Infinite stream of hotswapping events

[Artur-]

When using the Vaadin plugin in 2.0.0, I every now and then see an infinite stream of hotswapping events for the same class being sent to Hotswapper.onHotswap. Today it looks like

Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]
Hotswapping[com.github.javaparser.resolution.declarations.AssociableToAST]

and it continues forever. Would this be a problem in the Vaadin plugin, HotswapAgent or JBR?

The stack trace in IntelliJ does not really tell that much

[Artur-]

With trace logging enabled for HA, I see

HOTSWAP AGENT: 10:37:05.105 DEBUG (org.hotswap.agent.command.impl.SchedulerImpl) - Executing Command{class='com.vaadin.flow.hotswap.Hotswapper', methodName='onHotswap'}
HOTSWAP AGENT: 10:37:05.105 TRACE (org.hotswap.agent.command.impl.CommandExecutor) - Executing command Command{class='com.vaadin.flow.hotswap.Hotswapper', methodName='onHotswap'}
HOTSWAP AGENT: 10:37:05.106 TRACE (org.hotswap.agent.command.ReflectionCommand) - Executing command: requestedClassLoader=jdk.internal.loader.ClassLoaders$AppClassLoader@27ddd392, resolvedClassLoader=jdk.internal.loader.ClassLoaders$AppClassLoader@27ddd392, class=class com.vaadin.flow.hotswap.Hotswapper, method=onHotswap, params=[[Ljava.lang.String;@669856bd, false]
Hotswapping[com.vaadin.flow.component.dependency.StyleSheet]
HOTSWAP AGENT: 10:37:05.208 DEBUG (org.hotswap.agent.command.impl.SchedulerImpl) - Executing Command{class='com.vaadin.flow.hotswap.Hotswapper', methodName='onHotswap'}
HOTSWAP AGENT: 10:37:05.208 TRACE (org.hotswap.agent.command.impl.CommandExecutor) - Executing command Command{class='com.vaadin.flow.hotswap.Hotswapper', methodName='onHotswap'}
HOTSWAP AGENT: 10:37:05.208 TRACE (org.hotswap.agent.command.ReflectionCommand) - Executing command: requestedClassLoader=jdk.internal.loader.ClassLoaders$AppClassLoader@27ddd392, resolvedClassLoader=jdk.internal.loader.ClassLoaders$AppClassLoader@27ddd392, class=class com.vaadin.flow.hotswap.Hotswapper, method=onHotswap, params=[[Ljava.lang.String;@669856bd, false]
Hotswapping[com.vaadin.flow.component.dependency.StyleSheet]
HOTSWAP AGENT: 10:37:05.313 DEBUG (org.hotswap.agent.command.impl.SchedulerImpl) - Executing Command{class='com.vaadin.flow.hotswap.Hotswapper', methodName='onHotswap'}
HOTSWAP AGENT: 10:37:05.313 TRACE (org.hotswap.agent.command.impl.CommandExecutor) - Executing command Command{class='com.vaadin.flow.hotswap.Hotswapper', methodName='onHotswap'}
HOTSWAP AGENT: 10:37:05.313 TRACE (org.hotswap.agent.command.ReflectionCommand) - Executing command: requestedClassLoader=jdk.internal.loader.ClassLoaders$AppClassLoader@27ddd392, resolvedClassLoader=jdk.internal.loader.ClassLoaders$AppClassLoader@27ddd392, class=class com.vaadin.flow.hotswap.Hotswapper, method=onHotswap, params=[[Ljava.lang.String;@669856bd, false]
Hotswapping[com.vaadin.flow.component.dependency.StyleSheet]

[skybber]

Could you check please from which method SchedulerImpl.scheduleCommand() is called?

[Artur-]

It originates here https://github.com/HotswapProjects/HotswapAgent/blob/24007fd03a29309f54a05bdc3921ac142199ad76/plugin/hotswap-agent-vaadin-plugin/src/main/java/org/hotswap/agent/plugin/vaadin/VaadinPlugin.java#L257-L260

[Artur-]

But the Reloading class {} because of {}" is not constantly logged, so it would seem that scheduleCommand is only called once

[Artur-]

There are a lot of commands "running"

and in SchedulerImpl.finished() some gets removed from runningCommands but then when onHotswap is called again, scheduledCommands contain the same commands (in this case it is two, apparently it can also be one) and the ones in runningCommands also seem to remain

[skybber]

• Are you sure you need process LoadEvent.DEFINE as redefine event in Vaadin Hotswapper?:

@OnClassLoadEvent(classNameRegexp = ".*", events = {LoadEvent.DEFINE, LoadEvent.REDEFINE})

• commands should be remove by it.remove(); in SchedulerImpl

[Artur-]

The problem is that it.remove() does not remove the command. Also when debugging I can see that after

            for (Iterator<Map.Entry<Command, DuplicateScheduleConfig>> it = scheduledCommands.entrySet().iterator(); it.hasNext(); ) {
                Map.Entry<Command, DuplicateScheduleConfig> entry = it.next();

then scheduledCommands.containsKey(entry.getKey()) is false, or in other words scheduledCommands.containsKey(scheduledCommands.entrySet().iterator().next().getKey()) is false. This seems like the hash code of ReflectionCommand could change after adding the command to the map or something similar

[Artur-]

It can, because ReflectionCommand.getTargetClassLoader() modifies the targetClassLoader field when it is null, and after that, the hash code no longer matches

[skybber]

It looks like a bug. I suggest making all attributes in the ReflectionCommand class final and initializing them in the constructor.

[skybber]

A new fixed version is available at:

https://github.com/HotswapProjects/HotswapAgent/releases/tag/2.0.1-SNAPSHOT

Could you please check if it resolves your issue?

[Artur-]

Thanks! I think it resolves the issue but as it is a timing issue, I cannot say for sure

[Artur-]

Haven't seen it again so far

[skybber]

Problem is fixed in version 2.0.1 , is is released on maven https://mvnrepository.com/artifact/org.hotswapagent