{"record":{"id":"dc61ae83236215ed","repo":"apache/flink","slug":"failed-to-open-the-generatorfunction-dc61ae","errorCode":null,"errorMessage":"Failed to open the GeneratorFunction","messagePattern":"Failed to open the GeneratorFunction","errorType":"exception","errorClass":"FlinkRuntimeException","httpStatus":null,"severity":"error","filePath":"flink-connectors/flink-connector-datagen/src/main/java/org/apache/flink/connector/datagen/source/GeneratingIteratorSourceReader.java","lineNumber":69,"sourceCode":"    @Override\n    protected O convert(E value) {\n        try {\n            return generatorFunction.map(value);\n        } catch (Exception e) {\n            String message =\n                    String.format(\n                            \"A user-provided generator function threw an exception on this input: %s\",\n                            value.toString());\n            throw new FlinkRuntimeException(message, e);\n        }\n    }\n\n    @Override\n    public void start(SourceReaderContext context) {\n        try {\n            generatorFunction.open(context);\n        } catch (Exception e) {\n            throw new FlinkRuntimeException(\"Failed to open the GeneratorFunction\", e);\n        }\n    }\n\n    @Override\n    public void close() throws Exception {\n        generatorFunction.close();\n        super.close();\n    }\n}\n","sourceCodeStart":51,"sourceCodeEnd":79,"githubUrl":"https://github.com/apache/flink/blob/2f3c205e9266cb30240eb7f4fdab15cad629a70f/flink-connectors/flink-connector-datagen/src/main/java/org/apache/flink/connector/datagen/source/GeneratingIteratorSourceReader.java#L51-L79","documentation":"Thrown by start() in GeneratingIteratorSourceReader when the user-provided GeneratorFunction.open(context) throws an exception. The original exception is wrapped in FlinkRuntimeException. This is the production-oriented iterator source reader that applies a GeneratorFunction to transform iterator values.","triggerScenarios":"A custom GeneratorFunction whose open() method throws during source reader initialization. The reader calls generatorFunction.open(context) in its start() lifecycle phase.","commonSituations":"Generator function initializing external resources (database, network, file) in open() that fail; misconfigured SourceReaderContext; resource exhaustion or permission errors.","solutions":["Inspect the wrapped cause exception in the FlinkRuntimeException for the root failure.","Fix the root cause in the GeneratorFunction's open() method.","Ensure external resources are available and accessible before job submission.","Add proper error handling and retry logic in open() for transient failures."],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":"// Validate GeneratorFunction.open() works with a test context\nGeneratorFunction<E, O> fn = ...;\nfn.open(testContext);\nfn.close();","typeGuard":null,"tryCatchPattern":"try {\n    sourceReader.start(context);\n} catch (FlinkRuntimeException e) {\n    if (e.getMessage().equals(\"Failed to open the GeneratorFunction\")) {\n        // inspect e.getCause() for the root failure\n    }\n    throw e;\n}","preventionTips":["Unit-test GeneratorFunction.open() before deploying.","Ensure external resources are reachable.","Add retry and proper error handling in open() for transient failures."],"tags":["datagen","source-reader","generator-function","lifecycle"],"backgroundTag":null,"analyzedSha":"2f3c205e9266cb30240eb7f4fdab15cad629a70f","analyzedAt":"2026-08-14T08:48:24.518Z","schemaVersion":2},"datasetVersion":"2026-08-14T10:17:34.591Z"}