73 lines
2.8 KiB
Markdown
73 lines
2.8 KiB
Markdown
# Pollster
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Pollster is an incredibly minimal async executor for Rust that lets you block a thread until a future completes.
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[](
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https://crates.io/crates/pollster)
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[](
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https://docs.rs/pollster)
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[](
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https://github.com/zesterer/pollster)
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```rust
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use pollster::FutureExt as _;
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let my_fut = async {};
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let result = my_fut.block_on();
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```
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That's it. That's all it does. Nothing more, nothing less. No need to pull in 50 crates to evaluate a future.
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## Why is this useful?
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Now that `async` functions are stable, we're increasingly seeing libraries all over the Rust ecosystem expose `async`
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APIs. This is great for those wanting to build highly concurrent web applications!
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However, many of us are *not* building highly concurrent web applications, but end up faced with an `async` function
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that we can't easily call from synchronous code. If you're in this position, then `pollster` is for you: it allows you
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to evaluate a future in-place without spinning up a heavyweight runtime like `tokio` or `async_std`.
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## Minimalism
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Pollster is built with the [UNIX ethos](https://en.wikipedia.org/wiki/Unix_philosophy#Do_One_Thing_and_Do_It_Well) in
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mind: do one thing, and do it well. It has no dependencies, compiles quickly, and is composed of only ~100 lines of
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well-audited code.
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## Behaviour
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Pollster will synchronously block the thread until a future completes. It will not spin: instead, it will place the
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thread into a waiting state until the future has been polled to completion.
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## Compatibility
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Unfortunately, `pollster` will not work for *all* futures because some require a specific runtime or reactor. See
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[here](https://rust-lang.github.io/async-book/08_ecosystem/00_chapter.html#determining-ecosystem-compatibility) for more
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information about when and where `pollster` may be used. However, if you're already pulling in the required dependencies
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to create such a future in the first place, it's likely that you already have a version of `block_on` in your dependency
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tree that's designed to poll your future, so use that instead.
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## Macro
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When using the `macro` crate feature, an attribute-macro can be used to mark `async fn main()`:
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```rust,ignore
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#[pollster::main]
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async fn main() {
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let my_fut = async {};
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my_fut.await;
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}
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```
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Additionally if you have re-exported the crate with a different name then `pollster`, you have to specify it:
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```rust,ignore
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#[pollster::main(crate = "renamed-pollster")]
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async fn main() {
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let my_fut = async {};
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my_fut.await;
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}
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```
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You can also use `#[pollster::test]` for tests.
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