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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
use std::sync::{Arc, Condvar, Mutex};
pub struct StateCallback<T> {
callback: Arc<Mutex<Option<Box<dyn FnOnce(T) + Send>>>>,
observer: Arc<Mutex<Option<Box<dyn FnOnce() + Send>>>>,
condition: Arc<(Mutex<bool>, Condvar)>,
}
impl<T> StateCallback<T> {
// This is used for the Condvar, which requires this kind of construction
#[allow(clippy::mutex_atomic)]
pub fn new(cb: Box<dyn FnOnce(T) + Send>) -> Self {
Self {
callback: Arc::new(Mutex::new(Some(cb))),
observer: Arc::new(Mutex::new(None)),
condition: Arc::new((Mutex::new(true), Condvar::new())),
}
}
pub fn add_uncloneable_observer(&mut self, obs: Box<dyn FnOnce() + Send>) {
let mut opt = self.observer.lock().unwrap();
if opt.is_some() {
error!("Replacing an already-set observer.")
}
opt.replace(obs);
}
pub fn call(&self, rv: T) {
if let Some(cb) = self.callback.lock().unwrap().take() {
cb(rv);
if let Some(obs) = self.observer.lock().unwrap().take() {
obs();
}
}
let (lock, cvar) = &*self.condition;
let mut pending = lock.lock().unwrap();
*pending = false;
cvar.notify_all();
}
pub fn wait(&self) {
let (lock, cvar) = &*self.condition;
let _useless_guard = cvar
.wait_while(lock.lock().unwrap(), |pending| *pending)
.unwrap();
}
}
impl<T> Clone for StateCallback<T> {
fn clone(&self) -> Self {
Self {
callback: self.callback.clone(),
observer: Arc::new(Mutex::new(None)),
condition: self.condition.clone(),
}
}
}
#[cfg(test)]
mod tests {
use super::StateCallback;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::{Arc, Barrier};
use std::thread;
#[test]
fn test_statecallback_is_single_use() {
let counter = Arc::new(AtomicUsize::new(0));
let counter_clone = counter.clone();
let sc = StateCallback::new(Box::new(move |_| {
counter_clone.fetch_add(1, Ordering::SeqCst);
}));
assert_eq!(counter.load(Ordering::SeqCst), 0);
for _ in 0..10 {
sc.call(());
assert_eq!(counter.load(Ordering::SeqCst), 1);
}
for _ in 0..10 {
sc.clone().call(());
assert_eq!(counter.load(Ordering::SeqCst), 1);
}
}
#[test]
fn test_statecallback_observer_is_single_use() {
let counter = Arc::new(AtomicUsize::new(0));
let counter_clone = counter.clone();
let mut sc = StateCallback::<()>::new(Box::new(move |_| {}));
sc.add_uncloneable_observer(Box::new(move || {
counter_clone.fetch_add(1, Ordering::SeqCst);
}));
assert_eq!(counter.load(Ordering::SeqCst), 0);
for _ in 0..10 {
sc.call(());
assert_eq!(counter.load(Ordering::SeqCst), 1);
}
for _ in 0..10 {
sc.clone().call(());
assert_eq!(counter.load(Ordering::SeqCst), 1);
}
}
#[test]
fn test_statecallback_observer_only_runs_for_completing_callback() {
let cb_counter = Arc::new(AtomicUsize::new(0));
let cb_counter_clone = cb_counter.clone();
let sc = StateCallback::new(Box::new(move |_| {
cb_counter_clone.fetch_add(1, Ordering::SeqCst);
}));
let obs_counter = Arc::new(AtomicUsize::new(0));
for _ in 0..10 {
let obs_counter_clone = obs_counter.clone();
let mut c = sc.clone();
c.add_uncloneable_observer(Box::new(move || {
obs_counter_clone.fetch_add(1, Ordering::SeqCst);
}));
c.call(());
assert_eq!(cb_counter.load(Ordering::SeqCst), 1);
assert_eq!(obs_counter.load(Ordering::SeqCst), 1);
}
}
#[test]
#[allow(clippy::redundant_clone)]
fn test_statecallback_observer_unclonable() {
let mut sc = StateCallback::<()>::new(Box::new(move |_| {}));
sc.add_uncloneable_observer(Box::new(move || {}));
assert!(sc.observer.lock().unwrap().is_some());
// This is deliberate, to force an extra clone
assert!(sc.clone().observer.lock().unwrap().is_none());
}
#[test]
fn test_statecallback_wait() {
let sc = StateCallback::<()>::new(Box::new(move |_| {}));
let barrier = Arc::new(Barrier::new(2));
{
let c = sc.clone();
let b = barrier.clone();
thread::spawn(move || {
b.wait();
c.call(());
});
}
barrier.wait();
sc.wait();
}
}
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