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#![cfg(any(
target_os = "linux",
target_os = "android",
all(target_os = "emscripten", target_feature = "atomics")
))]
use crate::sync::atomic::AtomicI32;
use crate::time::Duration;
/// Wait for a futex_wake operation to wake us.
///
/// 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"))]
pub fn futex_wait(futex: &AtomicI32, expected: i32, timeout: Option<Duration>) -> bool {
use super::time::Timespec;
use crate::ptr::null;
use crate::sync::atomic::Ordering::Relaxed;
// Calculate the timeout as an absolute timespec.
//
// Overflows are rounded up to an infinite timeout (None).
let timespec =
timeout.and_then(|d| Some(Timespec::now(libc::CLOCK_MONOTONIC).checked_add_duration(&d)?));
loop {
// No need to wait if the value already changed.
if futex.load(Relaxed) != expected {
return true;
}
// 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 AtomicI32,
libc::FUTEX_WAIT_BITSET | libc::FUTEX_PRIVATE_FLAG,
expected,
timespec.as_ref().map_or(null(), |t| &t.t as *const libc::timespec),
null::<u32>(), // This argument is unused for FUTEX_WAIT_BITSET.
!0u32, // A full bitmask, to make it behave like a regular FUTEX_WAIT.
)
};
match (r < 0).then(super::os::errno) {
Some(libc::ETIMEDOUT) => return false,
Some(libc::EINTR) => continue,
_ => return true,
}
}
}
#[cfg(target_os = "emscripten")]
pub fn futex_wait(futex: &AtomicI32, expected: i32, timeout: Option<Duration>) {
extern "C" {
fn emscripten_futex_wait(
addr: *const AtomicI32,
val: libc::c_uint,
max_wait_ms: libc::c_double,
) -> libc::c_int;
}
unsafe {
emscripten_futex_wait(
futex as *const AtomicI32,
// `val` is declared unsigned to match the Emscripten headers, but since it's used as
// an opaque value, we can ignore the meaning of signed vs. unsigned and cast here.
expected as libc::c_uint,
timeout.map_or(crate::f64::INFINITY, |d| d.as_secs_f64() * 1000.0),
);
}
}
/// Wake up one thread that's blocked on futex_wait on this futex.
///
/// Returns true if this actually woke up such a thread,
/// or false if no thread was waiting on this futex.
#[cfg(any(target_os = "linux", target_os = "android"))]
pub fn futex_wake(futex: &AtomicI32) -> bool {
unsafe {
libc::syscall(
libc::SYS_futex,
futex as *const AtomicI32,
libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
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: &AtomicI32) {
unsafe {
libc::syscall(
libc::SYS_futex,
futex as *const AtomicI32,
libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
i32::MAX,
);
}
}
#[cfg(target_os = "emscripten")]
pub fn futex_wake(futex: &AtomicI32) -> bool {
extern "C" {
fn emscripten_futex_wake(addr: *const AtomicI32, count: libc::c_int) -> libc::c_int;
}
unsafe { emscripten_futex_wake(futex as *const AtomicI32, 1) > 0 }
}
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