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Clarify thread-safe event raising #17888

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Merged
merged 3 commits into from
Apr 17, 2020
Merged

Clarify thread-safe event raising #17888

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9b9d7b9
Clarify thread-safe event raising
pkulikov Apr 16, 2020
2012e12
Update docs/csharp/language-reference/operators/member-access-operato…
pkulikov Apr 17, 2020
d54f7d4
Minor update
pkulikov Apr 17, 2020
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4 changes: 3 additions & 1 deletion docs/csharp/language-reference/operators/member-access-operators.md
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@@ -1,7 +1,7 @@
---
title: "Member access operators and expressions - C# reference"
description: "Learn about C# operators that you can use to access type members."
ms.date: 03/31/2020
ms.date: 04/17/2020
author: pkulikov
f1_keywords:
- "._CSharpKeyword"
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}
```

That is a thread-safe way to ensure that only a non-null `handler` is invoked. Because delegate instances are immutable, no thread can change the value referenced by the `handler` local variable. In particular, if the code executed by another thread unsubscribes from the `PropertyChanged` event and `PropertyChanged` becomes `null` before `handler` is invoked, the value referenced by `handler` remains unaffected. The `?.` operator evaluates its left-hand operand no more than once, guaranteeing that it cannot be changed to `null` after being verified as non-null.

## Invocation expression ()

Use parentheses, `()`, to call a [method](../../programming-guide/classes-and-structs/methods.md) or invoke a [delegate](../../programming-guide/delegates/index.md).
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