[英]Is Thread managed by the thread pool?
我知道CLR給每個AppDomain
ThreadPool
時間片工作,但我想知道是否通過創建一個新的線程,如此Thread t = new Thread(...);
它是由CLR還是AppDomin ThreadPool
?
Thread t = new Thread();
不會被ThreadPool
管理。 但它是CLR在操作系統線程上提供的抽象。 ThreadPool是一個附加抽象,有助於重用線程和共享線程資源。
以下是.NET中線程的優秀資源: http : //www.albahari.com/threading/
如果您使用的是.NET 4.0,請考慮使用TPL。
使用Thread
類創建線程時, 您可以控制。 您可以根據需要創建它們,並定義它們是后台還是前景 (使調用進程保持活動狀態),設置Priority
,啟動和停止它們。
使用ThreadPool
或Task
(在幕后使用ThreadPool
),您可以讓ThreadPool
類管理線程的創建,並最大化線程的可重用性,從而節省創建新線程所需的時間。 需要注意的一點是,與Thread
默認值不同, ThreadPool
創建的ThreadPool
不會使調用進程保持活動狀態。
使用ThreadPool
一個巨大優勢是,您可以讓少量線程處理大量任務。 相反,假設池沒有殺死線程(因為它是為可重用性而設計的),如果你有一堆由ThreadPool
創建的ThreadPool
,但后來項目數量縮減, ThreadPool
閑置很多,浪費資源。
創建新線程時,它們不受線程池管理。
如果手動創建線程然后控制其生命周期,則它獨立於線程池。
以下示例顯示如何使用線程池。 它首先創建一個ManualResetEvent對象,該對象使程序能夠知道線程池何時完成了所有工作項的運行。 接下來,它嘗試將一個線程添加到線程池。 如果成功,則添加其余部分(本例中為4個)。 然后,線程池將工作項放入可用線程中。 調用eventX上的WaitOne方法,這會導致程序的其余部分等到事件被觸發(使用eventX.Set方法)。 最后,程序打印出線程上的加載(實際執行特定工作項的線程)。
// 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;
}
}
出局
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
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