Editing OpenSimulator Internals/Code Map/LLUDPServer (section)

== Threading Model ==

LLUDPServer runs three persistent threads per region:

{| class="wikitable"
|-
! Thread !! Started by !! Purpose
|-
| Inbound receive thread || <code>StartInbound()</code> via base class <code>OpenSimUDPBase</code> || Receives raw UDP datagrams from the OS socket and places them on <code>packetInbox</code>.
|-
| <code>IncomingPacketHandler</code> || <code>StartInbound()</code> || Drains <code>packetInbox</code>, dispatches packets to the correct <code>LLClientView</code> via <code>ProcessInPacket()</code>.
|-
| <code>OutgoingPacketHandler</code> || <code>StartOutbound()</code> || Drives per-client outbound queues, resends, ACKs, and pings on a timer loop.
|}

A fourth engine, <code>OqrEngine</code> (Outgoing Queue Refill Engine), runs as a
<code>JobEngine</code> thread pool to refill per-client outbound queues without
blocking the outgoing packet handler.

=== Inbound path ===

 OS socket
   → base class receive thread (OpenSimUDPBase)
     → PacketReceived()
       → decode + zerodecode
       → pending cache check (UseCircuitCode handling)
       → client lookup by endpoint
       → ACK processing (appended ACKs, PacketAck packets)
       → duplicate detection (PacketArchive)
       → packetInbox.Add()
         → IncomingPacketHandler thread
           → LLClientView.ProcessInPacket()

UseCircuitCode packets are handled specially: they are dispatched via
<code>FireAndForget</code> to <code>HandleUseCircuitCode()</code>, which
authenticates the circuit, creates a new <code>LLClientView</code> and
<code>LLUDPClient</code>, and then reinjects any packets that arrived while
the client was being set up (held in a per-endpoint pending queue).

=== Outbound path ===

 Scene code / region modules
   → LLClientView.SendXxx()
     → LLUDPServer.SendPacket() / SendPacketData() / SendUDPPacket()
       → optional zerocoding
       → OutgoingPacket constructed
       → LLUDPClient.EnqueueOutgoing()
         if queue full or not throttled:
           → SendPacketFinal() → SyncSend() → OS socket
         else:
           → sits in per-client priority queue
             → OutgoingPacketHandler → DequeueOutgoing() → SendPacketFinal()

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