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// Copyright 2016 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.
use cfg_if::cfg_if;
use core::{
arch::wasm32,
sync::atomic::{AtomicI32, Ordering},
};
use instant::Instant;
use std::time::Duration;
use std::{convert::TryFrom, thread};
cfg_if! {
if #[cfg(all(
target_arch = "wasm32",
target_os = "unknown",
target_vendor = "unknown"
))] {
// This function serves as a polyfill for `Instant::checked_duration_since`, which is
// currently not implemented for wasm32-unknown-unknown.
// TODO: Remove this shim once it
fn checked_duration_since_now(other: Instant) -> Option<Duration> {
let now = Instant::now();
if other < now {
None
} else {
Some(other.duration_since(now))
}
}
} else {
// If we are not targeting wasm32, we can use the native `checked_duration_since`.
fn checked_duration_since_now(timeout: Instant) -> Option<Duration> {
timeout.checked_duration_since(Instant::now())
}
}
}
// Helper type for putting a thread to sleep until some other thread wakes it up
pub struct ThreadParker {
parked: AtomicI32,
}
const UNPARKED: i32 = 0;
const PARKED: i32 = 1;
impl super::ThreadParkerT for ThreadParker {
type UnparkHandle = UnparkHandle;
const IS_CHEAP_TO_CONSTRUCT: bool = true;
#[inline]
fn new() -> ThreadParker {
ThreadParker {
parked: AtomicI32::new(UNPARKED),
}
}
#[inline]
unsafe fn prepare_park(&self) {
self.parked.store(PARKED, Ordering::Relaxed);
}
#[inline]
unsafe fn timed_out(&self) -> bool {
self.parked.load(Ordering::Relaxed) == PARKED
}
#[inline]
unsafe fn park(&self) {
while self.parked.load(Ordering::Acquire) == PARKED {
let r = wasm32::memory_atomic_wait32(self.ptr(), PARKED, -1);
// we should have either woken up (0) or got a not-equal due to a
// race (1). We should never time out (2)
debug_assert!(r == 0 || r == 1);
}
}
#[inline]
unsafe fn park_until(&self, timeout: Instant) -> bool {
while self.parked.load(Ordering::Acquire) == PARKED {
if let Some(left) = checked_duration_since_now(timeout) {
let nanos_left = i64::try_from(left.as_nanos()).unwrap_or(i64::max_value());
let r = wasm32::memory_atomic_wait32(self.ptr(), PARKED, nanos_left);
debug_assert!(r == 0 || r == 1 || r == 2);
} else {
return false;
}
}
true
}
#[inline]
unsafe fn unpark_lock(&self) -> UnparkHandle {
// We don't need to lock anything, just clear the state
self.parked.store(UNPARKED, Ordering::Release);
UnparkHandle(self.ptr())
}
}
impl ThreadParker {
#[inline]
fn ptr(&self) -> *mut i32 {
&self.parked as *const AtomicI32 as *mut i32
}
}
pub struct UnparkHandle(*mut i32);
impl super::UnparkHandleT for UnparkHandle {
#[inline]
unsafe fn unpark(self) {
let num_notified = wasm32::memory_atomic_notify(self.0 as *mut i32, 1);
debug_assert!(num_notified == 0 || num_notified == 1);
}
}
#[inline]
pub fn thread_yield() {
thread::yield_now();
}
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