LockRecursionException 類別

定義

public ref class LockRecursionException : Exception

public class LockRecursionException : Exception

[System.Serializable]
public class LockRecursionException : Exception

type LockRecursionException = class
    inherit Exception

[<System.Serializable>]
type LockRecursionException = class
    inherit Exception

Public Class LockRecursionException
Inherits Exception

繼承

Object

Exception

LockRecursionException

屬性

SerializableAttribute

範例

以下範例展示了使用該LockRecursionException類別時的ReaderWriterLockSlim兩個原因。 程式透過使用無參數建構子來建立 ， ReaderWriterLockSlim 該構造子不允許遞迴。 接著程式會啟動一個執行緒，進入鎖定的讀取模式。 執行緒嘗試以讀取模式遞迴進入鎖，並捕捉到產生的例外。 最後，執行緒嘗試進入寫入模式，這會造成死結的風險。 執行緒會捕捉到產生的例外。

using System;
using System.Threading;

class Example
{
    // By default, the lock recursion policy for a new 
    // ReaderWriterLockSlim does not allow recursion.
    static ReaderWriterLockSlim rwls = new ReaderWriterLockSlim();

    static void ThreadProc()
    {
        Console.WriteLine("Acquire the reader lock.");
        rwls.EnterReadLock();

        try
        {
            Console.WriteLine("\nAttempt to acquire the reader lock recursively:");
            rwls.EnterReadLock();
        }
        catch (LockRecursionException lre)
        {
            Console.WriteLine("{0}: {1}", 
                lre.GetType().Name, lre.Message);
        }

        try
        {
            Console.WriteLine("\nAttempt to acquire the writer lock recursively:");
            rwls.EnterWriteLock();
        }
        catch (LockRecursionException lre)
        {
            Console.WriteLine("{0}: {1}", 
                lre.GetType().Name, lre.Message);
        }
    }

    static void Main()
    {
        Thread t = new Thread(ThreadProc);
        t.Start();
        t.Join();
    }
}

/* This code example produces output similar to the following:

Acquire the reader lock.

Attempt to acquire the reader lock recursively:
LockRecursionException: Recursive read lock acquisitions not allowed in this mode.

Attempt to acquire the writer lock recursively:
LockRecursionException: Write lock may not be acquired with read lock held. This pattern is prone to deadlocks. Consider using the upgrade lock.
 */

Imports System.Threading

Class Example
    ' By default, the lock recursion policy for a new 
    ' ReaderWriterLockSlim does not allow recursion.
    Private Shared rwls As New ReaderWriterLockSlim()
    
    Shared Sub ThreadProc() 
        Console.WriteLine("Acquire the reader lock.")
        rwls.EnterReadLock()
        
        Try
            Console.WriteLine(vbCrLf & _
                "Attempt to acquire the reader lock recursively:")
            rwls.EnterReadLock()
        Catch lre As LockRecursionException
            Console.WriteLine("{0}: {1}", _
                lre.GetType().Name, lre.Message)
        End Try
        
        Try
            Console.WriteLine(vbCrLf & _
                "Attempt to acquire the writer lock recursively:")
            rwls.EnterWriteLock()
        Catch lre As LockRecursionException
            Console.WriteLine("{0}: {1}", _
                lre.GetType().Name, lre.Message)
        End Try
    
    End Sub 
    
    Shared Sub Main() 

        Dim t As New Thread(AddressOf ThreadProc)
        t.Start()
        t.Join()
    
    End Sub 
End Class 

' This code example produces output similar to the following:
'
'Acquire the reader lock.
'
'Attempt to acquire the reader lock recursively:
'LockRecursionException: Recursive read lock acquisitions not allowed in this mode.
'
'Attempt to acquire the writer lock recursively:
'LockRecursionException: Write lock may not be acquired with read lock held. This pattern is prone to deadlocks. Consider using the upgrade lock.
'

備註

LockRecursionException 被拋出的原因有幾個，包括以下幾點：

• 如果執行緒嘗試遞迴進入 的 ReaderWriterLockSlim 實例，但該實例不支援遞迴。

• 如果執行緒嘗試以寫入模式或可升級模式進入 ReaderWriterLockSlim 實例，而執行緒最初以讀取模式進入鎖。 這代表潛在的僵局，因此不被允許。

• 如果允許多一層遞迴，會超過用於追蹤遞迴的內部儲存計數器的最大值。 這個限制非常大，應用程式根本不應該遇到。

另請參閱

• ReaderWriterLockSlim