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/*
* Copyright 2014-2021 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
*/
package io.ktor.events
import io.ktor.util.*
import io.ktor.util.collections.*
import io.ktor.util.internal.*
import io.ktor.util.logging.*
import kotlinx.coroutines.*
@OptIn(InternalAPI::class)
public class Events {
@OptIn(InternalCoroutinesApi::class)
private val handlers = CopyOnWriteHashMap, LockFreeLinkedListHead>()
/**
* Subscribe [handler] to an event specified by [definition]
*/
public fun subscribe(definition: EventDefinition, handler: EventHandler): DisposableHandle {
val registration = HandlerRegistration(handler)
handlers.computeIfAbsent(definition) { LockFreeLinkedListHead() }.addLast(registration)
return registration
}
/**
* Unsubscribe [handler] from an event specified by [definition]
*/
public fun unsubscribe(definition: EventDefinition, handler: EventHandler) {
@OptIn(InternalCoroutinesApi::class)
handlers[definition]?.forEach {
if (it.handler == handler) it.remove()
}
}
/**
* Raises the event specified by [definition] with the [value] and calls all handlers.
*
* Handlers are called in order of subscriptions.
* If some handler throws an exception, all remaining handlers will still run. The exception will eventually be re-thrown.
*/
public fun raise(definition: EventDefinition, value: T) {
var exception: Throwable? = null
handlers[definition]?.forEach { registration ->
try {
@Suppress("UNCHECKED_CAST")
(registration.handler as EventHandler)(value)
} catch (e: Throwable) {
exception?.addSuppressed(e) ?: run { exception = e }
}
}
exception?.let { throw it }
}
private class HandlerRegistration(val handler: EventHandler<*>) : LockFreeLinkedListNode(), DisposableHandle {
override fun dispose() {
remove()
}
}
}
/**
* Raises an event the same way as [Events.raise] but catches an exception and logs it if the [logger] is provided
*/
public fun Events.raiseCatching(definition: EventDefinition, value: T, logger: Logger? = null) {
try {
raise(definition, value)
} catch (cause: Throwable) {
logger?.error("Some handlers have thrown an exception", cause)
}
}
/**
* Specifies signature for the event handler
*/
public typealias EventHandler = (T) -> Unit
// TODO: make two things: definition that is kept private to subsystem, and declaration which is public.
// Invoke only by definition, subscribe by declaration
/**
* Definition of an event.
* Event is used as a key so both [hashCode] and [equals] need to be implemented properly.
* Inheriting of this class is an experimental feature.
* Instantiate directly if inheritance not necessary.
*
* @param T specifies what is a type of value passed to the event
*/
public open class EventDefinition