Recycle removed slots

src/ArduinoJson/Collection/CollectionImpl.hpp

@@ -133,6 +133,7 @@ inline void CollectionData::releaseSlot(iterator it,
   if (it.ownsKey())
     resources->dereferenceString(it.key());
   it->setNull(resources);
+  resources->freeSlot(SlotWithId(it.slot_, it.currentId_));
 }
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Memory/ResourceManager.hpp

@@ -59,6 +59,10 @@ class ResourceManager {
     return p;
   }
 
+  void freeSlot(SlotWithId id) {
+    variantPools_.freeSlot(id);
+  }
+
   VariantSlot* getSlot(SlotId id) const {
     return variantPools_.getSlot(id);
   }

src/ArduinoJson/Memory/VariantPoolImpl.hpp

@@ -61,4 +61,17 @@ inline size_t VariantPool::slotsToBytes(SlotCount n) {
   return n * sizeof(VariantSlot);
 }
 
+inline SlotWithId VariantPoolList::allocFromFreeList() {
+  ARDUINOJSON_ASSERT(freeList_ != NULL_SLOT);
+  auto id = freeList_;
+  auto slot = getSlot(freeList_);
+  freeList_ = slot->next();
+  return {new (slot) VariantSlot, id};
+}
+
+inline void VariantPoolList::freeSlot(SlotWithId slot) {
+  slot->setNext(freeList_);
+  freeList_ = slot.id();
+}
+
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Memory/VariantPoolList.hpp

@@ -29,6 +29,11 @@ class VariantPoolList {
   }
 
   SlotWithId allocSlot(Allocator* allocator) {
+    // try to allocate from free list
+    if (freeList_ != NULL_SLOT) {
+      return allocFromFreeList();
+    }
+
     // try to allocate from last pool (other pools are full)
     if (pools_) {
       auto slot = allocFromLastPool();
@@ -44,6 +49,8 @@ class VariantPoolList {
     return allocFromLastPool();
   }
 
+  void freeSlot(SlotWithId slot);
+
   VariantSlot* getSlot(SlotId id) const {
     auto poolIndex = SlotId(id / ARDUINOJSON_POOL_CAPACITY);
     auto indexInPool = SlotId(id % ARDUINOJSON_POOL_CAPACITY);
@@ -82,6 +89,8 @@ class VariantPoolList {
   }
 
  private:
+  SlotWithId allocFromFreeList();
+
   SlotWithId allocFromLastPool() {
     ARDUINOJSON_ASSERT(pools_ != nullptr);
     auto poolIndex = SlotId(count_ - 1);
@@ -121,6 +130,7 @@ class VariantPoolList {
   VariantPool* pools_ = nullptr;
   size_t count_ = 0;
   size_t capacity_ = 0;
+  SlotId freeList_ = NULL_SLOT;
 };
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE