1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
use super::BOX_FUTURE_THRESHOLD;
use crate::runtime::blocking::BlockingPool;
use crate::runtime::scheduler::CurrentThread;
use crate::runtime::{context, EnterGuard, Handle};
use crate::task::JoinHandle;

use std::future::Future;
use std::time::Duration;

cfg_rt_multi_thread! {
    use crate::runtime::Builder;
    use crate::runtime::scheduler::MultiThread;

    cfg_unstable! {
        use crate::runtime::scheduler::MultiThreadAlt;
    }
}

/// The Tokio runtime.
///
/// The runtime provides an I/O driver, task scheduler, [timer], and
/// blocking pool, necessary for running asynchronous tasks.
///
/// Instances of `Runtime` can be created using [`new`], or [`Builder`].
/// However, most users will use the [`#[tokio::main]`][main] annotation on
/// their entry point instead.
///
/// See [module level][mod] documentation for more details.
///
/// # Shutdown
///
/// Shutting down the runtime is done by dropping the value, or calling
/// [`shutdown_background`] or [`shutdown_timeout`].
///
/// Tasks spawned through [`Runtime::spawn`] keep running until they yield.
/// Then they are dropped. They are not *guaranteed* to run to completion, but
/// *might* do so if they do not yield until completion.
///
/// Blocking functions spawned through [`Runtime::spawn_blocking`] keep running
/// until they return.
///
/// The thread initiating the shutdown blocks until all spawned work has been
/// stopped. This can take an indefinite amount of time. The `Drop`
/// implementation waits forever for this.
///
/// The [`shutdown_background`] and [`shutdown_timeout`] methods can be used if
/// waiting forever is undesired. When the timeout is reached, spawned work that
/// did not stop in time and threads running it are leaked. The work continues
/// to run until one of the stopping conditions is fulfilled, but the thread
/// initiating the shutdown is unblocked.
///
/// Once the runtime has been dropped, any outstanding I/O resources bound to
/// it will no longer function. Calling any method on them will result in an
/// error.
///
/// # Sharing
///
/// There are several ways to establish shared access to a Tokio runtime:
///
///  * Using an <code>[Arc]\<Runtime></code>.
///  * Using a [`Handle`].
///  * Entering the runtime context.
///
/// Using an <code>[Arc]\<Runtime></code> or [`Handle`] allows you to do various
/// things with the runtime such as spawning new tasks or entering the runtime
/// context. Both types can be cloned to create a new handle that allows access
/// to the same runtime. By passing clones into different tasks or threads, you
/// will be able to access the runtime from those tasks or threads.
///
/// The difference between <code>[Arc]\<Runtime></code> and [`Handle`] is that
/// an <code>[Arc]\<Runtime></code> will prevent the runtime from shutting down,
/// whereas a [`Handle`] does not prevent that. This is because shutdown of the
/// runtime happens when the destructor of the `Runtime` object runs.
///
/// Calls to [`shutdown_background`] and [`shutdown_timeout`] require exclusive
/// ownership of the `Runtime` type. When using an <code>[Arc]\<Runtime></code>,
/// this can be achieved via [`Arc::try_unwrap`] when only one strong count
/// reference is left over.
///
/// The runtime context is entered using the [`Runtime::enter`] or
/// [`Handle::enter`] methods, which use a thread-local variable to store the
/// current runtime. Whenever you are inside the runtime context, methods such
/// as [`tokio::spawn`] will use the runtime whose context you are inside.
///
/// [timer]: crate::time
/// [mod]: index.html
/// [`new`]: method@Self::new
/// [`Builder`]: struct@Builder
/// [`Handle`]: struct@Handle
/// [main]: macro@crate::main
/// [`tokio::spawn`]: crate::spawn
/// [`Arc::try_unwrap`]: std::sync::Arc::try_unwrap
/// [Arc]: std::sync::Arc
/// [`shutdown_background`]: method@Runtime::shutdown_background
/// [`shutdown_timeout`]: method@Runtime::shutdown_timeout
#[derive(Debug)]
pub struct Runtime {
    /// Task scheduler
    scheduler: Scheduler,

    /// Handle to runtime, also contains driver handles
    handle: Handle,

    /// Blocking pool handle, used to signal shutdown
    blocking_pool: BlockingPool,
}

/// The flavor of a `Runtime`.
///
/// This is the return type for [`Handle::runtime_flavor`](crate::runtime::Handle::runtime_flavor()).
#[derive(Debug, PartialEq, Eq)]
#[non_exhaustive]
pub enum RuntimeFlavor {
    /// The flavor that executes all tasks on the current thread.
    CurrentThread,
    /// The flavor that executes tasks across multiple threads.
    MultiThread,
    /// The flavor that executes tasks across multiple threads.
    #[cfg(tokio_unstable)]
    MultiThreadAlt,
}

/// The runtime scheduler is either a multi-thread or a current-thread executor.
#[derive(Debug)]
pub(super) enum Scheduler {
    /// Execute all tasks on the current-thread.
    CurrentThread(CurrentThread),

    /// Execute tasks across multiple threads.
    #[cfg(feature = "rt-multi-thread")]
    MultiThread(MultiThread),

    /// Execute tasks across multiple threads.
    #[cfg(all(tokio_unstable, feature = "rt-multi-thread"))]
    MultiThreadAlt(MultiThreadAlt),
}

impl Runtime {
    pub(super) fn from_parts(
        scheduler: Scheduler,
        handle: Handle,
        blocking_pool: BlockingPool,
    ) -> Runtime {
        Runtime {
            scheduler,
            handle,
            blocking_pool,
        }
    }

    /// Creates a new runtime instance with default configuration values.
    ///
    /// This results in the multi threaded scheduler, I/O driver, and time driver being
    /// initialized.
    ///
    /// Most applications will not need to call this function directly. Instead,
    /// they will use the  [`#[tokio::main]` attribute][main]. When a more complex
    /// configuration is necessary, the [runtime builder] may be used.
    ///
    /// See [module level][mod] documentation for more details.
    ///
    /// # Examples
    ///
    /// Creating a new `Runtime` with default configuration values.
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    ///
    /// let rt = Runtime::new()
    ///     .unwrap();
    ///
    /// // Use the runtime...
    /// ```
    ///
    /// [mod]: index.html
    /// [main]: ../attr.main.html
    /// [threaded scheduler]: index.html#threaded-scheduler
    /// [runtime builder]: crate::runtime::Builder
    #[cfg(feature = "rt-multi-thread")]
    #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
    pub fn new() -> std::io::Result<Runtime> {
        Builder::new_multi_thread().enable_all().build()
    }

    /// Returns a handle to the runtime's spawner.
    ///
    /// The returned handle can be used to spawn tasks that run on this runtime, and can
    /// be cloned to allow moving the `Handle` to other threads.
    ///
    /// Calling [`Handle::block_on`] on a handle to a `current_thread` runtime is error-prone.
    /// Refer to the documentation of [`Handle::block_on`] for more.
    ///
    /// # Examples
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    ///
    /// let rt = Runtime::new()
    ///     .unwrap();
    ///
    /// let handle = rt.handle();
    ///
    /// // Use the handle...
    /// ```
    pub fn handle(&self) -> &Handle {
        &self.handle
    }

    /// Spawns a future onto the Tokio runtime.
    ///
    /// This spawns the given future onto the runtime's executor, usually a
    /// thread pool. The thread pool is then responsible for polling the future
    /// until it completes.
    ///
    /// The provided future will start running in the background immediately
    /// when `spawn` is called, even if you don't await the returned
    /// `JoinHandle`.
    ///
    /// See [module level][mod] documentation for more details.
    ///
    /// [mod]: index.html
    ///
    /// # Examples
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    ///
    /// # fn dox() {
    /// // Create the runtime
    /// let rt = Runtime::new().unwrap();
    ///
    /// // Spawn a future onto the runtime
    /// rt.spawn(async {
    ///     println!("now running on a worker thread");
    /// });
    /// # }
    /// ```
    #[track_caller]
    pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
    where
        F: Future + Send + 'static,
        F::Output: Send + 'static,
    {
        if cfg!(debug_assertions) && std::mem::size_of::<F>() > BOX_FUTURE_THRESHOLD {
            self.handle.spawn_named(Box::pin(future), None)
        } else {
            self.handle.spawn_named(future, None)
        }
    }

    /// Runs the provided function on an executor dedicated to blocking operations.
    ///
    /// # Examples
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    ///
    /// # fn dox() {
    /// // Create the runtime
    /// let rt = Runtime::new().unwrap();
    ///
    /// // Spawn a blocking function onto the runtime
    /// rt.spawn_blocking(|| {
    ///     println!("now running on a worker thread");
    /// });
    /// # }
    /// ```
    #[track_caller]
    pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
    where
        F: FnOnce() -> R + Send + 'static,
        R: Send + 'static,
    {
        self.handle.spawn_blocking(func)
    }

    /// Runs a future to completion on the Tokio runtime. This is the
    /// runtime's entry point.
    ///
    /// This runs the given future on the current thread, blocking until it is
    /// complete, and yielding its resolved result. Any tasks or timers
    /// which the future spawns internally will be executed on the runtime.
    ///
    /// # Non-worker future
    ///
    /// Note that the future required by this function does not run as a
    /// worker. The expectation is that other tasks are spawned by the future here.
    /// Awaiting on other futures from the future provided here will not
    /// perform as fast as those spawned as workers.
    ///
    /// # Multi thread scheduler
    ///
    /// When the multi thread scheduler is used this will allow futures
    /// to run within the io driver and timer context of the overall runtime.
    ///
    /// Any spawned tasks will continue running after `block_on` returns.
    ///
    /// # Current thread scheduler
    ///
    /// When the current thread scheduler is enabled `block_on`
    /// can be called concurrently from multiple threads. The first call
    /// will take ownership of the io and timer drivers. This means
    /// other threads which do not own the drivers will hook into that one.
    /// When the first `block_on` completes, other threads will be able to
    /// "steal" the driver to allow continued execution of their futures.
    ///
    /// Any spawned tasks will be suspended after `block_on` returns. Calling
    /// `block_on` again will resume previously spawned tasks.
    ///
    /// # Panics
    ///
    /// This function panics if the provided future panics, or if called within an
    /// asynchronous execution context.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::runtime::Runtime;
    ///
    /// // Create the runtime
    /// let rt  = Runtime::new().unwrap();
    ///
    /// // Execute the future, blocking the current thread until completion
    /// rt.block_on(async {
    ///     println!("hello");
    /// });
    /// ```
    ///
    /// [handle]: fn@Handle::block_on
    #[track_caller]
    pub fn block_on<F: Future>(&self, future: F) -> F::Output {
        if cfg!(debug_assertions) && std::mem::size_of::<F>() > BOX_FUTURE_THRESHOLD {
            self.block_on_inner(Box::pin(future))
        } else {
            self.block_on_inner(future)
        }
    }

    #[track_caller]
    fn block_on_inner<F: Future>(&self, future: F) -> F::Output {
        #[cfg(all(
            tokio_unstable,
            tokio_taskdump,
            feature = "rt",
            target_os = "linux",
            any(target_arch = "aarch64", target_arch = "x86", target_arch = "x86_64")
        ))]
        let future = super::task::trace::Trace::root(future);

        #[cfg(all(tokio_unstable, feature = "tracing"))]
        let future = crate::util::trace::task(
            future,
            "block_on",
            None,
            crate::runtime::task::Id::next().as_u64(),
        );

        let _enter = self.enter();

        match &self.scheduler {
            Scheduler::CurrentThread(exec) => exec.block_on(&self.handle.inner, future),
            #[cfg(feature = "rt-multi-thread")]
            Scheduler::MultiThread(exec) => exec.block_on(&self.handle.inner, future),
            #[cfg(all(tokio_unstable, feature = "rt-multi-thread"))]
            Scheduler::MultiThreadAlt(exec) => exec.block_on(&self.handle.inner, future),
        }
    }

    /// Enters the runtime context.
    ///
    /// This allows you to construct types that must have an executor
    /// available on creation such as [`Sleep`] or [`TcpStream`]. It will
    /// also allow you to call methods such as [`tokio::spawn`].
    ///
    /// [`Sleep`]: struct@crate::time::Sleep
    /// [`TcpStream`]: struct@crate::net::TcpStream
    /// [`tokio::spawn`]: fn@crate::spawn
    ///
    /// # Example
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    /// use tokio::task::JoinHandle;
    ///
    /// fn function_that_spawns(msg: String) -> JoinHandle<()> {
    ///     // Had we not used `rt.enter` below, this would panic.
    ///     tokio::spawn(async move {
    ///         println!("{}", msg);
    ///     })
    /// }
    ///
    /// fn main() {
    ///     let rt = Runtime::new().unwrap();
    ///
    ///     let s = "Hello World!".to_string();
    ///
    ///     // By entering the context, we tie `tokio::spawn` to this executor.
    ///     let _guard = rt.enter();
    ///     let handle = function_that_spawns(s);
    ///
    ///     // Wait for the task before we end the test.
    ///     rt.block_on(handle).unwrap();
    /// }
    /// ```
    pub fn enter(&self) -> EnterGuard<'_> {
        self.handle.enter()
    }

    /// Shuts down the runtime, waiting for at most `duration` for all spawned
    /// work to stop.
    ///
    /// See the [struct level documentation](Runtime#shutdown) for more details.
    ///
    /// # Examples
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    /// use tokio::task;
    ///
    /// use std::thread;
    /// use std::time::Duration;
    ///
    /// fn main() {
    ///    let runtime = Runtime::new().unwrap();
    ///
    ///    runtime.block_on(async move {
    ///        task::spawn_blocking(move || {
    ///            thread::sleep(Duration::from_secs(10_000));
    ///        });
    ///    });
    ///
    ///    runtime.shutdown_timeout(Duration::from_millis(100));
    /// }
    /// ```
    pub fn shutdown_timeout(mut self, duration: Duration) {
        // Wakeup and shutdown all the worker threads
        self.handle.inner.shutdown();
        self.blocking_pool.shutdown(Some(duration));
    }

    /// Shuts down the runtime, without waiting for any spawned work to stop.
    ///
    /// This can be useful if you want to drop a runtime from within another runtime.
    /// Normally, dropping a runtime will block indefinitely for spawned blocking tasks
    /// to complete, which would normally not be permitted within an asynchronous context.
    /// By calling `shutdown_background()`, you can drop the runtime from such a context.
    ///
    /// Note however, that because we do not wait for any blocking tasks to complete, this
    /// may result in a resource leak (in that any blocking tasks are still running until they
    /// return.
    ///
    /// See the [struct level documentation](Runtime#shutdown) for more details.
    ///
    /// This function is equivalent to calling `shutdown_timeout(Duration::from_nanos(0))`.
    ///
    /// ```
    /// use tokio::runtime::Runtime;
    ///
    /// fn main() {
    ///    let runtime = Runtime::new().unwrap();
    ///
    ///    runtime.block_on(async move {
    ///        let inner_runtime = Runtime::new().unwrap();
    ///        // ...
    ///        inner_runtime.shutdown_background();
    ///    });
    /// }
    /// ```
    pub fn shutdown_background(self) {
        self.shutdown_timeout(Duration::from_nanos(0));
    }

    /// Returns a view that lets you get information about how the runtime
    /// is performing.
    pub fn metrics(&self) -> crate::runtime::RuntimeMetrics {
        self.handle.metrics()
    }
}

#[allow(clippy::single_match)] // there are comments in the error branch, so we don't want if-let
impl Drop for Runtime {
    fn drop(&mut self) {
        match &mut self.scheduler {
            Scheduler::CurrentThread(current_thread) => {
                // This ensures that tasks spawned on the current-thread
                // runtime are dropped inside the runtime's context.
                let _guard = context::try_set_current(&self.handle.inner);
                current_thread.shutdown(&self.handle.inner);
            }
            #[cfg(feature = "rt-multi-thread")]
            Scheduler::MultiThread(multi_thread) => {
                // The threaded scheduler drops its tasks on its worker threads, which is
                // already in the runtime's context.
                multi_thread.shutdown(&self.handle.inner);
            }
            #[cfg(all(tokio_unstable, feature = "rt-multi-thread"))]
            Scheduler::MultiThreadAlt(multi_thread) => {
                // The threaded scheduler drops its tasks on its worker threads, which is
                // already in the runtime's context.
                multi_thread.shutdown(&self.handle.inner);
            }
        }
    }
}

impl std::panic::UnwindSafe for Runtime {}

impl std::panic::RefUnwindSafe for Runtime {}