Reference-count shared strings

src/ArduinoJson/Memory/MemoryPool.hpp

@@ -28,6 +28,7 @@ constexpr size_t sizeofObject(size_t n) {
 struct StringNode {
   struct StringNode* next;
   uint16_t length;
+  uint16_t references;
   char data[1];
 };
 
@@ -112,6 +113,7 @@ class MemoryPool {
 
     auto node = findString(str);
     if (node) {
+      node->references++;
       return node->data;
     }
 
@@ -147,6 +149,7 @@ class MemoryPool {
         _allocator->allocate(sizeofString(length)));
     if (node) {
       node->length = uint16_t(length);
+      node->references = 1;
     } else {
       _overflowed = true;
     }
@@ -170,6 +173,23 @@ class MemoryPool {
     _allocator->deallocate(node);
   }
 
+  void dereferenceString(const char* s) {
+    StringNode* prev = nullptr;
+    for (auto node = _strings; node; node = node->next) {
+      if (node->data == s) {
+        if (--node->references == 0) {
+          if (prev)
+            prev->next = node->next;
+          else
+            _strings = node->next;
+          _allocator->deallocate(node);
+        }
+        return;
+      }
+      prev = node;
+    }
+  }
+
   void clear() {
     _right = _end;
     _overflowed = false;

src/ArduinoJson/StringStorage/StringCopier.hpp

@@ -33,6 +33,8 @@ class StringCopier {
       node = _pool->reallocString(_node, _size);
       _pool->addStringToList(node);
       _node = nullptr;  // next time we need a new string
+    } else {
+      node->references++;
     }
     return JsonString(node->data, node->length, JsonString::Copied);
   }

src/ArduinoJson/Variant/SlotFunctions.hpp

@@ -24,6 +24,8 @@ inline VariantData* slotData(VariantSlot* slot) {
 
 inline void slotRelease(const VariantSlot* slot, MemoryPool* pool) {
   ARDUINOJSON_ASSERT(slot != nullptr);
+  if (slot->ownsKey())
+    pool->dereferenceString(slot->key());
   variantRelease(slot->data(), pool);
 }
 

src/ArduinoJson/Variant/VariantFunctions.hpp

@@ -33,6 +33,10 @@ inline typename TVisitor::result_type variantAccept(const VariantData* var,
 
 inline void variantRelease(const VariantData* var, MemoryPool* pool) {
   ARDUINOJSON_ASSERT(var != nullptr);
+  auto s = var->getOwnedString();
+  if (s)
+    pool->dereferenceString(s);
+
   auto c = var->asCollection();
   if (c) {
     for (auto slot = c->head(); slot; slot = slot->next())