From 8c980b7c9433d19d6d558908718b5f4a83ca87d8 Mon Sep 17 00:00:00 2001
From: Taiki Endo <te316e89@gmail.com>
Date: Sat, 17 Jun 2023 22:30:38 +0900
Subject: [PATCH] Make crossbeam-epoch compatible with ThreadSanitizer

---
 ci/tsan                         | 3 ---
 crossbeam-epoch/build.rs        | 6 ++++++
 crossbeam-epoch/src/internal.rs | 8 +++++++-
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/ci/tsan b/ci/tsan
index 9ebb04b4f..67fad001a 100644
--- a/ci/tsan
+++ b/ci/tsan
@@ -1,8 +1,5 @@
 # TSAN suppressions file for crossbeam
 
-# The epoch-based GC uses fences.
-race:crossbeam_epoch
-
 # Push and steal operations in crossbeam-deque may cause data races, but such
 # data races are safe. If a data race happens, the value read by `steal` is
 # forgotten and the steal operation is then retried.
diff --git a/crossbeam-epoch/build.rs b/crossbeam-epoch/build.rs
index 86c3b6ff7..a198ec60b 100644
--- a/crossbeam-epoch/build.rs
+++ b/crossbeam-epoch/build.rs
@@ -54,4 +54,10 @@ fn main() {
     if !cfg.probe_rustc_version(1, 61) {
         println!("cargo:rustc-cfg=crossbeam_no_const_fn_trait_bound");
     }
+
+    // `cfg(sanitize = "..")` is not stabilized.
+    let sanitize = env::var("CARGO_CFG_SANITIZE").unwrap_or_default();
+    if sanitize.contains("thread") {
+        println!("cargo:rustc-cfg=crossbeam_sanitize_thread");
+    }
 }
diff --git a/crossbeam-epoch/src/internal.rs b/crossbeam-epoch/src/internal.rs
index 486993c63..c93d64601 100644
--- a/crossbeam-epoch/src/internal.rs
+++ b/crossbeam-epoch/src/internal.rs
@@ -250,10 +250,16 @@ impl Global {
                     if local_epoch.is_pinned() && local_epoch.unpinned() != global_epoch {
                         return global_epoch;
                     }
+
+                    if cfg!(crossbeam_sanitize_thread) {
+                        local.epoch.load(Ordering::Acquire);
+                    }
                 }
             }
         }
-        atomic::fence(Ordering::Acquire);
+        if !cfg!(crossbeam_sanitize_thread) {
+            atomic::fence(Ordering::Acquire);
+        }
 
         // All pinned participants were pinned in the current global epoch.
         // Now let's advance the global epoch...