stanfordnlp/CoreNLP · error · IllegalStateException

Cannot modify Redwood when within a track

Error message

Cannot modify Redwood when within a track

What it means

Redwood.RecordHandlerTree.addChild(handler) throws IllegalStateException when Redwood.depth != 0, i.e. when a logging track is currently open. The handler tree — the configuration of which log handlers are active — may only be modified at track depth 0, because mutating it mid-track would corrupt the active track stack.

Solutions

1. Move all Redwood.addChild/output/apply configuration calls to program startup, before any startTrack()
2. Defer configuration until after the tracked region ends (Redwood.depth == 0)
3. If dynamic handler changes are needed, end and restart the track around the reconfiguration
4. Assert Redwood.depth == 0 (or catch IllegalStateException) in helper code that configures logging

Example fix

// before
Redwood.startTrack("run");
Redwood.show(Redwood.ERR); // reconfigures handlers -> throws
// after
Redwood.show(Redwood.ERR);
Redwood.startTrack("run");
// ... work ...
Redwood.endTrack("run");

if (Redwood.depth != 0) {
  throw new IllegalStateException("Configure Redwood handlers only outside tracks");
}
Redwood.addChild(handler);

try {
  Redwood.addChild(handler);
} catch (IllegalStateException e) {
  log.warn("Deferred handler add: {}", e.getMessage());
  pendingHandlers.add(handler); // apply after endTrack
}

When it happens

Trigger: Calling Redwood.addChild(handler) (or convenience setters Redwood.output/stdout/stderr/slf4j/javaUtil/apply that delegate to it) between startTrack() and endTrack(), e.g. inside a logged region of code.

Common situations: Library code that reconfigures logging inside a tracked training loop; user code calling RedwoodConfiguration.apply(...) inside a track; handlers added per-request while a top-level track is open.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• OutputHandler received endTrack() without matching…
• Called remove() before any elements returned
• Cannot nest Redwood threaded environments
• Could not find Redwood log property:
• Must capture one of stderr or stdout

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/d0df28a817d5bf5c. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/logging/Redwood.java:649

      head = null;
    }

    public RecordHandlerTree(LogRecordHandler head) {
      this.isRoot = false;
      this.head = head;
    }

    // -- Core Tree Methods --
    public LogRecordHandler head(){
      return head;
    }
    public Iterator<RecordHandlerTree> children(){
      return children.iterator();
    }
    // -- Utility Methods --
    public void addChild(LogRecordHandler handler){
      if(Redwood.depth != 0){
        throw new IllegalStateException("Cannot modify Redwood when within a track");
      }
      children.add(new RecordHandlerTree(handler));
    }
    protected void addChildTree(RecordHandlerTree tree){
      if(Redwood.depth != 0){
        throw new IllegalStateException("Cannot modify Redwood when within a track");
      }
      children.add(tree);
    }
    public LogRecordHandler removeChild(LogRecordHandler handler){
      if(Redwood.depth != 0){
        throw new IllegalStateException("Cannot modify Redwood when within a track");
      }
      Iterator<RecordHandlerTree> iter = children();
      while(iter.hasNext()){
        LogRecordHandler cand = iter.next().head();
        if(cand == handler){
          iter.remove();

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