| use crate::ffi::{c_int, c_void}; |
| use crate::pin::Pin; |
| use crate::ptr::{null, null_mut}; |
| use crate::sync::atomic::{ |
| AtomicU64, |
| Ordering::{Acquire, Relaxed, Release}, |
| }; |
| use crate::time::Duration; |
| use libc::{_lwp_self, clockid_t, lwpid_t, time_t, timespec, CLOCK_MONOTONIC}; |
| |
| extern "C" { |
| fn ___lwp_park60( |
| clock_id: clockid_t, |
| flags: c_int, |
| ts: *mut timespec, |
| unpark: lwpid_t, |
| hint: *const c_void, |
| unparkhint: *const c_void, |
| ) -> c_int; |
| fn _lwp_unpark(lwp: lwpid_t, hint: *const c_void) -> c_int; |
| } |
| |
| /// The thread is not parked and the token is not available. |
| /// |
| /// Zero cannot be a valid LWP id, since it is used as empty value for the unpark |
| /// argument in _lwp_park. |
| const EMPTY: u64 = 0; |
| /// The token is available. Do not park anymore. |
| const NOTIFIED: u64 = u64::MAX; |
| |
| pub struct Parker { |
| /// The parker state. Contains either one of the two state values above or the LWP |
| /// id of the parked thread. |
| state: AtomicU64, |
| } |
| |
| impl Parker { |
| pub unsafe fn new(parker: *mut Parker) { |
| parker.write(Parker { state: AtomicU64::new(EMPTY) }) |
| } |
| |
| // Does not actually need `unsafe` or `Pin`, but the pthread implementation does. |
| pub unsafe fn park(self: Pin<&Self>) { |
| // If the token has already been made available, we can skip |
| // a bit of work, so check for it here. |
| if self.state.load(Acquire) != NOTIFIED { |
| let parked = _lwp_self() as u64; |
| let hint = self.state.as_mut_ptr().cast(); |
| if self.state.compare_exchange(EMPTY, parked, Relaxed, Acquire).is_ok() { |
| // Loop to guard against spurious wakeups. |
| loop { |
| ___lwp_park60(0, 0, null_mut(), 0, hint, null()); |
| if self.state.load(Acquire) == NOTIFIED { |
| break; |
| } |
| } |
| } |
| } |
| |
| // At this point, the change to NOTIFIED has always been observed with acquire |
| // ordering, so we can just use a relaxed store here (instead of a swap). |
| self.state.store(EMPTY, Relaxed); |
| } |
| |
| // Does not actually need `unsafe` or `Pin`, but the pthread implementation does. |
| pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) { |
| if self.state.load(Acquire) != NOTIFIED { |
| let parked = _lwp_self() as u64; |
| let hint = self.state.as_mut_ptr().cast(); |
| let mut timeout = timespec { |
| // Saturate so that the operation will definitely time out |
| // (even if it is after the heat death of the universe). |
| tv_sec: dur.as_secs().try_into().ok().unwrap_or(time_t::MAX), |
| tv_nsec: dur.subsec_nanos().into(), |
| }; |
| |
| if self.state.compare_exchange(EMPTY, parked, Relaxed, Acquire).is_ok() { |
| // Timeout needs to be mutable since it is modified on NetBSD 9.0 and |
| // above. |
| ___lwp_park60(CLOCK_MONOTONIC, 0, &mut timeout, 0, hint, null()); |
| // Use a swap to get acquire ordering even if the token was set after |
| // the timeout occurred. |
| self.state.swap(EMPTY, Acquire); |
| return; |
| } |
| } |
| |
| self.state.store(EMPTY, Relaxed); |
| } |
| |
| // Does not actually need `Pin`, but the pthread implementation does. |
| pub fn unpark(self: Pin<&Self>) { |
| let state = self.state.swap(NOTIFIED, Release); |
| if !matches!(state, EMPTY | NOTIFIED) { |
| let lwp = state as lwpid_t; |
| let hint = self.state.as_mut_ptr().cast(); |
| |
| // If the parking thread terminated and did not actually park, this will |
| // probably return an error, which is OK. In the worst case, another |
| // thread has received the same LWP id. It will then receive a spurious |
| // wakeup, but those are allowable per the API contract. The same reasoning |
| // applies if a timeout occurred before this call, but the state was not |
| // yet reset. |
| |
| // SAFETY: |
| // The syscall has no invariants to hold. Only unsafe because it is an |
| // extern function. |
| unsafe { |
| _lwp_unpark(lwp, hint); |
| } |
| } |
| } |
| } |