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//! Useful macros for working with timeouts on top of `embedded-hal` APIs //! //! The non-blocking APIs in the [`embedded-hal`] crate use `nb::Result` from //! the [`nb`] crate to signal whether an operation has finished. This can be //! a bit tedious to work with in non-trivial cases, for example if timeouts are //! involved. //! //! This crate defines macros that help working with timeouts on top of //! `embedded-hal` APIs. //! //! # Why Macros? //! //! A similar result could be achieved using functions and closures, so "Why use //! macros for this?" is a fair question. While macros can be confusing and hard //! to work with, they are also more powerful. Here are some things you can do //! using the macros in this crate, that you couldn't do with a //! function/closure-based approach: //! //! - You can `return` the current function, from within the closure. //! - You can `break`/`continue` an outer loop, from within the closure. //! - You can rely on the compiler's reasoning to support complicated moves. //! //! That last point is the least obvious, so it deserves some elaboration. Take //! the following example: //! //! ``` no_run //! let mut thing_being_idle = Thing::new(); //! //! loop { //! // `do_stuff` takes ownership of the idle thing and returns a new type //! // that represents the same thing, but no longer being idle and doing //! // stuff. //! let thing_doing_stuff = thing_being_idle.do_stuff(); //! //! // stuff is being done //! //! // `finish_doing_stuff` again takes ownership of the thing, and returns //! // the original type that represents the thing while it's being idle. //! // We move that new idle thing into the original variable. //! // //! // The compiler understands this, so even though we've moved out of //! // `thing_being_idle`, it's going to be available again in the next loop //! // iteration. //! thing_being_idle = thing_doing_stuff.finish_doing_stuff(); //! } //! //! //! struct Thing<State>(State); //! //! impl Thing<BeingIdle> { //! fn new() -> Self { //! Thing(BeingIdle) //! } //! //! fn do_stuff(self) -> Thing<DoingStuff> { //! // Start doing the important stuff //! // ... //! //! Thing(DoingStuff) //! } //! } //! //! impl Thing<DoingStuff> { //! fn finish_doing_stuff(self) -> Thing<BeingIdle> { //! // Finish doing the important stuff //! // ... //! //! Thing(BeingIdle) //! } //! } //! //! struct BeingIdle; //! struct DoingStuff; //! ``` //! //! Since the macros in this crate are basically just fancy loops that don't do //! anything complicated, the principle demonstrated above fully applies when //! using them. //! //! Contrast that with a closure-based approach: //! //! ``` ignore //! let mut thing_being_idle = Thing::new(); //! //! loop { //! let closure = || { //! // Since `do_stuff` takes ownership of the idle thing, the whole //! // closure takes ownership. We'll actually get a compiler error //! // here, as the compiler doesn't really understand that the closure //! // also gives this ownership back. See comment below. //! let thing_doing_stuff = thing_being_idle.do_stuff(); //! //! // stuff is being done //! //! // Like in the example above, we try to give ownership back, so we //! // can use the variable again in the next loop iteration. However, //! // the compiler doesn't seem to have a concept of closures giving //! // back ownership, so it won't understand this, and the whole //! // example will not compile. //! thing_being_idle = thing_doing_stuff.finish_doing_stuff(); //! }; //! //! closure(); //! } //! //! //! # struct Thing<State>(State); //! # //! # impl Thing<BeingIdle> { //! # fn new() -> Self { //! # Thing(BeingIdle) //! # } //! # //! # fn do_stuff(self) -> Thing<DoingStuff> { //! # // Start doing the important stuff //! # // ... //! # //! # Thing(DoingStuff) //! # } //! # } //! # //! # impl Thing<DoingStuff> { //! # fn finish_doing_stuff(self) -> Thing<BeingIdle> { //! # // Finish doing the important stuff //! # // ... //! # //! # Thing(BeingIdle) //! # } //! # } //! # //! # struct BeingIdle; //! # struct DoingStuff; //! ``` //! //! [`embedded-hal`]: https://crates.io/crates/embedded-hal //! [`nb`]: https://crates.io/crates/nb #![no_std] #![deny(missing_docs)] pub use embedded_hal; pub use nb; /// Blocks on a non-blocking operation until a timer times out /// /// Expects two arguments: /// /// - A timer that implements `embedded_hal::timer::CountDown` /// - An expression that evaluates to `nb::Result<T, E>` /// /// Evaluates the expression and returns `Result<T, TimeoutError<E>>`. /// /// # Example /// /// ``` rust /// use embedded_timeout_macros::{ /// block_timeout, /// TimeoutError, /// }; /// # /// # struct Timer; /// # /// # impl embedded_hal::timer::CountDown for Timer { /// # type Time = (); /// # fn start<T>(&mut self, _: T) {} /// # fn wait(&mut self) -> nb::Result<(), void::Void> { Ok(()) } /// # } /// # /// # let mut timer = Timer; /// /// let result: Result<(), TimeoutError<()>> = block_timeout!( /// &mut timer, /// { /// // The macro will keep evaluation this expression repeatedly until /// // it returns `Ok` or until the timer times out. /// // /// // We can do anything that returns `nb::Result` here. For this /// // simple example, we just return `Ok`. /// Ok(()) /// } /// ); /// /// match result { /// Ok(()) => { /// // success /// } /// Err(TimeoutError::Timeout) => { /// // the operation timed out /// } /// Err(TimeoutError::Other(error)) => { /// // the operation returned another error /// } /// } /// ``` #[macro_export] macro_rules! block_timeout { ($timer:expr, $op:expr) => { { use $crate::embedded_hal::prelude::*; // Make sure the timer has the right type. If it hasn't, the user // should at least get a good error message. fn check_type<T>(_: &mut T) where T: $crate::embedded_hal::timer::CountDown {} check_type($timer); loop { match $timer.wait() { Ok(()) => break Err($crate::TimeoutError::Timeout), Err($crate::nb::Error::WouldBlock) => (), Err(_) => unreachable!(), } match $op { Ok(result) => break Ok(result), Err($crate::nb::Error::WouldBlock) => (), Err($crate::nb::Error::Other(error)) => break Err($crate::TimeoutError::Other(error)), } } } } } /// Repeats an operation until a timer times out /// /// Expects four arguments: /// /// - A timer that implements `embedded_hal::timer::CountDown` /// - An expression that evaluates to `Result<T, E>` (the operation) /// - A pseudo-closure that will be called every time the operation succeeds /// This pseudo-closure is expected to take an argument of type `T`. The /// return value is ignored. /// - A pseudo-closure that will be called every time the operation fails /// This pseudo-closure is expected to take an argument of type `E`. The /// return value is ignored. /// /// `repeat_timeout!` will keep repeating the operation until the timer runs /// out, no matter whether it suceeds or fails. /// /// It uses a `loop` to do that, which is `break`s from when the timer runs out. /// Any of the expressions passed into the macro, the main expression, as well /// as the two pseudo-closures, can employ `break` and `continue` to manipulate /// that loop. /// /// # Example /// /// ``` rust /// use embedded_timeout_macros::{ /// repeat_timeout, /// TimeoutError, /// }; /// # /// # struct Timer; /// # /// # impl embedded_hal::timer::CountDown for Timer { /// # type Time = (); /// # fn start<T>(&mut self, _: T) {} /// # fn wait(&mut self) -> nb::Result<(), void::Void> { Ok(()) } /// # } /// # /// # let mut timer = Timer; /// /// repeat_timeout!( /// &mut timer, /// { /// // The macro will keep evaluating this expression repeatedly until /// // the timer times out. /// // /// // We can do anything that returns `Result` here. For this simple /// // example, we just return `Ok`. /// Ok(()) /// /// // We could also return an error. /// // Err("This is an error") /// }, /// // Here's a pseudo-closure with an argument in parentheses, which we can /// // name freely, followed by an expression whose return value is ignored. /// (result) { /// // The macro will evaluate this expression, if the main expression /// // above returns `Ok`. `result`, which we've named in the /// // parentheses above, will be whatever the contents of the `Ok` are. /// let result: () = result; /// }; /// (error) { /// // will be called by the macro, if the expression returns `Err` /// let error: &'static str = error; /// }; /// ); /// ``` #[macro_export] macro_rules! repeat_timeout { ( $timer:expr, $op:expr, ($result:ident) $on_success:expr; ($error:ident) $on_error:expr; ) => { { use $crate::embedded_hal::prelude::*; // Make sure the timer has the right type. If it hasn't, the user // should at least get a good error message. fn check_type<T>(_: &mut T) where T: $crate::embedded_hal::timer::CountDown {} check_type($timer); loop { match $timer.wait() { Ok(()) => break, Err($crate::nb::Error::WouldBlock) => (), Err(_) => unreachable!(), } match $op { Ok(result) => { let $result = result; $on_success; } Err(error) => { let $error = error; $on_error; } } } } } } /// An error that can either be a timeout or another error /// /// Returned by the [`block_timeout`] macro. #[derive(Debug)] pub enum TimeoutError<T> { /// The operation timed out Timeout, /// Another error occured Other(T), }