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69 lines
2.4 KiB
69 lines
2.4 KiB
1 year ago
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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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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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