NPC's and Timers

[Syntax2022]

Hello,

i seem to be having an issue with NPC timers maybe i am doing something wrong, the code below is what i currently have

what i am expecting to happen is the following when the NPC spawns start a timer called "time_till_despawn"

World.queue("await_for_player_to_move", 2) {
        val animatedArmour = npcs.add(npcToSpawn, target.tile, Direction.NORTH, 0)
        if (animatedArmour != null) {
            animatedArmour.target = player
            animatedArmour.say("I'm ALIVE")
            animatedArmour.softTimers.start("time_till_despawn")
            World.queue("await_npc_to_spawn_and_chat", 1) {
                animatedArmour.walkTo(Tile(baseTile.x, baseTile.y + 2))
            }
        }
    }

I have the code to handle when the NPC died to stop the timer (might not be required the engine probably stops the timer when the NPC dies)

npcDeath("animated*armour") { armour ->
    val animatedArmour: NPC = armour["animated*armour"] ?: return@npcDeath
    if(animatedArmour.softTimers.contains("time_till_despawn")) {
        animatedArmour.softTimers.stop("time_till_despawn")
        logger.info { "REMOVING TIMER FOR NPC DEATH" }
        if(!animatedArmour.contains("timer_till_despawn")){
            logger.info { "REMOVED TIMER FOR NPC DEATH" }
        }

    }
}

my issue lies after x minutes i want to remove the NPC from the world and that that i am using the following

npcTimerTick("time_till_despawn") { npc ->
    cancel()
    logger.warn { "TIMER TICKED FOR NPC" }
}

npcTimerStop("time_till_despawn") { npc ->
    npcs.remove(npc)
    logger.warn { "TIMER TIMER STOPPED FOR NPC" }
}

npcTimerStart("time_till_despawn") {
    interval = 10
    logger.warn { "TIMER STARTED FOR ANIMATED NPC" }
}

but when using npcs.remove(npc) i get an concurrent modification error, but i do not see how i am concurrently trying to modify the NPC or timer?

error

[WarriorsGuild] - TIMER TICKED FOR NPC
[WarriorsGuild] - TIMER TIMER STOPPED FOR NPC
[GameLoop] - Error in game loop!
java.util.ConcurrentModificationException: null
	at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1095)
	at java.base/java.util.ArrayList$Itr.next(ArrayList.java:1049)
	at world.gregs.voidps.engine.client.update.iterator.SequentialIterator.run(SequentialIterator.kt:15)
	at world.gregs.voidps.engine.client.update.CharacterTask.run(CharacterTask.kt:20)
	at world.gregs.voidps.engine.GameLoop.tick(GameLoop.kt:40)
	at world.gregs.voidps.engine.GameLoop.tick(GameLoop.kt:34)
	at world.gregs.voidps.engine.GameLoop$start$1.invokeSuspend(GameLoop.kt:19)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:231)
	at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:164)
	at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:470)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:504)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:493)
	at kotlinx.coroutines.CancellableContinuationImpl.resumeUndispatched(CancellableContinuationImpl.kt:591)
	at kotlinx.coroutines.ResumeUndispatchedRunnable.run(Executors.kt:189)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
	at java.base/java.lang.Thread.run(Thread.java:1583)

the only thing i could think of was, the engine might be trying to remove the timer at the same time i was removing the NPC? so i tried a different approach with the following code

            animatedArmour.queue("await_npc_idle_despawn", 10) {
                npcs.remove(animatedArmour)
            }

This appraoch doesn't throw any errors however, the NPC is "removed" but is still visible on client till i either leave that region or relog.

any help would be appreciated

[GregHib]

Just before getting into timers, try to use delay()'s instead of queue's for timing things. You might have seen older examples where I have used queue's but that was changed with #590 (I'll update docs soon). World queue especially shouldn't be used often as their names need to be unique or they'll override when a second player does the same action.

The issue here is:

npcTimerStop("time_till_despawn") { npc ->
    npcs.remove(npc)
    logger.warn { "TIMER TIMER STOPPED FOR NPC" }
}

Because the timer events are happening within the NPCTask, you end up trying to modify the npcs list while iterating through it, essentially:

for (npc in npcs) {
   npcs.remove(npc)
}

Which is why it results in a concurrent modification exception.

Using a softQueue is probably how it should be done, however this will also cause the same error. I should really add a safer way of removing npcs and players... #611 So for now calling out to World queue inside will fix it because it'll wait until outside of the NPCTask.

npc.softQueue("time_till_despawn", TimeUnit.MINUTES.toTicks(10)) {
    World.queue("${npc.id}_despawn") {
        npcs.remove(npc)
    }
}

[Syntax2022]

thank you very much and thank you for reminding me that world queues need to be uniqe

[GregHib]

Np and unique only for World.queue's, other queue's are fine