Bug 1628371 - Check whether JS holders are single-zone in nightly builds too r=mccr8

Differential Revision: https://phabricator.services.mozilla.com/D70220

--HG--
extra : moz-landing-system : lando

js/src/jsfriendapi.cpp

@@ -1465,8 +1465,6 @@ bool js::AddListFormatConstructor(JSContext* cx, JS::HandleObject intl) {
 
 #endif  // !JS_HAS_INTL_API
 
-#ifdef DEBUG
 JS_FRIEND_API JS::Zone* js::GetObjectZoneFromAnyThread(JSObject* obj) {
   return MaybeForwarded(obj)->zoneFromAnyThread();
 }
-#endif

js/src/jsfriendapi.h

@@ -2693,9 +2693,7 @@ extern JS_FRIEND_API void SetPerformanceHint(JSContext* cx,
 
 } /* namespace gc */
 
-#ifdef DEBUG
 extern JS_FRIEND_API JS::Zone* GetObjectZoneFromAnyThread(JSObject* obj);
-#endif
 
 } /* namespace js */
 

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -1070,7 +1070,11 @@ void mozilla::TraceScriptHolder(nsISupports* aHolder, JSTracer* aTracer) {
   participant->Trace(aHolder, JsGcTracer(), aTracer);
 }
 
-#ifdef DEBUG
+#if defined(NIGHTLY_BUILD) || defined(MOZ_DEV_EDITION) || defined(DEBUG)
+#  define CHECK_SINGLE_ZONE_JS_HOLDERS
+#endif
+
+#ifdef CHECK_SINGLE_ZONE_JS_HOLDERS
 
 // A tracer that checks that a JS holder only holds JS GC things in a single
 // JS::Zone.
@@ -1177,6 +1181,15 @@ static inline void CheckHolderIsSingleZone(
   aParticipant->Trace(aHolder, tracer, nullptr);
 }
 
+static inline bool ShouldCheckSingleZoneHolders() {
+#  ifdef DEBUG
+  return true;
+#  else
+  // Don't check every time to avoid performance impact.
+  return rand() % 256 == 0;
+#  endif
+}
+
 #endif
 
 void CycleCollectedJSRuntime::TraceNativeGrayRoots(JSTracer* aTracer) {
@@ -1184,9 +1197,14 @@ void CycleCollectedJSRuntime::TraceNativeGrayRoots(JSTracer* aTracer) {
   // would hurt to do this after the JS holders.
   TraceAdditionalNativeGrayRoots(aTracer);
 
-  mJSHolders.ForEach([aTracer](void* holder, nsScriptObjectTracer* tracer) {
-#ifdef DEBUG
-    if (!tracer->IsMultiZoneJSHolder()) {
+#ifdef CHECK_SINGLE_ZONE_JS_HOLDERS
+  bool checkSingleZoneHolders = ShouldCheckSingleZoneHolders();
+#endif
+
+  mJSHolders.ForEach([aTracer, checkSingleZoneHolders](
+                         void* holder, nsScriptObjectTracer* tracer) {
+#ifdef CHECK_SINGLE_ZONE_JS_HOLDERS
+    if (checkSingleZoneHolders && !tracer->IsMultiZoneJSHolder()) {
       CheckHolderIsSingleZone(holder, tracer);
     }
 #endif