Adding upstream version 115.7.0esr.upstream/115.7.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 199 insertions, 0 deletions

diff --git a/third_party/rust/tokio/src/task/blocking.rs b/third_party/rust/tokio/src/task/blocking.rs
new file mode 100644
index 0000000000..5fe358f3e5
--- /dev/null
+++ b/third_party/rust/tokio/src/task/blocking.rs
@@ -0,0 +1,199 @@
+use crate::task::JoinHandle;
+
+cfg_rt_multi_thread! {
+    /// Runs the provided blocking function on the current thread without
+    /// blocking the executor.
+    ///
+    /// In general, issuing a blocking call or performing a lot of compute in a
+    /// future without yielding is problematic, as it may prevent the executor
+    /// from driving other tasks forward. Calling this function informs the
+    /// executor that the currently executing task is about to block the thread,
+    /// so the executor is able to hand off any other tasks it has to a new
+    /// worker thread before that happens. See the [CPU-bound tasks and blocking
+    /// code][blocking] section for more information.
+    ///
+    /// Be aware that although this function avoids starving other independently
+    /// spawned tasks, any other code running concurrently in the same task will
+    /// be suspended during the call to `block_in_place`. This can happen e.g.
+    /// when using the [`join!`] macro. To avoid this issue, use
+    /// [`spawn_blocking`] instead of `block_in_place`.
+    ///
+    /// Note that this function cannot be used within a [`current_thread`] runtime
+    /// because in this case there are no other worker threads to hand off tasks
+    /// to. On the other hand, calling the function outside a runtime is
+    /// allowed. In this case, `block_in_place` just calls the provided closure
+    /// normally.
+    ///
+    /// Code running behind `block_in_place` cannot be cancelled. When you shut
+    /// down the executor, it will wait indefinitely for all blocking operations
+    /// to finish. You can use [`shutdown_timeout`] to stop waiting for them
+    /// after a certain timeout. Be aware that this will still not cancel the
+    /// tasks — they are simply allowed to keep running after the method
+    /// returns.
+    ///
+    /// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code
+    /// [`spawn_blocking`]: fn@crate::task::spawn_blocking
+    /// [`join!`]: macro@join
+    /// [`thread::spawn`]: fn@std::thread::spawn
+    /// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn docs() {
+    /// task::block_in_place(move || {
+    ///     // do some compute-heavy work or call synchronous code
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// Code running inside `block_in_place` may use `block_on` to reenter the
+    /// async context.
+    ///
+    /// ```
+    /// use tokio::task;
+    /// use tokio::runtime::Handle;
+    ///
+    /// # async fn docs() {
+    /// task::block_in_place(move || {
+    ///     Handle::current().block_on(async move {
+    ///         // do something async
+    ///     });
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called from a [`current_thread`] runtime.
+    ///
+    /// [`current_thread`]: fn@crate::runtime::Builder::new_current_thread
+    pub fn block_in_place<F, R>(f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        crate::runtime::thread_pool::block_in_place(f)
+    }
+}
+
+cfg_rt! {
+    /// Runs the provided closure on a thread where blocking is acceptable.
+    ///
+    /// In general, issuing a blocking call or performing a lot of compute in a
+    /// future without yielding is problematic, as it may prevent the executor from
+    /// driving other futures forward. This function runs the provided closure on a
+    /// thread dedicated to blocking operations. See the [CPU-bound tasks and
+    /// blocking code][blocking] section for more information.
+    ///
+    /// Tokio will spawn more blocking threads when they are requested through this
+    /// function until the upper limit configured on the [`Builder`] is reached.
+    /// After reaching the upper limit, the tasks are put in a queue.
+    /// The thread limit is very large by default, because `spawn_blocking` is often
+    /// used for various kinds of IO operations that cannot be performed
+    /// asynchronously.  When you run CPU-bound code using `spawn_blocking`, you
+    /// should keep this large upper limit in mind. When running many CPU-bound
+    /// computations, a semaphore or some other synchronization primitive should be
+    /// used to limit the number of computation executed in parallel. Specialized
+    /// CPU-bound executors, such as [rayon], may also be a good fit.
+    ///
+    /// This function is intended for non-async operations that eventually finish on
+    /// their own. If you want to spawn an ordinary thread, you should use
+    /// [`thread::spawn`] instead.
+    ///
+    /// Closures spawned using `spawn_blocking` cannot be cancelled. When you shut
+    /// down the executor, it will wait indefinitely for all blocking operations to
+    /// finish. You can use [`shutdown_timeout`] to stop waiting for them after a
+    /// certain timeout. Be aware that this will still not cancel the tasks — they
+    /// are simply allowed to keep running after the method returns.
+    ///
+    /// Note that if you are using the single threaded runtime, this function will
+    /// still spawn additional threads for blocking operations. The basic
+    /// scheduler's single thread is only used for asynchronous code.
+    ///
+    /// # Related APIs and patterns for bridging asynchronous and blocking code
+    ///
+    /// In simple cases, it is sufficient to have the closure accept input
+    /// parameters at creation time and return a single value (or struct/tuple, etc.).
+    ///
+    /// For more complex situations in which it is desirable to stream data to or from
+    /// the synchronous context, the [`mpsc channel`] has `blocking_send` and
+    /// `blocking_recv` methods for use in non-async code such as the thread created
+    /// by `spawn_blocking`.
+    ///
+    /// Another option is [`SyncIoBridge`] for cases where the synchronous context
+    /// is operating on byte streams.  For example, you might use an asynchronous
+    /// HTTP client such as [hyper] to fetch data, but perform complex parsing
+    /// of the payload body using a library written for synchronous I/O.
+    ///
+    /// Finally, see also [Bridging with sync code][bridgesync] for discussions
+    /// around the opposite case of using Tokio as part of a larger synchronous
+    /// codebase.
+    ///
+    /// [`Builder`]: struct@crate::runtime::Builder
+    /// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code
+    /// [rayon]: https://docs.rs/rayon
+    /// [`mpsc channel`]: crate::sync::mpsc
+    /// [`SyncIoBridge`]: https://docs.rs/tokio-util/0.6/tokio_util/io/struct.SyncIoBridge.html
+    /// [hyper]: https://docs.rs/hyper
+    /// [`thread::spawn`]: fn@std::thread::spawn
+    /// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout
+    /// [bridgesync]: https://tokio.rs/tokio/topics/bridging
+    ///
+    /// # Examples
+    ///
+    /// Pass an input value and receive result of computation:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn docs() -> Result<(), Box<dyn std::error::Error>>{
+    /// // Initial input
+    /// let mut v = "Hello, ".to_string();
+    /// let res = task::spawn_blocking(move || {
+    ///     // Stand-in for compute-heavy work or using synchronous APIs
+    ///     v.push_str("world");
+    ///     // Pass ownership of the value back to the asynchronous context
+    ///     v
+    /// }).await?;
+    ///
+    /// // `res` is the value returned from the thread
+    /// assert_eq!(res.as_str(), "Hello, world");
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// Use a channel:
+    ///
+    /// ```
+    /// use tokio::task;
+    /// use tokio::sync::mpsc;
+    ///
+    /// # async fn docs() {
+    /// let (tx, mut rx) = mpsc::channel(2);
+    /// let start = 5;
+    /// let worker = task::spawn_blocking(move || {
+    ///     for x in 0..10 {
+    ///         // Stand in for complex computation
+    ///         tx.blocking_send(start + x).unwrap();
+    ///     }
+    /// });
+    ///
+    /// let mut acc = 0;
+    /// while let Some(v) = rx.recv().await {
+    ///     acc += v;
+    /// }
+    /// assert_eq!(acc, 95);
+    /// worker.await.unwrap();
+    /// # }
+    /// ```
+    #[track_caller]
+    pub fn spawn_blocking<F, R>(f: F) -> JoinHandle<R>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        crate::runtime::spawn_blocking(f)
+    }
+}