From 5411bf906ded4f6df09624d2a34072b3df25b04f Mon Sep 17 00:00:00 2001
From: Gary Hsu <bghgary@users.noreply.github.com>
Date: Wed, 15 Apr 2026 17:04:55 -0700
Subject: [PATCH 1/2] Protect test hook callback with mutex for TSan safety

The beforeWaitCallback global std::function was accessed from multiple
threads without synchronization. Add a dedicated mutex and use
copy-under-lock, invoke-after-unlock pattern to avoid holding the
lock during arbitrary callback execution.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../threading/blocking_concurrent_queue.h     | 20 +++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/Source/Shared/arcana/threading/blocking_concurrent_queue.h b/Source/Shared/arcana/threading/blocking_concurrent_queue.h
index 24d5276..b01dd8b 100644
--- a/Source/Shared/arcana/threading/blocking_concurrent_queue.h
+++ b/Source/Shared/arcana/threading/blocking_concurrent_queue.h
@@ -21,6 +21,7 @@ namespace arcana
     {
         namespace detail
         {
+            inline std::mutex callbackMutex;
             inline std::function<void()> beforeWaitCallback{[]() {}};
         }
 
@@ -29,6 +30,7 @@ namespace arcana
         // lost-wakeup race conditions. Pass an empty lambda [](){} to reset.
         inline void set_before_wait_callback(std::function<void()> callback)
         {
+            std::lock_guard<std::mutex> lock{detail::callbackMutex};
             detail::beforeWaitCallback = std::move(callback);
         }
     }
@@ -121,7 +123,14 @@ namespace arcana
                 while (!cancel.cancelled() && m_data.empty())
                 {
 #ifdef ARCANA_TEST_HOOKS
-                    test_hooks::blocking_concurrent_queue::detail::beforeWaitCallback();
+                    {
+                        std::function<void()> cb;
+                        {
+                            std::lock_guard<std::mutex> cbLock{test_hooks::blocking_concurrent_queue::detail::callbackMutex};
+                            cb = test_hooks::blocking_concurrent_queue::detail::beforeWaitCallback;
+                        }
+                        cb();
+                    }
 #endif
                     m_dataReady.wait(lock);
                 }
@@ -145,7 +154,14 @@ namespace arcana
                 while (!cancel.cancelled() && m_data.empty())
                 {
 #ifdef ARCANA_TEST_HOOKS
-                    test_hooks::blocking_concurrent_queue::detail::beforeWaitCallback();
+                    {
+                        std::function<void()> cb;
+                        {
+                            std::lock_guard<std::mutex> cbLock{test_hooks::blocking_concurrent_queue::detail::callbackMutex};
+                            cb = test_hooks::blocking_concurrent_queue::detail::beforeWaitCallback;
+                        }
+                        cb();
+                    }
 #endif
                     m_dataReady.wait(lock);
                 }

From 761f88f914a27566c6ad0f271d357918a7e5e1b9 Mon Sep 17 00:00:00 2001
From: Gary Hsu <bghgary@users.noreply.github.com>
Date: Thu, 16 Apr 2026 09:00:46 -0700
Subject: [PATCH 2/2] Factor invoke_before_wait_callback into detail helper

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../threading/blocking_concurrent_queue.h     | 30 +++++++++----------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/Source/Shared/arcana/threading/blocking_concurrent_queue.h b/Source/Shared/arcana/threading/blocking_concurrent_queue.h
index b01dd8b..15eda2d 100644
--- a/Source/Shared/arcana/threading/blocking_concurrent_queue.h
+++ b/Source/Shared/arcana/threading/blocking_concurrent_queue.h
@@ -23,6 +23,18 @@ namespace arcana
         {
             inline std::mutex callbackMutex;
             inline std::function<void()> beforeWaitCallback{[]() {}};
+
+            // Copy the callback under the lock and invoke after releasing, avoiding
+            // potential deadlocks if the callback interacts with other locks.
+            inline void invoke_before_wait_callback()
+            {
+                std::function<void()> cb;
+                {
+                    std::lock_guard<std::mutex> lock{callbackMutex};
+                    cb = beforeWaitCallback;
+                }
+                cb();
+            }
         }
 
         // Set a callback to be invoked while holding the queue mutex, right before
@@ -123,14 +135,7 @@ namespace arcana
                 while (!cancel.cancelled() && m_data.empty())
                 {
 #ifdef ARCANA_TEST_HOOKS
-                    {
-                        std::function<void()> cb;
-                        {
-                            std::lock_guard<std::mutex> cbLock{test_hooks::blocking_concurrent_queue::detail::callbackMutex};
-                            cb = test_hooks::blocking_concurrent_queue::detail::beforeWaitCallback;
-                        }
-                        cb();
-                    }
+                    test_hooks::blocking_concurrent_queue::detail::invoke_before_wait_callback();
 #endif
                     m_dataReady.wait(lock);
                 }
@@ -154,14 +159,7 @@ namespace arcana
                 while (!cancel.cancelled() && m_data.empty())
                 {
 #ifdef ARCANA_TEST_HOOKS
-                    {
-                        std::function<void()> cb;
-                        {
-                            std::lock_guard<std::mutex> cbLock{test_hooks::blocking_concurrent_queue::detail::callbackMutex};
-                            cb = test_hooks::blocking_concurrent_queue::detail::beforeWaitCallback;
-                        }
-                        cb();
-                    }
+                    test_hooks::blocking_concurrent_queue::detail::invoke_before_wait_callback();
 #endif
                     m_dataReady.wait(lock);
                 }