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//! The default garbage collector.
//!
//! For each thread, a participant is lazily initialized on its first use, when the current thread
//! is registered in the default collector. If initialized, the thread's participant will get
//! destructed on thread exit, which in turn unregisters the thread.
use crate::collector::{Collector, LocalHandle};
use crate::guard::Guard;
use crate::primitive::thread_local;
#[cfg(not(crossbeam_loom))]
use once_cell::sync::Lazy;
/// The global data for the default garbage collector.
#[cfg(not(crossbeam_loom))]
static COLLECTOR: Lazy<Collector> = Lazy::new(Collector::new);
// FIXME: loom does not currently provide the equivalent of Lazy:
// https://github.com/tokio-rs/loom/issues/263
#[cfg(crossbeam_loom)]
loom::lazy_static! {
/// The global data for the default garbage collector.
static ref COLLECTOR: Collector = Collector::new();
}
thread_local! {
/// The per-thread participant for the default garbage collector.
static HANDLE: LocalHandle = COLLECTOR.register();
}
/// Pins the current thread.
#[inline]
pub fn pin() -> Guard {
with_handle(|handle| handle.pin())
}
/// Returns `true` if the current thread is pinned.
#[inline]
pub fn is_pinned() -> bool {
with_handle(|handle| handle.is_pinned())
}
/// Returns the default global collector.
pub fn default_collector() -> &'static Collector {
&COLLECTOR
}
#[inline]
fn with_handle<F, R>(mut f: F) -> R
where
F: FnMut(&LocalHandle) -> R,
{
HANDLE
.try_with(|h| f(h))
.unwrap_or_else(|_| f(&COLLECTOR.register()))
}
#[cfg(all(test, not(crossbeam_loom)))]
mod tests {
use crossbeam_utils::thread;
#[test]
fn pin_while_exiting() {
struct Foo;
impl Drop for Foo {
fn drop(&mut self) {
// Pin after `HANDLE` has been dropped. This must not panic.
super::pin();
}
}
thread_local! {
static FOO: Foo = Foo;
}
thread::scope(|scope| {
scope.spawn(|_| {
// Initialize `FOO` and then `HANDLE`.
FOO.with(|_| ());
super::pin();
// At thread exit, `HANDLE` gets dropped first and `FOO` second.
});
})
.unwrap();
}
}
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