Fix adapter process restart race conditions

- Replace fire-and-forget QTimer::singleShot in AdapterProcess::stop()
  with a cancellable QTimer that is stopped on start, stop, and process
  exit, preventing the kill timer from killing a newly started adapter.
- Suppress sessionError emission from onProcessError during STOPPING
  state to avoid spurious error signals during intentional shutdown.
- Disconnect sessionStopped from initAdapter on sessionError in
  ModbusPoll to prevent auto-restart after an unexpected crash.
- Add regression tests for processError during STOPPING state.

Author: jgeudens

src/ProtocolAdapter/adapterclient.cpp

@@ -140,8 +140,11 @@ void AdapterClient::onErrorReceived(int id, const QString& method, const QJsonOb
 void AdapterClient::onProcessError(const QString& message)
 {
     _handshakeTimer.stop();
-    _state = State::IDLE;
-    emit sessionError(message);
+    if (_state != State::STOPPING)
+    {
+        _state = State::IDLE;
+        emit sessionError(message);
+    }
 }
 
 void AdapterClient::onProcessFinished()

src/ProtocolAdapter/adapterprocess.cpp

@@ -13,6 +13,15 @@ AdapterProcess::AdapterProcess(QObject* parent) : QObject(parent)
     _pProcess = new QProcess(this);
     _pFramingReader = new FramingReader(this);
 
+    _pKillTimer = new QTimer(this);
+    _pKillTimer->setSingleShot(true);
+    connect(_pKillTimer, &QTimer::timeout, this, [this]() {
+        if (_pProcess->state() != QProcess::NotRunning)
+        {
+            _pProcess->kill();
+        }
+    });
+
     connect(_pProcess, &QProcess::readyReadStandardOutput, this, &AdapterProcess::onReadyReadStdout);
     connect(_pProcess, &QProcess::readyReadStandardError, this, &AdapterProcess::onReadyReadStderr);
     connect(_pProcess, &QProcess::finished, this, &AdapterProcess::onProcessFinished);
@@ -27,6 +36,7 @@ bool AdapterProcess::start(const QString& path)
         return true;
     }
 
+    _pKillTimer->stop();
     _pendingMethods.clear();
     _nextRequestId = 1;
 
@@ -51,12 +61,8 @@ void AdapterProcess::stop()
     if (_pProcess->state() != QProcess::NotRunning)
     {
         _pProcess->closeWriteChannel();
-        QTimer::singleShot(cStopTimeoutMs, this, [this]() {
-            if (_pProcess->state() != QProcess::NotRunning)
-            {
-                _pProcess->kill();
-            }
-        });
+        _pKillTimer->stop();
+        _pKillTimer->start(cStopTimeoutMs);
     }
 }
 
@@ -173,5 +179,6 @@ void AdapterProcess::onProcessFinished(int exitCode, QProcess::ExitStatus exitSt
 {
     qCInfo(scopeComm) << "AdapterProcess: process finished, exit code:" << exitCode << "status:" << exitStatus;
     _pendingMethods.clear();
+    _pKillTimer->stop();
     emit processFinished();
 }

src/ProtocolAdapter/adapterprocess.h

@@ -9,6 +9,7 @@
 #include <QObject>
 #include <QProcess>
 #include <QString>
+#include <QTimer>
 
 /*!
  * \brief Transport layer for an external adapter process communicating via JSON-RPC 2.0 over stdio.
@@ -104,6 +105,7 @@ private slots:
     bool writeFramed(const QByteArray& json);
 
     QProcess* _pProcess;
+    QTimer* _pKillTimer;
     FramingReader* _pFramingReader;
     QMap<int, QString> _pendingMethods;
     int _nextRequestId{ 1 };

src/communication/modbuspoll.cpp

@@ -28,6 +28,7 @@ ModbusPoll::ModbusPoll(SettingsModel* pSettingsModel, QObject* parent) : QObject
     connect(_pAdapterClient, &AdapterClient::sessionError, this, [this](QString message) {
         qCWarning(scopeComm) << "AdapterClient error:" << message;
         _bPollActive = false;
+        disconnect(_pAdapterClient, &AdapterClient::sessionStopped, this, &ModbusPoll::initAdapter);
     });
     connect(_pAdapterClient, &AdapterClient::sessionStopped, this, &ModbusPoll::initAdapter);
     connect(_pAdapterClient, &AdapterClient::diagnosticReceived, this, &ModbusPoll::onAdapterDiagnostic);

tests/ProtocolAdapter/tst_adapterclient.cpp

@@ -565,4 +565,49 @@ void TestAdapterClient::shutdownAckEmitsSessionStoppedAfterProcessExit()
     QCOMPARE(spyError.count(), 0);
 }
 
+void TestAdapterClient::processErrorDuringStoppingNoSessionError()
+{
+    auto* mock = new MockAdapterProcess();
+    AdapterClient client(mock);
+
+    QSignalSpy spyError(&client, &AdapterClient::sessionError);
+    QSignalSpy spyStopped(&client, &AdapterClient::sessionStopped);
+
+    client.prepareAdapter(QStringLiteral("./dummy"));
+    mock->injectResponse(1, "adapter.initialize", QJsonObject{ { "status", "ok" } });
+    mock->injectResponse(2, "adapter.describe", describeResult());
+    client.provideConfig(QJsonObject(), QStringList());
+    mock->injectResponse(3, "adapter.configure", QJsonObject{ { "status", "ok" } });
+    mock->injectResponse(4, "adapter.start", QJsonObject{ { "status", "ok" } });
+
+    client.stopSession();
+    mock->injectProcessError(QStringLiteral("Adapter process crashed"));
+
+    QCOMPARE(spyError.count(), 0);
+    QCOMPARE(spyStopped.count(), 0);
+}
+
+void TestAdapterClient::processErrorDuringStoppingThenProcessFinished()
+{
+    auto* mock = new MockAdapterProcess();
+    AdapterClient client(mock);
+
+    QSignalSpy spyError(&client, &AdapterClient::sessionError);
+    QSignalSpy spyStopped(&client, &AdapterClient::sessionStopped);
+
+    client.prepareAdapter(QStringLiteral("./dummy"));
+    mock->injectResponse(1, "adapter.initialize", QJsonObject{ { "status", "ok" } });
+    mock->injectResponse(2, "adapter.describe", describeResult());
+    client.provideConfig(QJsonObject(), QStringList());
+    mock->injectResponse(3, "adapter.configure", QJsonObject{ { "status", "ok" } });
+    mock->injectResponse(4, "adapter.start", QJsonObject{ { "status", "ok" } });
+
+    client.stopSession();
+    mock->injectProcessError(QStringLiteral("Adapter process crashed"));
+    mock->injectProcessFinished();
+
+    QCOMPARE(spyError.count(), 0);
+    QCOMPARE(spyStopped.count(), 1);
+}
+
 QTEST_GUILESS_MAIN(TestAdapterClient)

tests/ProtocolAdapter/tst_adapterclient.h

@@ -31,6 +31,8 @@ private slots:
     void awaitingConfigPausesBeforeConfigure();
     void stopSessionDuringAwaitingConfig();
     void shutdownAckEmitsSessionStoppedAfterProcessExit();
+    void processErrorDuringStoppingNoSessionError();
+    void processErrorDuringStoppingThenProcessFinished();
 };
 
 #endif // TST_ADAPTERCLIENT_H