I have written a blog post about a common misunderstanding about tasks [image] Elixir process timeout pitfall If you taken a look at Elixir, you may have come across something like the below code 1234567891011121314151617181920212223242526272829defmodule HardWorker do def work(id) do …

it should show you that running in parallel with timeouts is not just a Task.await away. That isn’t what this shows at all. This shows that if you want a timeout to apply to a group, you should write it to apply to a group. There’s even a function for it in the standard library: http://elixir-lan…

In fact, this actually perfectly demonstrates parallel execution at work. The total amount of sleeping time called is 49.5 seconds! 1..10 |> Enum.map(&(&1 * 900)) |> Enum.sum Despite this, the total wait time is only about as long as the longest item 9005.466 ms (not the 10 seconds in the article)…

timeout = 5000 urls = 1..10 |> Enum.to_list urls |> Enum.map(fn url -> Task.async(url) end) |> Enum.map(fn task -> Task.await(task, timeout) end) If we take the above code as an example, aren’t we setting different timeouts for different tasks? Is that what a reader would expect?

No, you’re setting the same timeout for each task. However, each call to Task.await is consecutive. Thus, the first task is given 5 seconds to timeout. Then the next task is given 5 seconds to timeout, and so forth. Every task is given 5 seconds. This is absolutely expected because the Task.await ca…

[image] benwilson512: No, you’re setting the same timeout for each task. However, each call to Task.await is consecutive. Thus, the first task is given 5 seconds to timeout. Then the next task is given 5 seconds to timeout, and so forth. Every task is given 5 seconds. This is absolutely expected…

Look, suppose you wrote the following code: task = Task.async(fn -> Process.sleep(:infinity) end) Process.sleep(5_000) Task.await(task, 5_000) How long before it times out? 10 seconds of course. But this is obvious and expected. This is exactly what you’re doing by making the Task.await calls con…

Put another way, Elixir functions aren’t gonna know about anything not passed to them directly. Thus if you want ALL tasks to have the same timeout, you’re gonna need to pass ALL tasks to some function that can handle dealing with them. If you only look at one task at a time, you’re gonna get that b…

I understand what you are saying. May be as a more experienced elixir dev it doesn’t confuse you :slight_smile: I got confused by that code in my project.

Look, I’m 100% behind having a blog post which says "hey, keep in mind that these calls will run sequentially, that’s why there’s Task.yield_many`. I mostly just feel like the sentence “it should show you that running in parallel with timeouts is not just a Task.await away.” implies that there’s so…

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Elixir task timeout pitfall

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minhajuddin October 31, 2016, 1:34pm 11

Valid points. I’ll update the blog post.