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Fix thread-safety: snapshot TieLineCollection before enumeration in GetRouteToSource #1401

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Fix thread-safety: snapshot TieLineCollection before enumeration in GetRouteToSource #1401

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Copilot Mar 18, 2026
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Fix thread-safety issue in GetRouteToSource - snapshot TieLineCollect…
Copilot Mar 18, 2026
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8 changes: 6 additions & 2 deletions src/PepperDash.Essentials.Core/Routing/Extensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -339,17 +339,21 @@ private static bool GetRouteToSource(this IRoutingInputs destination, IRoutingOu

RoutingInputPort goodInputPort = null;

// Take a snapshot to avoid InvalidOperationException if TieLineCollection.Default is
// modified concurrently (e.g. NVX tie line registration during route requests).
var tieLines = TieLineCollection.Default.ToList();
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Copilot AI Mar 30, 2026

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TieLineCollection.Default.ToList() still enumerates the underlying List<TieLine> and can throw InvalidOperationException if another thread modifies the collection during the snapshot. To fully address this, reads and writes of TieLineCollection.Default need synchronization (shared lock, or a thread-safe/copy-on-write collection), ideally via a safe snapshot method on TieLineCollection. Also, because this method is recursive, taking a new ToList() snapshot on every recursion can add significant allocation/CPU overhead; consider taking one snapshot in the public entry point and passing it down through the recursive calls.

Suggested change
var tieLines = TieLineCollection.Default.ToList();
List<TieLine> tieLines;
lock (TieLineCollection.Default)
{
tieLines = TieLineCollection.Default.ToList();
}

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IEnumerable<TieLine> destinationTieLines;
TieLine directTie = null;

if (destinationPort == null)
{
destinationTieLines = TieLineCollection.Default.Where(t =>
destinationTieLines = tieLines.Where(t =>
t.DestinationPort.ParentDevice.Key == destination.Key && (t.Type.HasFlag(signalType) || signalType == eRoutingSignalType.AudioVideo));
}
else
{
destinationTieLines = TieLineCollection.Default.Where(t => t.DestinationPort.ParentDevice.Key == destination.Key && t.DestinationPort.Key == destinationPort.Key && (t.Type.HasFlag(signalType)));
destinationTieLines = tieLines.Where(t => t.DestinationPort.ParentDevice.Key == destination.Key && t.DestinationPort.Key == destinationPort.Key && (t.Type.HasFlag(signalType)));
}

// find the TieLine without a port
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