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//! Mutex implementation backed by μITRON mutexes. Assumes `acre_mtx` and
//! `TA_INHERIT` are available.
use super::{
abi,
error::{expect_success, expect_success_aborting, fail, ItronError},
spin::SpinIdOnceCell,
};
pub struct Mutex {
/// The ID of the underlying mutex object
mtx: SpinIdOnceCell<()>,
}
pub type MovableMutex = Mutex;
/// Create a mutex object. This function never panics.
fn new_mtx() -> Result<abi::ID, ItronError> {
ItronError::err_if_negative(unsafe {
abi::acre_mtx(&abi::T_CMTX {
// Priority inheritance mutex
mtxatr: abi::TA_INHERIT,
// Unused
ceilpri: 0,
})
})
}
impl Mutex {
#[inline]
pub const fn new() -> Mutex {
Mutex { mtx: SpinIdOnceCell::new() }
}
pub unsafe fn init(&mut self) {
// Initialize `self.mtx` eagerly
let id = new_mtx().unwrap_or_else(|e| fail(e, &"acre_mtx"));
unsafe { self.mtx.set_unchecked((id, ())) };
}
/// Get the inner mutex's ID, which is lazily created.
fn raw(&self) -> abi::ID {
match self.mtx.get_or_try_init(|| new_mtx().map(|id| (id, ()))) {
Ok((id, ())) => id,
Err(e) => fail(e, &"acre_mtx"),
}
}
pub unsafe fn lock(&self) {
let mtx = self.raw();
expect_success(unsafe { abi::loc_mtx(mtx) }, &"loc_mtx");
}
pub unsafe fn unlock(&self) {
let mtx = unsafe { self.mtx.get_unchecked().0 };
expect_success_aborting(unsafe { abi::unl_mtx(mtx) }, &"unl_mtx");
}
pub unsafe fn try_lock(&self) -> bool {
let mtx = self.raw();
match unsafe { abi::ploc_mtx(mtx) } {
abi::E_TMOUT => false,
er => {
expect_success(er, &"ploc_mtx");
true
}
}
}
}
impl Drop for Mutex {
fn drop(&mut self) {
if let Some(mtx) = self.mtx.get().map(|x| x.0) {
expect_success_aborting(unsafe { abi::del_mtx(mtx) }, &"del_mtx");
}
}
}
pub(super) struct MutexGuard<'a>(&'a Mutex);
impl<'a> MutexGuard<'a> {
#[inline]
pub(super) fn lock(x: &'a Mutex) -> Self {
unsafe { x.lock() };
Self(x)
}
}
impl Drop for MutexGuard<'_> {
#[inline]
fn drop(&mut self) {
unsafe { self.0.unlock() };
}
}
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