try to stay within configured interval

src/main/scala/netty/ActorChannelConnector.scala

@@ -7,6 +7,8 @@ import io.netty.handler.codec.http.websocketx.*
 import io.netty.util.concurrent.{ Future as NettyFuture, GenericFutureListener }
 import org.apache.pekko.actor.typed.{ ActorRef, Scheduler }
 
+import scala.concurrent.duration.Deadline
+
 import lila.ws.Controller.Endpoint
 import lila.ws.netty.ProtocolHandler.key
 
@@ -20,7 +22,8 @@ final private class ActorChannelConnector(
   private val flushQ  = ActorChannelConnector.FlushQueue()
   private val monitor = Monitor.connector.flush
   private val flushThread = Future:
-    while !workers.isShuttingDown && !workers.isTerminated do Thread.sleep(flush())
+    while !workers.isShuttingDown && !workers.isTerminated do
+      Thread.sleep(0, flush().timeLeft.toNanos.toInt.atLeast(0))
 
   private object config:
     private def int(key: String) = settings.makeSetting(key, staticConfig.getInt(key))
@@ -62,8 +65,8 @@ final private class ActorChannelConnector(
       channel.write(TextWebSocketFrame(in.write))
       flushQ.add(channel)
 
-  private def flush(): Int =
-    val entryUsecs      = System.nanoTime() / 1000
+  private def flush(): Deadline =
+    val entered         = Deadline.now
     val qSize           = flushQ.estimateSize()
     val maxDelayFactor  = config.interval.get().toDouble / config.maxDelay.get().atLeast(1)
     var channelsToFlush = config.step.get().atLeast((qSize * maxDelayFactor).toInt)
@@ -75,13 +78,16 @@ final private class ActorChannelConnector(
           channelsToFlush -= 1
         case _ =>
           channelsToFlush = 0
+
     monitor.qSize.record(qSize)
     monitor.channelsToFlush.record(channelsToFlush)
-    monitor.loopRuntimeMicroseconds.record(System.nanoTime() / 1000 - entryUsecs)
+    monitor.loopRuntimeMicroseconds.record((Deadline.now - entered).toMicros)
 
-    if config.isFlushQEnabled() then config.interval.get()
-    else if qSize == 0 then 1000 // hibernate
-    else 1                       // interval is 0 but we still need to empty the queue
+    entered + {
+      if config.isFlushQEnabled() then config.interval.get().millis
+      else if qSize == 0 then 1000.millis // hibernate
+      else 1.millis                       // interval is 0 but we still need to empty the queue
+    }
 
 object ActorChannelConnector:
   private class FlushQueue: