From 78245286dcde9f2cf99a370ec0cd4383fa684404 Mon Sep 17 00:00:00 2001 From: joboet Date: Sat, 31 Dec 2022 11:00:54 +0100 Subject: [PATCH] std: use id-based thread parking on SOLID --- library/std/src/sys/itron/thread_parking.rs | 37 +++++++ library/std/src/sys/itron/wait_flag.rs | 72 ------------- library/std/src/sys/solid/mod.rs | 4 +- .../std/src/sys_common/thread_parking/mod.rs | 4 +- .../sys_common/thread_parking/wait_flag.rs | 102 ------------------ 5 files changed, 40 insertions(+), 179 deletions(-) create mode 100644 library/std/src/sys/itron/thread_parking.rs delete mode 100644 library/std/src/sys/itron/wait_flag.rs delete mode 100644 library/std/src/sys_common/thread_parking/wait_flag.rs diff --git a/library/std/src/sys/itron/thread_parking.rs b/library/std/src/sys/itron/thread_parking.rs new file mode 100644 index 0000000000000..fe9934439d152 --- /dev/null +++ b/library/std/src/sys/itron/thread_parking.rs @@ -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"); + } + } +} diff --git a/library/std/src/sys/itron/wait_flag.rs b/library/std/src/sys/itron/wait_flag.rs deleted file mode 100644 index e432edd207754..0000000000000 --- a/library/std/src/sys/itron/wait_flag.rs +++ /dev/null @@ -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"); - } -} diff --git a/library/std/src/sys/solid/mod.rs b/library/std/src/sys/solid/mod.rs index 5867979a2a729..923d27fd9369d 100644 --- a/library/std/src/sys/solid/mod.rs +++ b/library/std/src/sys/solid/mod.rs @@ -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; diff --git a/library/std/src/sys_common/thread_parking/mod.rs b/library/std/src/sys_common/thread_parking/mod.rs index 0ead6633c3501..e8e028bb3308f 100644 --- a/library/std/src/sys_common/thread_parking/mod.rs +++ b/library/std/src/sys_common/thread_parking/mod.rs @@ -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 { diff --git a/library/std/src/sys_common/thread_parking/wait_flag.rs b/library/std/src/sys_common/thread_parking/wait_flag.rs deleted file mode 100644 index d0f8899a94eb8..0000000000000 --- a/library/std/src/sys_common/thread_parking/wait_flag.rs +++ /dev/null @@ -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(); - } - } -}