread範例的Abort方法終止執行緒。
六、檢測執行緒狀態
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Start Program...");
Thread t1 = new Thread(PrintNumbersWithStatus);
Thread t2 = new Thread(DoNothing);
Console.WriteLine("t1 status:" + t1.ThreadState.ToString());//獲取範例執行緒狀態
t2.Start();
t1.Start();
for (int i = 0; i < 30; i++)
{
Console.WriteLine("t1 status:" + t1.ThreadState.ToString() + "t" + "t2 status:" + t2.ThreadState.ToString());
}
Thread.Sleep(TimeSpan.FromSeconds(7));
t1.Abort();
Console.WriteLine("thread t1 has been aborted");
Console.WriteLine("t1 status:" + t1.ThreadState.ToString());
Console.WriteLine("t2 status:" + t2.ThreadState.ToString());
Console.ReadLine();
}
private static void PrintNumbersWithStatus()
{
Console.WriteLine("1.Starting...");
Console.WriteLine("In 1.Starting t1 status:" + Thread.CurrentThread.ThreadState.ToString());//獲取當前執行緒狀態
for (int i = 0; i < 10; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(2));
Console.WriteLine("In 1.Starting:" + i);
}
}
private static void DoNothing()
{
Thread.Sleep(TimeSpan.FromSeconds(2));
Console.WriteLine("t2 Console...");
}
}註釋：使用Thread.ThreadState獲取執行緒的執行狀態。ThreadState是一個C#列舉。謹記：不要在程式中使用執行緒終止，否則可能會出現意想不到的結果
七、執行緒優先順序
class Program
{
static void Main(string[] args)
{
//讓作業系統的所有執行緒執行在多個CPU核心上
Console.WriteLine($"Current thread priority: {Thread.CurrentThread.Priority}");
Console.WriteLine("Running on all cores available");//獲取範例執行緒狀態
RunThreads();
Thread.Sleep(TimeSpan.FromSeconds(2));
Console.WriteLine("Running on a single Core");
//讓作業系統的所有執行緒執行在單個CPU核心上
Process.GetCurrentProcess().ProcessorAffinity = new IntPtr(1);
RunThreads();
Console.ReadLine();
}
private static void RunThreads()
{
var sample = new ThreadSample();
var t1 = new Thread(sample.CountNumbers);
t1.Name = "Thread One";
var t2 = new Thread(sample.CountNumbers);
t2.Name = "Thread Two";
t1.Priority = ThreadPriority.Highest;//使用Priority設定執行緒的優先順序
t2.Priority = ThreadPriority.Lowest;
t1.Start();
t2.Start();//此處t2優先順序低於t1,t2等待t1釋放資源。
Thread.Sleep(TimeSpan.FromSeconds(2));
sample.Stop();
}
}
class ThreadSample
{
private bool _isStopped = false;
public void Stop()
{
_isStopped = true;
}
public void CountNumbers()
{
long counter = 0;
while (!_isStopped)
{
counter++;
}
Console.WriteLine($"{Thread.CurrentThread.Name} with {Thread.CurrentThread.Priority} priority has a count={counter.ToString("N0")}");
}
}註釋：單核執行多執行緒耗費的時間比多核的多很多。
八、前臺執行緒和後臺執行緒
class Program
{
static void Main(string[] args)
{
var sampleForground = new ThreadSample(10);
var sampleBackground = new ThreadSample(20);
var t1 = new Thread(sampleForground.CountNumbers);//方法的參照
t1.Name = "ForegroundThread"; //沒有明確宣告的均為前臺執行緒
var t2 = new Thread(sampleBackground.CountNumbers);
t2.Name = "BackgroundThread";
t2.IsBackground = true; //設定為後臺執行緒
t1.Start();
t2.Start();
Console.ReadLine();
}
}
class ThreadSample
{
private readonly int _iteration;
public ThreadSample(int iteration)
{
_iteration = iteration;
}
public void CountNumbers()
{
for (int i = 0; i < _iteration; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(0.5));
Console.WriteLine($"{Thread.CurrentThread.Name} prints {i}");
}
}
}註釋：程序會等待所有的前臺執行緒完成後再結束工作，但是如果只剩下後臺執行緒，則會直接結束工作。
九、向執行緒傳遞引數
class Program
{
static void Main(string[] args)
{
ThreadSample sample = new ThreadSample(5);
Thread t1 = new Thread(sample.CountNumbers);
t1.Name = "ThreadOne";
t1.Start();
t1.Join();
Console.WriteLine("--------------------------");
Thread t2 = new Thread(Count);
t2.Name = "ThreadTwo";
t2.Start(3);
t2.Join();
Console.WriteLine("--------------------------");
//使用lambda表示式參照另一個C#對方的方式被稱為閉包。當在lambda表示式中使用任何區域性變數時，C#會生成一個類，並將該變數作為該類的一個屬性，但是我們無須定義該類，C#編譯器會自動幫我們實現
Thread t3 = new Thread(() => CountNumbers(5));
t3.Name = "ThreadThree";
t3.Start();
t3.Join();
Console.WriteLine("--------------------------");
int i = 10;
Thread t4 = new Thread(() => PrintNumber(i));
i = 20;
Thread t5 = new Thread(() => PrintNumber(i));
t4.Start();
t5.Start();
//t4, t5都會輸出20， 因為t4，t5沒有Start之前i已經變成20了
Console.ReadKey();
}
static void Count(object iterations)
{
CountNumbers((int)iterations);
}
static void CountNumbers(int iterations)
{
for (int i = 1; i <= iterations; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(0.5));
Console.WriteLine($"{Thread.CurrentThread.Name} prints {i}");
}
}
static void PrintNumber(int number)
{
Console.WriteLine(number);
}
}
class ThreadSample
{
private readonly int _iteration;
public ThreadSample(int iteration)
{
_iteration = iteration;
}
public void CountNumbers()
{
for (int i = 1; i <= _iteration; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(0.5));
Console.WriteLine($"{Thread.CurrentThread.Name} prints {i}");
}
}
}十、使用C# Lock 關鍵字
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Incorrect Counter");
Counter c1 = new Counter();
var t1 = new Thread(() => TestCounter(c1));
var t2 = new Thread(() => TestCounter(c1));
var t3 = new Thread(() => TestCounter(c1));
t1.Start();
t2.Start();
t3.Start();
t1.Join();
t2.Join();
t3.Join();
Console.WriteLine($"Total Count: {c1.Count}");
Console.WriteLine("------------------------");
//使用LOCK關鍵字，Count同一時刻只允許一個執行緒存取
Console.WriteLine("Correct counter");
CounterWithLock c2 = new CounterWithLock();
t1 = new Thread(() => TestCounter(c2));
t2 = new Thread(() => TestCounter(c2));
t3 = new Thread(() => TestCounter(c2));
t1.Start();
t2.Start();
t3.Start();
t1.Join();
t2.Join();
t3.Join();
Console.WriteLine($"Total count:{c2.Count}");
Console.ReadLine();
}
static void TestCounter(CounterBase c)
{
for (int i = 0; i < 100000; i++)
{
c.Increment();
c.Decrement();
}
}
//子類
class Counter : CounterBase
{
public int Count { get; private set; }
//重寫基礎類別方法
public override void Decrement()
{
Count--;
}
public override void Increment()
{
Count++;
}
}
//子類
class CounterWithLock : CounterBase
{
private readonly object _asyncRoot = new object();
public int Count { get; private set; }
//重寫基礎類別方法
public override void Decrement()
{
lock (_asyncRoot)
{
Count--;
}
}
public override void Increment()
{
lock (_asyncRoot)
{
Count++;
}
}
}
//基礎類別
abstract class CounterBase
{
public abstract void Increment();
public abstract void Decrement();
}
}
class ThreadSample
{
private readonly int _iteration;
public ThreadSample(int iteration)//建構函式
{
_iteration = iteration;
}
public void CountNumbers()
{
for (int i = 1; i <= _iteration; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(0.5));
Console.WriteLine($"{Thread.CurrentThread.Name} prints {i}");
}
}
}註釋：不加鎖，得出的結果不確定，競爭條件下很容易出錯。加鎖得出的結果是正確的，但是效能受到了影響
十一、使用Monitor類鎖定資源
class Program
{
static void Main(string[] args)
{
object lock1 = new object();
object lock2 = new object();
new Thread(() => LockTooMuch(lock1, lock2)).Start();
lock (lock2)
{
Thread.Sleep(1000);
Console.WriteLine("Monitor.TryEnter allows not to get stuck, returning false after a specified timeout is elapsed");
//直接使用Monitor.TryEnter, 如果在第二個引數之前還未獲取到lock保護的資源會返回false
if (Monitor.TryEnter(lock1, TimeSpan.FromSeconds(5)))
{
Console.WriteLine("Acquired a protected resource successfully");
}
else
{
Console.WriteLine("Timeout acquiring a resource");
}
}
new Thread(() => LockTooMuch(lock1, lock2)).Start();
Console.WriteLine("-----------------------------");
/* 下面程式碼會造成死鎖， 所以註釋掉
lock (lock2)
{
Console.WriteLine("This will be a deadlock!");
Thread.Sleep(1000);
lock (lock1)
{
Console.WriteLine("Acquired a protected resource successfully");
}
}
*/
}
static void LockTooMuch(object lock1, object lock2)
{
lock (lock1)
{
Thread.Sleep(1000);
lock (lock2);
}
}
}註釋：Monitor.TryEnter在指定的時間內嘗試獲取指定物件上的排他鎖
十二、處理異常
class Program
{
static void Main(string[] args)
{
Thread t = new Thread(FaultyThread);
t.Start();
t.Join();
try
{
t = new Thread(BadFaultyThread);
t.Start();
}
catch (Exception ex)
{
Console.WriteLine("We won't get here");
}
}
static void BadFaultyThread()
{
Console.WriteLine("Starting a bad faulty thread.....");
Thread.Sleep(TimeSpan.FromSeconds(2));
//這個異常主執行緒無法捕捉到，因為是在子執行緒丟擲的異常。需要在子執行緒中加入try...catch捕獲異常
throw new Exception("Boom!");
}
static void FaultyThread()
{
try
{
Console.WriteLine("Starting a faulty thread...");
Thread.Sleep(TimeSpan.FromSeconds(1));
throw new Exception("Boom!");
}
catch (Exception ex)
{
Console.WriteLine($"Exception handled: {ex.Message}");
}
}
}到此這篇關於c#多執行緒之執行緒基礎的文章就介紹到這了。希望對大家的學習有所幫助，也希望大家多多支援it145.com。
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