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//! Channel that never delivers messages.
//!
//! Messages cannot be sent into this kind of channel.
use std::marker::PhantomData;
use std::time::Instant;
use crate::context::Context;
use crate::err::{RecvTimeoutError, TryRecvError};
use crate::select::{Operation, SelectHandle, Token};
use crate::utils;
/// This flavor doesn't need a token.
pub(crate) type NeverToken = ();
/// Channel that never delivers messages.
pub(crate) struct Channel<T> {
_marker: PhantomData<T>,
}
impl<T> Channel<T> {
/// Creates a channel that never delivers messages.
#[inline]
pub(crate) fn new() -> Self {
Channel {
_marker: PhantomData,
}
}
/// Attempts to receive a message without blocking.
#[inline]
pub(crate) fn try_recv(&self) -> Result<T, TryRecvError> {
Err(TryRecvError::Empty)
}
/// Receives a message from the channel.
#[inline]
pub(crate) fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
utils::sleep_until(deadline);
Err(RecvTimeoutError::Timeout)
}
/// Reads a message from the channel.
#[inline]
pub(crate) unsafe fn read(&self, _token: &mut Token) -> Result<T, ()> {
Err(())
}
/// Returns `true` if the channel is empty.
#[inline]
pub(crate) fn is_empty(&self) -> bool {
true
}
/// Returns `true` if the channel is full.
#[inline]
pub(crate) fn is_full(&self) -> bool {
true
}
/// Returns the number of messages in the channel.
#[inline]
pub(crate) fn len(&self) -> usize {
0
}
/// Returns the capacity of the channel.
#[inline]
pub(crate) fn capacity(&self) -> Option<usize> {
Some(0)
}
}
impl<T> SelectHandle for Channel<T> {
#[inline]
fn try_select(&self, _token: &mut Token) -> bool {
false
}
#[inline]
fn deadline(&self) -> Option<Instant> {
None
}
#[inline]
fn register(&self, _oper: Operation, _cx: &Context) -> bool {
self.is_ready()
}
#[inline]
fn unregister(&self, _oper: Operation) {}
#[inline]
fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
self.try_select(token)
}
#[inline]
fn is_ready(&self) -> bool {
false
}
#[inline]
fn watch(&self, _oper: Operation, _cx: &Context) -> bool {
self.is_ready()
}
#[inline]
fn unwatch(&self, _oper: Operation) {}
}