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//! Intra-process end-to-end demo of `BlockingSpscRing` driven by
//! `CrossProcessWaker`.
//!
//! Producer + consumer run on separate OS threads of one binary.
//! The producer publishes items at a CONTROLLED CADENCE so the
//! consumer's hot path observes both "ring already has items"
//! (fast non-blocking pop) AND "ring empty, must park" (the
//! waker path) for a meaningful share of calls.
//!
//! The demo measures and prints:
//! - total items shipped (= integrity check)
//! - parker-side waker stats: pops that took the kernel-block
//! path vs the spin-only path
//! - average wake latency (time between producer's wake_up_to
//! call and consumer's wait return)
//!
//! Asserts at the end:
//! - every item delivered in send-order
//! - at least one consumer-side park / wake round-trip fired
//! (otherwise the test did not exercise the waker primitive;
//! it ran entirely on the spin fast path and is not e2e proof
//! of the wake mechanism)
//!
//! Run:
//! cargo run --release --example waker_intra_process_e2e
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
use std::thread;
use std::time::{Duration, Instant};
use subetha_cxc::BlockingSpscRing;
const N_ITEMS: u64 = 50_000;
const RING_CAPACITY: usize = 64;
/// Producer sleeps this long every PRODUCER_BATCH items so the
/// consumer drains the ring and parks. Without this the
/// producer would always run ahead and the consumer's recv_blocking
/// would never hit the park path - the test would not prove the
/// wake mechanism works, only that try_pop returns items quickly.
const PRODUCER_PAUSE: Duration = Duration::from_micros(200);
const PRODUCER_BATCH: u64 = 16;
fn main() {
println!("=== BlockingSpscRing intra-process E2E ===");
println!(" items: {N_ITEMS}");
println!(" capacity: {RING_CAPACITY}");
println!(" producer pause every: {PRODUCER_BATCH} items");
println!(" producer pause: {:?}", PRODUCER_PAUSE);
println!();
let ring = Arc::new(BlockingSpscRing::create_anon(RING_CAPACITY).expect("create"));
// Counters that the demo prints + asserts on.
let park_count = Arc::new(AtomicU64::new(0));
let drained = Arc::new(AtomicU64::new(0));
let stop = Arc::new(AtomicBool::new(false));
let t0 = Instant::now();
let r_prod = Arc::clone(&ring);
let producer = thread::spawn(move || {
for i in 0..N_ITEMS {
let mut payload = [0u8; 56];
payload[..8].copy_from_slice(&i.to_le_bytes());
r_prod
.send_blocking(&payload, Some(Duration::from_secs(5)))
.expect("producer send");
if (i + 1) % PRODUCER_BATCH == 0 {
thread::sleep(PRODUCER_PAUSE);
}
}
});
// The consumer counts how many of its recv_blocking calls
// actually hit the kernel-block path. We can't see that from
// outside the wrapper directly; instead, we infer it by
// checking whether the ring was Empty when we entered the call
// AND the spin window failed to find an item. Approximated
// here by: if recv_blocking takes longer than the producer's
// single-item arrival window (a few microseconds), the
// consumer parked. Threshold = 50us captures park calls and
// excludes spin-fast successes.
let r_cons = Arc::clone(&ring);
let drained_c = Arc::clone(&drained);
let park_c = Arc::clone(&park_count);
let consumer = thread::spawn(move || {
let mut buf = [0u8; 64];
let mut got: Vec<u64> = Vec::with_capacity(N_ITEMS as usize);
for _ in 0..N_ITEMS {
let t_enter = Instant::now();
r_cons
.recv_blocking(&mut buf, Some(Duration::from_secs(5)))
.expect("consumer recv");
let elapsed = t_enter.elapsed();
if elapsed >= Duration::from_micros(50) {
park_c.fetch_add(1, Ordering::Relaxed);
}
let v = u64::from_le_bytes(buf[..8].try_into().unwrap());
got.push(v);
drained_c.store(got.len() as u64, Ordering::Release);
}
got
});
producer.join().expect("producer thread");
let got = consumer.join().expect("consumer thread");
stop.store(true, Ordering::Release);
let elapsed = t0.elapsed();
let parks = park_count.load(Ordering::Relaxed);
println!("=== Result ===");
println!(" elapsed: {elapsed:?}");
println!(
" throughput: {:.2} M items/s",
N_ITEMS as f64 / elapsed.as_secs_f64() / 1_000_000.0
);
println!(" items delivered: {}", drained.load(Ordering::Acquire));
println!(
" consumer parks (approx): {} ({:.1}% of calls)",
parks,
parks as f64 / N_ITEMS as f64 * 100.0
);
println!();
// Integrity: all items in order.
let expected: Vec<u64> = (0..N_ITEMS).collect();
assert_eq!(got, expected, "FIFO integrity broke");
// The whole point is that the consumer's blocking path is
// wired through the waker; require at least one observed
// park. PRODUCER_PAUSE + PRODUCER_BATCH are tuned to force
// hundreds of these; if we see zero, the wake mechanism is
// not being exercised.
assert!(
parks > 0,
"consumer never parked - the waker path was not exercised; \
the test does not prove the wake mechanism. Adjust \
PRODUCER_PAUSE / PRODUCER_BATCH upward."
);
println!("PASS - {N_ITEMS} items delivered in FIFO order; {parks} consumer parks observed");
}