如何：在 SpinLock 中启用线程跟踪模式
System.Threading.SpinLock 是一个低级别的互斥锁，可用于等待时间非常短的场合。 SpinLock 不是可重入的。 在线程进入锁之后，它必须先正确地退出锁，然后才能再次进入锁。 通常，任何重新进入锁的尝试都会导致死锁，并且死锁非常难调试。 作为开发的辅助手段，System.Threading.SpinLock 支持一种线程跟踪模式，当线程尝试重新进入它已经持有的锁时，此模式将会导致引发异常。 这将让您更易于定位到锁未正确退出的点。 通过使用一个采用布尔输入形参的 SpinLock 构造函数并传入 true 实参，可以启用线程跟踪模式。 完成开发和测试阶段之后，应关闭线程跟踪模式以获得更好的性能。
示例
下面的代码示例阐释了线程跟踪模式。 示例中的用于正确退出锁的代码行都被注释掉了，以便模拟导致以下结果之一的编码错误：
如果通过使用 true（在 Visual Basic 中为 True）参数来创建 SpinLock，则引发异常。
如果通过使用 false（在 Visual Basic 中为 False）参数来创建 SpinLock，则导致死锁。
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Module Module1
Public Class SpinTest
' True means "enable thread tracking." This will cause an
' exception to be thrown when the first thread attempts to reenter the lock.
' Specify False to cause deadlock due to coding error below.
Private Shared _spinLock = New SpinLock(True)
Public Shared Sub Main()
Parallel.Invoke(
Sub() DoWork(),
Sub() DoWork(),
Sub() DoWork(),
Sub() DoWork()
)
Console.WriteLine("Press any key.")
Console.ReadKey()
End Sub
Public Shared Sub DoWork()
Dim sb = New StringBuilder()
For i As Integer = 1 To 9999
Dim lockTaken As Boolean = False
Try
_spinLock.Enter(lockTaken)
' do work here protected by the lock
Thread.SpinWait(50000)
sb.Append(Thread.CurrentThread.ManagedThreadId)
sb.Append(" Entered-")
Catch ex As LockRecursionException
Console.WriteLine("Thread {0} attempted to reenter the lock",
Thread.CurrentThread.ManagedThreadId)
Throw
Finally
' INTENTIONAL CODING ERROR TO DEMONSTRATE THREAD TRACKING!
' UNCOMMENT THE LINES FOR CORRECT SPINLOCK BEHAVIOR
' Commenting out these lines causes the same thread
' to attempt to reenter the lock. If the SpinLock was
' created with thread tracking enabled, the exception
' is thrown. Otherwise, if the SpinLock was created with a
' parameter of false, and these lines are left commented, the spinlock deadlocks.
If (lockTaken) Then
' _spinLock.Exit()
' sb.Append("Exited ")
End If
End Try
' Output for diagnostic display.
If (i Mod 4 <> 0) Then
Console.Write(sb.ToString())
Else
Console.WriteLine(sb.ToString())
End If
sb.Clear()
Next
End Sub
End Class
End Module
using System;
using System.Collections.Generic;
using System.Collections.Concurrent;
using System.Diagnostics;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace SpinLockDemo
{
// C#
public class SpinLockTest
{
// Specify true to enable thread tracking. This will cause
// exception to be thrown when the first thread attempts to reenter the lock.
// Specify false to cause deadlock due to coding error below.
private static SpinLock _spinLock = new SpinLock(true);
static void Main()
{
Parallel.Invoke(
() => DoWork(),
() => DoWork(),
() => DoWork(),
() => DoWork()
);
Console.WriteLine("Press any key.");
Console.ReadKey();
}
public static void DoWork()
{
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 100; i++)
{
bool lockTaken = false;
try
{
_spinLock.Enter(ref lockTaken);
// do work here protected by the lock
Thread.SpinWait(50000);
sb.Append(Thread.CurrentThread.ManagedThreadId);
sb.Append(" Entered-");
}
catch (LockRecursionException ex)
{
Console.WriteLine("Thread {0} attempted to reenter the lock",
Thread.CurrentThread.ManagedThreadId);
throw;
}
finally
{
// INTENTIONAL CODING ERROR TO DEMONSTRATE THREAD TRACKING!
// UNCOMMENT THE LINES FOR CORRECT SPINLOCK BEHAVIOR
// Commenting out these lines causes the same thread
// to attempt to reenter the lock. If the SpinLock was
// created with thread tracking enabled, the exception
// is thrown. Otherwise the spinlock deadlocks.
if (lockTaken)
{
// _spinLock.Exit(false);
// sb.Append("Exited ");
}
}
// Output for diagnostic display.
if(i % 4 != 0)
Console.Write(sb.ToString());
else
Console.WriteLine(sb.ToString());
sb.Clear();
}
}
}
}