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…unication failures Logs gateway lifecycle events (creation, closure) with thread and identity information to help diagnose the root cause of "Cannot obtain a new communication channel" errors. Tracks gateway ownership through object hash codes for correlation. - DefaultPythonGateway.close(): Log PID and calling thread at INFO level - PythonScriptingSession: Log gateway hash and thread at creation (INFO) and shutdown (ERROR) - PythonGatewayTracker.clear(): Log process count and triggering thread at ERROR level - QueuedPythonGatewayFactory: Log eviction count and thread at gate-close (WARN) - PythonGatewayCreationGate: Include thread name in P2 phase event logs (INFO) - PythonScriptNodeModel: Handle no-cause "Cannot obtain" variant with improved error message When this error occurs again, correlating gateway hash and PID across log entries will reveal which code path triggered the unexpected shutdown. AP-25563 (Investigate "Cannot obtain a new communication channel" Python failures)
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Pull request overview
Adds diagnostic logging and improved error messaging across the KNIME Java↔Python (Py4J) gateway lifecycle to help trace intermittent “Cannot obtain a new communication channel” failures by correlating gateway identity, PID, and thread context.
Changes:
- Add structured lifecycle logs (thread, gateway hash, PID, eviction counts) across gateway creation/closure and installation gating.
- Improve handling of the no-cause “Cannot obtain a new communication channel” Py4J exception with a clearer KNIMEException message and resolutions.
- Enhance installation-phase logs and tracker diagnostics to better identify who/what triggered gateway shutdown/termination.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.
Show a summary per file
| File | Description |
|---|---|
| org.knime.python3/src/main/java/org/knime/python3/QueuedPythonGatewayFactory.java | Logs eviction count/thread when the gateway creation gate closes before evicting queued gateways. |
| org.knime.python3/src/main/java/org/knime/python3/PythonGatewayTracker.java | Adds process count + triggering thread to the “aborting running Python processes” log entry. |
| org.knime.python3/src/main/java/org/knime/python3/PythonGatewayCreationGate.java | Adds thread name to P2 phase transition INFO logs controlling gateway creation blocking/unblocking. |
| org.knime.python3/src/main/java/org/knime/python3/DefaultPythonGateway.java | Logs PID + calling thread when closing a Python gateway. |
| org.knime.python3.scripting.nodes/src/main/java/org/knime/python3/scripting/nodes2/PythonScriptingSession.java | Logs gateway identity hash on creation; adds targeted ERROR diagnostics when CallbackClient is already shut down. |
| org.knime.python3.scripting.nodes/src/main/java/org/knime/python3/scripting/nodes2/PythonScriptNodeModel.java | Adds a dedicated handler branch for the no-cause “Cannot obtain…” error with a clearer user-facing message. |
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| 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); |
| @Override | ||
| public void close() throws IOException { | ||
| if (m_clientServer != null) { | ||
| LOGGER.infoWithFormat("Closing PythonGateway (PID=%s) from thread '%s'", m_pid, |
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| LOGGER.info("Blocking Python process startup during installation (thread='" | ||
| + Thread.currentThread().getName() + "')"); |
| + "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. " |
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…unication failures
Logs gateway lifecycle events (creation, closure) with thread and identity information to help diagnose the root cause of "Cannot obtain a new communication channel" errors. Tracks gateway ownership through object hash codes for correlation.
When this error occurs again, correlating gateway hash and PID across log entries will reveal which code path triggered the unexpected shutdown.
AP-25563 (Investigate "Cannot obtain a new communication channel" Python failures)