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Merge main into live #43315

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merged 20 commits into from
Nov 5, 2024
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Merge main into live #43315

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33cd37b
[Diagnostics] Add EventSource Callback Possible Deadlock Warning
mdh1418 Oct 24, 2024
8c7eb9c
Move warning to more relevant doc
mdh1418 Oct 25, 2024
b2aa5b2
Elaborate on avoiding complex operations
mdh1418 Oct 25, 2024
59fb983
Expand list of common pitfalls
mdh1418 Oct 25, 2024
3279637
Update rationale for pitfalls
mdh1418 Oct 25, 2024
64ac663
Add re-entrancy guard tip
mdh1418 Oct 25, 2024
96fad7b
Clarify precaution
mdh1418 Oct 29, 2024
20c29b7
What's new in F# 9
0101 Oct 30, 2024
abf85dd
change blog-style code blocks to regular
0101 Oct 30, 2024
0c1ede7
Apply suggestions from code review
0101 Oct 31, 2024
d329193
Fixed formatting, made language changes H2
0101 Oct 31, 2024
4c5db39
update
0101 Oct 31, 2024
53f7ef1
update
0101 Oct 31, 2024
dee1058
update
0101 Oct 31, 2024
9ecbe97
markdown lint
0101 Nov 1, 2024
3a65014
Apply suggestions from code review
0101 Nov 4, 2024
e26076e
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0101 Nov 4, 2024
8366cfa
Random improvements to config articles (#43273)
gewarren Nov 4, 2024
2fbaea2
Merge pull request #43197 from mdh1418/add_deadlock_warning_for_event…
mdh1418 Nov 4, 2024
30839a4
Merge pull request #43260 from 0101/whats-new-in-fsharp-9
0101 Nov 5, 2024
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31 changes: 31 additions & 0 deletions docs/core/diagnostics/eventsource-collect-and-view-traces.md
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Expand Up @@ -272,3 +272,34 @@ this isn't required. Following is an example `EventListener` implementation that
3/24/2022 9:23:35 AM RequestStart
3/24/2022 9:23:35 AM RequestStop
```

> [!WARNING]
> Potential Pitfalls when implementing EventSource Callbacks via EventListener include deadlocks, infinite recursions, and uninitialized types.
>
> EventSource instances are initialized early in the runtime, before some core features are fully initialized. As a result, acquiring locks inside an EventSource callback like <xref:System.Diagnostics.Tracing.EventListener.OnEventWritten%2A> when the thread normally would not have done so may cause deadlocks.
>
> To mitigate this risk, consider the following precautions:
>
> - **Use Queues to Defer Work**: There are a variety of APIs you might want to call in OnEventWritten() that do non-trivial work, for example File IO, Console, or Http. For most events, these APIs work fine, but if you tried to call Console.WriteLine() in an event handler during the initialization of the Console class then it would probably fail. If you don't know whether a given event handler occurs at a time when APIs are safe to call, consider adding some information about the event to an in-memory queue instead. Then, on a separate thread, process items in the queue.
> - **Minimize Lock Duration**: Ensure that any locks acquired within the callback are not held for extended periods.
> - **Use Non-blocking APIs**: Prefer using non-blocking APIs within the callback to avoid potential deadlocks.
> - **Implement a Re-entrancy Guard**: Use a re-entrancy guard to prevent infinite recursion. For example:
>
> ```csharp
> [ThreadStatic] private static bool t_insideCallback;
>
> public void OnEventWritten(...)
> {
> if (t_insideCallback) return; // if our callback triggered the event to occur recursively
> // exit now to avoid infinite recursion
> try
> {
> t_insideCallback = true;
> // do callback work
> }
> finally
> {
> t_insideCallback = false;
> }
> }
> ```
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