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|
use crate::{
cfg::{self, CfgPrivate},
page,
sync::{
atomic::{AtomicUsize, Ordering},
lazy_static, thread_local, Mutex,
},
Pack,
};
use std::{
cell::{Cell, UnsafeCell},
collections::VecDeque,
fmt,
marker::PhantomData,
};
/// Uniquely identifies a thread.
pub(crate) struct Tid<C> {
id: usize,
_not_send: PhantomData<UnsafeCell<()>>,
_cfg: PhantomData<fn(C)>,
}
#[derive(Debug)]
struct Registration(Cell<Option<usize>>);
struct Registry {
next: AtomicUsize,
free: Mutex<VecDeque<usize>>,
}
lazy_static! {
static ref REGISTRY: Registry = Registry {
next: AtomicUsize::new(0),
free: Mutex::new(VecDeque::new()),
};
}
thread_local! {
static REGISTRATION: Registration = Registration::new();
}
// === impl Tid ===
impl<C: cfg::Config> Pack<C> for Tid<C> {
const LEN: usize = C::MAX_SHARDS.trailing_zeros() as usize + 1;
type Prev = page::Addr<C>;
#[inline(always)]
fn as_usize(&self) -> usize {
self.id
}
#[inline(always)]
fn from_usize(id: usize) -> Self {
Self {
id,
_not_send: PhantomData,
_cfg: PhantomData,
}
}
}
impl<C: cfg::Config> Tid<C> {
#[inline]
pub(crate) fn current() -> Self {
REGISTRATION
.try_with(Registration::current)
.unwrap_or_else(|_| Self::poisoned())
}
pub(crate) fn is_current(self) -> bool {
REGISTRATION
.try_with(|r| self == r.current::<C>())
.unwrap_or(false)
}
#[inline(always)]
pub fn new(id: usize) -> Self {
Self::from_usize(id)
}
}
impl<C> Tid<C> {
#[cold]
fn poisoned() -> Self {
Self {
id: std::usize::MAX,
_not_send: PhantomData,
_cfg: PhantomData,
}
}
/// Returns true if the local thread ID was accessed while unwinding.
pub(crate) fn is_poisoned(&self) -> bool {
self.id == std::usize::MAX
}
}
impl<C> fmt::Debug for Tid<C> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
if self.is_poisoned() {
f.debug_tuple("Tid")
.field(&format_args!("<poisoned>"))
.finish()
} else {
f.debug_tuple("Tid")
.field(&format_args!("{}", self.id))
.finish()
}
}
}
impl<C> PartialEq for Tid<C> {
fn eq(&self, other: &Self) -> bool {
self.id == other.id
}
}
impl<C> Eq for Tid<C> {}
impl<C: cfg::Config> Clone for Tid<C> {
fn clone(&self) -> Self {
*self
}
}
impl<C: cfg::Config> Copy for Tid<C> {}
// === impl Registration ===
impl Registration {
fn new() -> Self {
Self(Cell::new(None))
}
#[inline(always)]
fn current<C: cfg::Config>(&self) -> Tid<C> {
if let Some(tid) = self.0.get().map(Tid::new) {
return tid;
}
self.register()
}
#[cold]
fn register<C: cfg::Config>(&self) -> Tid<C> {
let id = REGISTRY
.free
.lock()
.ok()
.and_then(|mut free| {
if free.len() > 1 {
free.pop_front()
} else {
None
}
})
.unwrap_or_else(|| {
let id = REGISTRY.next.fetch_add(1, Ordering::AcqRel);
if id > Tid::<C>::BITS {
panic_in_drop!(
"creating a new thread ID ({}) would exceed the \
maximum number of thread ID bits specified in {} \
({})",
id,
std::any::type_name::<C>(),
Tid::<C>::BITS,
);
}
id
});
self.0.set(Some(id));
Tid::new(id)
}
}
// Reusing thread IDs doesn't work under loom, since this `Drop` impl results in
// an access to a `loom` lazy_static while the test is shutting down, which
// panics. T_T
// Just skip TID reuse and use loom's lazy_static macro to ensure we have a
// clean initial TID on every iteration, instead.
#[cfg(not(all(loom, any(feature = "loom", test))))]
impl Drop for Registration {
fn drop(&mut self) {
use std::sync::PoisonError;
if let Some(id) = self.0.get() {
let mut free_list = REGISTRY.free.lock().unwrap_or_else(PoisonError::into_inner);
free_list.push_back(id);
}
}
}
#[cfg(all(test, not(loom)))]
pub(crate) fn with<R>(tid: usize, f: impl FnOnce() -> R) -> R {
struct Guard(Option<usize>);
impl Drop for Guard {
fn drop(&mut self) {
REGISTRATION.with(|r| r.0.set(self.0.take()));
}
}
let prev = REGISTRATION.with(|r| r.0.replace(Some(tid)));
let _guard = Guard(prev);
f()
}
|
