ReaderWriterLockSlim.ExitUpgradeableReadLock Method ()

 

Reduces the recursion count for upgradeable mode, and exits upgradeable mode if the resulting count is 0 (zero).

Namespace:   System.Threading
Assembly:  System.Core (in System.Core.dll)

public void ExitUpgradeableReadLock()

Exception Condition
SynchronizationLockException

The current thread has not entered the lock in upgradeable mode.

This method is not sensitive to recursion order. For example, if a thread enters a lock in upgradeable mode and then enters the lock in write mode, the order in which the thread exits the two modes does not matter. If a lock allows recursion, a thread can enter the lock in write mode and then enter it recursively in upgradeable mode; the order in which the thread exits upgradeable mode and write mode does not matter.

Exiting the lock might signal other waiting threads.

The following example shows how to use a finally block to execute the ExitUpgradeableReadLock method, ensuring that the caller exits upgradeable mode.

The method shown in the example retrieves the value associated with a key and compares it with a new value. If the value is unchanged, the method returns a status indicating no change. It no value is found for the key, the key/value pair is inserted. If the value has changed, it is updated. Upgradeable mode allows the thread to upgrade the read lock as needed, without risk of deadlocks.

The example uses the default constructor to create the lock, so recursion is not allowed. Programming the ReaderWriterLockSlim is simpler and less prone to error when the lock does not allow recursion.

This code is part of a larger example provided for the ReaderWriterLockSlim class.

private ReaderWriterLockSlim cacheLock = new ReaderWriterLockSlim();
private Dictionary<int, string> innerCache = new Dictionary<int, string>();
public AddOrUpdateStatus AddOrUpdate(int key, string value)
{
    cacheLock.EnterUpgradeableReadLock();
    try
    {
        string result = null;
        if (innerCache.TryGetValue(key, out result))
        {
            if (result == value)
            {
                return AddOrUpdateStatus.Unchanged;
            }
            else
            {
                cacheLock.EnterWriteLock();
                try
                {
                    innerCache[key] = value;
                }
                finally
                {
                    cacheLock.ExitWriteLock();
                }
                return AddOrUpdateStatus.Updated;
            }
        }
        else
        {
            cacheLock.EnterWriteLock();
            try
            {
                innerCache.Add(key, value);
            }
            finally
            {
                cacheLock.ExitWriteLock();
            }
            return AddOrUpdateStatus.Added;
        }
    }
    finally
    {
        cacheLock.ExitUpgradeableReadLock();
    }
}
public enum AddOrUpdateStatus
{
    Added,
    Updated,
    Unchanged
};

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
Return to top
Show: