Bug 1730534 - Part 2: Add an iterator for JSHolderMap's EntryVector r=mccr8

This replaces use of the ForEach method that takes an EntryVector with an iterator.

Differential Revision: https://phabricator.services.mozilla.com/D125427

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -483,12 +483,30 @@ JSHolderMap::Entry::Entry(void* aHolder, nsScriptObjectTracer* aTracer,
 {
 }
 
+void JSHolderMap::EntryVectorIter::Settle() {
+  if (Done()) {
+    return;
+  }
+
+  Entry* entry = &mIter.Get();
+
+  // If the entry has been cleared, remove it and shrink the vector.
+  if (!entry->mHolder && !mHolderMap.RemoveEntry(mVector, entry)) {
+    // We removed the last entry, so reset the iterator to an empty one.
+    mIter = EntryVector().Iter();
+    MOZ_ASSERT(Done());
+  }
+}
+
 JSHolderMap::JSHolderMap() : mJSHolderMap(256) {}
 
 template <typename F>
 inline void JSHolderMap::ForEach(F&& f, WhichHolders aWhich) {
   // Multi-zone JS holders must always be considered.
-  ForEach(mAnyZoneJSHolders, f, nullptr);
+  for (EntryVectorIter entry(*this, mAnyZoneJSHolders); !entry.Done();
+       entry.Next()) {
+    f(entry->mHolder, entry->mTracer, nullptr);
+  }
 
   for (auto i = mPerZoneJSHolders.modIter(); !i.done(); i.next()) {
     if (aWhich == HoldersInGrayMarkingZones &&
@@ -496,30 +514,19 @@ inline void JSHolderMap::ForEach(F&& f, WhichHolders aWhich) {
       continue;
     }
 
+    JS::Zone* zone = i.get().key();
     EntryVector* holders = i.get().value().get();
-    ForEach(*holders, f, i.get().key());
+    for (EntryVectorIter entry(*this, *holders); !entry.Done(); entry.Next()) {
+      MOZ_ASSERT(entry->mZone == zone);
+      f(entry->mHolder, entry->mTracer, zone);
+    }
+
     if (holders->IsEmpty()) {
       i.remove();
     }
   }
 }
 
-template <typename F>
-inline void JSHolderMap::ForEach(EntryVector& aJSHolders, const F& f,
-                                 JS::Zone* aZone) {
-  for (auto iter = aJSHolders.Iter(); !iter.Done(); iter.Next()) {
-    Entry* entry = &iter.Get();
-
-    // If the entry has been cleared, remove it and shrink the vector.
-    if (!entry->mHolder && !RemoveEntry(aJSHolders, entry)) {
-      break;  // Removed the last entry.
-    }
-
-    MOZ_ASSERT_IF(aZone, entry->mZone == aZone);
-    f(entry->mHolder, entry->mTracer, aZone);
-  }
-}
-
 bool JSHolderMap::RemoveEntry(EntryVector& aJSHolders, Entry* aEntry) {
   MOZ_ASSERT(aEntry);
   MOZ_ASSERT(!aEntry->mHolder);

xpcom/base/CycleCollectedJSRuntime.h

@@ -124,8 +124,7 @@ class JSHolderMap {
       mozilla::HashMap<JS::Zone*, UniquePtr<EntryVector>,
                        DefaultHasher<JS::Zone*>, InfallibleAllocPolicy>;
 
-  template <typename F>
-  void ForEach(EntryVector& aJSHolders, const F& f, JS::Zone* aZone);
+  class EntryVectorIter;
 
   bool RemoveEntry(EntryVector& aJSHolders, Entry* aEntry);
 
@@ -144,6 +143,35 @@ class JSHolderMap {
   EntryVectorMap mPerZoneJSHolders;
 };
 
+// An iterator over an EntryVector that skips over removed entries and removes
+// them from the map.
+class JSHolderMap::EntryVectorIter {
+ public:
+  EntryVectorIter(JSHolderMap& aMap, EntryVector& aVector)
+      : mHolderMap(aMap), mVector(aVector), mIter(aVector.Iter()) {
+    Settle();
+  }
+
+  const EntryVector& Vector() const { return mVector; }
+
+  bool Done() const { return mIter.Done(); }
+  const Entry& Get() const { return mIter.Get(); }
+  void Next() {
+    mIter.Next();
+    Settle();
+  }
+
+  operator const Entry*() const { return &Get(); }
+  const Entry* operator->() const { return &Get(); }
+
+ private:
+  void Settle();
+
+  JSHolderMap& mHolderMap;
+  EntryVector& mVector;
+  EntryVector::IterImpl mIter;
+};
+
 class CycleCollectedJSRuntime {
   friend class JSGCThingParticipant;
   friend class JSZoneParticipant;