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use super::{Executor, Enter, SpawnError};
use futures::Future;
use std::cell::Cell;
#[cfg(feature = "unstable-futures")]
use futures2;
#[derive(Debug, Clone)]
pub struct DefaultExecutor {
_dummy: (),
}
impl DefaultExecutor {
pub fn current() -> DefaultExecutor {
DefaultExecutor {
_dummy: (),
}
}
#[inline]
fn with_current<F: FnOnce(&mut 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 Executor),
Active
}
thread_local!(static EXECUTOR: Cell<State> = Cell::new(State::Empty));
impl super::Executor for DefaultExecutor {
fn spawn(&mut self, future: Box<Future<Item = (), Error = ()> + Send>)
-> Result<(), SpawnError>
{
DefaultExecutor::with_current(|executor| executor.spawn(future))
.unwrap_or_else(|| Err(SpawnError::shutdown()))
}
#[cfg(feature = "unstable-futures")]
fn spawn2(&mut self, future: Box<futures2::Future<Item = (), Error = futures2::Never> + Send>)
-> Result<(), futures2::executor::SpawnError>
{
DefaultExecutor::with_current(|executor| executor.spawn2(future))
.unwrap_or_else(|| Err(futures2::executor::SpawnError::shutdown()))
}
fn status(&self) -> Result<(), SpawnError> {
DefaultExecutor::with_current(|executor| executor.status())
.unwrap_or_else(|| Err(SpawnError::shutdown()))
}
}
pub fn spawn<T>(future: T)
where T: Future<Item = (), Error = ()> + Send + 'static,
{
DefaultExecutor::current().spawn(Box::new(future))
.unwrap()
}
#[cfg(feature = "unstable-futures")]
pub fn spawn2<T>(future: T)
where T: futures2::Future<Item = (), Error = futures2::Never> + Send + 'static,
{
DefaultExecutor::current().spawn2(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
{
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)
})
}
unsafe fn hide_lt<'a>(p: *mut (Executor + 'a)) -> *mut (Executor + 'static) {
use std::mem;
mem::transmute(p)
}
#[cfg(test)]
mod tests {
use super::{Executor, DefaultExecutor, with_default};
#[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())
}
}