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use super::{Enter, Executor, SpawnError};
use futures::{future, Future};
use std::cell::Cell;
#[derive(Debug, Clone)]
pub struct DefaultExecutor {
_dummy: (),
}
#[derive(Debug)]
pub struct DefaultGuard {
_p: (),
}
impl DefaultExecutor {
pub fn current() -> DefaultExecutor {
DefaultExecutor { _dummy: () }
}
#[inline]
fn with_current<F: FnOnce(&mut dyn Executor) -> R, R>(f: F) -> Option<R> {
EXECUTOR.with(
|current_executor| match current_executor.replace(State::Active) {
State::Ready(executor_ptr) => {
let executor = unsafe { &mut *executor_ptr };
let result = f(executor);
current_executor.set(State::Ready(executor_ptr));
Some(result)
}
State::Empty | State::Active => None,
},
)
}
}
#[derive(Clone, Copy)]
enum State {
Empty,
Ready(*mut dyn Executor),
Active,
}
thread_local! {
static EXECUTOR: Cell<State> = Cell::new(State::Empty)
}
impl super::Executor for DefaultExecutor {
fn spawn(
&mut self,
future: Box<dyn Future<Item = (), Error = ()> + Send>,
) -> Result<(), SpawnError> {
DefaultExecutor::with_current(|executor| executor.spawn(future))
.unwrap_or_else(|| Err(SpawnError::shutdown()))
}
fn status(&self) -> Result<(), SpawnError> {
DefaultExecutor::with_current(|executor| executor.status())
.unwrap_or_else(|| Err(SpawnError::shutdown()))
}
}
impl<T> super::TypedExecutor<T> for DefaultExecutor
where
T: Future<Item = (), Error = ()> + Send + 'static,
{
fn spawn(&mut self, future: T) -> Result<(), SpawnError> {
super::Executor::spawn(self, Box::new(future))
}
fn status(&self) -> Result<(), SpawnError> {
super::Executor::status(self)
}
}
impl<T> future::Executor<T> for DefaultExecutor
where
T: Future<Item = (), Error = ()> + Send + 'static,
{
fn execute(&self, future: T) -> Result<(), future::ExecuteError<T>> {
if let Err(e) = super::Executor::status(self) {
let kind = if e.is_at_capacity() {
future::ExecuteErrorKind::NoCapacity
} else {
future::ExecuteErrorKind::Shutdown
};
return Err(future::ExecuteError::new(kind, future));
}
let _ = DefaultExecutor::with_current(|executor| executor.spawn(Box::new(future)));
Ok(())
}
}
pub fn spawn<T>(future: T)
where
T: Future<Item = (), Error = ()> + Send + 'static,
{
DefaultExecutor::current().spawn(Box::new(future)).unwrap()
}
pub fn with_default<T, F, R>(executor: &mut T, enter: &mut Enter, f: F) -> R
where
T: Executor,
F: FnOnce(&mut Enter) -> R,
{
unsafe fn hide_lt<'a>(p: *mut (dyn Executor + 'a)) -> *mut (dyn Executor + 'static) {
use std::mem;
mem::transmute(p)
}
EXECUTOR.with(|cell| {
match cell.get() {
State::Ready(_) | State::Active => {
panic!("default executor already set for execution context")
}
_ => {}
}
struct Reset<'a>(&'a Cell<State>);
impl<'a> Drop for Reset<'a> {
fn drop(&mut self) {
self.0.set(State::Empty);
}
}
let _reset = Reset(cell);
let executor = unsafe { hide_lt(executor as &mut _ as *mut _) };
cell.set(State::Ready(executor));
f(enter)
})
}
pub fn set_default<T>(executor: T) -> DefaultGuard
where
T: Executor + 'static,
{
EXECUTOR.with(|cell| {
match cell.get() {
State::Ready(_) | State::Active => {
panic!("default executor already set for execution context")
}
_ => {}
}
let executor = Box::new(executor);
cell.set(State::Ready(Box::into_raw(executor)));
});
DefaultGuard { _p: () }
}
impl Drop for DefaultGuard {
fn drop(&mut self) {
let _ = EXECUTOR.try_with(|cell| {
if let State::Ready(prev) = cell.replace(State::Empty) {
unsafe {
let prev = Box::from_raw(prev);
drop(prev);
};
}
});
}
}
#[cfg(test)]
mod tests {
use super::{with_default, DefaultExecutor, Executor};
#[test]
fn default_executor_is_send_and_sync() {
fn assert_send_sync<T: Send + Sync>() {}
assert_send_sync::<DefaultExecutor>();
}
#[test]
fn nested_default_executor_status() {
let mut enter = super::super::enter().unwrap();
let mut executor = DefaultExecutor::current();
let result = with_default(&mut executor, &mut enter, |_| {
DefaultExecutor::current().status()
});
assert!(result.err().unwrap().is_shutdown())
}
}