How to tokio::join on a vector of futures

help
1

I've stared on this doc join in tokio - Rust for hours but can not figure out a way to wait on a vector of futures.

Although there is JoinSet, but it is an unstable API.

Any ideas? Thanks

2

It seems futures_util::future::join_all can do the job, am I correct?

I tried to use it, and my code can compile and run.

3

I would say that the best approach is to spawn them:

let mut handles = Vec::with_capacity(futures.len());

for fut in futures {
    handles.push(tokio::spawn(fut));
}

let mut results = Vec::with_capacity(handles.len());
for handle in handles {
    results.push(handle.await.unwrap());
}

Using join_all is also an option, but it's less efficient and has some pitfalls (e.g. it makes it easy to accidentally ignore errors).

5 Likes
4

Got it, I'll go back to tokio::task::spawn then. Thanks a lot for the suggestion!

5

Hi @alice , in your solution, how to fail all tasks immediately if any task fails? I want to fail all tasks immediately if one of them fails.

6

Since the JoinSet type is still unstable, you have to do that yourself. The easiest way is to wrap the vector in a struct with a destructor that calls abort on all of them.

7

Good idea! Thanks

8

I would say that the best approach is to spawn them

There is still a difference between spawn and join: the second one is not parallel, and it could matter a lot, because it would allow for example using mutable objects without needing to encapsulate them inside a Mutex.
Maybe it doesn't matter in most cases, but It could be worth to mention in this thread.

1 Like
9

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