From 426e07a992aa85983f9825e7d297a0bb8a82ddb7 Mon Sep 17 00:00:00 2001
From: Eliza Weisman <eliza@buoyant.io>
Date: Fri, 1 Oct 2021 09:44:27 -0700
Subject: [PATCH 1/3] core: additional deprecation fixes

---
 tracing-core/src/spin/once.rs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/tracing-core/src/spin/once.rs b/tracing-core/src/spin/once.rs
index 219eb31540..fe4b53f183 100644
--- a/tracing-core/src/spin/once.rs
+++ b/tracing-core/src/spin/once.rs
@@ -76,10 +76,11 @@ impl<T> Once<T> {
         let mut status = self.state.load(Ordering::SeqCst);
 
         if status == INCOMPLETE {
-            status = self
+            if self
                 .state
-                .compare_and_swap(INCOMPLETE, RUNNING, Ordering::SeqCst);
-            if status == INCOMPLETE {
+                .compare_exchange(INCOMPLETE, RUNNING, Ordering::SeqCst, Ordering::SeqCst)
+                .is_ok()
+            {
                 // We init
                 // We use a guard (Finish) to catch panics caused by builder
                 let mut finish = Finish {
@@ -101,6 +102,8 @@ impl<T> Once<T> {
             match status {
                 INCOMPLETE => unreachable!(),
                 RUNNING => {
+                    // TODO(eliza): replace with `core::hint::spin_loop` once our MSRV supports it.
+                    #[allow(deprecated)]
                     // We spin
                     cpu_relax();
                     status = self.state.load(Ordering::SeqCst)
@@ -126,7 +129,12 @@ impl<T> Once<T> {
         loop {
             match self.state.load(Ordering::SeqCst) {
                 INCOMPLETE => return None,
-                RUNNING => cpu_relax(), // We spin
+
+                RUNNING => {
+                    // TODO(eliza): replace with `core::hint::spin_loop` once our MSRV supports it.
+                    #[allow(deprecated)]
+                    cpu_relax() // We spin
+                }
                 COMPLETE => return Some(self.force_get()),
                 PANICKED => panic!("Once has panicked"),
                 _ => unsafe { unreachable() },

From 22c7ea6c5a6bd20648439cf1e68b814e10472804 Mon Sep 17 00:00:00 2001
From: Eliza Weisman <eliza@buoyant.io>
Date: Fri, 1 Oct 2021 09:53:45 -0700
Subject: [PATCH 2/3] fix status not being updated if cas fails

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
---
 tracing-core/src/spin/once.rs | 46 ++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 19 deletions(-)

diff --git a/tracing-core/src/spin/once.rs b/tracing-core/src/spin/once.rs
index fe4b53f183..096d9f11cf 100644
--- a/tracing-core/src/spin/once.rs
+++ b/tracing-core/src/spin/once.rs
@@ -76,25 +76,33 @@ impl<T> Once<T> {
         let mut status = self.state.load(Ordering::SeqCst);
 
         if status == INCOMPLETE {
-            if self
-                .state
-                .compare_exchange(INCOMPLETE, RUNNING, Ordering::SeqCst, Ordering::SeqCst)
-                .is_ok()
-            {
-                // We init
-                // We use a guard (Finish) to catch panics caused by builder
-                let mut finish = Finish {
-                    state: &self.state,
-                    panicked: true,
-                };
-                unsafe { *self.data.get() = Some(builder()) };
-                finish.panicked = false;
-
-                status = COMPLETE;
-                self.state.store(status, Ordering::SeqCst);
-
-                // This next line is strictly an optimization
-                return self.force_get();
+            status = match self.state.compare_exchange(
+                INCOMPLETE,
+                RUNNING,
+                Ordering::SeqCst,
+                Ordering::SeqCst,
+            ) {
+                Ok(status) => {
+                    debug_assert_eq!(
+                        status, INCOMPLETE,
+                        "if compare_exchange succeeded, previous status must be incomplete",
+                    );
+                    // We init
+                    // We use a guard (Finish) to catch panics caused by builder
+                    let mut finish = Finish {
+                        state: &self.state,
+                        panicked: true,
+                    };
+                    unsafe { *self.data.get() = Some(builder()) };
+                    finish.panicked = false;
+
+                    status = COMPLETE;
+                    self.state.store(status, Ordering::SeqCst);
+
+                    // This next line is strictly an optimization
+                    return self.force_get();
+                }
+                Err(s) => status = s,
             }
         }
 

From 1879769e1355b7cbcf64acf606ca85b8058e5e07 Mon Sep 17 00:00:00 2001
From: Eliza Weisman <eliza@buoyant.io>
Date: Fri, 1 Oct 2021 09:57:03 -0700
Subject: [PATCH 3/3] there we go

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
---
 tracing-core/src/spin/once.rs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tracing-core/src/spin/once.rs b/tracing-core/src/spin/once.rs
index 096d9f11cf..8643d472b2 100644
--- a/tracing-core/src/spin/once.rs
+++ b/tracing-core/src/spin/once.rs
@@ -96,13 +96,12 @@ impl<T> Once<T> {
                     unsafe { *self.data.get() = Some(builder()) };
                     finish.panicked = false;
 
-                    status = COMPLETE;
-                    self.state.store(status, Ordering::SeqCst);
+                    self.state.store(COMPLETE, Ordering::SeqCst);
 
                     // This next line is strictly an optimization
                     return self.force_get();
                 }
-                Err(s) => status = s,
+                Err(status) => status,
             }
         }