/// <summary>
/// Updates an item if it exists in the dictionary
/// </summary>
/// <param name="target">The target concurrent dictionary</param>
/// <param name="key">The key of the item to the update</param>
/// <param name="update">A callback that performs the update</param>
/// <param name="newValue">Receives the new value if the dictionary was updated</param>
/// <returns>True if the item was updated, False if it does not exist</returns>
/// <remarks>Implements a loop around TryGetValue and TryUpdate</remarks>
public static bool TryUpdate <TKey, TValue>(this ConcurrentDictionary <TKey, TValue> target, TKey key, Func <TKey, TValue, TValue> update,
#if !NETSTANDARD2_0 && !NET40
[MaybeNullWhen(false)]
#endif
out TValue newValue) where TKey : notnull
{
while (target.TryGetValue(key, out var OldValue))
{
var NewValue = update(key, OldValue);
if (target.TryUpdate(key, NewValue, OldValue))
{
newValue = NewValue;
return(true);
}
}
newValue = default !;
//****************************************
/// <summary>
/// Adds or replaces a key/value pair
/// </summary>
/// <param name="key">The key to add or replace</param>
/// <param name="value">The value to associate with the key</param>
public void AddOrReplace(TKey key, TValue value)
{ //****************************************
GCReference NewHandle;
//****************************************
if (value == null)
{
throw new InvalidOperationException("Cannot add null to a Weak Dictionary");
}
for (; ;)
{
// Is this key already in the dictionary?
if (_Dictionary.TryGetValue(key, out var MyHandle))
{
try
{
var OldValue = (TValue?)MyHandle.Target;
// Yes. If the reference is the same, no need to change anything
if (object.ReferenceEquals(OldValue, value))
{
return;
}
}
catch (InvalidOperationException)
{
// The GCHandle was disposed, try again
continue;
}
// Reference has changed, create a new GCReference
NewHandle = new GCReference(value, _HandleType);
// Try and update the dictionary with the replacement value
if (_Dictionary.TryUpdate(key, NewHandle, MyHandle))
{
// Success, now we can safely expire the old handle
MyHandle.Dispose();
return;
}
// Key was updated elsewhere, ditch the updated value and try again
NewHandle.Dispose();
continue;
}
// Create a GC Handle to reference the object
NewHandle = new GCReference(value, _HandleType);
// Try and add it to the dictionary
if (_Dictionary.TryAdd(key, NewHandle))
{
return; // Success, return the result
}
// Key was added concurrently, free the handle we no longer need
NewHandle.Dispose();
// Loop back and try again
}
}