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40 lines
1.3 KiB
40 lines
1.3 KiB
//! Benchmark the overhead that the synchronization of `OnceCell::get` causes.
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//! We do some other operations that write to memory to get an imprecise but somewhat realistic
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//! measurement.
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use once_cell::sync::OnceCell;
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use std::sync::atomic::{AtomicUsize, Ordering};
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const N_THREADS: usize = 16;
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const N_ROUNDS: usize = 1_000_000;
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static CELL: OnceCell<usize> = OnceCell::new();
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static OTHER: AtomicUsize = AtomicUsize::new(0);
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fn main() {
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let start = std::time::Instant::now();
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let threads =
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(0..N_THREADS).map(|i| std::thread::spawn(move || thread_main(i))).collect::<Vec<_>>();
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for thread in threads {
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thread.join().unwrap();
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}
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println!("{:?}", start.elapsed());
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println!("{:?}", OTHER.load(Ordering::Relaxed));
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}
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#[inline(never)]
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fn thread_main(i: usize) {
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// The operations we do here don't really matter, as long as we do multiple writes, and
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// everything is messy enough to prevent the compiler from optimizing the loop away.
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let mut data = [i; 128];
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let mut accum = 0usize;
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for _ in 0..N_ROUNDS {
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let _value = CELL.get_or_init(|| i + 1);
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let k = OTHER.fetch_add(data[accum & 0x7F] as usize, Ordering::Relaxed);
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for j in data.iter_mut() {
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*j = (*j).wrapping_add(accum);
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accum = accum.wrapping_add(k);
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}
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}
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}
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