How do I narrow down the cause of extreme delays/hangs?

[emeraldcheshire]

I have a fairly large C++ project that I've been using with CDT for 10 years. Recently I noticed a certain files experience extremely slow performance with anything related to code analysis (syntax, completion, hover tips etc). I'm not sure when this started and can't pin it to an Eclipse version change. It manifests as taking 30-60 seconds to fully syntax highlighting the file, taking forever to update syntax highlights when I type, anything analysis related. Sometimes it will show EnclosingASTNameJob as the action taking place in the bottom right, but other times it won't say anything is going on other than being slow. When this is going on, Eclipse is burning CPU.

The file in question isn't always large. It seems related to particular classes being derived from, but I have not been able to isolate a single cause. By commenting stuff out and incrementally simplifying some of the base classes I was able to identify the following class which could trigger the problem:

Note that I closed Eclipse and deleted the pdom file between each test.

  template<class DERIVED_T, class KEY_T>
  class multiton_t {
  public:
    typedef multiton_t<DERIVED_T, KEY_T> multiton_type_t;
    multiton_t(KEY_T key);
    ~multiton_t(void);

    static DERIVED_T *instance(const KEY_T& param);

  private:
    typedef utl::adt::map<KEY_T, DERIVED_T*> instances_t;

    static instances_t instances;
    KEY_T              key;
  };

By further trimming, I found that the instance() function was triggering the problem and, strangely, simply renaming instance() to something else would make the problem stop. I tested going back and forth to confirm. Just renaming that member function would make the laggy file speedy and normal.

However, when I put back everything else I had previously stripped the file became laggy again. That stuff involved some ugly template stuff (deriving from a template argument). So either there's something about templates or I'm chasing a red herring.

Any suggestions on how I can get more insight into what exactly it's getting stuck/slow on?

[iloveeclipse]

Make sure you run with UI Freeze Monitoring enabled and check the error log view after hangs, it should report stack traces for the code that freezes UI:

[emeraldcheshire]

Well, the UI doesn't completely freeze. It's not even particularly unresponsive, just the analysis and all functionality related to it are super slow/laggy. Maybe I shouldn't describe it as a hang, since the UI doesn't hang, but further analysis actions seems to get blocked by some slow background operation.

For example, I can type auto x = 1 + 2; and it will take 60 seconds to fully syntax highlight. And while waiting for the result of typing to finish, hovering over a symbol will cause EnclosingASTNameJob to show up waiting in the bottom right.

I turned on the UI freeze monitoring to see if it would trigger, but it doesn't appear to.

I did notice there's 4 of these errors from each analysis though..
Cannot serialize @1868271001 (org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.FunctionSetType)

[iloveeclipse]

If the delays are long enough to start jstack , please do that and create few thread dumps.

[emeraldcheshire]

I made several jstack dumps while it was burning CPU thinking about CDT analysis. They're all in FinalOverriderMap.mergeOverriders().

There's an open bug which shares part of this traceback, but the complaint there is a hang during actual indexing so potentially not the same issue. https://bugs.eclipse.org/bugs/show_bug.cgi?id=515827

"org.eclipse.cdt.internal.ui.text.CReconciler" #86 [17584] daemon prio=1 os_prio=-2 cpu=52140.62ms elapsed=363.55s allocated=2088M defined_classes=16 tid=0x00000203fea7b130 nid=17584 runnable  [0x000000d83aafd000]
   java.lang.Thread.State: RUNNABLE
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPInheritance$FinalOverriderMap.mergeOverriders(CPPInheritance.java:109)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPInheritance$FinalOverriderMap.addOverriders(CPPInheritance.java:96)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPInheritance$FinalOverriderAnalysis.collectFinalOverriders(CPPInheritance.java:244)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPInheritance$FinalOverriderAnalysis.computeFinalOverriderMap(CPPInheritance.java:174)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPInheritance.getFinalOverriderMap(CPPInheritance.java:140)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPInheritance.getFinalOverrider(CPPInheritance.java:153)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPSemantics.postResolution(CPPSemantics.java:1032)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPSemantics.resolveBinding(CPPSemantics.java:399)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPVisitor.resolveBinding(CPPVisitor.java:1528)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPVisitor.createBinding(CPPVisitor.java:351)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTName.createIntermediateBinding(CPPASTName.java:67)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTNameBase.resolvePreBinding(CPPASTNameBase.java:98)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTFieldReference.createEvaluation(CPPASTFieldReference.java:303)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTFieldReference.getEvaluation(CPPASTFieldReference.java:291)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTFunctionCallExpression.computeEvaluation(CPPASTFunctionCallExpression.java:309)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTFunctionCallExpression.getEvaluation(CPPASTFunctionCallExpression.java:295)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.LookupData.setFunctionArguments(LookupData.java:529)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPSemantics.createLookupData(CPPSemantics.java:1193)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPSemantics.resolveBinding(CPPSemantics.java:373)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.semantics.CPPVisitor.createBinding(CPPVisitor.java:326)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTName.createIntermediateBinding(CPPASTName.java:67)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTNameBase.resolveBinding(CPPASTNameBase.java:111)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTQualifiedName.resolveBinding(CPPASTQualifiedName.java:112)
	at org.eclipse.cdt.internal.ui.editor.SemanticToken.getBinding(SemanticToken.java:50)
	at org.eclipse.cdt.internal.ui.editor.SemanticHighlightings$ParameterVariableHighlighting.consumes(SemanticHighlightings.java:965)
	at org.eclipse.cdt.internal.ui.editor.SemanticHighlightingReconciler$AbstractPositionCollector.visitNode(SemanticHighlightingReconciler.java:232)
	at org.eclipse.cdt.internal.ui.editor.SemanticHighlightingReconciler$AbstractPositionCollector.visit(SemanticHighlightingReconciler.java:194)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTQualifiedName.accept(CPPASTQualifiedName.java:236)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTConstructorChainInitializer.accept(CPPASTConstructorChainInitializer.java:120)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTFunctionDefinition.accept(CPPASTFunctionDefinition.java:213)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTCompositeTypeSpecifier.accept(CPPASTCompositeTypeSpecifier.java:201)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTSimpleDeclaration.accept(CPPASTSimpleDeclaration.java:112)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTNamespaceDefinition.accept(CPPASTNamespaceDefinition.java:144)
	at org.eclipse.cdt.internal.core.dom.parser.cpp.CPPASTNamespaceDefinition.accept(CPPASTNamespaceDefinition.java:144)
	at org.eclipse.cdt.internal.core.dom.parser.ASTTranslationUnit.accept(ASTTranslationUnit.java:289)
	at org.eclipse.cdt.internal.ui.editor.SemanticHighlightingReconciler.reconcilePositions(SemanticHighlightingReconciler.java:450)
	at org.eclipse.cdt.internal.ui.editor.SemanticHighlightingReconciler.reconciled(SemanticHighlightingReconciler.java:413)
	at org.eclipse.cdt.internal.ui.editor.CEditor.reconciled(CEditor.java:3107)
	at org.eclipse.cdt.internal.ui.text.CReconcilingStrategy.reconcile(CReconcilingStrategy.java:100)
	at org.eclipse.cdt.internal.ui.text.CReconcilingStrategy.reconcile(CReconcilingStrategy.java:64)
	at org.eclipse.cdt.internal.ui.text.CompositeReconcilingStrategy.reconcile(CompositeReconcilingStrategy.java:89)
	at org.eclipse.cdt.internal.ui.text.CCompositeReconcilingStrategy.reconcile(CCompositeReconcilingStrategy.java:90)
	at org.eclipse.jface.text.reconciler.MonoReconciler.process(MonoReconciler.java:78)
	at org.eclipse.cdt.internal.ui.text.CReconciler.process(CReconciler.java:346)
	at org.eclipse.jface.text.reconciler.AbstractReconciler$BackgroundThread.run(AbstractReconciler.java:207)

   Locked ownable synchronizers:
	- None

Hmmm. Symbol names in the traceback suggest an issue involving inheritance, which I already suspected from trial and error mentioned earlier. I'm not able to make sense of why certain changes to the derivation affect things the way they do.

For example, this is fine:

namespace A {
  class base_thing_t {};
  template<class BASE> template_thing_t : public BASE {}
}
namespace B {
  class problem_t : public A::template_thing_t<base_thing_t> {}
}

But it has the huge lag issue when I have another class in the heirarchy, even if it's empty:

namespace B {
  class derived_thing_t : public A::base_thing_t {}
  class problem_t : public A::template_thing_t<derived_thing_t> {}
}

I'm continuing to investigate as well as trying stuff from the FAQ @jonahgraham linked.
So far fussing with indexer settings hasn't changed any behavior (other than speeding up my indexing :D) and the .options debug stuff produces no output while burning CPU in mergeOverriders() .

[jonahgraham]

It may be worth reading the notes on indexer issues in the FAQ here: https://github.com/eclipse-cdt/cdt/blob/main/FAQ/Indexer.md