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Speeding up Truffle debugging #9142

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Speeding up Truffle debugging #9142

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9e24c44
Commenting out this line speeds Truffle debugger 10 times
jtulach Jan 14, 2026
6268481
Observe an invocation of to com.oracle.truffle.polyglot.PolyglotImpl.…
jtulach Jan 16, 2026
4bff9f1
Logging out time to doInitDebuggerRemoteService
jtulach Jan 22, 2026
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3 changes: 3 additions & 0 deletions ...gger.jpda.truffle/src/org/netbeans/modules/debugger/jpda/truffle/DebugManagerHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -163,7 +163,10 @@ void newPolyglotEngineInstance(ObjectReference engine, JPDAThreadImpl thread) {

void initDebuggerRemoteService(JPDAThread thread) {
if (inited.compareAndSet(false, true)) {
long now = System.currentTimeMillis();
doInitDebuggerRemoteService(thread);
long took = System.currentTimeMillis() - now;
LOG.log(Level.FINE, "doInitDebuggerRemoteService took {0} ms", took);
}
}

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48 changes: 29 additions & 19 deletions ...gger.jpda.truffle/src/org/netbeans/modules/debugger/jpda/truffle/TruffleDebugManager.java
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Expand Up @@ -59,43 +59,50 @@
*/
@DebuggerServiceRegistration(types=LazyDebuggerManagerListener.class)
public class TruffleDebugManager extends DebuggerManagerAdapter {

private static final Logger LOG = Logger.getLogger(TruffleDebugManager.class.getName());

private static final String ENGINE_CLASS = "org.graalvm.polyglot.Engine"; // NOI18N
private static final String ENGINE_BUILDER_CLASS = "org.graalvm.polyglot.Engine$Builder"; // NOI18N
private static final String POLY_IMPL_CLASS = "com.oracle.truffle.polyglot.PolyglotImpl"; // NOI18N
private static final String POLY_IMPL_BUILD_METHOD = "buildEngine"; // NOI18N
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@jtulach jtulach Feb 2, 2026

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  • the big question to ask:
  • can we rely on com.oracle.truffle.polyglot.PolyglotImpl.buildEngine being there in subsequent releases of Truffle API?
  • Engine.Builder.build() was an official API - it is not going to go away
  • PolyglotImpl.buildEngine(...) is just an implementation
  • but the speedup improvement is tempting

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@entlicher entlicher Feb 2, 2026

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This might be an option, even though it's prone to break when the impl changes. I don't expect Truffle to change much these days, it's much more mature than it was during the engines and instrumentation development, which broke our Truffle debugger in the past. Even though we never know what happens to the private stuff.

I'll test the class loading order - maybe we could test if PolyglotImpl.buildEngine() is there and if yes then use it, if not then fall back to the public method.

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@jtulach jtulach Feb 6, 2026

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test if PolyglotImpl.buildEngine() is there and if yes then use it, if not then fall back to the public method.

That's would be optimal and robust! Now I just need to find out how to test for existence of a method in the debuggee?

private static final String REMOTE_SERVICES_TRIGGER_CLASS = "com.oracle.truffle.api.Truffle"; // NOI18N
private static final String REMOTE_SERVICES_TRIGGER_METHOD = "getRuntime"; // NOI18N
// Breakpoint on this class triggers search of existing engines
private static final String EXISTING_ENGINES_TRIGGER = "com.oracle.truffle.api.frame.Frame"; // NOI18N
private JPDABreakpoint debugManagerLoadBP;

private MethodBreakpoint debugManagerLoadBP;
private Map<JPDADebugger, JPDABreakpoint> initServiceBPs = new HashMap<>();
private static final Map<JPDADebugger, Boolean> haveExistingEnginesTrigger = new WeakHashMap<>();
private static final Map<JPDADebugger, DebugManagerHandler> dmHandlers = new HashMap<>();
private static final Map<JPDADebugger, JPDABreakpointListener> debugBPListeners = new HashMap<>();

public TruffleDebugManager() {
}

@Override
public Breakpoint[] initBreakpoints() {
initLoadBP();
return new Breakpoint[] { debugManagerLoadBP };
}

private synchronized void initLoadBP() {
if (debugManagerLoadBP != null) {
return ;
}
/* Must NOT use a method exit breakpoint! It caused a massive degradation of application performance.
debugManagerLoadBP = MethodBreakpoint.create(SESSION_CREATION_BP_CLASS, SESSION_CREATION_BP_METHOD);
((MethodBreakpoint) debugManagerLoadBP).setBreakpointType(MethodBreakpoint.TYPE_METHOD_EXIT);
/*
- Must NOT use a method exit breakpoint!
- It caused a massive degradation of application performance.
- we will attach an exit breakpoint, but the later the better
- we need a method that's called the "latest" before returning
- from `Engine.Builder.build()`
- as of GraalVM 25.0.1 it is:
- [this one](https://github.com/oracle/graal/blob/05ec02567a77a30cc41b8ad9174de0dc5737ceaf/sdk/src/org.graalvm.polyglot/src/org/graalvm/polyglot/Engine.java#L843)
*/
debugManagerLoadBP = MethodBreakpoint.create(ENGINE_BUILDER_CLASS, "build");
((MethodBreakpoint) debugManagerLoadBP).setBreakpointType(MethodBreakpoint.TYPE_METHOD_ENTRY);
debugManagerLoadBP = MethodBreakpoint.create(POLY_IMPL_CLASS, POLY_IMPL_BUILD_METHOD);
debugManagerLoadBP.setBreakpointType(MethodBreakpoint.TYPE_METHOD_ENTRY);
debugManagerLoadBP.setHidden(true);

LOG.log(Level.FINE, "TruffleDebugManager.initBreakpoints(): submitted BP {0}", debugManagerLoadBP);
TruffleAccess.init();
}
Expand Down Expand Up @@ -182,7 +189,8 @@ private JPDABreakpointListener addPolyglotEngineCreationBP(final JPDADebugger de
public void breakpointReached(JPDABreakpointEvent event) {
try {
if (event.getDebugger() == debugger) {
handleEngineBuilder(debugger, event);
LOG.log(Level.FINE, "Building of an Engine is in progress");
handleJustBuiltEngine(debugger, event.getThread());
}
} finally {
event.resume();
Expand Down Expand Up @@ -225,18 +233,20 @@ public void propertyChange(PropertyChangeEvent evt) {
* We need to submit a temporary method-exit breakpoint on the build method.
* We must not keep the method exit breakpoint active as it causes a significant performance degradation.
*/
private void handleEngineBuilder(final JPDADebugger debugger, JPDABreakpointEvent entryEvent) {
private void handleJustBuiltEngine(final JPDADebugger debugger, JPDAThread onThread) {
MethodBreakpoint builderExitBreakpoint = MethodBreakpoint.create(ENGINE_BUILDER_CLASS, "build");
builderExitBreakpoint.setBreakpointType(MethodBreakpoint.TYPE_METHOD_EXIT);
builderExitBreakpoint.setThreadFilters(debugger, new JPDAThread[]{entryEvent.getThread()});
builderExitBreakpoint.setThreadFilters(debugger, new JPDAThread[]{onThread});
builderExitBreakpoint.setSuspend(JPDABreakpoint.SUSPEND_EVENT_THREAD);
builderExitBreakpoint.setSession(debugger);
builderExitBreakpoint.setHidden(true);
builderExitBreakpoint.addJPDABreakpointListener(exitEvent -> {
try {
builderExitBreakpoint.disable();
DebuggerManager.getDebuggerManager().removeBreakpoint(builderExitBreakpoint);
haveNewPE(debugger, (JPDAThreadImpl) exitEvent.getThread(), (ObjectReference) ((JDIVariable) exitEvent.getVariable()).getJDIValue());
final ObjectReference ref = (ObjectReference) ((JDIVariable) exitEvent.getVariable()).getJDIValue();
LOG.log(Level.FINE, "New Engine has just been built: {0}", ref);
haveNewPE(debugger, (JPDAThreadImpl) exitEvent.getThread(), ref);
} finally {
exitEvent.resume();
}
Expand Down Expand Up @@ -326,7 +336,7 @@ public void breakpointRemoved(Breakpoint breakpoint) {
}
}
}

public static ClassType getDebugAccessorClass(JPDADebugger debugger) {
synchronized (dmHandlers) {
DebugManagerHandler dmh = dmHandlers.get(debugger);
Expand All @@ -337,7 +347,7 @@ public static ClassType getDebugAccessorClass(JPDADebugger debugger) {
}
}
}

public static JPDAClassType getDebugAccessorJPDAClass(JPDADebugger debugger) {
synchronized (dmHandlers) {
DebugManagerHandler dmh = dmHandlers.get(debugger);
Expand Down
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