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Sep 14, 2024
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macros: render more comprehensible documentation for try_join! #6841

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220 changes: 116 additions & 104 deletions tokio/src/macros/try_join.rs
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Original file line number Diff line number Diff line change
@@ -1,106 +1,118 @@
/// Waits on multiple concurrent branches, returning when **all** branches
/// complete with `Ok(_)` or on the first `Err(_)`.
///
/// The `try_join!` macro must be used inside of async functions, closures, and
/// blocks.
///
/// Similar to [`join!`], the `try_join!` macro takes a list of async
/// expressions and evaluates them concurrently on the same task. Each async
/// expression evaluates to a future and the futures from each expression are
/// multiplexed on the current task. The `try_join!` macro returns when **all**
/// branches return with `Ok` or when the **first** branch returns with `Err`.
///
/// [`join!`]: macro@join
///
/// # Notes
///
/// The supplied futures are stored inline and do not require allocating a
/// `Vec`.
///
/// ### Runtime characteristics
///
/// By running all async expressions on the current task, the expressions are
/// able to run **concurrently** but not in **parallel**. This means all
/// expressions are run on the same thread and if one branch blocks the thread,
/// all other expressions will be unable to continue. If parallelism is
/// required, spawn each async expression using [`tokio::spawn`] and pass the
/// join handle to `try_join!`.
///
/// [`tokio::spawn`]: crate::spawn
///
/// # Examples
///
/// Basic `try_join` with two branches.
///
/// ```
/// async fn do_stuff_async() -> Result<(), &'static str> {
/// // async work
/// # Ok(())
/// }
///
/// async fn more_async_work() -> Result<(), &'static str> {
/// // more here
/// # Ok(())
/// }
///
/// #[tokio::main]
/// async fn main() {
/// let res = tokio::try_join!(
/// do_stuff_async(),
/// more_async_work());
///
/// match res {
/// Ok((first, second)) => {
/// // do something with the values
/// }
/// Err(err) => {
/// println!("processing failed; error = {}", err);
/// }
/// }
/// }
/// ```
///
/// Using `try_join!` with spawned tasks.
///
/// ```
/// use tokio::task::JoinHandle;
///
/// async fn do_stuff_async() -> Result<(), &'static str> {
/// // async work
/// # Err("failed")
/// }
///
/// async fn more_async_work() -> Result<(), &'static str> {
/// // more here
/// # Ok(())
/// }
///
/// async fn flatten<T>(handle: JoinHandle<Result<T, &'static str>>) -> Result<T, &'static str> {
/// match handle.await {
/// Ok(Ok(result)) => Ok(result),
/// Ok(Err(err)) => Err(err),
/// Err(err) => Err("handling failed"),
/// }
/// }
///
/// #[tokio::main]
/// async fn main() {
/// let handle1 = tokio::spawn(do_stuff_async());
/// let handle2 = tokio::spawn(more_async_work());
/// match tokio::try_join!(flatten(handle1), flatten(handle2)) {
/// Ok(val) => {
/// // do something with the values
/// }
/// Err(err) => {
/// println!("Failed with {}.", err);
/// # assert_eq!(err, "failed");
/// }
/// }
/// }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
macro_rules! try_join {
macro_rules! doc {
($try_join:item) => {
/// Waits on multiple concurrent branches, returning when **all** branches
/// complete with `Ok(_)` or on the first `Err(_)`.
///
/// The `try_join!` macro must be used inside of async functions, closures, and
/// blocks.
///
/// Similar to [`join!`], the `try_join!` macro takes a list of async
/// expressions and evaluates them concurrently on the same task. Each async
/// expression evaluates to a future and the futures from each expression are
/// multiplexed on the current task. The `try_join!` macro returns when **all**
/// branches return with `Ok` or when the **first** branch returns with `Err`.
///
/// [`join!`]: macro@join
///
/// # Notes
///
/// The supplied futures are stored inline and do not require allocating a
/// `Vec`.
///
/// ### Runtime characteristics
///
/// By running all async expressions on the current task, the expressions are
/// able to run **concurrently** but not in **parallel**. This means all
/// expressions are run on the same thread and if one branch blocks the thread,
/// all other expressions will be unable to continue. If parallelism is
/// required, spawn each async expression using [`tokio::spawn`] and pass the
/// join handle to `try_join!`.
///
/// [`tokio::spawn`]: crate::spawn
///
/// # Examples
///
/// Basic `try_join` with two branches.
///
/// ```
/// async fn do_stuff_async() -> Result<(), &'static str> {
/// // async work
/// # Ok(())
/// }
///
/// async fn more_async_work() -> Result<(), &'static str> {
/// // more here
/// # Ok(())
/// }
///
/// #[tokio::main]
/// async fn main() {
/// let res = tokio::try_join!(
/// do_stuff_async(),
/// more_async_work());
///
/// match res {
/// Ok((first, second)) => {
/// // do something with the values
/// }
/// Err(err) => {
/// println!("processing failed; error = {}", err);
/// }
/// }
/// }
/// ```
///
/// Using `try_join!` with spawned tasks.
///
/// ```
/// use tokio::task::JoinHandle;
///
/// async fn do_stuff_async() -> Result<(), &'static str> {
/// // async work
/// # Err("failed")
/// }
///
/// async fn more_async_work() -> Result<(), &'static str> {
/// // more here
/// # Ok(())
/// }
///
/// async fn flatten<T>(handle: JoinHandle<Result<T, &'static str>>) -> Result<T, &'static str> {
/// match handle.await {
/// Ok(Ok(result)) => Ok(result),
/// Ok(Err(err)) => Err(err),
/// Err(err) => Err("handling failed"),
/// }
/// }
///
/// #[tokio::main]
/// async fn main() {
/// let handle1 = tokio::spawn(do_stuff_async());
/// let handle2 = tokio::spawn(more_async_work());
/// match tokio::try_join!(flatten(handle1), flatten(handle2)) {
/// Ok(val) => {
/// // do something with the values
/// }
/// Err(err) => {
/// println!("Failed with {}.", err);
/// # assert_eq!(err, "failed");
/// }
/// }
/// }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
$try_join
};
}

#[cfg(doc)]
doc! {macro_rules! try_join {
($($future:expr),*) => { unimplemented!() }
}}

#[cfg(not(doc))]
doc! {macro_rules! try_join {
(@ {
// One `_` for each branch in the `try_join!` macro. This is not used once
// normalization is complete.
Expand Down Expand Up @@ -215,4 +227,4 @@ macro_rules! try_join {
};

() => { async { Ok(()) }.await }
}
}}
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