Add Lifecycle Event system

This event system is separate from Bukkit's event system and is
meant for managing resources across reloads and from points in the
PluginBootstrap.

paper-server/src/main/java/io/papermc/paper/plugin/bootstrap/PluginBootstrapContextImpl.java

@@ -1,6 +1,8 @@
 package io.papermc.paper.plugin.bootstrap;
 
 import io.papermc.paper.plugin.configuration.PluginMeta;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventManager;
+import io.papermc.paper.plugin.lifecycle.event.PaperLifecycleEventManager;
 import io.papermc.paper.plugin.provider.PluginProvider;
 import java.nio.file.Path;
 import net.kyori.adventure.text.logger.slf4j.ComponentLogger;
@@ -12,6 +14,10 @@ public final class PluginBootstrapContextImpl implements BootstrapContext {
     private final Path dataFolder;
     private final ComponentLogger logger;
     private final Path pluginSource;
+    // Paper start - lifecycle events
+    private boolean allowsLifecycleRegistration = true;
+    private final PaperLifecycleEventManager<BootstrapContext> lifecycleEventManager = new PaperLifecycleEventManager<>(this, () -> this.allowsLifecycleRegistration); // Paper - lifecycle events
+    // Paper end - lifecycle events
 
     public PluginBootstrapContextImpl(PluginMeta config, Path dataFolder, ComponentLogger logger, Path pluginSource) {
         this.config = config;
@@ -45,4 +51,20 @@ public final class PluginBootstrapContextImpl implements BootstrapContext {
     public @NotNull Path getPluginSource() {
         return this.pluginSource;
     }
+
+    // Paper start - lifecycle event system
+    @Override
+    public @NotNull PluginMeta getPluginMeta() {
+        return this.config;
+    }
+
+    @Override
+    public LifecycleEventManager<BootstrapContext> getLifecycleManager() {
+        return this.lifecycleEventManager;
+    }
+
+    public void lockLifecycleEventRegistration() {
+        this.allowsLifecycleRegistration = false;
+    }
+    // Paper end
 }

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/LifecycleEventRunner.java

@@ -0,0 +1,100 @@
+package io.papermc.paper.plugin.lifecycle.event;
+
+import io.papermc.paper.plugin.lifecycle.event.registrar.PaperRegistrar;
+import io.papermc.paper.plugin.lifecycle.event.registrar.RegistrarEvent;
+import io.papermc.paper.plugin.lifecycle.event.registrar.RegistrarEventImpl;
+import io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent;
+import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
+import io.papermc.paper.plugin.lifecycle.event.types.LifecycleEventType;
+import io.papermc.paper.plugin.lifecycle.event.types.OwnerAwareLifecycleEvent;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Predicate;
+import org.bukkit.plugin.Plugin;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public class LifecycleEventRunner {
+
+    public static final LifecycleEventRunner INSTANCE = new LifecycleEventRunner();
+
+    private final List<LifecycleEventType<?, ?, ?>> lifecycleEventTypes = new ArrayList<>();
+    private boolean blockPluginReloading = false;
+
+    public <O extends LifecycleEventOwner> void checkRegisteredHandler(final O owner, final AbstractLifecycleEventType<O, ?, ?> eventType) {
+        /*
+        Lifecycle event handlers for reloadable events that are registered from the BootstrapContext prevent
+        the server from reloading plugins. This is because reloading plugins requires disabling all the plugins,
+        running the reload logic (which would include places where these events should fire) and then re-enabling plugins.
+         */
+        if (eventType.blocksReloading(owner)) {
+            this.blockPluginReloading = true;
+        }
+    }
+
+    public boolean blocksPluginReloading() {
+        return this.blockPluginReloading;
+    }
+
+    public <O extends LifecycleEventOwner, E extends LifecycleEvent, ET extends LifecycleEventType<O, E, ?>> void addEventType(final ET eventType) {
+        this.lifecycleEventTypes.add(eventType);
+    }
+
+    public <O extends LifecycleEventOwner, E extends PaperLifecycleEvent> void callEvent(final LifecycleEventType<O, ? super E, ?> eventType, final E event) {
+        this.callEvent(eventType, event, $ -> true);
+    }
+
+    public <O extends LifecycleEventOwner, E extends PaperLifecycleEvent> void callEvent(final LifecycleEventType<O, ? super E, ?> eventType, final E event, final Predicate<? super O> ownerPredicate) {
+        final AbstractLifecycleEventType<O, ? super E, ?> lifecycleEventType = (AbstractLifecycleEventType<O, ? super E, ?>) eventType;
+        lifecycleEventType.forEachHandler(event, registeredHandler -> {
+            try {
+                if (event instanceof final OwnerAwareLifecycleEvent<?> ownerAwareEvent) {
+                    ownerAwareGenericHelper(ownerAwareEvent, registeredHandler.owner());
+                }
+                registeredHandler.lifecycleEventHandler().run(event);
+            } catch (final Throwable ex) {
+                throw new RuntimeException("Could not run '%s' lifecycle event handler from %s".formatted(lifecycleEventType.name(), registeredHandler.owner().getPluginMeta().getDisplayName()), ex);
+            } finally {
+                if (event instanceof final OwnerAwareLifecycleEvent<?> ownerAwareEvent) {
+                    ownerAwareEvent.setOwner(null);
+                }
+            }
+        }, handler -> ownerPredicate.test(handler.owner()));
+        event.invalidate();
+    }
+
+    private static <O extends LifecycleEventOwner> void ownerAwareGenericHelper(final OwnerAwareLifecycleEvent<O> event, final LifecycleEventOwner possibleOwner) {
+        final @Nullable O owner = event.castOwner(possibleOwner);
+        if (owner != null) {
+            event.setOwner(owner);
+        } else {
+            throw new IllegalStateException("Found invalid owner " + possibleOwner + " for event " + event);
+        }
+    }
+
+    public void unregisterAllEventHandlersFor(final Plugin plugin) {
+        for (final LifecycleEventType<?, ?, ?> lifecycleEventType : this.lifecycleEventTypes) {
+            this.removeEventHandlersOwnedBy(lifecycleEventType, plugin);
+        }
+    }
+
+    private <O extends LifecycleEventOwner> void removeEventHandlersOwnedBy(final LifecycleEventType<O, ?, ?> eventType, final Plugin possibleOwner) {
+        final AbstractLifecycleEventType<O, ?, ?> lifecycleEventType = (AbstractLifecycleEventType<O, ?, ?>) eventType;
+        lifecycleEventType.removeMatching(registeredHandler -> registeredHandler.owner().getPluginMeta().getName().equals(possibleOwner.getPluginMeta().getName()));
+    }
+
+    @SuppressWarnings("unchecked")
+    public <O extends LifecycleEventOwner, R extends PaperRegistrar<? super O>> void callStaticRegistrarEvent(final LifecycleEventType<O, ? extends RegistrarEvent<? super R>, ?> lifecycleEventType, final R registrar, final Class<? extends O> ownerClass) {
+        this.callEvent((LifecycleEventType<O, RegistrarEvent<? super R>, ?>) lifecycleEventType, new RegistrarEventImpl<>(registrar, ownerClass), ownerClass::isInstance);
+    }
+
+    @SuppressWarnings("unchecked")
+    public <O extends LifecycleEventOwner, R extends PaperRegistrar<? super O>> void callReloadableRegistrarEvent(final LifecycleEventType<O, ? extends ReloadableRegistrarEvent<? super R>, ?> lifecycleEventType, final R registrar, final Class<? extends O> ownerClass, final ReloadableRegistrarEvent.Cause cause) {
+        this.callEvent((LifecycleEventType<O, ReloadableRegistrarEvent<? super R>, ?>) lifecycleEventType, new RegistrarEventImpl.ReloadableImpl<>(registrar, ownerClass, cause), ownerClass::isInstance);
+    }
+
+    private LifecycleEventRunner() {
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/PaperLifecycleEvent.java

@@ -0,0 +1,10 @@
+package io.papermc.paper.plugin.lifecycle.event;
+
+public interface PaperLifecycleEvent extends LifecycleEvent {
+
+    // called after all handlers have been run. Can be
+    // used to invalid various contexts to plugins can't
+    // try to re-use them by storing them from the event
+    default void invalidate() {
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/PaperLifecycleEventManager.java

@@ -0,0 +1,26 @@
+package io.papermc.paper.plugin.lifecycle.event;
+
+import com.google.common.base.Preconditions;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.AbstractLifecycleEventHandlerConfiguration;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.LifecycleEventHandlerConfiguration;
+import java.util.function.BooleanSupplier;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public final class PaperLifecycleEventManager<O extends LifecycleEventOwner> implements LifecycleEventManager<O> {
+
+    private final O owner;
+    public final BooleanSupplier registrationCheck;
+
+    public PaperLifecycleEventManager(final O owner, final BooleanSupplier registrationCheck) {
+        this.owner = owner;
+        this.registrationCheck = registrationCheck;
+    }
+
+    @Override
+    public void registerEventHandler(final LifecycleEventHandlerConfiguration<? super O> handlerConfiguration) {
+        Preconditions.checkState(this.registrationCheck.getAsBoolean(), "Cannot register lifecycle event handlers");
+        ((AbstractLifecycleEventHandlerConfiguration<? super O, ?>) handlerConfiguration).registerFrom(this.owner);
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/handler/configuration/AbstractLifecycleEventHandlerConfiguration.java

@@ -0,0 +1,28 @@
+package io.papermc.paper.plugin.lifecycle.event.handler.configuration;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
+import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public abstract class AbstractLifecycleEventHandlerConfiguration<O extends LifecycleEventOwner, E extends LifecycleEvent> implements LifecycleEventHandlerConfiguration<O> {
+
+    private final LifecycleEventHandler<? super E> handler;
+    private final AbstractLifecycleEventType<O, E, ?> type;
+
+    protected AbstractLifecycleEventHandlerConfiguration(final LifecycleEventHandler<? super E> handler, final AbstractLifecycleEventType<O, E, ?> type) {
+        this.handler = handler;
+        this.type = type;
+    }
+
+    public final void registerFrom(final O owner) {
+        this.type.tryRegister(owner, this);
+    }
+
+    public LifecycleEventHandler<? super E> handler() {
+        return this.handler;
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/handler/configuration/MonitorLifecycleEventHandlerConfigurationImpl.java

@@ -0,0 +1,28 @@
+package io.papermc.paper.plugin.lifecycle.event.handler.configuration;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
+import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public class MonitorLifecycleEventHandlerConfigurationImpl<O extends LifecycleEventOwner, E extends LifecycleEvent> extends AbstractLifecycleEventHandlerConfiguration<O, E> implements MonitorLifecycleEventHandlerConfiguration<O> {
+
+    private boolean monitor = false;
+
+    public MonitorLifecycleEventHandlerConfigurationImpl(final LifecycleEventHandler<? super E> handler, final AbstractLifecycleEventType<O, E, ?> eventType) {
+        super(handler, eventType);
+    }
+
+    public boolean isMonitor() {
+        return this.monitor;
+    }
+
+    @Override
+    public MonitorLifecycleEventHandlerConfiguration<O> monitor() {
+        this.monitor = true;
+        return this;
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/handler/configuration/PrioritizedLifecycleEventHandlerConfigurationImpl.java

@@ -0,0 +1,40 @@
+package io.papermc.paper.plugin.lifecycle.event.handler.configuration;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
+import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
+import java.util.OptionalInt;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public class PrioritizedLifecycleEventHandlerConfigurationImpl<O extends LifecycleEventOwner, E extends LifecycleEvent>
+    extends AbstractLifecycleEventHandlerConfiguration<O, E>
+    implements PrioritizedLifecycleEventHandlerConfiguration<O> {
+
+    private static final OptionalInt DEFAULT_PRIORITY = OptionalInt.of(0);
+    private static final OptionalInt MONITOR_PRIORITY = OptionalInt.empty();
+
+    private OptionalInt priority = DEFAULT_PRIORITY;
+
+    public PrioritizedLifecycleEventHandlerConfigurationImpl(final LifecycleEventHandler<? super E> handler, final AbstractLifecycleEventType<O, E, ?> eventType) {
+        super(handler, eventType);
+    }
+
+    public OptionalInt priority() {
+        return this.priority;
+    }
+
+    @Override
+    public PrioritizedLifecycleEventHandlerConfiguration<O> priority(final int priority) {
+        this.priority = OptionalInt.of(priority);
+        return this;
+    }
+
+    @Override
+    public PrioritizedLifecycleEventHandlerConfiguration<O> monitor() {
+        this.priority = MONITOR_PRIORITY;
+        return this;
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/registrar/PaperRegistrar.java

@@ -0,0 +1,15 @@
+package io.papermc.paper.plugin.lifecycle.event.registrar;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public interface PaperRegistrar<O extends LifecycleEventOwner> extends Registrar {
+
+    void setCurrentContext(@Nullable O owner);
+
+    default void invalidate() {
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/registrar/RegistrarEventImpl.java

@@ -0,0 +1,70 @@
+package io.papermc.paper.plugin.lifecycle.event.registrar;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.PaperLifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.types.OwnerAwareLifecycleEvent;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public class RegistrarEventImpl<R extends PaperRegistrar<? super O>, O extends LifecycleEventOwner> implements PaperLifecycleEvent, OwnerAwareLifecycleEvent<O>, RegistrarEvent<R> {
+
+    private final R registrar;
+    private final Class<? extends O> ownerClass;
+
+    public RegistrarEventImpl(final R registrar, final Class<? extends O> ownerClass) {
+        this.registrar = registrar;
+        this.ownerClass = ownerClass;
+    }
+
+    @Override
+    public R registrar() {
+        return this.registrar;
+    }
+
+    @Override
+    public final void setOwner(final @Nullable O owner) {
+        this.registrar.setCurrentContext(owner);
+    }
+
+    @Override
+    public final @Nullable O castOwner(final LifecycleEventOwner owner) {
+        return this.ownerClass.isInstance(owner) ? this.ownerClass.cast(owner) : null;
+    }
+
+    @Override
+    public void invalidate() {
+        this.registrar.invalidate();
+    }
+
+    @Override
+    public String toString() {
+        return "RegistrarEventImpl{" +
+            "registrar=" + this.registrar +
+            ", ownerClass=" + this.ownerClass +
+            '}';
+    }
+
+    public static class ReloadableImpl<R extends PaperRegistrar<? super O>, O extends LifecycleEventOwner> extends RegistrarEventImpl<R, O> implements ReloadableRegistrarEvent<R> {
+
+        private final ReloadableRegistrarEvent.Cause cause;
+
+        public ReloadableImpl(final R registrar, final Class<? extends O> ownerClass, final Cause cause) {
+            super(registrar, ownerClass);
+            this.cause = cause;
+        }
+
+        @Override
+        public Cause cause() {
+            return this.cause;
+        }
+
+        @Override
+        public String toString() {
+            return "ReloadableImpl{" +
+                "cause=" + this.cause +
+                "} " + super.toString();
+        }
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/AbstractLifecycleEventType.java

@@ -0,0 +1,62 @@
+package io.papermc.paper.plugin.lifecycle.event.types;
+
+import io.papermc.paper.plugin.bootstrap.BootstrapContext;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventRunner;
+import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.AbstractLifecycleEventHandlerConfiguration;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.LifecycleEventHandlerConfiguration;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public abstract class AbstractLifecycleEventType<O extends LifecycleEventOwner, E extends LifecycleEvent, C extends LifecycleEventHandlerConfiguration<O>> implements LifecycleEventType<O, E, C> {
+
+    private final String name;
+    private final Class<? extends O> ownerType;
+
+    protected AbstractLifecycleEventType(final String name, final Class<? extends O> ownerType) {
+        this.name = name;
+        this.ownerType = ownerType;
+        LifecycleEventRunner.INSTANCE.addEventType(this);
+    }
+
+    @Override
+    public String name() {
+        return this.name;
+    }
+
+    private void verifyOwner(final O owner) {
+        if (!this.ownerType.isInstance(owner)) {
+            throw new IllegalArgumentException("You cannot register the lifecycle event '" + this.name + "' on " + owner);
+        }
+    }
+
+    public boolean blocksReloading(final O eventOwner) {
+        return eventOwner instanceof BootstrapContext;
+    }
+
+    public abstract boolean hasHandlers();
+
+    public abstract void forEachHandler(E event, Consumer<RegisteredHandler<O, E>> consumer, Predicate<RegisteredHandler<O, E>> predicate);
+
+    public abstract void removeMatching(Predicate<RegisteredHandler<O, E>> predicate);
+
+    protected abstract void register(O owner, AbstractLifecycleEventHandlerConfiguration<O, E> config);
+
+    public final void tryRegister(final O owner, final AbstractLifecycleEventHandlerConfiguration<O, E> config) {
+        this.verifyOwner(owner);
+        LifecycleEventRunner.INSTANCE.checkRegisteredHandler(owner, this);
+        this.register(owner, config);
+    }
+
+    public record RegisteredHandler<O extends LifecycleEventOwner, E extends LifecycleEvent>(O owner, AbstractLifecycleEventHandlerConfiguration<O, E> config) {
+
+        public LifecycleEventHandler<? super E> lifecycleEventHandler() {
+            return this.config().handler();
+        }
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/LifecycleEventTypeProviderImpl.java

@@ -0,0 +1,25 @@
+package io.papermc.paper.plugin.lifecycle.event.types;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventRunner;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public final class LifecycleEventTypeProviderImpl implements LifecycleEventTypeProvider {
+
+    public static LifecycleEventTypeProviderImpl instance() {
+        return (LifecycleEventTypeProviderImpl) LifecycleEventTypeProvider.provider();
+    }
+
+    @Override
+    public <O extends LifecycleEventOwner, E extends LifecycleEvent> LifecycleEventType.Monitorable<O, E> monitor(final String name, final Class<? extends O> ownerType) {
+        return new MonitorableLifecycleEventType<>(name, ownerType);
+    }
+
+    @Override
+    public <O extends LifecycleEventOwner, E extends LifecycleEvent> LifecycleEventType.Prioritizable<O, E> prioritized(final String name, final Class<? extends O> ownerType) {
+        return new PrioritizableLifecycleEventType.Simple<>(name, ownerType);
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/MonitorableLifecycleEventType.java

@@ -0,0 +1,63 @@
+package io.papermc.paper.plugin.lifecycle.event.types;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.AbstractLifecycleEventHandlerConfiguration;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.MonitorLifecycleEventHandlerConfiguration;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.MonitorLifecycleEventHandlerConfigurationImpl;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public class MonitorableLifecycleEventType<O extends LifecycleEventOwner, E extends LifecycleEvent> extends AbstractLifecycleEventType<O, E, MonitorLifecycleEventHandlerConfiguration<O>> implements LifecycleEventType.Monitorable<O, E> {
+
+    final List<RegisteredHandler<O, E>> handlers = new ArrayList<>();
+    int nonMonitorIdx = 0;
+
+    public MonitorableLifecycleEventType(final String name, final Class<? extends O> ownerType) {
+        super(name, ownerType);
+    }
+
+    @Override
+    public boolean hasHandlers() {
+        return !this.handlers.isEmpty();
+    }
+
+    @Override
+    public MonitorLifecycleEventHandlerConfigurationImpl<O, E> newHandler(final LifecycleEventHandler<? super E> handler) {
+        return new MonitorLifecycleEventHandlerConfigurationImpl<>(handler, this);
+    }
+
+    @Override
+    protected void register(final O owner, final AbstractLifecycleEventHandlerConfiguration<O, E> config) {
+        if (!(config instanceof final MonitorLifecycleEventHandlerConfigurationImpl<?,?> monitor)) {
+            throw new IllegalArgumentException("Configuration must be a MonitorLifecycleEventHandlerConfiguration");
+        }
+        final RegisteredHandler<O, E> registeredHandler = new RegisteredHandler<>(owner, config);
+        if (!monitor.isMonitor()) {
+            this.handlers.add(this.nonMonitorIdx, registeredHandler);
+            this.nonMonitorIdx++;
+        } else {
+            this.handlers.add(registeredHandler);
+        }
+    }
+
+    @Override
+    public void forEachHandler(final E event, final Consumer<RegisteredHandler<O, E>> consumer, final Predicate<RegisteredHandler<O, E>> predicate) {
+        for (final RegisteredHandler<O, E> handler : this.handlers) {
+            if (predicate.test(handler)) {
+                consumer.accept(handler);
+            }
+        }
+    }
+
+    @Override
+    public void removeMatching(final Predicate<RegisteredHandler<O, E>> predicate) {
+        this.handlers.removeIf(predicate);
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/OwnerAwareLifecycleEvent.java

@@ -0,0 +1,15 @@
+package io.papermc.paper.plugin.lifecycle.event.types;
+
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public interface OwnerAwareLifecycleEvent<O extends LifecycleEventOwner> extends LifecycleEvent {
+
+    void setOwner(@Nullable O owner);
+
+    @Nullable O castOwner(LifecycleEventOwner owner);
+}

paper-server/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/PrioritizableLifecycleEventType.java

@@ -0,0 +1,79 @@
+package io.papermc.paper.plugin.lifecycle.event.types;
+
+import com.google.common.base.Preconditions;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
+import io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner;
+import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.AbstractLifecycleEventHandlerConfiguration;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.PrioritizedLifecycleEventHandlerConfiguration;
+import io.papermc.paper.plugin.lifecycle.event.handler.configuration.PrioritizedLifecycleEventHandlerConfigurationImpl;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public abstract class PrioritizableLifecycleEventType<
+    O extends LifecycleEventOwner,
+    E extends LifecycleEvent,
+    C extends PrioritizedLifecycleEventHandlerConfiguration<O>
+> extends AbstractLifecycleEventType<O, E, C> {
+
+    private static final Comparator<RegisteredHandler<?, ?>> COMPARATOR = Comparator.comparing(handler -> ((PrioritizedLifecycleEventHandlerConfigurationImpl<?, ?>) handler.config()).priority(), (o1, o2) -> {
+        if (o1.equals(o2)) {
+            return 0;
+        } else if (o1.isEmpty()) {
+            return 1;
+        } else if (o2.isEmpty()) {
+            return -1;
+        } else {
+            return Integer.compare(o1.getAsInt(), o2.getAsInt());
+        }
+    });
+
+    private final List<RegisteredHandler<O, E>> handlers = new ArrayList<>();
+
+    public PrioritizableLifecycleEventType(final String name, final Class<? extends O> ownerType) {
+        super(name, ownerType);
+    }
+
+    @Override
+    public boolean hasHandlers() {
+        return !this.handlers.isEmpty();
+    }
+
+    @Override
+    protected void register(final O owner, final AbstractLifecycleEventHandlerConfiguration<O, E> config) {
+        Preconditions.checkArgument(config instanceof PrioritizedLifecycleEventHandlerConfigurationImpl<?, ?>, "Configuration must be a PrioritizedLifecycleEventHandlerConfiguration");
+        this.handlers.add(new RegisteredHandler<>(owner, config));
+        this.handlers.sort(COMPARATOR);
+    }
+
+    @Override
+    public void forEachHandler(final E event, final Consumer<RegisteredHandler<O, E>> consumer, final Predicate<RegisteredHandler<O, E>> predicate) {
+        for (final RegisteredHandler<O, E> handler : this.handlers) {
+            if (predicate.test(handler)) {
+                consumer.accept(handler);
+            }
+        }
+    }
+
+    @Override
+    public void removeMatching(final Predicate<RegisteredHandler<O, E>> predicate) {
+        this.handlers.removeIf(predicate);
+    }
+
+    public static class Simple<O extends LifecycleEventOwner, E extends LifecycleEvent> extends PrioritizableLifecycleEventType<O, E, PrioritizedLifecycleEventHandlerConfiguration<O>> implements LifecycleEventType.Prioritizable<O, E> {
+        public Simple(final String name, final Class<? extends O> ownerType) {
+            super(name, ownerType);
+        }
+
+        @Override
+        public PrioritizedLifecycleEventHandlerConfiguration<O> newHandler(final LifecycleEventHandler<? super E> handler) {
+            return new PrioritizedLifecycleEventHandlerConfigurationImpl<>(handler, this);
+        }
+    }
+}

paper-server/src/main/java/io/papermc/paper/plugin/manager/PaperPluginInstanceManager.java

@@ -293,6 +293,15 @@ class PaperPluginInstanceManager {
                 + pluginName + " (Is it up to date?)", ex, plugin); // Paper
         }
 
+        // Paper start - lifecycle event system
+        try {
+            io.papermc.paper.plugin.lifecycle.event.LifecycleEventRunner.INSTANCE.unregisterAllEventHandlersFor(plugin);
+        } catch (Throwable ex) {
+            this.handlePluginException("Error occurred (in the plugin loader) while unregistering lifecycle event handlers for "
+                + pluginName + " (Is it up to date?)", ex, plugin);
+        }
+        // Paper end
+
         try {
             this.server.getMessenger().unregisterIncomingPluginChannel(plugin);
             this.server.getMessenger().unregisterOutgoingPluginChannel(plugin);

paper-server/src/main/java/io/papermc/paper/plugin/storage/BootstrapProviderStorage.java

@@ -32,8 +32,9 @@ public class BootstrapProviderStorage extends SimpleProviderStorage<PluginBootst
             @Override
             public boolean load(PluginProvider<PluginBootstrap> provider, PluginBootstrap provided) {
                 try {
-                    BootstrapContext context = PluginBootstrapContextImpl.create(provider, PluginInitializerManager.instance().pluginDirectoryPath());
+                    PluginBootstrapContextImpl context = PluginBootstrapContextImpl.create(provider, PluginInitializerManager.instance().pluginDirectoryPath()); // Paper - lifecycle events
                     provided.bootstrap(context);
+                    context.lockLifecycleEventRegistration(); // Paper - lifecycle events
                     return true;
                 } catch (Throwable e) {
                     LOGGER.error("Failed to run bootstrapper for %s. This plugin will not be loaded.".formatted(provider.getSource()), e);

paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java

@@ -1062,6 +1062,11 @@ public final class CraftServer implements Server {
 
     @Override
     public void reload() {
+        // Paper start - lifecycle events
+        if (io.papermc.paper.plugin.lifecycle.event.LifecycleEventRunner.INSTANCE.blocksPluginReloading()) {
+            throw new IllegalStateException("A lifecycle event handler has been registered which makes reloading plugins not possible");
+        }
+        // Paper end - lifecycle events
         org.spigotmc.WatchdogThread.hasStarted = false; // Paper - Disable watchdog early timeout on reload
         this.reloadCount++;
         this.configuration = YamlConfiguration.loadConfiguration(this.getConfigFile());

paper-server/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java

@@ -649,6 +649,13 @@ public final class CraftMagicNumbers implements UnsafeValues {
     }
     // Paper end - spawn egg color visibility
 
+    // Paper start - lifecycle event API
+    @Override
+    public io.papermc.paper.plugin.lifecycle.event.LifecycleEventManager<org.bukkit.plugin.Plugin> createPluginLifecycleEventManager(final org.bukkit.plugin.java.JavaPlugin plugin, final java.util.function.BooleanSupplier registrationCheck) {
+        return new io.papermc.paper.plugin.lifecycle.event.PaperLifecycleEventManager<>(plugin, registrationCheck);
+    }
+    // Paper end - lifecycle event API
+
     /**
      * This helper class represents the different NBT Tags.
      * <p>

paper-server/src/main/resources/META-INF/services/io.papermc.paper.plugin.lifecycle.event.types.LifecycleEventTypeProvider

@@ -0,0 +1 @@
+io.papermc.paper.plugin.lifecycle.event.types.LifecycleEventTypeProviderImpl

paper-server/src/test/java/io/papermc/paper/plugin/PaperTestPlugin.java

@@ -143,4 +143,11 @@ public class PaperTestPlugin extends PluginBase {
     public List<String> onTabComplete(CommandSender sender, Command command, String alias, String[] args) {
         throw new UnsupportedOperationException("Not supported.");
     }
+
+    // Paper start - lifecycle events
+    @Override
+    public io.papermc.paper.plugin.lifecycle.event.LifecycleEventManager<org.bukkit.plugin.Plugin> getLifecycleManager() {
+        throw new UnsupportedOperationException("Not supported.");
+    }
+    // Paper end - lifecycle events
 }