Concurrent connections during a live reload

[FroMage]

In quarkiverse/quarkus-renarde#266 a user reported an issue which happens when triggering multiple connections during a live reload.

Apparently, according to

quarkus/extensions/vertx-http/runtime/src/main/java/io/quarkus/vertx/http/runtime/devmode/VertxHttpHotReplacementSetup.java

Line 144 in c183b3d

routingContext.next();

we continue serving requests while a live reload is happening:

quarkus/extensions/vertx-http/runtime/src/main/java/io/quarkus/vertx/http/runtime/devmode/VertxHttpHotReplacementSetup.java

Lines 147 to 208 in c183b3d

	ClassLoader current = Thread.currentThread().getContextClassLoader();
	VertxCoreRecorder.getVertx().get().getOrCreateContext().executeBlocking(new Callable<Boolean>() {
	@Override
	public Boolean call() {
	//the blocking pool may have a stale TCCL
	Thread.currentThread().setContextClassLoader(current);
	boolean restart = false;
	try {
	DevConsoleManager.setDoingHttpInitiatedReload(true);
	synchronized (this) {
	if (nextUpdate < System.currentTimeMillis() || hotReplacementContext.isTest()) {
	nextUpdate = System.currentTimeMillis() + HOT_REPLACEMENT_INTERVAL;
	Object currentState = VertxHttpRecorder.getCurrentApplicationState();
	try {
	restart = hotReplacementContext.doScan(true);
	} catch (Exception e) {
	throw new IllegalStateException("Unable to perform live reload scanning", e);
	}
	if (currentState != VertxHttpRecorder.getCurrentApplicationState()) {
	//its possible a Kafka message or some other source triggered a reload,
	//so we could wait for the restart (due to the scan lock)
	//but then fail to dispatch to the new application
	restart = true;
	}
	}
	}
	if (hotReplacementContext.getDeploymentProblem() != null) {
	throw new NoStackTraceException(hotReplacementContext.getDeploymentProblem());
	}
	if (restart) {
	//close all connections on close, except for this one
	//this prevents long-running requests such as SSE or websockets
	//from holding onto the old deployment
	Set<ConnectionBase> connections = new HashSet<>(openConnections);
	for (ConnectionBase con : connections) {
	if (con != connectionBase) {
	con.close();
	}
	}
	}
	} finally {
	DevConsoleManager.setDoingHttpInitiatedReload(false);
	}
	return restart;
	}
	}, false).onComplete(new Handler<AsyncResult<Boolean>>() {
	@Override
	public void handle(AsyncResult<Boolean> event) {
	if (event.failed()) {
	handleDeploymentProblem(routingContext, event.cause());
	} else {
	boolean restart = event.result();
	if (restart) {
	QuarkusExecutorFactory.reinitializeDevModeExecutor();
	routingContext.request().headers().set(HEADER_NAME, "true");
	VertxHttpRecorder.getRootHandler().handle(routingContext.request());
	} else {
	routingContext.next();
	}
	}
	}
	});

As such, what's happening is that the user makes a change, hits reload, but it's probably taking too long, so they hit reload again, and the second connection is served while the first is still handling the hot reload.

But midway during the request serving, the reload is happening and we're shutting down the Arc Container so the request fails with a really weird and confusing exception.

I could fix the symptom, but that's a waste of time because other applications would fail in different ways.

We could either make new connections (after the hot reload started) wait for the hot reload to be finished, or we could make them serve an error page mentioning that a hot reload is in progress. I suspect the first option is more user-friendly.

To reproduce:

• Download https://github.com/gbourant/renarde-live-reload-bug
• Start the app via mvn quarkus:dev
• Open a browser at http://localhost:8080/hello
• Edit HelloResource.java and change "Hello from Quarkus REST" (save the file)
• Go back to the browser, press F5 so it will refresh BUT before it finishes the refresh/live-reload press again F5 fast. (If you just press once the F5 it works as expected)

This should be easy to reproduce with a hot reload test if we make sure the reload takes an artificially long time (not sure how, perhaps a 1s sleep during a custom build step, or a startup bean?).