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Auto merge of #96510 - m-ou-se:futex-bsd, r=Amanieu

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Use futex-based locks and thread parker on {Free, Open, DragonFly}BSD.

This switches *BSD to our futex-based locks and thread parker.

Tracking issue: https://github.com/rust-lang/rust/issues/93740

This is a draft, because this still needs a new version of the `libc` crate to be published that includes https://github.com/rust-lang/libc/pull/2770.

r? `@Amanieu`
This commit is contained in:
bors 2022-05-06 07:20:04 +00:00
commit 7f9e013ba6
8 changed files with 172 additions and 50 deletions
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4
Cargo.lock
View File

@ -2073,9 +2073,9 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
[[package]]
name = "libc"
version = "0.2.121"
version = "0.2.125"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "efaa7b300f3b5fe8eb6bf21ce3895e1751d9665086af2d64b42f19701015ff4f"
checksum = "5916d2ae698f6de9bfb891ad7a8d65c09d232dc58cc4ac433c7da3b2fd84bc2b"
dependencies = [
"rustc-std-workspace-core",
]

2
library/std/Cargo.toml
View File

@ -15,7 +15,7 @@ cfg-if = { version = "0.1.8", features = ['rustc-dep-of-std'] }
panic_unwind = { path = "../panic_unwind", optional = true }
panic_abort = { path = "../panic_abort" }
core = { path = "../core" }
libc = { version = "0.2.116", default-features = false, features = ['rustc-dep-of-std'] }
libc = { version = "0.2.125", default-features = false, features = ['rustc-dep-of-std'] }
compiler_builtins = { version = "0.1.71" }
profiler_builtins = { path = "../profiler_builtins", optional = true }
unwind = { path = "../unwind" }

21
library/std/src/sync/condvar/tests.rs
View File

@ -188,24 +188,3 @@ fn wait_timeout_wake() {
break;
}
}
#[test]
#[should_panic]
#[cfg(all(unix, not(target_os = "linux"), not(target_os = "android")))]
fn two_mutexes() {
let m = Arc::new(Mutex::new(()));
let m2 = m.clone();
let c = Arc::new(Condvar::new());
let c2 = c.clone();
let mut g = m.lock().unwrap();
let _t = thread::spawn(move || {
let _g = m2.lock().unwrap();
c2.notify_one();
});
g = c.wait(g).unwrap();
drop(g);
let m = Mutex::new(());
let _ = c.wait(m.lock().unwrap()).unwrap();
}

160
library/std/src/sys/unix/futex.rs
View File

@ -1,7 +1,10 @@
#![cfg(any(
target_os = "linux",
target_os = "android",
all(target_os = "emscripten", target_feature = "atomics")
all(target_os = "emscripten", target_feature = "atomics"),
target_os = "freebsd",
target_os = "openbsd",
target_os = "dragonfly",
))]
use crate::sync::atomic::AtomicU32;
@ -12,7 +15,7 @@ use crate::time::Duration;
/// Returns directly if the futex doesn't hold the expected value.
///
/// Returns false on timeout, and true in all other cases.
#[cfg(any(target_os = "linux", target_os = "android"))]
#[cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd"))]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
use super::time::Timespec;
use crate::ptr::null;
@ -30,9 +33,30 @@ pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -
return true;
}
let r = unsafe {
cfg_if::cfg_if! {
if #[cfg(target_os = "freebsd")] {
// FreeBSD doesn't have futex(), but it has
// _umtx_op(UMTX_OP_WAIT_UINT_PRIVATE), which is nearly
// identical. It supports absolute timeouts through a flag
// in the _umtx_time struct.
let umtx_timeout = timespec.map(|t| libc::_umtx_time {
_timeout: t.t,
_flags: libc::UMTX_ABSTIME,
_clockid: libc::CLOCK_MONOTONIC as u32,
});
let umtx_timeout_ptr = umtx_timeout.as_ref().map_or(null(), |t| t as *const _);
let umtx_timeout_size = umtx_timeout.as_ref().map_or(0, |t| crate::mem::size_of_val(t));
libc::_umtx_op(
futex as *const AtomicU32 as *mut _,
libc::UMTX_OP_WAIT_UINT_PRIVATE,
expected as libc::c_ulong,
crate::ptr::invalid_mut(umtx_timeout_size),
umtx_timeout_ptr as *mut _,
)
} else if #[cfg(any(target_os = "linux", target_os = "android"))] {
// Use FUTEX_WAIT_BITSET rather than FUTEX_WAIT to be able to give an
// absolute time rather than a relative time.
let r = unsafe {
libc::syscall(
libc::SYS_futex,
futex as *const AtomicU32,
@ -42,6 +66,10 @@ pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -
null::<u32>(), // This argument is unused for FUTEX_WAIT_BITSET.
!0u32, // A full bitmask, to make it behave like a regular FUTEX_WAIT.
)
} else {
compile_error!("unknown target_os");
}
}
};
match (r < 0).then(super::os::errno) {
@ -56,31 +84,133 @@ pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -
///
/// Returns true if this actually woke up such a thread,
/// or false if no thread was waiting on this futex.
///
/// On some platforms, this always returns false.
#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn futex_wake(futex: &AtomicU32) -> bool {
unsafe {
libc::syscall(
libc::SYS_futex,
futex as *const AtomicU32,
libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
1,
) > 0
}
let ptr = futex as *const AtomicU32;
let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
unsafe { libc::syscall(libc::SYS_futex, ptr, op, 1) > 0 }
}
/// Wake up all threads that are waiting on futex_wait on this futex.
#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn futex_wake_all(futex: &AtomicU32) {
let ptr = futex as *const AtomicU32;
let op = libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG;
unsafe {
libc::syscall(
libc::SYS_futex,
futex as *const AtomicU32,
libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
libc::syscall(libc::SYS_futex, ptr, op, i32::MAX);
}
}
// FreeBSD doesn't tell us how many threads are woken up, so this always returns false.
#[cfg(target_os = "freebsd")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
use crate::ptr::null_mut;
unsafe {
libc::_umtx_op(
futex as *const AtomicU32 as *mut _,
libc::UMTX_OP_WAKE_PRIVATE,
1,
null_mut(),
null_mut(),
)
};
false
}
#[cfg(target_os = "freebsd")]
pub fn futex_wake_all(futex: &AtomicU32) {
use crate::ptr::null_mut;
unsafe {
libc::_umtx_op(
futex as *const AtomicU32 as *mut _,
libc::UMTX_OP_WAKE_PRIVATE,
i32::MAX as libc::c_ulong,
null_mut(),
null_mut(),
)
};
}
#[cfg(target_os = "openbsd")]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
use crate::convert::TryInto;
use crate::ptr::{null, null_mut};
let timespec = timeout.and_then(|d| {
Some(libc::timespec {
// Sleep forever if the timeout is longer than fits in a timespec.
tv_sec: d.as_secs().try_into().ok()?,
// This conversion never truncates, as subsec_nanos is always <1e9.
tv_nsec: d.subsec_nanos() as _,
})
});
let r = unsafe {
libc::futex(
futex as *const AtomicU32 as *mut u32,
libc::FUTEX_WAIT,
expected as i32,
timespec.as_ref().map_or(null(), |t| t as *const libc::timespec),
null_mut(),
)
};
r == 0 || super::os::errno() != libc::ETIMEDOUT
}
#[cfg(target_os = "openbsd")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
use crate::ptr::{null, null_mut};
unsafe {
libc::futex(futex as *const AtomicU32 as *mut u32, libc::FUTEX_WAKE, 1, null(), null_mut())
> 0
}
}
#[cfg(target_os = "openbsd")]
pub fn futex_wake_all(futex: &AtomicU32) {
use crate::ptr::{null, null_mut};
unsafe {
libc::futex(
futex as *const AtomicU32 as *mut u32,
libc::FUTEX_WAKE,
i32::MAX,
null(),
null_mut(),
);
}
}
#[cfg(target_os = "dragonfly")]
pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
use crate::convert::TryFrom;
// A timeout of 0 means infinite.
// We round smaller timeouts up to 1 millisecond.
// Overflows are rounded up to an infinite timeout.
let timeout_ms =
timeout.and_then(|d| Some(i32::try_from(d.as_millis()).ok()?.max(1))).unwrap_or(0);
let r = unsafe {
libc::umtx_sleep(futex as *const AtomicU32 as *const i32, expected as i32, timeout_ms)
};
r == 0 || super::os::errno() != libc::ETIMEDOUT
}
// DragonflyBSD doesn't tell us how many threads are woken up, so this always returns false.
#[cfg(target_os = "dragonfly")]
pub fn futex_wake(futex: &AtomicU32) -> bool {
unsafe { libc::umtx_wakeup(futex as *const AtomicU32 as *const i32, 1) };
false
}
#[cfg(target_os = "dragonfly")]
pub fn futex_wake_all(futex: &AtomicU32) {
unsafe { libc::umtx_wakeup(futex as *const AtomicU32 as *const i32, i32::MAX) };
}
#[cfg(target_os = "emscripten")]
extern "C" {
fn emscripten_futex_wake(addr: *const AtomicU32, count: libc::c_int) -> libc::c_int;

4
library/std/src/sys/unix/locks/futex_rwlock.rs
View File

@ -284,6 +284,10 @@ impl RwLock {
fn wake_writer(&self) -> bool {
self.writer_notify.fetch_add(1, Release);
futex_wake(&self.writer_notify)
// Note that FreeBSD and DragonFlyBSD don't tell us whether they woke
// up any threads or not, and always return `false` here. That still
// results in correct behaviour: it just means readers get woken up as
// well in case both readers and writers were waiting.
}
/// Spin for a while, but stop directly at the given condition.

3
library/std/src/sys/unix/locks/mod.rs
View File

@ -3,6 +3,9 @@ cfg_if::cfg_if! {
target_os = "linux",
target_os = "android",
all(target_os = "emscripten", target_feature = "atomics"),
target_os = "freebsd",
target_os = "openbsd",
target_os = "dragonfly",
))] {
mod futex;
mod futex_rwlock;

5
library/std/src/sys/unix/thread_parker.rs
View File

@ -3,7 +3,10 @@
#![cfg(not(any(
target_os = "linux",
target_os = "android",
all(target_os = "emscripten", target_feature = "atomics")
all(target_os = "emscripten", target_feature = "atomics"),
target_os = "freebsd",
target_os = "openbsd",
target_os = "dragonfly",
)))]
use crate::cell::UnsafeCell;

3
library/std/src/sys_common/thread_parker/mod.rs
View File

@ -3,6 +3,9 @@ cfg_if::cfg_if! {
target_os = "linux",
target_os = "android",
all(target_arch = "wasm32", target_feature = "atomics"),
target_os = "freebsd",
target_os = "openbsd",
target_os = "dragonfly",
))] {
mod futex;
pub use futex::Parker;