fuchsia_async/runtime/fuchsia/executor/
send.rs

1// Copyright 2021 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use super::common::{Executor, ExecutorTime};
6use super::scope::ScopeHandle;
7use fuchsia_sync::{Condvar, Mutex};
8
9use crate::runtime::instrument::TaskInstrument;
10use futures::FutureExt;
11use std::future::Future;
12use std::sync::Arc;
13use std::sync::atomic::Ordering;
14use std::time::Duration;
15use std::{fmt, thread};
16
17/// A multi-threaded port-based executor for Fuchsia. Requires that tasks scheduled on it
18/// implement `Send` so they can be load balanced between worker threads.
19///
20/// Having a `SendExecutor` in scope allows the creation and polling of zircon objects, such as
21/// [`fuchsia_async::Channel`].
22///
23/// # Panics
24///
25/// `SendExecutor` will panic on drop if any zircon objects attached to it are still alive. In other
26/// words, zircon objects backed by a `SendExecutor` must be dropped before it.
27pub struct SendExecutor {
28    /// The inner executor state.
29    inner: Arc<Executor>,
30    // LINT.IfChange
31    /// The root scope.
32    root_scope: ScopeHandle,
33    // LINT.ThenChange(//src/developer/debug/zxdb/console/commands/verb_async_backtrace.cc)
34    /// Worker thread handles
35    threads: Vec<thread::JoinHandle<()>>,
36    worker_init: Option<Arc<dyn Fn() + Send + Sync + 'static>>,
37}
38
39impl fmt::Debug for SendExecutor {
40    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
41        f.debug_struct("SendExecutor").field("port", &self.inner.port).finish()
42    }
43}
44
45impl SendExecutor {
46    fn new_inner(
47        num_threads: u8,
48        worker_init: Option<Arc<dyn Fn() + Send + Sync + 'static>>,
49        instrument: Option<Arc<dyn TaskInstrument>>,
50    ) -> Self {
51        let inner = Arc::new(Executor::new(
52            ExecutorTime::RealTime,
53            /* is_local */ false,
54            num_threads,
55            instrument,
56        ));
57        let root_scope = ScopeHandle::root(inner.clone());
58        Executor::set_local(root_scope.clone());
59        Self { inner, root_scope, threads: Vec::default(), worker_init }
60    }
61
62    /// Get a reference to the Fuchsia `zx::Port` being used to listen for events.
63    pub fn port(&self) -> &zx::Port {
64        &self.inner.port
65    }
66
67    /// Run `future` to completion, using this thread and `num_threads` workers in a pool to
68    /// poll active tasks.
69    // The debugger looks for this function on the stack, so if its (fully-qualified) name changes,
70    // the debugger needs to be updated.
71    // LINT.IfChange
72    pub fn run<F>(&mut self, future: F) -> F::Output
73    // LINT.ThenChange(//src/developer/debug/zxdb/console/commands/verb_async_backtrace.cc)
74    where
75        F: Future + Send + 'static,
76        F::Output: Send + 'static,
77    {
78        assert!(self.inner.is_real_time(), "Error: called `run` on an executor using fake time");
79
80        let pair = Arc::new((Mutex::new(None), Condvar::new()));
81        let pair2 = pair.clone();
82
83        // Spawn a future which will set the result upon completion.
84        let task = self.root_scope.new_task(future.map(move |fut_result| {
85            let (lock, cvar) = &*pair2;
86            let mut result = lock.lock();
87            *result = Some(fut_result);
88            cvar.notify_one();
89        }));
90        task.detach();
91        assert!(self.root_scope.insert_task(task, false));
92
93        // Start worker threads, handing off timers from the current thread.
94        self.inner.done.store(false, Ordering::SeqCst);
95        self.create_worker_threads();
96
97        // Wait until the signal the future has completed.
98        let (lock, cvar) = &*pair;
99        let mut result = lock.lock();
100        if result.is_none() {
101            let mut last_polled = 0;
102            let mut last_tasks_ready = false;
103            loop {
104                // This timeout is chosen to be quite high since it impacts all processes that have
105                // multi-threaded async executors, and it exists to workaround arguably misbehaving
106                // users (see the comment below).
107                cvar.wait_for(&mut result, Duration::from_millis(250));
108                if result.is_some() {
109                    break;
110                }
111                let polled = self.inner.polled.load(Ordering::Relaxed);
112                let tasks_ready = !self.inner.ready_tasks.is_empty();
113                if polled == last_polled && last_tasks_ready && tasks_ready {
114                    // If this log message is printed, it most likely means that a task has blocked
115                    // making a reentrant synchronous call that doesn't involve a port message being
116                    // processed by this same executor. This can arise even if you would expect
117                    // there to normally be other port messages involved. One example (that has
118                    // actually happened): spawn a task to service a fuchsia.io connection, then try
119                    // and synchronously connect to that service. If the task hasn't had a chance to
120                    // run, then the async channel might not be registered with the executor, and so
121                    // sending messages to the channel doesn't trigger a port message. Typically,
122                    // the way to solve these issues is to run the service in a different executor
123                    // (which could be the same or a different process).
124                    eprintln!("Tasks might be stalled!");
125                    self.inner.wake_one_thread();
126                }
127                last_polled = polled;
128                last_tasks_ready = tasks_ready;
129            }
130        }
131
132        // Spin down worker threads
133        self.join_all();
134
135        // Unwrap is fine because of the check to `is_none` above.
136        result.take().unwrap()
137    }
138
139    #[doc(hidden)]
140    /// Returns the root scope of the executor.
141    pub fn root_scope(&self) -> &ScopeHandle {
142        &self.root_scope
143    }
144
145    /// Add `self.num_threads` worker threads to the executor's thread pool.
146    /// `timers`: timers from the "main" thread which would otherwise be lost.
147    fn create_worker_threads(&mut self) {
148        for _ in 0..self.inner.num_threads {
149            let inner = self.inner.clone();
150            let root_scope = self.root_scope.clone();
151            let worker_init = self.worker_init.clone();
152            let thread = thread::Builder::new()
153                .name("executor_worker".to_string())
154                .spawn(move || {
155                    Executor::set_local(root_scope);
156                    if let Some(init) = worker_init.as_ref() {
157                        init();
158                    }
159                    inner.worker_lifecycle::</* UNTIL_STALLED: */ false>(None);
160                })
161                .expect("must be able to spawn threads");
162            self.threads.push(thread);
163        }
164    }
165
166    fn join_all(&mut self) {
167        self.inner.mark_done();
168
169        // Join the worker threads
170        for thread in self.threads.drain(..) {
171            thread.join().expect("Couldn't join worker thread.");
172        }
173    }
174}
175
176impl Drop for SendExecutor {
177    fn drop(&mut self) {
178        self.join_all();
179        self.inner.on_parent_drop(&self.root_scope);
180    }
181}
182
183/// A builder for `SendExecutor`.
184#[derive(Default)]
185pub struct SendExecutorBuilder {
186    num_threads: Option<u8>,
187    worker_init: Option<Arc<dyn Fn() + Send + Sync + 'static>>,
188    instrument: Option<Arc<dyn TaskInstrument>>,
189}
190
191impl SendExecutorBuilder {
192    /// Creates a new builder used for constructing a `SendExecutor`.
193    pub fn new() -> Self {
194        Self::default()
195    }
196
197    /// Sets the number of threads for the executor.
198    pub fn num_threads(mut self, num_threads: u8) -> Self {
199        self.num_threads = Some(num_threads);
200        self
201    }
202
203    /// Sets the worker initialization function.
204    pub fn worker_init(mut self, worker_init: impl Fn() + Send + Sync + 'static) -> Self {
205        self.worker_init = Some(Arc::new(worker_init));
206        self
207    }
208
209    /// Sets the instrumentation hook.
210    pub fn instrument(mut self, instrument: Option<Arc<dyn TaskInstrument>>) -> Self {
211        self.instrument = instrument;
212        self
213    }
214
215    /// Builds the `SendExecutor`, consuming this `SendExecutorBuilder`.
216    pub fn build(self) -> SendExecutor {
217        SendExecutor::new_inner(self.num_threads.unwrap_or(1), self.worker_init, self.instrument)
218    }
219}
220
221// TODO(https://fxbug.dev/42156503) test SendExecutor with unit tests
222
223#[cfg(test)]
224mod tests {
225    use super::SendExecutorBuilder;
226    use crate::{Task, Timer};
227
228    use fuchsia_sync::{Condvar, Mutex};
229    use futures::channel::oneshot;
230    use std::sync::Arc;
231    use std::sync::atomic::{AtomicU64, Ordering};
232
233    #[test]
234    fn test_stalled_triggers_wake_up() {
235        SendExecutorBuilder::new().num_threads(2).build().run(async {
236            // The timer will only fire on one thread, so use one so we can get to a point where
237            // only one thread is running.
238            Timer::new(zx::MonotonicDuration::from_millis(10)).await;
239
240            let (tx, rx) = oneshot::channel();
241            let pair = Arc::new((Mutex::new(false), Condvar::new()));
242            let pair2 = pair.clone();
243
244            let _task = Task::spawn(async move {
245                // Send a notification to the other task.
246                tx.send(()).unwrap();
247                // Now block the thread waiting for the result.
248                let (lock, cvar) = &*pair;
249                let mut done = lock.lock();
250                while !*done {
251                    cvar.wait(&mut done);
252                }
253            });
254
255            rx.await.unwrap();
256            let (lock, cvar) = &*pair2;
257            *lock.lock() = true;
258            cvar.notify_one();
259        });
260    }
261
262    #[test]
263    fn worker_init_called_once_per_worker() {
264        static NUM_INIT_CALLS: AtomicU64 = AtomicU64::new(0);
265        fn initialize_test_worker() {
266            NUM_INIT_CALLS.fetch_add(1, Ordering::SeqCst);
267        }
268
269        let mut exec =
270            SendExecutorBuilder::new().num_threads(2).worker_init(initialize_test_worker).build();
271        exec.run(async {});
272        assert_eq!(NUM_INIT_CALLS.load(Ordering::SeqCst), 2);
273        exec.run(async {});
274        assert_eq!(NUM_INIT_CALLS.load(Ordering::SeqCst), 4);
275    }
276}
fuchsia_async/runtime/fuchsia/executor/send.rs

fuchsia_async/runtime/fuchsia/executor/
send.rs
