LockRecursionPolicy Enumeración

Definición

Especifica si el mismo subproceso puede entrar varias veces en un bloqueo.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
Herencia
LockRecursionPolicy

Campos

NoRecursion 0

Si un subproceso intenta entrar en un bloqueo de forma recursiva, se inicia una excepción.If a thread tries to enter a lock recursively, an exception is thrown. Algunas clases pueden permitir cierta recursividad cuando se aplica esta configuración.Some classes may allow certain recursions when this setting is in effect.

SupportsRecursion 1

Un subproceso puede entrar en un bloqueo de forma recursiva.A thread can enter a lock recursively. Algunas clases pueden limitar esta posibilidad.Some classes may restrict this capability.

Ejemplos

En el ejemplo siguiente se muestran dos escenarios de excepción, uno que LockRecursionPolicy depende de la configuración y otro que no lo hace.The following example shows two exception scenarios, one that depends on the LockRecursionPolicy setting and one that does not.

En el primer escenario, el subproceso entra en el bloqueo en modo de lectura y, a continuación, intenta entrar en modo de lectura de forma recursiva.In the first scenario, the thread enters the lock in read mode and then tries to enter read mode recursively. Si se ReaderWriterLockSlim crea mediante el constructor sin parámetros, que establece la Directiva de recursividad en recursividad, se produce una excepción.If the ReaderWriterLockSlim is created by using the parameterless constructor, which sets recursion policy to NoRecursion, an exception is thrown. Si se usa SupportsRecursion para crear el ReaderWriterLockSlim, no se produce ninguna excepción.If SupportsRecursion is used to create the ReaderWriterLockSlim, no exception is thrown.

En el segundo escenario, el subproceso entra en el bloqueo en modo de lectura y, a continuación, intenta entrar en el bloqueo en modo de escritura.In the second scenario, the thread enters the lock in read mode and then tries to enter the lock in write mode. LockRecursionExceptionse produce independientemente de la Directiva de recursividad de bloqueo.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.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.
' 

Comentarios

La Directiva de recursividad predeterminada depende del tipo de bloqueo.The default recursion policy depends on the type of lock. Para la directiva predeterminada y el comportamiento preciso de la recursividad de bloqueo para cualquier tipo de bloqueo determinado, consulte la documentación del tipo.For the default policy and the precise behavior of lock recursion for any given lock type, see the documentation for the type. Por ejemplo, la ReaderWriterLockSlim clase no permite a un subproceso entrar en el bloqueo en modo de escritura si ya ha entrado en el bloqueo en modo de lectura, independientemente de la configuración de la Directiva de bloqueo, con el fin de reducir la posibilidad de interbloqueos.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.

Actualmente solo un bloqueo usa esta enumeración:Currently only one lock uses this enumeration:

Se aplica a