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use once_cell instead of static mut #2958

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use once_cell instead of static mut #2958

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74 changes: 23 additions & 51 deletions tracing-core/src/dispatch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,8 @@ use alloc::sync::{Arc, Weak};
#[cfg(feature = "alloc")]
use core::ops::Deref;

use once_cell::sync::OnceCell;

/// `Dispatch` trace data to a [`Collect`].
#[derive(Clone)]
pub struct Dispatch {
Expand Down Expand Up @@ -214,21 +216,12 @@ thread_local! {
}

static EXISTS: AtomicBool = AtomicBool::new(false);
static GLOBAL_INIT: AtomicUsize = AtomicUsize::new(UNINITIALIZED);

#[cfg(feature = "std")]
static SCOPED_COUNT: AtomicUsize = AtomicUsize::new(0);

const UNINITIALIZED: usize = 0;
const INITIALIZING: usize = 1;
const INITIALIZED: usize = 2;
static GLOBAL_DISPATCH: OnceCell<Dispatch> = OnceCell::new();

static mut GLOBAL_DISPATCH: Dispatch = Dispatch {
#[cfg(feature = "alloc")]
collector: Kind::Global(&NO_COLLECTOR),
#[cfg(not(feature = "alloc"))]
collector: &NO_COLLECTOR,
};
static NONE: Dispatch = Dispatch {
#[cfg(feature = "alloc")]
collector: Kind::Global(&NO_COLLECTOR),
Expand Down Expand Up @@ -329,42 +322,28 @@ pub fn set_default(dispatcher: &Dispatch) -> DefaultGuard {
/// [span]: super::span
/// [`Event`]: super::event::Event
pub fn set_global_default(dispatcher: Dispatch) -> Result<(), SetGlobalDefaultError> {
// if `compare_exchange` returns Result::Ok(_), then `new` has been set and
// `current`—now the prior value—has been returned in the `Ok()` branch.
if GLOBAL_INIT
.compare_exchange(
UNINITIALIZED,
INITIALIZING,
Ordering::SeqCst,
Ordering::SeqCst,
)
.is_ok()
{
#[cfg(feature = "alloc")]
let collector = {
let collector = match dispatcher.collector {
Kind::Global(s) => s,
Kind::Scoped(s) => unsafe {
// safety: this leaks the collector onto the heap. the
// reference count will always be at least 1.
&*Arc::into_raw(s)
},
};
Kind::Global(collector)
#[cfg(feature = "alloc")]
let collector = {
let collector = match dispatcher.collector {
Kind::Global(s) => s,
Kind::Scoped(s) => unsafe {
// safety: this leaks the collector onto the heap. the
// reference count will always be at least 1.
&*Arc::into_raw(s)
},
};
Kind::Global(collector)
};

#[cfg(not(feature = "alloc"))]
let collector = dispatcher.collector;
#[cfg(not(feature = "alloc"))]
let collector = dispatcher.collector;

unsafe {
GLOBAL_DISPATCH = Dispatch { collector };
}
GLOBAL_INIT.store(INITIALIZED, Ordering::SeqCst);
EXISTS.store(true, Ordering::Release);
Ok(())
} else {
Err(SetGlobalDefaultError { _no_construct: () })
}
let result = GLOBAL_DISPATCH
.set(Dispatch { collector })
.map_err(|_| SetGlobalDefaultError { _no_construct: () });
EXISTS.store(true, Ordering::Release);

result
}

/// Returns true if a `tracing` dispatcher has ever been set.
Expand Down Expand Up @@ -504,14 +483,7 @@ where

#[inline(always)]
pub(crate) fn get_global() -> &'static Dispatch {
if GLOBAL_INIT.load(Ordering::Acquire) != INITIALIZED {
return &NONE;
}
unsafe {
// This is safe given the invariant that setting the global dispatcher
// also sets `GLOBAL_INIT` to `INITIALIZED`.
&GLOBAL_DISPATCH
}
GLOBAL_DISPATCH.get().unwrap_or(&NONE)
}

#[cfg(feature = "std")]
Expand Down