Julio Biason
1 year ago
1 changed files with 68 additions and 0 deletions
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title = "Timeout With Command in Tokio" |
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date = 2023-08-31 |
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[taxonomies] |
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tags = ["random", "rust", "tokio", "spawn", "process", "command", "timeout"] |
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+++ |
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How to spawn an external command and give it a timeout in Rust, with Tokio |
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<!-- more --> |
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The entry point for running external applications in Rust is the |
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[Command](https://doc.rust-lang.org/std/process/struct.Command.html) structure, |
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in the process module. This whole structure is duplicated [on Tokio, with |
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async](https://docs.rs/tokio/latest/tokio/process/struct.Command.html). |
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But there is one thing that exist in other languages (like Python) that Rust |
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doesn't have: Having a timeout for the command (and killing it if it runs over |
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the timeout). The usual solution is to run the command on a specialized thread |
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and, with another thread, make sure to kill the first if the second finishes |
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first. |
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But Tokio have a funcionality that saves a lot of code when dealing with this: |
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[timeout](https://docs.rs/tokio/latest/tokio/time/fn.timeout.html). While it |
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doesn't apply to the Command itself, it applies to Futures, and waiting for a |
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command is an async function, which means it is wrapped around a Future, and we |
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can leverage this. |
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```rust |
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use std::time::Duration; |
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use tokio::process::Command; |
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use tokio::time::timeout; |
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#[tokio::main(flavor = "current_thread")] |
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async fn main() { |
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let sleep = "sleep"; |
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println!("Run 3 secs"); |
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let mut cmd = Command::new(&sleep).arg("3s").spawn().unwrap(); |
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if let Err(_) = timeout(Duration::from_secs(4), cmd.wait()).await { |
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println!("Got timeout!"); |
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cmd.kill().await.unwrap(); |
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} else { |
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println!("No timeout"); |
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} |
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println!("Run 25 secs"); |
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let mut cmd = Command::new(&sleep).arg("25s").spawn().unwrap(); |
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if let Err(_) = timeout(Duration::from_secs(4), cmd.wait()).await { |
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println!("Got timeout"); |
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cmd.kill().await.unwrap(); |
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} else { |
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println!("No timeout"); |
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} |
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} |
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``` |
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The thing here is `.wait()`. That's when Tokio wraps the command call into a |
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Future. But, because the task is dead, it doesn't actually kill the command, |
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and that's why we need to call `.kill()` in case of timeout -- otherwise the |
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command will still run (you can check this by removing the `.kill()` call on |
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the 25s block, and calling `ps` after the application finishes). |
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Just note that the `if let Err(_)` is for timeout; `.wait()` also returns a |
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`Result`, and that's the one that needs to be checked for the actual success of |
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the execution. |
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