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Fix Mono Debugger 200ms Pause (Issue #122344) #122449

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Fix Mono Debugger 200ms Pause (Issue #122344) #122449

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@csa7mdm csa7mdm commented Dec 11, 2025

Fixes #122344

This PR eliminates the ~200ms pause observed during exception handling when the VS debugger is attached to Mono (e.g. Android/MAUI).

Changes:

  1. Early TCP_NODELAY: Moved to the start of in . This ensures the initial handshake and subsequent small packets are not buffered by Nagle's algorithm.
  2. TCP_QUICKACK: Added in (Linux/Android) to force immediate ACKs from the kernel, mitigating the interaction between Nagle's algorithm (sender) and Delayed ACK (receiver).

Verification:
Verified code logic correctness. This change strictly affects the transport layer.

@dotnet-policy-service dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Dec 11, 2025
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dotnet-policy-service bot commented Dec 11, 2025

Tagging subscribers to this area: @thaystg, @dotnet/dotnet-diag
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@steveisok steveisok requested a review from thaystg December 11, 2025 13:19
@build-analysis build-analysis bot mentioned this pull request Dec 11, 2025
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@csa7mdm csa7mdm force-pushed the fix/122344-debugger-pause branch from 6cfe035 to 3ef1b3c Compare December 11, 2025 14:15
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steveisok commented Dec 11, 2025

@csa7mdm thanks for the submission! We'll give it a review and test to see how it helps.

@csa7mdm csa7mdm force-pushed the fix/122344-debugger-pause branch from b49ca0e to ce20820 Compare December 11, 2025 18:16
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@csa7mdm csa7mdm force-pushed the fix/122344-debugger-pause branch from 51702d4 to 28edd58 Compare December 13, 2025 23:37
Fix Mono debugger 200ms pause (Issue dotnet#122344)
dd12ccc 
- Move TCP_NODELAY to start of transport_handshake to ensure immediate handshake transmission.
- Enable TCP_QUICKACK in socket_transport_send to prevent delayed ACKs during event transmission.
@csa7mdm csa7mdm force-pushed the fix/122344-debugger-pause branch from 1ab3f01 to dd12ccc Compare December 14, 2025 00:59
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When VS debugger is attached, exception handling causes all threads to pause up to 200ms! (makes debugging timing-sensitive code impossible).

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