C# Events and Thread Safety

Question

UPDATE

As of C# 6, the answer to this question is:

SomeEvent?.Invoke(this, e);

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I frequently hear/read the fo

Answer 1

"Why is explicit-null-check the 'standard pattern'?"

I suspect the reason for this might be that the null-check is more performant.

If you always subscribe an empty delegate to your events when they are created, there will be some overheads:

• Cost of constructing the empty delegate.
• Cost of constructing a delegate chain to contain it.
• Cost of invoking the pointless delegate every single time the event is raised.

(Note that UI controls often have a large number of events, most of which are never subscribed to. Having to create a dummy subscriber to each event and then invoke it would likely be a significant performance hit.)

I did some cursory performance testing to see the impact of the subscribe-empty-delegate approach, and here are my results:

Executing 50000000 iterations . . .
OnNonThreadSafeEvent took:      432ms
OnClassicNullCheckedEvent took: 490ms
OnPreInitializedEvent took:     614ms <--
Subscribing an empty delegate to each event . . .
Executing 50000000 iterations . . .
OnNonThreadSafeEvent took:      674ms
OnClassicNullCheckedEvent took: 674ms
OnPreInitializedEvent took:     2041ms <--
Subscribing another empty delegate to each event . . .
Executing 50000000 iterations . . .
OnNonThreadSafeEvent took:      2011ms
OnClassicNullCheckedEvent took: 2061ms
OnPreInitializedEvent took:     2246ms <--
Done

Note that for the case of zero or one subscribers (common for UI controls, where events are plentiful), the event pre-initialised with an empty delegate is notably slower (over 50 million iterations...)

For more information and source code, visit this blog post on .NET Event invocation thread safety that I published just the day before this question was asked (!)

(My test set-up may be flawed so feel free to download the source code and inspect it yourself. Any feedback is much appreciated.)