如何：在SpinLock中啟用 Thread-Tracking 模式

System.Threading.SpinLock 是一種低層次的互斥鎖，您可以用於等候時間非常短的情境。 SpinLock 不可重入。 線程進入鎖後，必須先正確釋放鎖，才能再次進入。 一般而言，任何重新輸入鎖定的嘗試都會導致死結，而死結可能會非常難以偵錯。 System.Threading.SpinLock 支援一種線程追蹤模式，作為開發輔助功能，當線程嘗試重新進入已持有的鎖定時，會導致拋出例外狀況。 這可讓您更輕鬆地找出鎖定未正確解除的位置。 您可以使用採用布爾值輸入參數的SpinLock建構函式，並傳入true來開啟執行緒追蹤模式。 完成開發和測試階段之後，請關閉線程追蹤模式以提升效能。

範例

下列範例示範線程追蹤模式。 正確解除鎖定的程式碼行被加上註釋，以模擬導致下列其中一個結果的程式碼錯誤：

• 如果SpinLock是使用true的參數建立的，則會擲回例外狀況（在 Visual Basic 中為True）。

• 如果使用 SpinLock 作為參數 false（在 Visual Basic 中為 False）創建死結，則會發生死鎖。

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 {Thread.CurrentThread.ManagedThreadId} attempted to reenter the lock");
                    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();
            }
        }
    }
}

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

另請參閱

• SpinLock