What causes "-threads [number]: was not given a valid number: " in stanfordnlp/CoreNLP?

Pass a plain integer, e.g. -threads 4

-threads [number]: was not given a valid number:

Error message

-threads [number]: was not given a valid number:

What it means

StanfordCoreNLP's -threads command-line option must parse as an integer. When Integer.parseInt fails on the provided value, this error message is logged and the thread count silently falls back to the default of 1.

Solutions

Pass a plain integer, e.g. -threads 4
Quote the value in the shell if needed: -threads "4"
Verify no stray characters (units, commas) after the number
Remember the fallback is 1 thread; check output timing if performance matters

Example fix

// before
java StanfordCoreNLP -threads auto -filelist f.txt
// after
java StanfordCoreNLP -threads 8 -filelist f.txt

Defensive patterns

Strategy: validation

Validate before calling

int threads = 1;
if (argsThreads != null && argsThreads.matches("\\d+")) {
    threads = Integer.parseInt(argsThreads);
}

Prevention

Always pass -threads as a bare positive integer
Quote arguments in shell scripts to avoid stray characters
Check logs after startup to confirm the intended thread count took effect

When it happens

Trigger: Running java StanfordCoreNLP -threads "four" or -threads 4x or any non-numeric string; parseThreads-like helper in StanfordCoreNLP main catches NumberFormatException.

Common situations: Shell quoting issues or typos; passing a comma list like -threads 2,4; copy-pasting options from another tool; expecting the flag name to be --threads instead of -threads so the value string is odd.

Understand the failure class

Background: "Unknown argument", "Invalid value", and "must be one of": invalid CLI argument errors explained — this error's family across 35 libraries.

Related errors

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/a6d824e7d4a656e7. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/pipeline/StanfordCoreNLP.java:1437

  }

  public void run() throws IOException {
    run(false);
  }

  public void run(boolean clearPool) throws IOException {
    Timing tim = new Timing();
    StanfordRedwoodConfiguration.minimalSetup();

    // multithreading thread count
    String numThreadsString = this.properties.getProperty("threads");
    int numThreads = 1;
    try {
      if (numThreadsString != null) {
        numThreads = Integer.parseInt(numThreadsString);
      }
    } catch (NumberFormatException e) {
      logger.err("-threads [number]: was not given a valid number: " + numThreadsString);
    }

    // blank line after all the loading statements to make output more readable
    logger.info("");

    //
    // Process one file or a directory of files
    //
    if (properties.containsKey("file") || properties.containsKey("textFile")) {
      String fileName = properties.getProperty("file");
      if (fileName == null) {
        fileName = properties.getProperty("textFile");
      }
      Collection<File> files = new FileSequentialCollection(new File(fileName), properties.getProperty("extension"), true);
      this.processFiles(null, files, numThreads, clearPool, Optional.of(tim));
    }

    //

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