Learning async: a simple progress bar

[listboss]

Thanks Alice, for providing useful links and information. (agreed CPU-bound example was not a good ex for the question)

I think I am almost getting there building a mental model of async.
Combining your great description of Future and Wake notification:

@alice

Imagine you had a list of one thousand elements called futures. Each future has a function called poll , which does a little bit of work and then returns quickly. By looping through the list and calling poll on each future, you can do work on all one thousand tasks at once in a single thread.

@alice

Now the question is, if you are implementing delay_for , how do you trigger a wake-up when the timer elapses? You need some sort of code running externally to the future itself to do this.

• Is it safe to assume that the external code/thread will only trigger the wake() function of futures and don't touch anything else? I am asking because if there is another thread with access to futures, why can't futures use it to do some work while mother executor is busy with other children?
• If events that are supposed to wake up a future are not part of mainstream class of network/file IO, timer,... events then one has to implement their own other thread to send notification for polling? or tokio et. al provide utilities for this scenario?
• Can one think of a task in async rust as collection of some futures plus an executor ctx (which has information about the current thread running the task)?