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std: use id-based thread parking on SOLID

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joboet 2022-12-31 11:00:54 +01:00
parent 247e44e61d
commit 78245286dc
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GPG Key ID: 704E0149B0194B3C
5 changed files with 40 additions and 179 deletions
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37
library/std/src/sys/itron/thread_parking.rs Normal file
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@ -0,0 +1,37 @@
use super::abi;
use super::error::expect_success_aborting;
use super::time::with_tmos;
use crate::time::Duration;
pub type ThreadId = abi::ID;
pub use super::task::current_task_id_aborting as current;
pub fn park(_hint: usize) {
match unsafe { abi::slp_tsk() } {
abi::E_OK | abi::E_RLWAI => {}
err => {
expect_success_aborting(err, &"slp_tsk");
}
}
}
pub fn park_timeout(dur: Duration, _hint: usize) {
match with_tmos(dur, |tmo| unsafe { abi::tslp_tsk(tmo) }) {
abi::E_OK | abi::E_RLWAI | abi::E_TMOUT => {}
err => {
expect_success_aborting(err, &"tslp_tsk");
}
}
}
pub fn unpark(id: ThreadId, _hint: usize) {
match unsafe { abi::wup_tsk(id) } {
// It is allowed to try to wake up a destroyed or unrelated task, so we ignore all
// errors that could result from that situation.
abi::E_OK | abi::E_NOEXS | abi::E_OBJ | abi::E_QOVR => {}
err => {
expect_success_aborting(err, &"wup_tsk");
}
}
}

72
library/std/src/sys/itron/wait_flag.rs
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@ -1,72 +0,0 @@
use crate::mem::MaybeUninit;
use crate::time::Duration;
use super::{
abi,
error::{expect_success, fail},
time::with_tmos,
};
const CLEAR: abi::FLGPTN = 0;
const RAISED: abi::FLGPTN = 1;
/// A thread parking primitive that is not susceptible to race conditions,
/// but provides no atomic ordering guarantees and allows only one `raise` per wait.
pub struct WaitFlag {
flag: abi::ID,
}
impl WaitFlag {
/// Creates a new wait flag.
pub fn new() -> WaitFlag {
let flag = expect_success(
unsafe {
abi::acre_flg(&abi::T_CFLG {
flgatr: abi::TA_FIFO | abi::TA_WSGL | abi::TA_CLR,
iflgptn: CLEAR,
})
},
&"acre_flg",
);
WaitFlag { flag }
}
/// Wait for the wait flag to be raised.
pub fn wait(&self) {
let mut token = MaybeUninit::uninit();
expect_success(
unsafe { abi::wai_flg(self.flag, RAISED, abi::TWF_ORW, token.as_mut_ptr()) },
&"wai_flg",
);
}
/// Wait for the wait flag to be raised or the timeout to occur.
///
/// Returns whether the flag was raised (`true`) or the operation timed out (`false`).
pub fn wait_timeout(&self, dur: Duration) -> bool {
let mut token = MaybeUninit::uninit();
let res = with_tmos(dur, |tmout| unsafe {
abi::twai_flg(self.flag, RAISED, abi::TWF_ORW, token.as_mut_ptr(), tmout)
});
match res {
abi::E_OK => true,
abi::E_TMOUT => false,
error => fail(error, &"twai_flg"),
}
}
/// Raise the wait flag.
///
/// Calls to this function should be balanced with the number of successful waits.
pub fn raise(&self) {
expect_success(unsafe { abi::set_flg(self.flag, RAISED) }, &"set_flg");
}
}
impl Drop for WaitFlag {
fn drop(&mut self) {
expect_success(unsafe { abi::del_flg(self.flag) }, &"del_flg");
}
}

4
library/std/src/sys/solid/mod.rs
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@ -13,9 +13,9 @@ mod itron {
pub(super) mod spin;
pub(super) mod task;
pub mod thread;
pub mod thread_parking;
pub(super) mod time;
use super::unsupported;
pub mod wait_flag;
}
pub mod alloc;
@ -43,8 +43,8 @@ pub use self::itron::thread;
pub mod memchr;
pub mod thread_local_dtor;
pub mod thread_local_key;
pub use self::itron::thread_parking;
pub mod time;
pub use self::itron::wait_flag;
mod rwlock;

4
library/std/src/sys_common/thread_parking/mod.rs
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@ -14,12 +14,10 @@ cfg_if::cfg_if! {
} else if #[cfg(any(
target_os = "netbsd",
all(target_vendor = "fortanix", target_env = "sgx"),
target_os = "solid_asp3",
))] {
mod id;
pub use id::Parker;
} else if #[cfg(target_os = "solid_asp3")] {
mod wait_flag;
pub use wait_flag::Parker;
} else if #[cfg(any(windows, target_family = "unix"))] {
pub use crate::sys::thread_parking::Parker;
} else {

102
library/std/src/sys_common/thread_parking/wait_flag.rs
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@ -1,102 +0,0 @@
//! A wait-flag-based thread parker.
//!
//! Some operating systems provide low-level parking primitives like wait counts,
//! event flags or semaphores which are not susceptible to race conditions (meaning
//! the wakeup can occur before the wait operation). To implement the `std` thread
//! parker on top of these primitives, we only have to ensure that parking is fast
//! when the thread token is available, the atomic ordering guarantees are maintained
//! and spurious wakeups are minimized.
//!
//! To achieve this, this parker uses an atomic variable with three states: `EMPTY`,
//! `PARKED` and `NOTIFIED`:
//! * `EMPTY` means the token has not been made available, but the thread is not
//! currently waiting on it.
//! * `PARKED` means the token is not available and the thread is parked.
//! * `NOTIFIED` means the token is available.
//!
//! `park` and `park_timeout` change the state from `EMPTY` to `PARKED` and from
//! `NOTIFIED` to `EMPTY`. If the state was `NOTIFIED`, the thread was unparked and
//! execution can continue without calling into the OS. If the state was `EMPTY`,
//! the token is not available and the thread waits on the primitive (here called
//! "wait flag").
//!
//! `unpark` changes the state to `NOTIFIED`. If the state was `PARKED`, the thread
//! is or will be sleeping on the wait flag, so we raise it.
use crate::pin::Pin;
use crate::sync::atomic::AtomicI8;
use crate::sync::atomic::Ordering::{Acquire, Relaxed, Release};
use crate::sys::wait_flag::WaitFlag;
use crate::time::Duration;
const EMPTY: i8 = 0;
const PARKED: i8 = -1;
const NOTIFIED: i8 = 1;
pub struct Parker {
state: AtomicI8,
wait_flag: WaitFlag,
}
impl Parker {
/// Construct a parker for the current thread. The UNIX parker
/// implementation requires this to happen in-place.
pub unsafe fn new_in_place(parker: *mut Parker) {
parker.write(Parker { state: AtomicI8::new(EMPTY), wait_flag: WaitFlag::new() })
}
// This implementation doesn't require `unsafe` and `Pin`, but other implementations do.
pub unsafe fn park(self: Pin<&Self>) {
match self.state.fetch_sub(1, Acquire) {
// NOTIFIED => EMPTY
NOTIFIED => return,
// EMPTY => PARKED
EMPTY => (),
_ => panic!("inconsistent park state"),
}
// Avoid waking up from spurious wakeups (these are quite likely, see below).
loop {
self.wait_flag.wait();
match self.state.compare_exchange(NOTIFIED, EMPTY, Acquire, Relaxed) {
Ok(_) => return,
Err(PARKED) => (),
Err(_) => panic!("inconsistent park state"),
}
}
}
// This implementation doesn't require `unsafe` and `Pin`, but other implementations do.
pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) {
match self.state.fetch_sub(1, Acquire) {
NOTIFIED => return,
EMPTY => (),
_ => panic!("inconsistent park state"),
}
self.wait_flag.wait_timeout(dur);
// Either a wakeup or a timeout occurred. Wakeups may be spurious, as there can be
// a race condition when `unpark` is performed between receiving the timeout and
// resetting the state, resulting in the eventflag being set unnecessarily. `park`
// is protected against this by looping until the token is actually given, but
// here we cannot easily tell.
// Use `swap` to provide acquire ordering.
match self.state.swap(EMPTY, Acquire) {
NOTIFIED => (),
PARKED => (),
_ => panic!("inconsistent park state"),
}
}
// This implementation doesn't require `Pin`, but other implementations do.
pub fn unpark(self: Pin<&Self>) {
let state = self.state.swap(NOTIFIED, Release);
if state == PARKED {
self.wait_flag.raise();
}
}
}