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use std::cell::{Cell, RefCell};
use std::sync::Arc;
pub trait Executor: Send + Sync + 'static {
fn execute<F>(&self, f: F)
where F: FnOnce() + Send + 'static,
Self: Sized
{
self.execute_boxed(Box::new(f))
}
fn execute_boxed(&self, f: Box<ExecuteCallback>);
}
pub static DEFAULT: Limited = Limited;
impl<T: Executor + ?Sized + Send + Sync + 'static> Executor for Box<T> {
fn execute_boxed(&self, f: Box<ExecuteCallback>) {
(**self).execute_boxed(f)
}
}
impl<T: Executor + ?Sized + Send + Sync + 'static> Executor for Arc<T> {
fn execute_boxed(&self, f: Box<ExecuteCallback>) {
(**self).execute_boxed(f)
}
}
pub trait ExecuteCallback: Send + 'static {
#[allow(missing_docs)]
fn call(self: Box<Self>);
}
impl<F: FnOnce() + Send + 'static> ExecuteCallback for F {
fn call(self: Box<F>) {
(*self)()
}
}
pub struct Inline;
impl Executor for Inline {
fn execute<F: FnOnce() + Send + 'static>(&self, f: F) {
f()
}
fn execute_boxed(&self, f: Box<ExecuteCallback>) {
f.call()
}
}
pub struct Limited;
thread_local!(static LIMITED: LimitState = LimitState::new());
const LIMIT: usize = 100;
struct LimitState {
count: Cell<usize>,
deferred: RefCell<Vec<Box<ExecuteCallback>>>,
}
impl Executor for Limited {
fn execute<F>(&self, f: F) where F: FnOnce() + Send + 'static {
LIMITED.with(|state| state.execute(f))
}
fn execute_boxed(&self, f: Box<ExecuteCallback>) {
self.execute(|| f.call());
}
}
impl LimitState {
fn new() -> LimitState {
LimitState {
count: Cell::new(0),
deferred: RefCell::new(Vec::new()),
}
}
fn execute<F>(&self, f: F) where F: FnOnce() + Send + 'static {
match self.count.get() {
0 => {
self.count.set(1);
f();
loop {
let cb = self.deferred.borrow_mut().pop();
match cb {
Some(f) => f.call(),
None => break,
}
}
self.count.set(0);
}
n if n < LIMIT => {
self.count.set(n + 1);
f();
self.count.set(n);
}
_ => self.deferred.borrow_mut().push(Box::new(f)),
}
}
}
#[cfg(test)]
mod tests {
use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, Ordering};
use super::{Executor, Limited};
#[test]
fn limited() {
fn doit(ex: Arc<Executor>, hits: Arc<AtomicUsize>, i: usize) {
if i == 0 {
return
}
hits.fetch_add(1, Ordering::SeqCst);
let ex2 = ex.clone();
ex.execute(move || {
doit(ex2, hits, i - 1);
})
}
let n = 1_000_000;
let hits = Arc::new(AtomicUsize::new(0));
doit(Arc::new(Limited), hits.clone(), n);
assert_eq!(hits.load(Ordering::SeqCst), n);
}
}