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
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
//! The Tokio runtime.
//!
//! Unlike other Rust programs, asynchronous applications require runtime
//! support. In particular, the following runtime services are necessary:
//!
//! * An **I/O event loop**, called the driver, which drives I/O resources and
//!   dispatches I/O events to tasks that depend on them.
//! * A **scheduler** to execute [tasks] that use these I/O resources.
//! * A **timer** for scheduling work to run after a set period of time.
//!
//! Tokio's [`Runtime`] bundles all of these services as a single type, allowing
//! them to be started, shut down, and configured together. However, often it is
//! not required to configure a [`Runtime`] manually, and a user may just use the
//! [`tokio::main`] attribute macro, which creates a [`Runtime`] under the hood.
//!
//! # Usage
//!
//! When no fine tuning is required, the [`tokio::main`] attribute macro can be
//! used.
//!
//! ```no_run
//! use tokio::net::TcpListener;
//! use tokio::io::{AsyncReadExt, AsyncWriteExt};
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     let listener = TcpListener::bind("127.0.0.1:8080").await?;
//!
//!     loop {
//!         let (mut socket, _) = listener.accept().await?;
//!
//!         tokio::spawn(async move {
//!             let mut buf = [0; 1024];
//!
//!             // In a loop, read data from the socket and write the data back.
//!             loop {
//!                 let n = match socket.read(&mut buf).await {
//!                     // socket closed
//!                     Ok(n) if n == 0 => return,
//!                     Ok(n) => n,
//!                     Err(e) => {
//!                         println!("failed to read from socket; err = {:?}", e);
//!                         return;
//!                     }
//!                 };
//!
//!                 // Write the data back
//!                 if let Err(e) = socket.write_all(&buf[0..n]).await {
//!                     println!("failed to write to socket; err = {:?}", e);
//!                     return;
//!                 }
//!             }
//!         });
//!     }
//! }
//! ```
//!
//! From within the context of the runtime, additional tasks are spawned using
//! the [`tokio::spawn`] function. Futures spawned using this function will be
//! executed on the same thread pool used by the [`Runtime`].
//!
//! A [`Runtime`] instance can also be used directly.
//!
//! ```no_run
//! use tokio::net::TcpListener;
//! use tokio::io::{AsyncReadExt, AsyncWriteExt};
//! use tokio::runtime::Runtime;
//!
//! fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     // Create the runtime
//!     let rt  = Runtime::new()?;
//!
//!     // Spawn the root task
//!     rt.block_on(async {
//!         let listener = TcpListener::bind("127.0.0.1:8080").await?;
//!
//!         loop {
//!             let (mut socket, _) = listener.accept().await?;
//!
//!             tokio::spawn(async move {
//!                 let mut buf = [0; 1024];
//!
//!                 // In a loop, read data from the socket and write the data back.
//!                 loop {
//!                     let n = match socket.read(&mut buf).await {
//!                         // socket closed
//!                         Ok(n) if n == 0 => return,
//!                         Ok(n) => n,
//!                         Err(e) => {
//!                             println!("failed to read from socket; err = {:?}", e);
//!                             return;
//!                         }
//!                     };
//!
//!                     // Write the data back
//!                     if let Err(e) = socket.write_all(&buf[0..n]).await {
//!                         println!("failed to write to socket; err = {:?}", e);
//!                         return;
//!                     }
//!                 }
//!             });
//!         }
//!     })
//! }
//! ```
//!
//! ## Runtime Configurations
//!
//! Tokio provides multiple task scheduling strategies, suitable for different
//! applications. The [runtime builder] or `#[tokio::main]` attribute may be
//! used to select which scheduler to use.
//!
//! #### Multi-Thread Scheduler
//!
//! The multi-thread scheduler executes futures on a _thread pool_, using a
//! work-stealing strategy. By default, it will start a worker thread for each
//! CPU core available on the system. This tends to be the ideal configuration
//! for most applications. The multi-thread scheduler requires the `rt-multi-thread`
//! feature flag, and is selected by default:
//! ```
//! use tokio::runtime;
//!
//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
//! let threaded_rt = runtime::Runtime::new()?;
//! # Ok(()) }
//! ```
//!
//! Most applications should use the multi-thread scheduler, except in some
//! niche use-cases, such as when running only a single thread is required.
//!
//! #### Current-Thread Scheduler
//!
//! The current-thread scheduler provides a _single-threaded_ future executor.
//! All tasks will be created and executed on the current thread. This requires
//! the `rt` feature flag.
//! ```
//! use tokio::runtime;
//!
//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
//! let basic_rt = runtime::Builder::new_current_thread()
//!     .build()?;
//! # Ok(()) }
//! ```
//!
//! #### Resource drivers
//!
//! When configuring a runtime by hand, no resource drivers are enabled by
//! default. In this case, attempting to use networking types or time types will
//! fail. In order to enable these types, the resource drivers must be enabled.
//! This is done with [`Builder::enable_io`] and [`Builder::enable_time`]. As a
//! shorthand, [`Builder::enable_all`] enables both resource drivers.
//!
//! ## Lifetime of spawned threads
//!
//! The runtime may spawn threads depending on its configuration and usage. The
//! multi-thread scheduler spawns threads to schedule tasks and for `spawn_blocking`
//! calls.
//!
//! While the `Runtime` is active, threads may shutdown after periods of being
//! idle. Once `Runtime` is dropped, all runtime threads are forcibly shutdown.
//! Any tasks that have not yet completed will be dropped.
//!
//! [tasks]: crate::task
//! [`Runtime`]: Runtime
//! [`tokio::spawn`]: crate::spawn
//! [`tokio::main`]: ../attr.main.html
//! [runtime builder]: crate::runtime::Builder
//! [`Runtime::new`]: crate::runtime::Runtime::new
//! [`Builder::basic_scheduler`]: crate::runtime::Builder::basic_scheduler
//! [`Builder::threaded_scheduler`]: crate::runtime::Builder::threaded_scheduler
//! [`Builder::enable_io`]: crate::runtime::Builder::enable_io
//! [`Builder::enable_time`]: crate::runtime::Builder::enable_time
//! [`Builder::enable_all`]: crate::runtime::Builder::enable_all

// At the top due to macros
#[cfg(test)]
#[cfg(not(target_arch = "wasm32"))]
#[macro_use]
mod tests;

pub(crate) mod enter;

pub(crate) mod task;

cfg_metrics! {
    mod metrics;
    pub use metrics::RuntimeMetrics;

    pub(crate) use metrics::{MetricsBatch, SchedulerMetrics, WorkerMetrics};

    cfg_net! {
       pub(crate) use metrics::IoDriverMetrics;
    }
}

cfg_not_metrics! {
    pub(crate) mod metrics;
    pub(crate) use metrics::{SchedulerMetrics, WorkerMetrics, MetricsBatch};
}

cfg_rt! {
    mod basic_scheduler;
    use basic_scheduler::BasicScheduler;

    mod blocking;
    use blocking::BlockingPool;
    pub(crate) use blocking::spawn_blocking;

    cfg_trace! {
        pub(crate) use blocking::Mandatory;
    }

    cfg_fs! {
        pub(crate) use blocking::spawn_mandatory_blocking;
    }

    mod builder;
    pub use self::builder::Builder;

    pub(crate) mod context;
    mod driver;

    use self::enter::enter;

    mod handle;
    pub use handle::{EnterGuard, Handle, TryCurrentError};
    pub(crate) use handle::{HandleInner, ToHandle};

    mod spawner;
    use self::spawner::Spawner;
}

cfg_rt_multi_thread! {
    use driver::Driver;

    pub(crate) mod thread_pool;
    use self::thread_pool::ThreadPool;
}

cfg_rt! {
    use crate::task::JoinHandle;

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

    /// 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]` 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. The current
    /// thread will block until the shut down operation has completed.
    ///
    /// * Drain any scheduled work queues.
    /// * Drop any futures that have not yet completed.
    /// * Drop the reactor.
    ///
    /// Once the reactor has dropped, any outstanding I/O resources bound to
    /// that reactor will no longer function. Calling any method on them will
    /// result in an error.
    ///
    /// # Sharing
    ///
    /// The Tokio runtime implements `Sync` and `Send` to allow you to wrap it
    /// in a `Arc`. Most fn take `&self` to allow you to call them concurrently
    /// across multiple threads.
    ///
    /// Calls to `shutdown` and `shutdown_timeout` require exclusive ownership of
    /// the runtime type and this can be achieved via `Arc::try_unwrap` when only
    /// one strong count reference is left over.
    ///
    /// [timer]: crate::time
    /// [mod]: index.html
    /// [`new`]: method@Self::new
    /// [`Builder`]: struct@Builder
    #[derive(Debug)]
    pub struct Runtime {
        /// Task executor
        kind: Kind,

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

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

    /// The runtime executor is either a thread-pool or a current-thread executor.
    #[derive(Debug)]
    enum Kind {
        /// Execute all tasks on the current-thread.
        CurrentThread(BasicScheduler),

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

    /// After thread starts / before thread stops
    type Callback = std::sync::Arc<dyn Fn() + Send + Sync>;

    impl Runtime {
        /// 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
        /// [basic scheduler]: index.html#basic-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.
        ///
        /// # 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.
        ///
        /// 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,
        {
            self.handle.spawn(future)
        }

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

            let _enter = self.enter();

            match &self.kind {
                Kind::CurrentThread(exec) => exec.block_on(future),
                #[cfg(feature = "rt-multi-thread")]
                Kind::ThreadPool(exec) => exec.block_on(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;
        ///
        /// fn function_that_spawns(msg: String) {
        ///     // 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();
        ///     function_that_spawns(s);
        /// }
        /// ```
        pub fn enter(&self) -> EnterGuard<'_> {
            self.handle.enter()
        }

        /// Shuts down the runtime, waiting for at most `duration` for all spawned
        /// task to shutdown.
        ///
        /// Usually, dropping a `Runtime` handle is sufficient as tasks are able to
        /// shutdown in a timely fashion. However, dropping a `Runtime` will wait
        /// indefinitely for all tasks to terminate, and there are cases where a long
        /// blocking task has been spawned, which can block dropping `Runtime`.
        ///
        /// In this case, calling `shutdown_timeout` with an explicit wait timeout
        /// can work. The `shutdown_timeout` will signal all tasks to shutdown and
        /// will wait for at most `duration` for all spawned tasks to terminate. If
        /// `timeout` elapses before all tasks are dropped, the function returns and
        /// outstanding tasks are potentially leaked.
        ///
        /// # 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.clone().shutdown();
            self.blocking_pool.shutdown(Some(duration));
        }

        /// Shuts down the runtime, without waiting for any spawned tasks to shutdown.
        ///
        /// 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.
        ///
        /// This function is equivalent to calling `shutdown_timeout(Duration::of_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))
        }
    }

    #[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.kind {
                Kind::CurrentThread(basic) => {
                    // This ensures that tasks spawned on the basic runtime are dropped inside the
                    // runtime's context.
                    match self::context::try_enter(self.handle.clone()) {
                        Some(guard) => basic.set_context_guard(guard),
                        None => {
                            // The context thread-local has already been destroyed.
                            //
                            // We don't set the guard in this case. Calls to tokio::spawn in task
                            // destructors would fail regardless if this happens.
                        },
                    }
                },
                #[cfg(feature = "rt-multi-thread")]
                Kind::ThreadPool(_) => {
                    // The threaded scheduler drops its tasks on its worker threads, which is
                    // already in the runtime's context.
                },
            }
        }
    }

    cfg_metrics! {
        impl Runtime {
            /// TODO
            pub fn metrics(&self) -> RuntimeMetrics {
                self.handle.metrics()
            }
        }
    }
}