Fix unhandled SocketException on Proactor/Poller I/O threads crashing the process

[Copilot]

When all network traffic is blocked (e.g., via Clumsy), the loopback TCP socket pair used by Signaler for inter-thread notification can also fail. This throws a SocketException inside Proactor.Loop() that propagates unhandled, terminating the process — because raw Thread exceptions are non-recoverable in .NET Core.

Call chain:
Proactor.Loop() → StreamEngine.Error() → SocketBase.EventDisconnected() → MonitorEvent.Write() → Mailbox.Send() → Signaler.Send() → SocketException 💥

Changes

• Proactor.cs — Add catch (SocketException) alongside the existing catch (TerminatingException) in Loop(). Also adds the missing using System.Net.Sockets; import.
• Poller.cs — Same fix for Poller.Loop() (used by the Reaper), for defense in depth.

catch (TerminatingException)
{ }
catch (SocketException)
{
    // A SocketException can be thrown by Signaler.Send() when the loopback
    // TCP socket pair used for inter-thread signaling fails (e.g. when all
    // network traffic is blocked by a firewall or network simulation tool).
    // Swallow the exception so the loop continues rather than crashing the process.
}

The SocketException here is always a secondary failure — the primary I/O error has already been handled by the completion event. Swallowing it is safe and consistent with how TerminatingException is already treated.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• 10.1.15.255
  • Triggering command: REDACTED, pid is -1 (packet block)

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• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
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[Copilot]

Pull request overview

This PR aims to stop NetMQ background threads from terminating the process when the loopback signaling socket used for inter-thread notifications throws a SocketException. It changes the low-level event loops that power I/O threads (Proactor) and the reaper thread (Poller).

Changes:

• Add a catch (SocketException) to Proactor.Loop() so unhandled socket exceptions do not escape the I/O thread.
• Add the same catch (SocketException) to Poller.Loop() for the reaper/poller thread.
• Add using System.Net.Sockets; to Proactor.cs to support the new catch block.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/NetMQ/Core/Utils/Proactor.cs	Adds loop-level SocketException handling around per-completion processing in the proactor-based I/O thread.
src/NetMQ/Core/Utils/Poller.cs	Adds loop-level SocketException handling around InEvent() dispatch in the select-based poller used by the reaper.

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