class TaskQueue internal constructor(
  internal val taskRunner: TaskRunner,
  internal val name: String
) {
    internal val futureTasks = mutableListOf<Task>()
}

  /** Queues with tasks that are currently executing their [TaskQueue.activeTask]. */
  private val busyQueues = mutableListOf<TaskQueue>()

  /** Queues not in [busyQueues] that have non-empty [TaskQueue.futureTasks]. */
  private val readyQueues = mutableListOf<TaskQueue>()

  fun awaitTaskToRun(): Task? {
    this.assertThreadHoldsLock()

    while (true) {
      if (readyQueues.isEmpty()) {
        return null // Nothing to do.
      }

      val now = backend.nanoTime()
      var minDelayNanos = Long.MAX_VALUE
      var readyTask: Task? = null
      var multipleReadyTasks = false

      // Decide what to run. This loop's goal wants to:
      //  * Find out what this thread should do (either run a task or sleep)
      //  * Find out if there's enough work to start another thread.
      eachQueue@ for (queue in readyQueues) {
        val candidate = queue.futureTasks[0]
        val candidateDelay = maxOf(0L, candidate.nextExecuteNanoTime - now)

        when {
          // Compute the delay of the soonest-executable task.
          candidateDelay > 0L -> {
            minDelayNanos = minOf(candidateDelay, minDelayNanos)
            continue@eachQueue
          }

          // If we already have more than one task, that's enough work for now. Stop searching.
          readyTask != null -> {
            multipleReadyTasks = true
            break@eachQueue
          }

          // We have a task to execute when we complete the loop.
          else -> {
            readyTask = candidate
          }
        }
      }

      // Implement the decision.
      when {
        // We have a task ready to go. Get ready.
        readyTask != null -> {
          beforeRun(readyTask)

          // Also start another thread if there's more work or scheduling to do.
          if (multipleReadyTasks || !coordinatorWaiting && readyQueues.isNotEmpty()) {
            backend.execute(runnable)
          }

          return readyTask
        }

        // Notify the coordinator of a task that's coming up soon.
        coordinatorWaiting -> {
          if (minDelayNanos < coordinatorWakeUpAt - now) {
            backend.coordinatorNotify(this@TaskRunner)
          }
          return null
        }

        // No other thread is coordinating. Become the coordinator!
        else -> {
          coordinatorWaiting = true
          coordinatorWakeUpAt = now + minDelayNanos
          try {
            backend.coordinatorWait(this@TaskRunner, minDelayNanos)
          } catch (_: InterruptedException) {
            // Will cause all tasks to exit unless more are scheduled!
            cancelAll()
          } finally {
            coordinatorWaiting = false
          }
        }
      }
    }
  }

Message next() {
        ...
        
        for (;;) {
            ...
            nativePollOnce(ptr, nextPollTimeoutMillis);

            synchronized (this) {
                // Try to retrieve the next message.  Return if found.
                final long now = SystemClock.uptimeMillis();
                Message prevMsg = null;
                Message msg = mMessages;
                if (msg != null && msg.target == null) {
                    // Stalled by a barrier.  Find the next asynchronous message in the queue.
                    do {
                        prevMsg = msg;
                        msg = msg.next;
                    } while (msg != null && !msg.isAsynchronous());
                }
                if (msg != null) {
                    if (now < msg.when) {
                        // Next message is not ready.  Set a timeout to wake up when it is ready.
                        nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);
                    } else {
                        // Got a message.
                        mBlocked = false;
                        if (prevMsg != null) {
                            prevMsg.next = msg.next;
                        } else {
                            mMessages = msg.next;
                        }
                        msg.next = null;
                        if (DEBUG) Log.v(TAG, "Returning message: " + msg);
                        msg.markInUse();
                        return msg;
                    }
                } else {
                    // No more messages.
                    nextPollTimeoutMillis = -1;
                }
                
                ...
                
                // Process the quit message now that all pending messages have been handled.
                if (mQuitting) {
                    dispose();
                    return null;
                }
                
                ...
                if (pendingIdleHandlerCount <= 0) {
                    // No idle handlers to run.  Loop and wait some more.
                    mBlocked = true;
                    continue;
                }
                ...
            }
                
        }
}

 public static void loop() {
        final Looper me = myLooper();
        ...
        final MessageQueue queue = me.mQueue;

        // Make sure the identity of this thread is that of the local process,
        // and keep track of what that identity token actually is.
        Binder.clearCallingIdentity();
        final long ident = Binder.clearCallingIdentity();

        for (;;) {
            Message msg = queue.next(); // might block
            ...
            try {
                msg.target.dispatchMessage(msg);
                end = (slowDispatchThresholdMs == 0) ? 0 :
            } finally {
            ...
            }
            ...
            msg.recycleUnchecked();
        }
    }