Made thread update reactive

And avoid calling stacktrace when not suspended (some LS such as
vscode-js-debug may not answer in such case)

org.eclipse.lsp4e.debug/src/org/eclipse/lsp4e/debug/debugmodel/DSPDebugTarget.java

@@ -21,7 +21,6 @@
 import java.io.OutputStream;
 import java.io.PrintWriter;
 import java.util.Arrays;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -31,13 +30,13 @@
 import java.util.TreeMap;
 import java.util.Map.Entry;
 import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
-import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Predicate;
 import java.util.function.Supplier;
 import java.util.function.UnaryOperator;
+import java.util.stream.Collectors;
 
 import org.eclipse.core.resources.IMarkerDelta;
 import org.eclipse.core.runtime.CoreException;
@@ -79,7 +78,7 @@
 import org.eclipse.lsp4j.debug.TerminatedEventArguments;
 import org.eclipse.lsp4j.debug.Thread;
 import org.eclipse.lsp4j.debug.ThreadEventArguments;
-import org.eclipse.lsp4j.debug.ThreadsResponse;
+import org.eclipse.lsp4j.debug.ThreadEventArgumentsReason;
 import org.eclipse.lsp4j.debug.launch.DSPLauncher;
 import org.eclipse.lsp4j.debug.services.IDebugProtocolClient;
 import org.eclipse.lsp4j.debug.services.IDebugProtocolServer;
@@ -130,10 +129,6 @@ public class DSPDebugTarget extends DSPDebugElement implements IDebugTarget, IDe
 	 * they are up to date (against the {@link #refreshThreads} flag).
 	 */
 	private final Map<Integer, DSPThread> threads = Collections.synchronizedMap(new TreeMap<>());
-	/**
-	 * Set to true to update the threads list from the debug adapter.
-	 */
-	private final AtomicBoolean refreshThreads = new AtomicBoolean(true);
 
 	private boolean fTerminated = false;
 	private boolean fSentTerminateRequest = false;
@@ -556,46 +551,7 @@ public IProcess getProcess() {
 
 	@Override
 	public DSPThread[] getThreads() {
-		if (!refreshThreads.getAndSet(false)) {
-			synchronized (threads) {
-				Collection<DSPThread> values = threads.values();
-				return values.toArray(new DSPThread[values.size()]);
-			}
-		}
-		try {
-			var server = getDebugProtocolServer();
-			if (server == null) {
-				return new DSPThread[0];
-			}
-			CompletableFuture<ThreadsResponse> threads2 = server.threads();
-			CompletableFuture<DSPThread[]> future = threads2.thenApplyAsync(threadsResponse -> {
-				synchronized (threads) {
-					final var lastThreads = new TreeMap<Integer, DSPThread>(threads);
-					threads.clear();
-					Thread[] body = threadsResponse.getThreads();
-					for (Thread thread : body) {
-						DSPThread dspThread = lastThreads.get(thread.getId());
-						if (dspThread == null) {
-							dspThread = new DSPThread(this, thread.getId());
-						}
-						dspThread.update(thread);
-						threads.put(thread.getId(), dspThread);
-						// fireChangeEvent(DebugEvent.CONTENT);
-					}
-					Collection<DSPThread> values = threads.values();
-					return values.toArray(new DSPThread[values.size()]);
-				}
-			});
-			return future.get();
-		} catch (RuntimeException | ExecutionException e) {
-			if (isTerminated()) {
-				return new DSPThread[0];
-			}
-			DSPPlugin.logError(e);
-		} catch (InterruptedException e) {
-			java.lang.Thread.currentThread().interrupt();
-		}
-		return new DSPThread[0];
+		return threads.values().toArray(DSPThread[]::new);
 	}
 
 	/**
@@ -632,8 +588,31 @@ public void exited(ExitedEventArguments args) {
 
 	@Override
 	public void thread(ThreadEventArguments args) {
-		refreshThreads.set(true);
-		fireChangeEvent(DebugEvent.CONTENT);
+		// update according to current event
+		if (ThreadEventArgumentsReason.EXITED.equals(args.getReason())) {
+			threads.remove(args.getThreadId());
+			fireChangeEvent(DebugEvent.CONTENT);
+		} else if (ThreadEventArgumentsReason.STARTED.equals(args.getReason())) {
+			var newThread = new DSPThread(this, args.getThreadId());
+			threads.put(args.getThreadId(), newThread);
+			fireChangeEvent(DebugEvent.CONTENT);
+		}
+		// and trigger a further update
+		// then update threads
+		getDebugProtocolServer().threads().thenAcceptAsync(threadsResponse -> {
+			var threadIds = Arrays.stream(threadsResponse.getThreads()).map(Thread::getId).collect(Collectors.toSet());
+			if (threads.keySet().removeIf(Predicate.not(threadIds::contains))) {
+				fireChangeEvent(DebugEvent.CONTENT);
+			}
+			for (Thread thread : threadsResponse.getThreads()) {
+				DSPThread dspThread = threads.get(thread.getId());
+				if (dspThread == null) {
+					dspThread = new DSPThread(this, thread.getId());
+					fireChangeEvent(DebugEvent.CONTENT);
+				}
+				dspThread.update(thread);
+			}
+		});
 	}
 
 	@Override

org.eclipse.lsp4e.debug/src/org/eclipse/lsp4e/debug/debugmodel/DSPThread.java

@@ -65,9 +65,11 @@ public DSPThread(DSPDebugTarget debugTarget, Integer threadId) {
 	 */
 	public void update(Thread thread) {
 		Assert.isTrue(Objects.equals(this.id, thread.getId()));
-		this.name = thread.getName();
+		if (!Objects.equals(this.name, thread.getName())) {
+			fireChangeEvent(DebugEvent.STATE);
+			this.name = thread.getName();
+		}
 		refreshFrames.set(true);
-		// fireChangeEvent(DebugEvent.STATE);
 	}
 
 	@Override
@@ -101,7 +103,7 @@ public void continued() {
 	public void stopped() {
 		isSuspended = true;
 		stepping = false;
-		refreshFrames.set(true);
+		frames.clear();
 	}
 
 	@Override
@@ -226,8 +228,10 @@ public IStackFrame getTopStackFrame() throws DebugException {
 		}
 	}
 
-	@Override
-	public IStackFrame[] getStackFrames() throws DebugException {
+	@Override public IStackFrame[] getStackFrames() throws DebugException {
+		if (!isSuspended()) {
+			return new IStackFrame[0];
+		}
 		if (!refreshFrames.getAndSet(false)) {
 			synchronized (frames) {
 				return frames.toArray(new DSPStackFrame[frames.size()]);