[nexus] remove active node tracking (#12754)

This commit removes the active node tracking logic from the Nexus
simulation framework.

Previously, `Core` maintained a pointer to the `mActiveNode` and updated
it dynamically during processing and network events. This was necessary
so that log messages could be attributed to the correct node/instance.

With the recent introduction of "instance-aware logging" in the OpenThread
core, the logging mechanism natively knows which `otInstance` generated a
log. Therefore, manually tracking and context-switching the active node
in the Nexus framework is no longer required.

This change simplifies `nexus::Core`, removes context-switching overhead
from heavily utilized inline methods like `Node::Get<Type>()`, and allows
us to simplify the signature of `InfraIf::Receive()`.

tests/nexus/platform/nexus_core.cpp

@@ -44,7 +44,6 @@ Core::Core(void)
     : mCurNodeId(0)
     , mPendingAction(false)
     , mNow(0)
-    , mActiveNode(nullptr)
 {
     const char *pcapFile;
 
@@ -379,8 +378,6 @@ void Core::AdvanceTime(uint32_t aDuration)
 
 void Core::Process(Node &aNode)
 {
-    SetActiveNode(&aNode);
-
     otTaskletsProcess(&aNode.GetInstance());
 
     ProcessRadio(aNode);
@@ -400,8 +397,6 @@ void Core::Process(Node &aNode)
         aNode.mAlarmMicro.mScheduled = false;
         otPlatAlarmMicroFired(&aNode.GetInstance());
     }
-
-    SetActiveNode(nullptr);
 }
 
 void Core::ProcessRadio(Node &aNode)
@@ -620,7 +615,7 @@ void Core::ProcessInfraIf(Node &aNode)
                 continue;
             }
 
-            rxNode.mInfraIf.Receive(aNode, *message);
+            rxNode.mInfraIf.Receive(*message);
         }
 
         message->Free();

tests/nexus/platform/nexus_core.hpp

@@ -76,9 +76,6 @@ public:
     //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     // Used by platform implementation
 
-    void  SetActiveNode(Node *aNode) { mActiveNode = aNode; }
-    Node *GetActiveNode(void) { return mActiveNode; }
-
     void UpdateNextAlarmMilli(const Alarm &aAlarm);
     void UpdateNextAlarmMicro(const Alarm &aAlarm);
     void MarkPendingAction(void) { mPendingAction = true; }
@@ -134,7 +131,6 @@ private:
     bool                  mPendingAction;
     uint64_t              mNow;
     uint64_t              mNextAlarmTime;
-    Node                 *mActiveNode;
 };
 
 void Log(const char *aFormat, ...) OT_TOOL_PRINTF_STYLE_FORMAT_ARG_CHECK(1, 2);

tests/nexus/platform/nexus_infra_if.cpp

@@ -410,20 +410,18 @@ void InfraIf::SendUdp(const Ip6::Address &aSrcAddress,
         Message *loopbackMessage = aPayload.Clone<kNoReservedHeader>();
 
         VerifyOrQuit(loopbackMessage != nullptr);
-        Receive(GetNode(), *loopbackMessage);
+        Receive(*loopbackMessage);
         loopbackMessage->Free();
     }
 
     mPendingTxQueue.Enqueue(aPayload);
 }
 
-void InfraIf::Receive(Node &aSrcNode, Message &aMessage)
+void InfraIf::Receive(Message &aMessage)
 {
     Node        &node = GetNode();
     Ip6::Headers headers;
 
-    Core::Get().SetActiveNode(&node);
-
     aMessage.SetOffset(0);
     SuccessOrExit(headers.ParseFrom(aMessage));
 
@@ -515,7 +513,7 @@ void InfraIf::Receive(Node &aSrcNode, Message &aMessage)
     }
 
 exit:
-    Core::Get().SetActiveNode(&aSrcNode);
+    return;
 }
 
 void InfraIf::HandleEchoRequest(const Ip6::Header &aHeader, Message &aMessage)

tests/nexus/platform/nexus_infra_if.hpp

@@ -84,7 +84,7 @@ public:
                  uint16_t            aDestPort,
                  Message            &aPayload);
 
-    void Receive(Node &aSrcNode, Message &aMessage);
+    void Receive(Message &aMessage);
     void GetLinkLayerAddress(LinkLayerAddress &aLinkLayerAddress) const;
 
     typedef void (*EchoReplyHandler)(void *aContext, const Ip6::Address &aSource, uint16_t aId, uint16_t aSequence);

tests/nexus/platform/nexus_node.cpp

@@ -166,8 +166,6 @@ void Node::HandleReceive(otMessage *aMessage)
 
     VerifyOrExit(header->GetDestination().GetScope() > Ip6::Address::kRealmLocalScope);
 
-    Core::Get().SetActiveNode(this);
-
     if (header->GetDestination().IsMulticast())
     {
         VerifyOrExit(Get<BackboneRouter::Local>().IsPrimary());

tests/nexus/platform/nexus_node.hpp

@@ -121,17 +121,9 @@ public:
 
     //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
-    template <typename Type> Type &Get(void)
-    {
-        Core::Get().SetActiveNode(this);
-        return Instance::Get<Type>();
-    }
+    template <typename Type> Type &Get(void) { return Instance::Get<Type>(); }
 
-    Instance &GetInstance(void)
-    {
-        Core::Get().SetActiveNode(this);
-        return *this;
-    }
+    Instance &GetInstance(void) { return *this; }
 
     uint32_t GetId(void) { return GetInstance().GetId(); }