From 7438e9d4335e4f0228dd796ca4d7a1b8a0484e17 Mon Sep 17 00:00:00 2001
From: Jason Simmons <jsimmons@google.com>
Date: Wed, 16 Mar 2022 13:42:17 -0700
Subject: [PATCH] Wrap the global timeline event handler callback in a
 std::atomic

Fixes https://github.com/flutter/flutter/issues/100238
---
 fml/trace_event.cc | 10 ++++++----
 fml/trace_event.h  | 14 +++++++-------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/fml/trace_event.cc b/fml/trace_event.cc
index 8ee1bed590504..20acb36306aa2 100644
--- a/fml/trace_event.cc
+++ b/fml/trace_event.cc
@@ -19,7 +19,7 @@ namespace tracing {
 
 namespace {
 AsciiTrie gAllowlist;
-TimelineEventHandler gTimelineEventHandler;
+std::atomic<TimelineEventHandler> gTimelineEventHandler;
 
 inline void FlutterTimelineEvent(const char* label,
                                  int64_t timestamp0,
@@ -28,9 +28,11 @@ inline void FlutterTimelineEvent(const char* label,
                                  intptr_t argument_count,
                                  const char** argument_names,
                                  const char** argument_values) {
-  if (gTimelineEventHandler && gAllowlist.Query(label)) {
-    gTimelineEventHandler(label, timestamp0, timestamp1_or_async_id, type,
-                          argument_count, argument_names, argument_values);
+  TimelineEventHandler handler =
+      gTimelineEventHandler.load(std::memory_order_relaxed);
+  if (handler && gAllowlist.Query(label)) {
+    handler(label, timestamp0, timestamp1_or_async_id, type, argument_count,
+            argument_names, argument_values);
   }
 }
 }  // namespace
diff --git a/fml/trace_event.h b/fml/trace_event.h
index d89e421a7bec6..2c41ce45c3a72 100644
--- a/fml/trace_event.h
+++ b/fml/trace_event.h
@@ -147,13 +147,13 @@ using TraceIDArg = int64_t;
 
 void TraceSetAllowlist(const std::vector<std::string>& allowlist);
 
-using TimelineEventHandler = std::function<void(const char*,
-                                                int64_t,
-                                                int64_t,
-                                                Dart_Timeline_Event_Type,
-                                                intptr_t,
-                                                const char**,
-                                                const char**)>;
+typedef void (*TimelineEventHandler)(const char*,
+                                     int64_t,
+                                     int64_t,
+                                     Dart_Timeline_Event_Type,
+                                     intptr_t,
+                                     const char**,
+                                     const char**);
 
 void TraceSetTimelineEventHandler(TimelineEventHandler handler);