{"id":11615,"date":"2025-08-18T20:13:42","date_gmt":"2025-08-18T20:13:42","guid":{"rendered":"https:\/\/putridparrot.com\/blog\/?p=11615"},"modified":"2025-08-18T20:13:42","modified_gmt":"2025-08-18T20:13:42","slug":"async-await-using-tokio-and-rust","status":"publish","type":"post","link":"https:\/\/putridparrot.com\/blog\/async-await-using-tokio-and-rust\/","title":{"rendered":"Async\/await using tokio and Rust"},"content":{"rendered":"

Rust supports async\/await in a similar way to C# although these are supplied via runtimes, for example Tokio, async-std and others. <\/p>\n

In this post we’ll look at the tokio runtime option.<\/p>\n

The first thing we need to do is add tokio to the Cargo.toml, for example<\/p>\n

\r\n[dependencies]\r\ntokio = { version = "1", features = ["full"] }\r\n<\/pre>\n
Now, let’s create a simple async function<\/p>\n
\r\nasync fn execute() {\r\n   println!("Execution in async function");\r\n}\r\n<\/pre>\n
Notice we do not return a Task like C# or any type in this case, but this is essentially syntactic sugar for<\/p>\n
\r\nfn execute() -> impl Future<Output = ()> \r\n<\/pre>\n
Hence, we can see async functions return a Future (similar to a Promise in Javascript etc.).<\/p>\n
The Future trait has a poll<\/em> function which can be checked to see if the async function is ready to return a value or if it’s pending.<\/p>\n
To await an async function we use te following syntax<\/p>\n
\r\nexecute().await;\r\n<\/pre>\n
The await will ofcourse cause the current Future to return to the caller but the code after the await will not execute until the Future completes\/is ready. <\/p>\n
If you come from C# this is much the same, i.e. running a continuation when completed etc.<\/p>\n
To use asyc\/await on main<\/em> we need to make a couple of changes, first to make main async but this alone will not work without the runtime, hence main looks like this<\/p>\n
\r\n#[tokio::main]\r\nasync fn main() {\r\n  execute().await;\r\n}\r\n<\/pre>\n
Futures are lazy loaded. Meaning, that the future will not execute until the await is called.<\/p>\n
As you can see Futures do not run in a thread, they are just polling futures. However we can use tokio tasks (which looks a lot like std lib threads) the execute the code on a thread<\/p>\n
 \r\nlet handle = tokio::spawn(asyc move {\r\n   execute().await;\r\n}\r\n\r\nhandle.await.unwrap();\r\n<\/pre>\n
By default tokio executes on a threadpool but we could change things, as below<\/p>\n
\r\n#[tokio::main(flavor = "current_thread")]\r\n<\/pre>\n
Which then uses time slicing instead of threads.<\/p>\n
Tokio is good for non blocking IO, but tokio uses a single thread for it’s main event loop hence heavy CPU will basically slow down other tasks. Hence we would need to spawn threads as already discussed.<\/p>\n
Slight detour<\/strong><\/p>\n
As a slight detour from async\/await – tokio can also create “green” threads (lightweight threads from the runtime – not OS threads), for example<\/p>\n
\r\nasync fn execute() {\r\n   time::sleep(time::Duration::from_secs(1)).await;\r\n}\r\n\r\nfn main() {\r\n  let runtime = tokio::runtime::Runtime::new().unwrap();\r\n  \r\n  let future = execute();\r\n\r\n  runtime.block_on(future);\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
Rust supports async\/await in a similar way to C# although these are supplied via runtimes, for example Tokio, async-std and others. In this post we’ll look at the tokio runtime option. The first thing we need to do is add tokio to the Cargo.toml, for example [dependencies] tokio = { version = "1", features = […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[191],"tags":[],"class_list":["post-11615","post","type-post","status-publish","format-standard","hentry","category-rust"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/11615","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/comments?post=11615"}],"version-history":[{"count":5,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/11615\/revisions"}],"predecessor-version":[{"id":11653,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/11615\/revisions\/11653"}],"wp:attachment":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/media?parent=11615"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/categories?post=11615"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/tags?post=11615"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}