LockRecursionPolicy LockRecursionPolicy LockRecursionPolicy LockRecursionPolicy Enum

Определение

Указывает, можно ли несколько раз войти в блокировку из одного и того же потока.Specifies whether a lock can be entered multiple times by the same thread.

public enum class LockRecursionPolicy
public enum LockRecursionPolicy
type LockRecursionPolicy = 
Public Enum LockRecursionPolicy
Наследование
LockRecursionPolicyLockRecursionPolicyLockRecursionPolicyLockRecursionPolicy

Поля

NoRecursion NoRecursion NoRecursion NoRecursion 0

Если поток пытается войти в блокировку рекурсивно, выдается ошибка.If a thread tries to enter a lock recursively, an exception is thrown. Некоторые классы могут допускать определенные виды рекурсий при активированном параметре.Some classes may allow certain recursions when this setting is in effect.

SupportsRecursion SupportsRecursion SupportsRecursion SupportsRecursion 1

Допускается рекурсивный вход потока в блокировку.A thread can enter a lock recursively. Некоторые классы могут игнорировать эту возможность.Some classes may restrict this capability.

Примеры

В следующем примере показано два сценария исключения, который зависит от LockRecursionPolicy параметр, а другая — нет.The following example shows two exception scenarios, one that depends on the LockRecursionPolicy setting and one that does not.

В первом случае поток вошел в блокировку в режиме чтения, а затем пытается войти в режим чтения рекурсивно.In the first scenario, the thread enters the lock in read mode and then tries to enter read mode recursively. Если ReaderWriterLockSlim создается с помощью конструктора по умолчанию, который задает политику рекурсии в NoRecursion, возникает исключение.If the ReaderWriterLockSlim is created by using the default constructor, which sets recursion policy to NoRecursion, an exception is thrown. Если SupportsRecursion используется для создания ReaderWriterLockSlim, исключение не создается.If SupportsRecursion is used to create the ReaderWriterLockSlim, no exception is thrown.

Во втором сценарии поток вошел в блокировку в режиме чтения, а затем пытается войти в блокировку в режиме записи.In the second scenario, the thread enters the lock in read mode and then tries to enter the lock in write mode. LockRecursionException создается независимо от политику рекурсии блокировки.LockRecursionException is thrown regardless of the lock recursion policy.

using System;
using System.Threading;

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

    static void ThreadProc()
    { 
        Console.WriteLine("1. Enter the read lock recursively.");
        ReadRecursive(rwls);
        ReadRecursive(rwlsWithRecursion);

        Console.WriteLine("\n2. Enter the write lock recursively from the read lock.");
        ReadWriteRecursive(rwls);
        ReadWriteRecursive(rwlsWithRecursion);
    } 

    static void ReadRecursive(ReaderWriterLockSlim rwls)
    {
        Console.WriteLine("LockRecursionPolicy.{0}:", rwls.RecursionPolicy);
        rwls.EnterReadLock();

        try {
            rwls.EnterReadLock();
            Console.WriteLine("\nThe read lock was entered recursively.");
            rwls.ExitReadLock();
        }    
        catch (LockRecursionException lre) {
            Console.WriteLine("\n{0}: {1}",
                lre.GetType().Name, lre.Message);
        }

        rwls.ExitReadLock();
    }

    static void ReadWriteRecursive(ReaderWriterLockSlim rwls)
    {
        Console.WriteLine("LockRecursionPolicy.{0}:", rwls.RecursionPolicy);
        rwls.EnterReadLock();

        try {
            rwls.EnterWriteLock();
            Console.WriteLine("\nThe write lock was entered recursively.");
        }
        catch (LockRecursionException lre) {
            Console.WriteLine("\n{0}: {1}", 
                lre.GetType().Name, lre.Message);
        }

        rwls.ExitReadLock();
    }

    static void Main() 
    {
        Thread t = new Thread(ThreadProc);
        t.Start();
        t.Join();
        
        // Dispose of ReaderWriterLockSlim objects' unmanaged resources.
        if (rwls != null) rwls.Dispose();
        if (rwlsWithRecursion != null) rwlsWithRecursion.Dispose();
    } 
} 
// This example displays output similar to the following:
//    1. Enter the read lock recursively.
//    LockRecursionPolicy.NoRecursion:
//    
//    LockRecursionException: Recursive read lock acquisitions not allowed in this mode.
//    LockRecursionPolicy.SupportsRecursion:
//    
//    The read lock was entered recursively.
//    
//    2. Enter the write lock recursively from the read lock.
//    LockRecursionPolicy.NoRecursion:
//    
//    LockRecursionException: Write lock may not be acquired with read lock held. This pattern i
//    s prone to deadlocks. Please ensure that read locks are released before taking a write loc
//    k. If an upgrade is necessary, use an upgrade lock in place of the read lock.
//    LockRecursionPolicy.SupportsRecursion:
//    
//    LockRecursionException: Write lock may not be acquired with read lock held. This pattern i
//    s prone to deadlocks. Please ensure that read locks are released before taking a write loc
//    k. If an upgrade is necessary, use an upgrade lock in place of the read lock.
Imports System
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()
    Private Shared rwlsWithRecursion _
        As New ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion)
    
    Shared Sub ThreadProc() 
        
        Console.WriteLine("1. Enter the read lock recursively.")
        ReadRecursive(rwls)
        ReadRecursive(rwlsWithRecursion)
    
        Console.WriteLine(vbCrLf & _
            "2. Enter the write lock recursively from the read lock.")
        ReadWriteRecursive(rwls)
        ReadWriteRecursive(rwlsWithRecursion)

    End Sub 

    Shared Sub ReadRecursive(ByVal rwls As ReaderWriterLockSlim)

        Console.WriteLine("LockRecursionPolicy.{0}:", rwls.RecursionPolicy)
        rwls.EnterReadLock()
        
        Try
            rwls.EnterReadLock()
            Console.WriteLine(vbTab & _
                "The read lock was entered recursively.")
            rwls.ExitReadLock()
        Catch lre As LockRecursionException
            Console.WriteLine(vbTab & "{0}: {1}", _
                lre.GetType().Name, lre.Message)
        End Try

        rwls.ExitReadLock()
    End Sub

    Shared Sub ReadWriteRecursive(ByVal rwls As ReaderWriterLockSlim)

        Console.WriteLine("LockRecursionPolicy.{0}:", rwls.RecursionPolicy)
        rwls.EnterReadLock()

        Try
            rwls.EnterWriteLock()
            Console.WriteLine(vbTab & _
                "The write lock was entered recursively.")
        Catch lre As LockRecursionException
            Console.WriteLine(vbTab & "{0}: {1}", _
                lre.GetType().Name, lre.Message)
        End Try

        rwls.ExitReadLock()
    End Sub
    
    Shared Sub Main() 

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

        ' Dispose of ReaderWriterLockSlim objects' unmanaged resources.
        If rwls IsNot Nothing Then rwls.Dispose()
        If rwlsWithRecursion IsNot Nothing Then _
           rwlsWithRecursion.Dispose()
    End Sub 
End Class 

' This code example produces output similar to the following:
'
'1. Enter the read lock recursively.
'LockRecursionPolicy.NoRecursion:
'        LockRecursionException: Recursive read lock acquisitions not allowed in this mode.
'LockRecursionPolicy.SupportsRecursion:
'        The read lock was entered recursively.
'
'2. Enter the write lock recursively from the read lock.
'LockRecursionPolicy.NoRecursion:
'        LockRecursionException: Write lock may not be acquired with read lock held. This pattern is prone to deadlocks. Consider using the upgrade lock.
'LockRecursionPolicy.SupportsRecursion:
'        LockRecursionException: Write lock may not be acquired with read lock held. This pattern is prone to deadlocks. Consider using the upgrade lock.
' 

Комментарии

Политику рекурсии по умолчанию зависит от типа блокировки.The default recursion policy depends on the type of lock. Политика по умолчанию и точное поведение рекурсии блокировки типа блокировки см. в документации для типа.For the default policy and the precise behavior of lock recursion for any given lock type, see the documentation for the type. Например ReaderWriterLockSlim класс не позволяет потоку войти в блокировку в режиме записи, если он уже вошел в блокировку в режиме чтения, независимо от того, данный параметр политики блокировки, чтобы снизить вероятность возникновения взаимоблокировок.For example, the ReaderWriterLockSlim class does not allow a thread to enter the lock in write mode if it already entered the lock in read mode, regardless of the lock policy setting, in order to reduce the chance of deadlocks.

В настоящее время только это перечисление используется одна блокировка:Currently only one lock uses this enumeration:

Применяется к