Bug 1477761 - Fix sketchy timestamp computation for unlimited slice budget r=sfink

js/public/SliceBudget.h

@@ -37,13 +37,7 @@ struct JS_PUBLIC_API(WorkBudget)
  */
 class JS_PUBLIC_API(SliceBudget)
 {
-    const mozilla::TimeStamp &UnlimitedDeadline() const {
-        mozilla::recordreplay::AutoPassThroughThreadEvents pt;
-        static const mozilla::TimeStamp unlimitedDeadline =
-            mozilla::TimeStamp::Now() + mozilla::TimeDuration::Forever();
-        return unlimitedDeadline;
-    }
-
+    static mozilla::TimeStamp unlimitedDeadline;
     static const intptr_t unlimitedStartCounter = INTPTR_MAX;
 
     bool checkOverBudget();
@@ -75,7 +69,8 @@ class JS_PUBLIC_API(SliceBudget)
     explicit SliceBudget(WorkBudget work);
 
     void makeUnlimited() {
-        deadline = UnlimitedDeadline();
+        MOZ_ASSERT(unlimitedDeadline);
+        deadline = unlimitedDeadline;
         counter = unlimitedStartCounter;
     }
 
@@ -91,9 +86,11 @@ class JS_PUBLIC_API(SliceBudget)
 
     bool isWorkBudget() const { return deadline.IsNull(); }
     bool isTimeBudget() const { return !deadline.IsNull() && !isUnlimited(); }
-    bool isUnlimited() const { return deadline == UnlimitedDeadline(); }
+    bool isUnlimited() const { return deadline == unlimitedDeadline; }
 
     int describe(char* buffer, size_t maxlen) const;
+
+    static void Init();
 };
 
 } // namespace js

js/src/gc/GC.cpp

@@ -3234,6 +3234,16 @@ ArenaLists::queueForegroundThingsForSweep()
     gcScriptArenasToUpdate = arenaListsToSweep(AllocKind::SCRIPT);
 }
 
+mozilla::TimeStamp SliceBudget::unlimitedDeadline;
+
+void
+SliceBudget::Init()
+{
+    MOZ_ASSERT(!unlimitedDeadline);
+    uint64_t oneYearsInSeconds = 365 * 24 * 60 * 60;
+    unlimitedDeadline = ReallyNow() + mozilla::TimeDuration::FromSeconds(100 * oneYearsInSeconds);
+}
+
 SliceBudget::SliceBudget()
   : timeBudget(UnlimitedTimeBudget), workBudget(UnlimitedWorkBudget)
 {

js/src/vm/Initialization.cpp

@@ -88,6 +88,8 @@ JS::detail::InitWithFailureDiagnostic(bool isDebugBuild)
 
     PRMJ_NowInit();
 
+    js::SliceBudget::Init();
+
     // The first invocation of `ProcessCreation` creates a temporary thread
     // and crashes if that fails, i.e. because we're out of memory. To prevent
     // that from happening at some later time, get it out of the way during