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</pre><div class="example-wrap"><pre class="rust ">
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">task</span>::<span class="ident">JoinHandle</span>;
<span class="macro">cfg_rt_multi_thread</span><span class="macro">!</span> {
<span class="doccomment">/// Runs the provided blocking function on the current thread without</span>
<span class="doccomment">/// blocking the executor.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In general, issuing a blocking call or performing a lot of compute in a</span>
<span class="doccomment">/// future without yielding is not okay, as it may prevent the executor from</span>
<span class="doccomment">/// driving other futures forward. This function runs the closure on the</span>
<span class="doccomment">/// current thread by having the thread temporarily cease from being a core</span>
<span class="doccomment">/// thread, and turns it into a blocking thread. See the [CPU-bound tasks</span>
<span class="doccomment">/// and blocking code][blocking] section for more information.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Although this function avoids starving other independently spawned</span>
<span class="doccomment">/// tasks, any other code running concurrently in the same task will be</span>
<span class="doccomment">/// suspended during the call to `block_in_place`. This can happen e.g. when</span>
<span class="doccomment">/// using the [`join!`] macro. To avoid this issue, use [`spawn_blocking`]</span>
<span class="doccomment">/// instead.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this function can only be used when using the `multi_thread` runtime.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Code running behind `block_in_place` cannot be cancelled. When you shut</span>
<span class="doccomment">/// down the executor, it will wait indefinitely for all blocking operations</span>
<span class="doccomment">/// to finish. You can use [`shutdown_timeout`] to stop waiting for them</span>
<span class="doccomment">/// after a certain timeout. Be aware that this will still not cancel the</span>
<span class="doccomment">/// tasks — they are simply allowed to keep running after the method</span>
<span class="doccomment">/// returns.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code</span>
<span class="doccomment">/// [`spawn_blocking`]: fn@crate::task::spawn_blocking</span>
<span class="doccomment">/// [`join!`]: macro@join</span>
<span class="doccomment">/// [`thread::spawn`]: fn@std::thread::spawn</span>
<span class="doccomment">/// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use tokio::task;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # async fn docs() {</span>
<span class="doccomment">/// task::block_in_place(move || {</span>
<span class="doccomment">/// // do some compute-heavy work or call synchronous code</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">block_in_place</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">R</span>
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-</span><span class="op">></span> <span class="ident">R</span>,
{
<span class="kw">crate</span>::<span class="ident">runtime</span>::<span class="ident">thread_pool</span>::<span class="ident">block_in_place</span>(<span class="ident">f</span>)
}
}
<span class="macro">cfg_rt</span><span class="macro">!</span> {
<span class="doccomment">/// Runs the provided closure on a thread where blocking is acceptable.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In general, issuing a blocking call or performing a lot of compute in a</span>
<span class="doccomment">/// future without yielding is problematic, as it may prevent the executor from</span>
<span class="doccomment">/// driving other futures forward. This function runs the provided closure on a</span>
<span class="doccomment">/// thread dedicated to blocking operations. See the [CPU-bound tasks and</span>
<span class="doccomment">/// blocking code][blocking] section for more information.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Tokio will spawn more blocking threads when they are requested through this</span>
<span class="doccomment">/// function until the upper limit configured on the [`Builder`] is reached.</span>
<span class="doccomment">/// This limit is very large by default, because `spawn_blocking` is often used</span>
<span class="doccomment">/// for various kinds of IO operations that cannot be performed asynchronously.</span>
<span class="doccomment">/// When you run CPU-bound code using `spawn_blocking`, you should keep this</span>
<span class="doccomment">/// large upper limit in mind. When running many CPU-bound computations, a</span>
<span class="doccomment">/// semaphore or some other synchronization primitive should be used to limit</span>
<span class="doccomment">/// the number of computation executed in parallel. Specialized CPU-bound</span>
<span class="doccomment">/// executors, such as [rayon], may also be a good fit.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is intended for non-async operations that eventually finish on</span>
<span class="doccomment">/// their own. If you want to spawn an ordinary thread, you should use</span>
<span class="doccomment">/// [`thread::spawn`] instead.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Closures spawned using `spawn_blocking` cannot be cancelled. When you shut</span>
<span class="doccomment">/// down the executor, it will wait indefinitely for all blocking operations to</span>
<span class="doccomment">/// finish. You can use [`shutdown_timeout`] to stop waiting for them after a</span>
<span class="doccomment">/// certain timeout. Be aware that this will still not cancel the tasks — they</span>
<span class="doccomment">/// are simply allowed to keep running after the method returns.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that if you are using the single threaded runtime, this function will</span>
<span class="doccomment">/// still spawn additional threads for blocking operations. The basic</span>
<span class="doccomment">/// scheduler's single thread is only used for asynchronous code.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Builder`]: struct@crate::runtime::Builder</span>
<span class="doccomment">/// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code</span>
<span class="doccomment">/// [rayon]: https://docs.rs/rayon</span>
<span class="doccomment">/// [`thread::spawn`]: fn@std::thread::spawn</span>
<span class="doccomment">/// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use tokio::task;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # async fn docs() -> Result<(), Box<dyn std::error::Error>>{</span>
<span class="doccomment">/// let res = task::spawn_blocking(move || {</span>
<span class="doccomment">/// // do some compute-heavy work or call synchronous code</span>
<span class="doccomment">/// "done computing"</span>
<span class="doccomment">/// }).await?;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(res, "done computing");</span>
<span class="doccomment">/// # Ok(())</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">tokio_track_caller</span>, <span class="ident">track_caller</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">spawn_blocking</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">JoinHandle</span><span class="op"><</span><span class="ident">R</span><span class="op">></span>
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-</span><span class="op">></span> <span class="ident">R</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'static</span>,
<span class="ident">R</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'static</span>,
{
<span class="kw">crate</span>::<span class="ident">runtime</span>::<span class="ident">spawn_blocking</span>(<span class="ident">f</span>)
}
}
</pre></div>
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