HOW TO：啟用 SpinLock 中的執行緒追蹤模式
System.Threading.SpinLock 是一種低階互斥鎖定，可讓您用於等候時間非常短的案例。 SpinLock 不可重新進入。 在執行緒進入鎖定之後，它就必須先正確結束鎖定，然後才能再次進入。 一般而言，任何嘗試重新進入鎖定的行為都會導致死結，而且死結非常難以偵錯。 為了協助開發，System.Threading.SpinLock 支援執行緒追蹤模式，可讓系統在執行緒嘗試重新進入已經持有的鎖定時擲回例外狀況。 這種模式可讓您更輕鬆地找出鎖定沒有正確結束的點。 您可以使用採用布林值輸入參數的 SpinLock 建構函式並傳入 true 引數，藉以開啟執行緒追蹤模式。 在您完成開發和測試階段之後，請關閉執行緒追蹤模式以提高效能。
範例
下列範例示範執行緒追蹤模式。 正確結束鎖定的行會標記為註解，以便模擬導致下列其中一種結果的程式碼錯誤：
如果 SpinLock 是使用 true (Visual Basic 中的 True) 引數建立的，就會擲回例外狀況。
如果 SpinLock 是使用 false (Visual Basic 中的 False) 引數建立的，就會發生死結。
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();
}
}
}
}