knime · HedgehogCode · Mar 13, 2026
@@ -232,7 +232,7 @@ protected PortObject[] execute(final PortObject[] inObjects, final ExecutionCont
 
     /**
      * Throw a nicer error message if the exception we are seeing is an "Error while obtaining a new communication
-     * channel"
+     * channel" or "Cannot obtain a new communication channel" (CallbackClient already shut down)
      *
      * @param ex The exception
      * @throws KNIMEException A more human-readable exception
@@ -245,6 +245,17 @@ private void handleNewCommunicationChannelError(final Py4JException ex) throws K
                 "The Python process we prepared in the background got killed. Try again to start a new one.");
             throw KNIMEException.of(messageBuilder.build().orElseThrow(), ex);
         }
+        // Handle the case where the CallbackClient was already shut down (no cause)
+        if (ex.getCause() == null && ex.getMessage() != null
+            && ex.getMessage().startsWith("Cannot obtain a new communication channel")) {
+            var messageBuilder = createMessageBuilder();
+            messageBuilder.withSummary("The Python communication channel was unexpectedly shut down before use. "
+                + "Details: " + ex.getMessage());
+            messageBuilder.addResolutions("This is a known intermittent issue. Please try executing again.",
+                "Check the KNIME log for entries around this error for more information about "
+                    + "what shut down the communication channel.");
+            throw KNIMEException.of(messageBuilder.build().orElseThrow(), ex);
+        }
     }
 
     private void runUserScript(final PythonScriptingSession session)

@@ -161,6 +161,8 @@ final class PythonScriptingSession implements AsynchronousCloseable<IOException>
         m_fileStoreHandlerSupplier = fileStoreHandlerSupplier;
         m_gateway = createGateway(pythonCommand);
         m_entryPoint = m_gateway.getEntryPoint();
+        LOGGER.infoWithFormat("PythonScriptingSession created gateway (hash=%s) on thread '%s'",
+            Integer.toHexString(System.identityHashCode(m_gateway)), Thread.currentThread().getName());
         m_tableConverter = new PythonArrowTableConverter(EXECUTOR_SERVICE, ARROW_STORE_FACTORY,
             fileStoreHandlerSupplier.getWriteFileStoreHandler());
         m_outputRedirector = PythonGatewayUtils.redirectGatewayOutput(m_gateway, LOGGER::info, LOGGER::info);
@@ -495,6 +497,13 @@ private void setCurrentWorkingDirectory() {
             Optional.ofNullable(workflowDirRef).map(r -> r.getFile().toString())
                 .ifPresent(m_entryPoint::setCurrentWorkingDirectory);
         } catch (Py4JException ex) {
+            // Log detailed diagnostics if the CallbackClient was already shut down
+            if (ex.getCause() == null && ex.getMessage() != null
+                && ex.getMessage().startsWith("Cannot obtain a new communication channel")) {
+                LOGGER.error("CallbackClient was shut down before first use. " + "Gateway hash="
+                    + Integer.toHexString(System.identityHashCode(m_gateway)) + ", thread='"
+                    + Thread.currentThread().getName() + "'", ex);
+            }
             PythonProcessTerminatedException.throwIfTerminated(m_gateway, ex);
             throw ex;
         } catch (Exception ex) { // NOSONAR: We want to catch any exception here

@@ -327,6 +327,8 @@ public T getEntryPoint() {
     @Override
     public void close() throws IOException {
         if (m_clientServer != null) {
+            LOGGER.infoWithFormat("Closing PythonGateway (PID=%s) from thread '%s'", m_pid,
+                Thread.currentThread().getName());
             m_entryPoint = null;
             m_clientServer.shutdown();
             m_clientServer = null;

@@ -182,18 +182,21 @@ public void notify(final EventObject o) {
         if (o instanceof PhaseEvent && ((PhaseEvent)o).getPhaseId().equals(PhaseSetFactory.PHASE_INSTALL)
             && ((PhaseEvent)o).getType() == PhaseEvent.TYPE_START) {
             // lock if we enter the "install" phase
-            LOGGER.info("Blocking Python process startup during installation");
+            LOGGER.info("Blocking Python process startup during installation (thread='"
+                + Thread.currentThread().getName() + "')");
             INSTANCE.blockPythonCreation();
         } else if (o instanceof PhaseEvent && ((PhaseEvent)o).getPhaseId().equals(PhaseSetFactory.PHASE_CONFIGURE)
             && ((PhaseEvent)o).getType() == PhaseEvent.TYPE_START) {
             // "configure" is the normal phase after install, so we can unlock Python processes again
-            LOGGER.info("Allowing Python process startup again after installation");
+            LOGGER.info("Allowing Python process startup again after installation (thread='"
+                + Thread.currentThread().getName() + "')");
             INSTANCE.allowPythonCreation();
         } else if (o instanceof RollbackOperationEvent && !INSTANCE.isPythonGatewayCreationAllowed()) {
             // According to org.eclipse.equinox.internal.p2.engine.Engine.perform() -> L92,
             // a RollbackOperationEvent will be fired if an operation failed, and this event is only fired in that case,
             // so we unlock if we are currently locked.
-            LOGGER.info("Allowing Python process startup again after installation failed");
+            LOGGER.info("Allowing Python process startup again after installation failed (thread='"
+                + Thread.currentThread().getName() + "')");
             INSTANCE.allowPythonCreation();
         }
     }

@@ -111,9 +111,11 @@ void clear() throws IOException {
             return;
         }
 
-        LOGGER.error("Found running Python processes. Aborting them to allow installation process. "
-            + "If this leads to failures in node execution, "
-            + "please restart those nodes once the installation has finished");
+        LOGGER.errorWithFormat(
+            "Found running Python processes (%d). Aborting them to allow installation process. "
+                + "If this leads to failures in node execution, "
+                + "please restart those nodes once the installation has finished. Triggered from thread '%s'.",
+            m_openGateways.size(), Thread.currentThread().getName());
 
         var exceptions = new ArrayList<Exception>();
         for (var gateway : m_openGateways) {

@@ -217,11 +217,13 @@ public void onPythonGatewayCreationGateOpen() {
 
                 @Override
                 public void onPythonGatewayCreationGateClose() {
-                    evictGateways(//
-                        m_gateways.values().stream()//
-                            .flatMap(Collection::stream)//
-                            .collect(Collectors.toList())//
-                    );
+                    var gatewaysToEvict = m_gateways.values().stream()//
+                        .flatMap(Collection::stream)//
+                        .collect(Collectors.toList());
+                    LOGGER.warnWithFormat(
+                        "PythonGatewayCreationGate closed: evicting %d queued gateways from thread '%s'",
+                        gatewaysToEvict.size(), Thread.currentThread().getName());
+                    evictGateways(gatewaysToEvict);
                 }
             });
         }