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use std::sync::Arc;
use crossbeam::sync::Parker;
use crate::event::EventRead;
use crate::ring_buffer::{EventWrapper, RingBuffer};
use crate::sequence::Sequence;
use crate::WaitStrategy;
pub struct Subscriber<T> {
ring: Arc<RingBuffer>,
sequence: Arc<Sequence>,
_marker: std::marker::PhantomData<T>,
}
impl<T: 'static> Subscriber<T>
where
T: Send,
{
pub(crate) fn new(ring: Arc<RingBuffer>, sequence: Arc<Sequence>) -> Self {
Self {
ring,
sequence,
_marker: std::marker::PhantomData,
}
}
pub fn sequence(&self) -> u64 {
self.sequence.get()
}
pub(crate) fn read_event<'b>(&self, envelope: EventWrapper) -> Option<EventRead<'b, T>> {
let event_opt: Option<EventRead<T>> = unsafe { envelope.read() };
envelope.stop_waiting();
self.sequence.increment();
return event_opt;
}
pub fn recv<'b>(&self) -> EventRead<'b, T> {
loop {
let sequence = self.sequence.get();
let envelope = self
.ring
.get_envelope(sequence)
.expect("ring buffer was not pre-populated with empty event envelopes")
.clone();
envelope.start_waiting();
let envelope_sequence = envelope.sequence();
if sequence == envelope_sequence {
if let Some(event) = self.read_event(envelope) {
return event;
}
} else if sequence > envelope_sequence {
let parker = Parker::new();
envelope.add_subscriber(Box::new(parker.unparker().clone()));
parker.park();
if let Some(event) = self.read_event(envelope) {
return event;
}
} else {
match self.ring.wait_strategy() {
WaitStrategy::AllSubscribers => unreachable!(),
_ => {
self.sequence.set(envelope_sequence);
}
}
}
}
}
}