线程处理教程
教程
该教程包含下列示例：
示例 1：创建线程、启动线程和线程间交互
本示例说明如何创建和启动线程，并显示了同时在同一进程内运行的两个线程间的交互。请注意，不必停止或释放线程。这由 .NET Framework 公共语言运行库自动完成。
程序从创建 Alpha 类型的对象 (oAlpha) 和引用 Alpha 类的 Beta 方法的线程 (oThread) 开始。然后启动该线程。线程的 IsAlive 属性允许程序等待，直到线程被初始化（被创建、被分配等）为止。主线程通过 Thread 访问，而 Sleep 方法通知线程放弃其时间片并在一定毫秒数期间停止执行。然后 oThread 被停止和联接。联接一个线程将使主线程等待它死亡或等待它在指定的时间后过期（有关更多详细信息，请参见 oThread，但由于线程无法在停止（中止）后重新启动而告失败。有关临时停止执行的信息，请参见
// StopJoin.cs
using System;
using System.Threading;
public class Alpha
{
// This method that will be called when the thread is started
public void Beta()
{
while (true)
{
Console.WriteLine("Alpha.Beta is running in its own thread.");
}
}
};
public class Simple
{
public static int Main()
{
Console.WriteLine("Thread Start/Stop/Join Sample");
Alpha oAlpha = new Alpha();
// Create the thread object, passing in the Alpha.Beta method
// via a ThreadStart delegate. This does not start the thread.
Thread oThread = new Thread(new ThreadStart(oAlpha.Beta));
// Start the thread
oThread.Start();
// Spin for a while waiting for the started thread to become
// alive:
while (!oThread.IsAlive);
// Put the Main thread to sleep for 1 millisecond to allow oThread
// to do some work:
Thread.Sleep(1);
// Request that oThread be stopped
oThread.Abort();
// Wait until oThread finishes. Join also has overloads
// that take a millisecond interval or a TimeSpan object.
oThread.Join();
Console.WriteLine();
Console.WriteLine("Alpha.Beta has finished");
try
{
Console.WriteLine("Try to restart the Alpha.Beta thread");
oThread.Start();
}
catch (ThreadStateException)
{
Console.Write("ThreadStateException trying to restart Alpha.Beta. ");
Console.WriteLine("Expected since aborted threads cannot be restarted.");
}
return 0;
}
}
输出示例
Thread Start/Stop/Join Sample Alpha.Beta is running in its own thread. Alpha.Beta is running in its own thread. Alpha.Beta is running in its own thread. ... ... Alpha.Beta has finished Try to restart the Alpha.Beta thread ThreadStateException trying to restart Alpha.Beta. Expected since aborted threads cannot be restarted.
示例 2：同步两个线程：制造者和使用者
下面的示例显示如何使用 C# lock 关键字和 Monitor 对象的 Pulse 方法完成同步。Pulse 方法通知等待队列中的线程对象的状态已更改。（有关脉冲的更多详细信息，请参见
本示例创建一个 Cell 对象，它具有两个方法：ReadFromCell 和 WriteToCell。从 CellProd 和 CellCons 类创建另外两个对象；这两个对象均具有调用 ReadFromCell 和 WriteToCell 的 ThreadRun 方法。通过等待依次到达的来自 Monitor 对象的“脉冲”即可完成同步。也就是说，首先产生一个项（此时使用者等待脉冲），然后发生一个脉冲，接着使用者使用所产生的项（此时制造者等待脉冲），依此类推。
// MonitorSample.cs
// This example shows use of the following methods of the C# lock keyword
// and the Monitor class
// in threads:
// Monitor.Pulse(Object)
// Monitor.Wait(Object)
using System;
using System.Threading;
public class MonitorSample
{
public static void Main(String[] args)
{
int result = 0; // Result initialized to say there is no error
Cell cell = new Cell( );
CellProd prod = new CellProd(cell, 20); // Use cell for storage,
// produce 20 items
CellCons cons = new CellCons(cell, 20); // Use cell for storage,
// consume 20 items
Thread producer = new Thread(new ThreadStart(prod.ThreadRun));
Thread consumer = new Thread(new ThreadStart(cons.ThreadRun));
// Threads producer and consumer have been created,
// but not started at this point.
try
{
producer.Start( );
consumer.Start( );
producer.Join( ); // Join both threads with no timeout
// Run both until done.
consumer.Join( );
// threads producer and consumer have finished at this point.
}
catch (ThreadStateException e)
{
Console.WriteLine(e); // Display text of exception
result = 1; // Result says there was an error
}
catch (ThreadInterruptedException e)
{
Console.WriteLine(e); // This exception means that the thread
// was interrupted during a Wait
result = 1; // Result says there was an error
}
// Even though Main returns void, this provides a return code to
// the parent process.
Environment.ExitCode = result;
}
}
public class CellProd
{
Cell cell; // Field to hold cell object to be used
int quantity = 1; // Field for how many items to produce in cell
public CellProd(Cell box, int request)
{
cell = box; // Pass in what cell object to be used
quantity = request; // Pass in how many items to produce in cell
}
public void ThreadRun( )
{
for(int looper=1; looper<=quantity; looper++)
cell.WriteToCell(looper); // "producing"
}
}
public class CellCons
{
Cell cell; // Field to hold cell object to be used
int quantity = 1; // Field for how many items to consume from cell
public CellCons(Cell box, int request)
{
cell = box; // Pass in what cell object to be used
quantity = request; // Pass in how many items to consume from cell
}
public void ThreadRun( )
{
int valReturned;
for(int looper=1; looper<=quantity; looper++)
// Consume the result by placing it in valReturned.
valReturned=cell.ReadFromCell( );
}
}
public class Cell
{
int cellContents; // Cell contents
bool readerFlag = false; // State flag
public int ReadFromCell( )
{
lock(this) // Enter synchronization block
{
if (!readerFlag)
{ // Wait until Cell.WriteToCell is done producing
try
{
// Waits for the Monitor.Pulse in WriteToCell
Monitor.Wait(this);
}
catch (SynchronizationLockException e)
{
Console.WriteLine(e);
}
catch (ThreadInterruptedException e)
{
Console.WriteLine(e);
}
}
Console.WriteLine("Consume: {0}",cellContents);
readerFlag = false; // Reset the state flag to say consuming
// is done.
Monitor.Pulse(this); // Pulse tells Cell.WriteToCell that
// Cell.ReadFromCell is done.
} // Exit synchronization block
return cellContents;
}
public void WriteToCell(int n)
{
lock(this) // Enter synchronization block
{
if (readerFlag)
{ // Wait until Cell.ReadFromCell is done consuming.
try
{
Monitor.Wait(this); // Wait for the Monitor.Pulse in
// ReadFromCell
}
catch (SynchronizationLockException e)
{
Console.WriteLine(e);
}
catch (ThreadInterruptedException e)
{
Console.WriteLine(e);
}
}
cellContents = n;
Console.WriteLine("Produce: {0}",cellContents);
readerFlag = true; // Reset the state flag to say producing
// is done
Monitor.Pulse(this); // Pulse tells Cell.ReadFromCell that
// Cell.WriteToCell is done.
} // Exit synchronization block
}
}
输出示例
Produce: 1 Consume: 1 Produce: 2 Consume: 2 Produce: 3 Consume: 3 ... ... Produce: 20 Consume: 20
示例 3：使用线程池
以下示例显示如何使用线程池。首先创建 ManualResetEvent 对象，此对象使程序能够知道线程池何时运行完所有的工作项。接着，尝试向线程池添加一个线程。如果添加成功，则添加其余的线程（本例中为 4 个）。然后线程池将工作项放入可用线程中。调用 eventX 上的 WaitOne 方法，这会使程序的其余部分等待，直到用 eventX.Set 方法触发事件为止。最后，程序打印出线程上的负载（实际执行某一特定工作项的线程）。
// SimplePool.cs
// Simple thread pool example
using System;
using System.Collections;
using System.Threading;
// Useful way to store info that can be passed as a state on a work item
public class SomeState
{
public int Cookie;
public SomeState(int iCookie)
{
Cookie = iCookie;
}
}
public class Alpha
{
public Hashtable HashCount;
public ManualResetEvent eventX;
public static int iCount = 0;
public static int iMaxCount = 0;
public Alpha(int MaxCount)
{
HashCount = new Hashtable(MaxCount);
iMaxCount = MaxCount;
}
// Beta is the method that will be called when the work item is
// serviced on the thread pool.
// That means this method will be called when the thread pool has
// an available thread for the work item.
public void Beta(Object state)
{
// Write out the hashcode and cookie for the current thread
Console.WriteLine(" {0} {1} :", Thread.CurrentThread.GetHashCode(),
((SomeState)state).Cookie);
// The lock keyword allows thread-safe modification
// of variables accessible across multiple threads.
Console.WriteLine(
"HashCount.Count=={0}, Thread.CurrentThread.GetHashCode()=={1}",
HashCount.Count,
Thread.CurrentThread.GetHashCode());
lock (HashCount)
{
if (!HashCount.ContainsKey(Thread.CurrentThread.GetHashCode()))
HashCount.Add (Thread.CurrentThread.GetHashCode(), 0);
HashCount[Thread.CurrentThread.GetHashCode()] =
((int)HashCount[Thread.CurrentThread.GetHashCode()])+1;
}
// Do some busy work.
// Note: Depending on the speed of your machine, if you
// increase this number, the dispersement of the thread
// loads should be wider.
int iX = 2000;
Thread.Sleep(iX);
// The Interlocked.Increment method allows thread-safe modification
// of variables accessible across multiple threads.
Interlocked.Increment(ref iCount);
if (iCount == iMaxCount)
{
Console.WriteLine();
Console.WriteLine("Setting eventX ");
eventX.Set();
}
}
}
public class SimplePool
{
public static int Main(string[] args)
{
Console.WriteLine("Thread Pool Sample:");
bool W2K = false;
int MaxCount = 10; // Allow a total of 10 threads in the pool
// Mark the event as unsignaled.
ManualResetEvent eventX = new ManualResetEvent(false);
Console.WriteLine("Queuing {0} items to Thread Pool", MaxCount);
Alpha oAlpha = new Alpha(MaxCount); // Create the work items.
// Make sure the work items have a reference to the signaling event.
oAlpha.eventX = eventX;
Console.WriteLine("Queue to Thread Pool 0");
try
{
// Queue the work items, which has the added effect of checking
// which OS is running.
ThreadPool.QueueUserWorkItem(new WaitCallback(oAlpha.Beta),
new SomeState(0));
W2K = true;
}
catch (NotSupportedException)
{
Console.WriteLine("These API's may fail when called on a non-Windows 2000 system.");
W2K = false;
}
if (W2K) // If running on an OS which supports the ThreadPool methods.
{
for (int iItem=1;iItem < MaxCount;iItem++)
{
// Queue the work items:
Console.WriteLine("Queue to Thread Pool {0}", iItem);
ThreadPool.QueueUserWorkItem(new WaitCallback(oAlpha.Beta),new SomeState(iItem));
}
Console.WriteLine("Waiting for Thread Pool to drain");
// The call to exventX.WaitOne sets the event to wait until
// eventX.Set() occurs.
// (See oAlpha.Beta).
// Wait until event is fired, meaning eventX.Set() was called:
eventX.WaitOne(Timeout.Infinite,true);
// The WaitOne won't return until the event has been signaled.
Console.WriteLine("Thread Pool has been drained (Event fired)");
Console.WriteLine();
Console.WriteLine("Load across threads");
foreach(object o in oAlpha.HashCount.Keys)
Console.WriteLine("{0} {1}", o, oAlpha.HashCount[o]);
}
return 0;
}
}
输出示例
注意 下列输出随计算机的不同而不同。
Thread Pool Sample: Queuing 10 items to Thread Pool Queue to Thread Pool 0 Queue to Thread Pool 1 ... ... Queue to Thread Pool 9 Waiting for Thread Pool to drain 98 0 : HashCount.Count==0, Thread.CurrentThread.GetHashCode()==98 100 1 : HashCount.Count==1, Thread.CurrentThread.GetHashCode()==100 98 2 : ... ... Setting eventX Thread Pool has been drained (Event fired) Load across threads 101 2 100 3 98 4 102 1
示例 4：使用 Mutex 对象
可以使用 mutex 对象保护共享资源不被多个线程或进程同时访问。mutex 对象的状态或者设置为终止（当它不属于任何线程时），或者设置为非终止（当它属于某个线程时）。同时只能有一个线程拥有一个 mutex 对象。例如，为了防止两个线程同时写入共享内存，每个线程在执行访问该共享内存的代码之前等待 mutex 对象的所属权。写入共享内存后，线程将释放该 mutex 对象。
此示例阐释如何在处理线程过程中使用 Mutex 类、AutoResetEvent 类和 WaitHandle 类。它还阐释在处理 mutex 对象过程中所用的方法。
// Mutex.cs
// Mutex object example
using System;
using System.Threading;
public class MutexSample
{
static Mutex gM1;
static Mutex gM2;
const int ITERS = 100;
static AutoResetEvent Event1 = new AutoResetEvent(false);
static AutoResetEvent Event2 = new AutoResetEvent(false);
static AutoResetEvent Event3 = new AutoResetEvent(false);
static AutoResetEvent Event4 = new AutoResetEvent(false);
public static void Main(String[] args)
{
Console.WriteLine("Mutex Sample ...");
// Create Mutex initialOwned, with name of "MyMutex".
gM1 = new Mutex(true,"MyMutex");
// Create Mutex initialOwned, with no name.
gM2 = new Mutex(true);
Console.WriteLine(" - Main Owns gM1 and gM2");
AutoResetEvent[] evs = new AutoResetEvent[4];
evs[0] = Event1; // Event for t1
evs[1] = Event2; // Event for t2
evs[2] = Event3; // Event for t3
evs[3] = Event4; // Event for t4
MutexSample tm = new MutexSample( );
Thread t1 = new Thread(new ThreadStart(tm.t1Start));
Thread t2 = new Thread(new ThreadStart(tm.t2Start));
Thread t3 = new Thread(new ThreadStart(tm.t3Start));
Thread t4 = new Thread(new ThreadStart(tm.t4Start));
t1.Start( ); // Does Mutex.WaitAll(Mutex[] of gM1 and gM2)
t2.Start( ); // Does Mutex.WaitOne(Mutex gM1)
t3.Start( ); // Does Mutex.WaitAny(Mutex[] of gM1 and gM2)
t4.Start( ); // Does Mutex.WaitOne(Mutex gM2)
Thread.Sleep(2000);
Console.WriteLine(" - Main releases gM1");
gM1.ReleaseMutex( ); // t2 and t3 will end and signal
Thread.Sleep(1000);
Console.WriteLine(" - Main releases gM2");
gM2.ReleaseMutex( ); // t1 and t4 will end and signal
// Waiting until all four threads signal that they are done.
WaitHandle.WaitAll(evs);
Console.WriteLine("... Mutex Sample");
}
public void t1Start( )
{
Console.WriteLine("t1Start started, Mutex.WaitAll(Mutex[])");
Mutex[] gMs = new Mutex[2];
gMs[0] = gM1; // Create and load an array of Mutex for WaitAll call
gMs[1] = gM2;
Mutex.WaitAll(gMs); // Waits until both gM1 and gM2 are released
Thread.Sleep(2000);
Console.WriteLine("t1Start finished, Mutex.WaitAll(Mutex[]) satisfied");
Event1.Set( ); // AutoResetEvent.Set() flagging method is done
}
public void t2Start( )
{
Console.WriteLine("t2Start started, gM1.WaitOne( )");
gM1.WaitOne( ); // Waits until Mutex gM1 is released
Console.WriteLine("t2Start finished, gM1.WaitOne( ) satisfied");
Event2.Set( ); // AutoResetEvent.Set() flagging method is done
}
public void t3Start( )
{
Console.WriteLine("t3Start started, Mutex.WaitAny(Mutex[])");
Mutex[] gMs = new Mutex[2];
gMs[0] = gM1; // Create and load an array of Mutex for WaitAny call
gMs[1] = gM2;
Mutex.WaitAny(gMs); // Waits until either Mutex is released
Console.WriteLine("t3Start finished, Mutex.WaitAny(Mutex[])");
Event3.Set( ); // AutoResetEvent.Set() flagging method is done
}
public void t4Start( )
{
Console.WriteLine("t4Start started, gM2.WaitOne( )");
gM2.WaitOne( ); // Waits until Mutex gM2 is released
Console.WriteLine("t4Start finished, gM2.WaitOne( )");
Event4.Set( ); // AutoResetEvent.Set() flagging method is done
}
}
示例输出
Mutex Sample ... - Main Owns gM1 and gM2 t1Start started, Mutex.WaitAll(Mutex[]) t2Start started, gM1.WaitOne( ) t3Start started, Mutex.WaitAny(Mutex[]) t4Start started, gM2.WaitOne( ) - Main releases gM1 t2Start finished, gM1.WaitOne( ) satisfied t3Start finished, Mutex.WaitAny(Mutex[]) - Main releases gM2 t1Start finished, Mutex.WaitAll(Mutex[]) satisfied t4Start finished, gM2.WaitOne( ) ... Mutex Sample
注意 此示例的输出可能在每台计算机上以及每次运行时均各不相同。运行此示例的计算机的速度及其操作系统都能影响输出的顺序。在多线程环境中，事件可能并不按预期的顺序发生。
