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| 1 | +use std::{ |
| 2 | + cell::Cell, |
| 3 | + future::Future, |
| 4 | + pin::Pin, |
| 5 | + ptr, |
| 6 | + task::{Context, Poll, RawWaker, RawWakerVTable, Waker}, |
| 7 | + thread, |
| 8 | + time::Duration, |
| 9 | +}; |
| 10 | + |
| 11 | +use crate::Error; |
| 12 | + |
| 13 | +const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new( |
| 14 | + // Cloning just returns a new no-op raw waker |
| 15 | + |_| NOOP_RAW_WAKER, |
| 16 | + // `wake` does nothing |
| 17 | + |_| {}, |
| 18 | + // `wake_by_ref` does nothing |
| 19 | + |_| {}, |
| 20 | + // Dropping does nothing as we don't allocate anything |
| 21 | + |_| {}, |
| 22 | +); |
| 23 | +const NOOP_RAW_WAKER: RawWaker = RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE); |
| 24 | + |
| 25 | +#[derive(Default)] |
| 26 | +pub(super) struct YieldOnce(bool); |
| 27 | + |
| 28 | +impl Future for YieldOnce { |
| 29 | + type Output = (); |
| 30 | + |
| 31 | + fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<()> { |
| 32 | + let flag = &mut std::pin::Pin::into_inner(self).0; |
| 33 | + if !*flag { |
| 34 | + *flag = true; |
| 35 | + Poll::Pending |
| 36 | + } else { |
| 37 | + Poll::Ready(()) |
| 38 | + } |
| 39 | + } |
| 40 | +} |
| 41 | + |
| 42 | +/// Execute the futures and return when they are all done. |
| 43 | +/// |
| 44 | +/// Here we use our own homebrew async executor since cc is used in the build |
| 45 | +/// script of many popular projects, pulling in additional dependencies would |
| 46 | +/// significantly slow down its compilation. |
| 47 | +pub(super) fn block_on<Fut1, Fut2>( |
| 48 | + mut fut1: Fut1, |
| 49 | + mut fut2: Fut2, |
| 50 | + has_made_progress: &Cell<bool>, |
| 51 | +) -> Result<(), Error> |
| 52 | +where |
| 53 | + Fut1: Future<Output = Result<(), Error>>, |
| 54 | + Fut2: Future<Output = Result<(), Error>>, |
| 55 | +{ |
| 56 | + // Shadows the future so that it can never be moved and is guaranteed |
| 57 | + // to be pinned. |
| 58 | + // |
| 59 | + // The same trick used in `pin!` macro. |
| 60 | + // |
| 61 | + // TODO: Once MSRV is bumped to 1.68, replace this with `std::pin::pin!` |
| 62 | + let mut fut1 = Some(unsafe { Pin::new_unchecked(&mut fut1) }); |
| 63 | + let mut fut2 = Some(unsafe { Pin::new_unchecked(&mut fut2) }); |
| 64 | + |
| 65 | + // TODO: Once `Waker::noop` stablised and our MSRV is bumped to the version |
| 66 | + // which it is stablised, replace this wth `Waker::noop`. |
| 67 | + let waker = unsafe { Waker::from_raw(NOOP_RAW_WAKER) }; |
| 68 | + let mut context = Context::from_waker(&waker); |
| 69 | + |
| 70 | + let mut backoff_cnt = 0; |
| 71 | + |
| 72 | + loop { |
| 73 | + has_made_progress.set(false); |
| 74 | + |
| 75 | + if let Some(fut) = fut2.as_mut() { |
| 76 | + if let Poll::Ready(res) = fut.as_mut().poll(&mut context) { |
| 77 | + fut2 = None; |
| 78 | + res?; |
| 79 | + } |
| 80 | + } |
| 81 | + |
| 82 | + if let Some(fut) = fut1.as_mut() { |
| 83 | + if let Poll::Ready(res) = fut.as_mut().poll(&mut context) { |
| 84 | + fut1 = None; |
| 85 | + res?; |
| 86 | + } |
| 87 | + } |
| 88 | + |
| 89 | + if fut1.is_none() && fut2.is_none() { |
| 90 | + return Ok(()); |
| 91 | + } |
| 92 | + |
| 93 | + if !has_made_progress.get() { |
| 94 | + if backoff_cnt > 3 { |
| 95 | + // We have yielded at least three times without making' |
| 96 | + // any progress, so we will sleep for a while. |
| 97 | + let duration = Duration::from_millis(100 * (backoff_cnt - 3).min(10)); |
| 98 | + thread::sleep(duration); |
| 99 | + } else { |
| 100 | + // Given that we spawned a lot of compilation tasks, it is unlikely |
| 101 | + // that OS cannot find other ready task to execute. |
| 102 | + // |
| 103 | + // If all of them are done, then we will yield them and spawn more, |
| 104 | + // or simply return. |
| 105 | + // |
| 106 | + // Thus this will not be turned into a busy-wait loop and it will not |
| 107 | + // waste CPU resource. |
| 108 | + thread::yield_now(); |
| 109 | + } |
| 110 | + } |
| 111 | + |
| 112 | + backoff_cnt = if has_made_progress.get() { |
| 113 | + 0 |
| 114 | + } else { |
| 115 | + backoff_cnt + 1 |
| 116 | + }; |
| 117 | + } |
| 118 | +} |
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