From 246f239d9f40f633160f0c18f87a20922d4e77bb Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:06:37 +0200 Subject: Merging debian version 1.65.0+dfsg1-2. Signed-off-by: Daniel Baumann --- library/std/src/sys/unix/thread_parker/netbsd.rs | 113 +++++++++++++++++++++++ 1 file changed, 113 insertions(+) create mode 100644 library/std/src/sys/unix/thread_parker/netbsd.rs (limited to 'library/std/src/sys/unix/thread_parker/netbsd.rs') diff --git a/library/std/src/sys/unix/thread_parker/netbsd.rs b/library/std/src/sys/unix/thread_parker/netbsd.rs new file mode 100644 index 000000000..7657605b5 --- /dev/null +++ b/library/std/src/sys/unix/thread_parker/netbsd.rs @@ -0,0 +1,113 @@ +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); + } + } + } +} -- cgit v1.2.3