minecraftforge / eventbus

Event Bus

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1.19.x	Legacy

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eventbus's Issues

Cannot listen to abstract Event classes

It is not possible to listen to an Event that is declared as an abstract class. The code in EventBus.addToListeners attempts to construct an instance of the event before using that instance to obtain the ListenerList.

EventBus/src/main/java/net/minecraftforge/eventbus/EventBus.java

Lines 209 to 211 in 070c412

	Constructor<?> ctr = eventType.getConstructor();
	ctr.setAccessible(true);
	Event event = (Event)ctr.newInstance();

Note that this is not a new issue with the separation: examination shows the same code in 1.12 and earlier versions for Forge, with the same issue.

AIOB during event build, occasionally

[31Dec.2020 16:49:56.583] [modloading-worker-5/ERROR] [net.minecraftforge.fml.javafmlmod.FMLModContainer/LOADING]: Failed to create mod instance. ModID: cookingforblockheads, class net.blay09.mods.cookingforblockheads.CookingForBlockheads
java.lang.ExceptionInInitializerError: null
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[?:?]
at jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[?:?]
at java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500) ~[?:?]
at java.lang.reflect.Constructor.newInstance(Constructor.java:481) ~[?:?]
at net.minecraftforge.eventbus.api.EventListenerHelper.computeListenerList(EventListenerHelper.java:98) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.api.EventListenerHelper.getListenerListInternal(EventListenerHelper.java:63) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.api.EventListenerHelper.getListenerList(EventListenerHelper.java:48) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.EventBus.addToListeners(EventBus.java:263) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.EventBus.addListener(EventBus.java:239) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.EventBus.addListener(EventBus.java:231) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.EventBus.addListener(EventBus.java:186) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.EventBus.addListener(EventBus.java:180) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.EventBus.addListener(EventBus.java:174) ~[eventbus-3.0.5-service.jar:?]
at net.blay09.mods.cookingforblockheads.CookingForBlockheads.(CookingForBlockheads.java:86) ~[cookingforblockheads:9.2.2]
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[?:?]
at jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[?:?]
at java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500) ~[?:?]
at java.lang.reflect.ReflectAccess.newInstance(ReflectAccess.java:124) ~[?:?]
at jdk.internal.reflect.ReflectionFactory.newInstance(ReflectionFactory.java:346) ~[?:?]
at java.lang.Class.newInstance(Class.java:604) ~[?:?]
at net.minecraftforge.fml.javafmlmod.FMLModContainer.constructMod(FMLModContainer.java:81) ~[forge:35.1]
at net.minecraftforge.fml.ModContainer.lambda$buildTransitionHandler$4(ModContainer.java:120) ~[forge:?]
at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1800) [?:?]
at java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1792) [?:?]
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290) [?:?]
at java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1016) [?:?]
at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1665) [?:?]
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1598) [?:?]
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183) [?:?]
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 2 out of bounds for length 0
at java.util.ArrayList.add(ArrayList.java:455) ~[?:?]
at java.util.ArrayList.add(ArrayList.java:467) ~[?:?]
at net.minecraftforge.eventbus.ListenerList$ListenerListInst.addChild(ListenerList.java:239) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.ListenerList$ListenerListInst.(ListenerList.java:180) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.ListenerList$ListenerListInst.(ListenerList.java:143) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.ListenerList.resizeLists(ListenerList.java:97) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.eventbus.ListenerList.(ListenerList.java:52) ~[eventbus-3.0.5-service.jar:?]
at net.minecraftforge.fml.event.server.FMLServerStartedEvent.(FMLServerStartedEvent.java) ~[forge:?]
... 31 more

ListerList resize thread issue.

Yet another potential listener list threading issue.
https://gist.githubusercontent.com/yrsegal/4f9ca65d13b74dbf69dea24e6a9d548a/raw/6e6b9e6d05be7fbc72e1e4be7156301688e13e11/Crashlog

"Reported" Here: https://www.minecraftforge.net/forum/topic/75210-race-condition-within-listenerlist-resize-behavior/

Seems to be an issue when a event bus is created, while a event listener is being added. But I am unable to reproduce.

I've modified the ParallelEventTest to try and reproduce, but it doesn't seem to be working. It gets stuck on the sync lock, as it should.

package net.minecraftforge.eventbus.test;

import net.minecraftforge.eventbus.ListenerList;
import net.minecraftforge.eventbus.api.BusBuilder;
import net.minecraftforge.eventbus.api.IEventBus;
import net.minecraftforge.eventbus.testjar.DummyEvent;

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.RepeatedTest;
import org.powermock.reflect.Whitebox;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.Consumer;

public class ParallelEventTest
{
    private static final int BUS_COUNT = 16;
    private static final int LISTENER_COUNT = 1000;
    private static final int RUN_ITERATIONS = 1000;

    private final AtomicLong COUNTER = new AtomicLong();
    private ExecutorService POOL;

    @BeforeEach
    public void setup() {
        COUNTER.set(0);
        POOL = Executors.newWorkStealingPool();
    }

    @AfterEach
    public void destroy() throws InterruptedException {
        POOL.shutdown();
        while(!POOL.isTerminated())
            Thread.sleep(10);
    }

    private <T> void executeAll(Collection<T> stream, final Consumer<T> task) {
        List<Callable<?>> tasks = new ArrayList<>();
        stream.forEach(m -> tasks.add(() -> {
            task.accept(m);
            return null;
        }));
        try {
            POOL.invokeAll(tasks);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    //@Disabled
    @RepeatedTest(100)
    public void testMultipleThreadsMultipleBus() throws InterruptedException {
        Set<IEventBus> busSet = new HashSet<>();

        Collection<Callable<IEventBus>> builders = new ArrayList<>();
        for (int i = 0; i < BUS_COUNT; i++) {
            builders.add(BusBuilder.builder().setTrackPhases(false)::build); //make buses for concurrent testing
        }
        POOL.invokeAll(builders).stream().map(f -> {
            try {
                return f.get();
            } catch (InterruptedException | ExecutionException e) {
                throw new RuntimeException(e);
            }
        }).forEach(busSet::add);

        executeAll(busSet, iEventBus -> { //execute parallel listener adding
            for (int i = 0; i < LISTENER_COUNT; i++) {
                BusBuilder.builder().setTrackPhases(false).build();
                iEventBus.addListener(this::handle);
            }
        });
        executeAll(busSet, iEventBus -> { //post events parallel
            for (int i = 0; i < RUN_ITERATIONS; i++)
                iEventBus.post(new DummyEvent.GoodEvent());
        });

        long expected = BUS_COUNT * LISTENER_COUNT * RUN_ITERATIONS;
        Assertions.assertEquals(expected, COUNTER.get());
    }

    //@Disabled
    @RepeatedTest(100)
    public void testMultipleThreadsOneBus() {
        IEventBus bus = BusBuilder.builder().setTrackPhases(false).build();

        Set<Runnable> toAdd = new HashSet<>();

        for (int i = 0; i < LISTENER_COUNT; i++) { //prepare parallel listener adding
            toAdd.add(() -> {
                BusBuilder.builder().setTrackPhases(false).build();
                bus.addListener(this::handle);
            });
        }
        executeAll(toAdd, Runnable::run); //execute parallel listener adding

        toAdd = new HashSet<>();
        for (int i = 0; i < RUN_ITERATIONS; i++) //prepare parallel event posting
            toAdd.add(() -> bus.post(new DummyEvent.GoodEvent()));
        executeAll(toAdd, Runnable::run); //post events parallel

        try {
            long expected = LISTENER_COUNT * RUN_ITERATIONS;
            final ListenerList listenerList = Whitebox.invokeMethod(new DummyEvent.GoodEvent(), "getListenerList");
            int busid = Whitebox.getInternalState(bus, "busID");
            Assertions.assertAll(
                    ()->Assertions.assertEquals(expected, COUNTER.get()),
                    ()->Assertions.assertEquals(LISTENER_COUNT, listenerList.getListeners(busid).length - 1)

            );
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void handle(DummyEvent.GoodEvent event) {
        COUNTER.incrementAndGet();
    }
}

ASMClassLoader delegates class loading to the wrong class loader

EventBus/src/main/java/net/minecraftforge/eventbus/ASMEventHandler.java

Line 181 in 6d3407c

return Class.forName(name, resolve, Thread.currentThread().getContextClassLoader());

forces classes to be loaded with the thread's context class loader instead of whatever loaded the subscribing class in the first place.

The thread context class loader is not an universally appropriate substitute, it breaks with threads living outside any application context such as the ForkJoinPool common pool. This breaks popular uses such as parallelStream() or the default executor CompletableFuture overloads, leading to exceptions such as this:

java.lang.NoClassDefFoundError: org/cyclops/cyclopscore/modcompat/capabilities/CapabilityConstructorRegistry$ItemStackEventListener
        at net.minecraftforge.eventbus.ASMEventHandler_73_ItemStackEventListener_onItemStackLoad_AttachCapabilitiesEvent.invoke(.dynamic)
        at MC-BOOTSTRAP/[email protected]/net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:85)
        at MC-BOOTSTRAP/[email protected]/net.minecraftforge.eventbus.EventBus.post(EventBus.java:302)
        at MC-BOOTSTRAP/[email protected]/net.minecraftforge.eventbus.EventBus.post(EventBus.java:283)
        at TRANSFORMER/[email protected]/net.minecraftforge.event.ForgeEventFactory.gatherCapabilities(ForgeEventFactory.java:584)
        at TRANSFORMER/[email protected]/net.minecraftforge.event.ForgeEventFactory.gatherCapabilities(ForgeEventFactory.java:578)
        at TRANSFORMER/[email protected]/net.minecraftforge.common.capabilities.CapabilityProvider.doGatherCapabilities(CapabilityProvider.java:87)
        at TRANSFORMER/[email protected]/net.minecraftforge.common.capabilities.CapabilityProvider.getCapabilities(CapabilityProvider.java:101)
        at TRANSFORMER/[email protected]/net.minecraftforge.common.capabilities.CapabilityProvider.areCapsCompatible(CapabilityProvider.java:113)
        at TRANSFORMER/[email protected]/net.minecraft.world.item.ItemStack.m_41658_(ItemStack.java:411)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.api.util.Comparators.lambda$static$0(Comparators.java:39)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.compound.container.itemstack.ItemStackContainer.compareTo(ItemStackContainer.java:167)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.compound.container.itemstack.ItemStackContainer.compareTo(ItemStackContainer.java:23)
        at java.base/java.util.TreeMap.compare(TreeMap.java:1569)
        at java.base/java.util.TreeMap.addEntryToEmptyMap(TreeMap.java:776)
        at java.base/java.util.TreeMap.put(TreeMap.java:785)
        at java.base/java.util.TreeMap.put(TreeMap.java:534)
        at java.base/java.util.TreeSet.add(TreeSet.java:255)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.recipe.equivalency.InstancedEquivalency.<init>(InstancedEquivalency.java:21)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.bootstrap.WorldBootstrapper.lambda$doBootstrapInstancedEquivalencies$0(WorldBootstrapper.java:111)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.bootstrap.WorldBootstrapper.lambda$doBootstrapInstancedEquivalencies$1(WorldBootstrapper.java:133)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.instanced.InstancedEquivalencyHandlerRegistry.process(InstancedEquivalencyHandlerRegistry.java:35)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.bootstrap.WorldBootstrapper.lambda$doBootstrapInstancedEquivalencies$2(WorldBootstrapper.java:104)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
        at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:992)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
        at java.base/java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
        at java.base/java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:754)
        at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
        at java.base/java.util.concurrent.ForkJoinTask.invoke(ForkJoinTask.java:686)
        at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateParallel(ForEachOps.java:159)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateParallel(ForEachOps.java:173)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:233)
        at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
        at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:765)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.bootstrap.WorldBootstrapper.doBootstrapInstancedEquivalencies(WorldBootstrapper.java:104)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.bootstrap.WorldBootstrapper.onWorldReload(WorldBootstrapper.java:49)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.analysis.AequivaleoReloadListener$AequivaleoWorldAnalysisRunner.reloadEquivalencyData(AequivaleoReloadListener.java:454)
        at TRANSFORMER/[email protected]/com.ldtteam.aequivaleo.analysis.AequivaleoReloadListener$AequivaleoWorldAnalysisRunner.run(AequivaleoReloadListener.java:444)
        at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
        at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.ClassNotFoundException: org.cyclops.cyclopscore.modcompat.capabilities.CapabilityConstructorRegistry$ItemStackEventListener
        ... 44 more

Such a class load issue additionally incurs failure to load the affected class in the future with throwing NoClassDefFoundError. In the above example any later attempts to use the CapabilityConstructorRegistry$ItemStackEventListener type fail on other threads, including the regular server thread which presumably has the context class loader set properly.

To fix the problem ASMEventHandler will most likely have to grab+store the appropriate class loader upon its creation (may be as simple method.getDeclaringClass().getClassLoader()?) and use that to define the generated class. In practice this would mean having an ASMClassLoader instance for each target class loader encountered, adapting a single instance every time is not advisable.

More specifically:

• add a classLoader instance field to ASMEventHandler
• populate classLoader with method.getDeclaringClass().getClassLoader() in the constructor
• change LOADER to be ConcurrentHashMap<ClassLoader, ASMClassLoader>
• add a classLoader field to ASMClassLoader and populate it from the constructor
• make ASMClassLoader.loadClass use classLoader instead of Thread.currentThread().getContextClassLoader()
• change the LOADER.define invocation to LOADER.computeIfAbsent(classLoader, ASMClassLoader::new).define

Listeners are not cleaned up immediately when calling EventBus#unregister

ListenerList#forceRebuild simply sets a boolean to true, and relies on the next event post to do the actual cleanup:

https://github.com/MinecraftForge/EventBus/blob/master/src/main/java/net/minecraftforge/eventbus/ListenerList.java#L223-L231

This means that if unregister is called and the event is never fired again (such as for startup events) the event listener will not be released from memory.

Additionally, there's no way to do this manually even though getListeners is public, since it requires the bus ID which is not exposed.

Forge ModThreadContext and FMLModLoadingContext not updated

The EventBus doesn't update the ModThreadContext or FMLModLoadingContext when dispatching to listeners. I posted the same issue on the Forge repository which has more details. MinecraftForge/MinecraftForge#5375

Listeners being registered as null

There appears to be an edge case where it is passing a null reference to the registration in ListenerListInst. I have written unit test to reproduce the error along with the error output I had when running said test: https://gist.github.com/OhYea777/82bd5880f436f7ef2393a32fbdfd54ad

Note: due to the nature of the issue, it does not always throw an error, in this case the test needs to be ran numerous times before it fails

Update ASM to 7

Update ASM to 7

Figure out how to alert when addListener is used inappropriately with a GenericEvent

addListener with a GenericEvent subclass is missing the generic event filter, causing the event to fire for all events.

See MinecraftForge/MinecraftForge#5387

Support JarInJar event registration

I am currently working on adding Forge support for my mod GriefDefender and am unable to register events on the Forge event bus when calling MinecraftForge.EVENT_BUS from within my jarinjar.

Here are the errors I receive :

https://gist.github.com/bloodmc/7cac83645c015973a5065fedd5b1a884

Any way to add support for event registration for jarinjar mods?

LuckPerms also requires this but has added a workaround for the time being.

Thanks!

Toposort based event loading

Sometimes, an event listener just want to be before/after one specific other listener rather than shifting the whole phase up or down. In this case, topological sort may help and the compatibility with the old index/comparable based sort is retained.

Error Launching MC 1.14.3 + Forge 27.0.25

Unable to download re-requisite librararies:

Failed to download file.
Name: eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar
URL: https://modloaders.forgecdn.net/647622546/maven/net/minecraftforge/eventbus/0.10.3-milestone.0.1+1a5fa31-service/eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar
Error details: The requested URL returned error: 403 Forbidden
Filename on disk: eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar
Path: C:\Users\jbruneau\Twitch\Minecraft\Install\libraries\net\minecraftforge\eventbus\0.10.3-milestone.0.1+1a5fa31-service\eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar
Exists: Nonexistent

Accessing the URL in Google Chrome:

(Error)
(Code)AccessDenied(/Code)
(Message)Access Denied(/Message)
(RequestId)76B6FEECF7DC890D(/RequestId)
(HostId)
9InSbQL46MY9DjXXhq3Y6JvrGxy6E9YW9kL2xY/mJewFxLAWoA5FURhSQgGj1vNot2s5JliM0d4=
(/HostId)
(/Error)

Cannot listen to abstract Event classes

It is not possible to listen to an Event that is declared as an abstract class. The code in EventBus.addToListeners attempts to construct an instance of the event before using that instance to obtain the ListenerList.

EventBus/src/main/java/net/minecraftforge/eventbus/EventBus.java

Lines 209 to 211 in 070c412

	Constructor<?> ctr = eventType.getConstructor();
	ctr.setAccessible(true);
	Event event = (Event)ctr.newInstance();

Note that this is not a new issue with the separation: examination shows the same code in 1.12 and earlier versions for Forge, with the same issue.