Optimization of msgpack::zone size on the stack and deferred memory allocation

Author: Arenoros

include/msgpack/v1/detail/cpp11_zone.hpp

@@ -25,81 +25,59 @@ namespace msgpack {
 /// @cond
 MSGPACK_API_VERSION_NAMESPACE(v1) {
 /// @endcond
-
+    
 class zone {
 private:
     struct finalizer {
-        finalizer(void (*func)(void*), void* data):m_func(func), m_data(data) {}
+        finalizer(void (*func)(void*), void* data, finalizer* next): m_func(func), m_data(data), m_next(next) {}
         void operator()() { m_func(m_data); }
         void (*m_func)(void*);
         void* m_data;
+        finalizer* m_next{};
     };
     struct finalizer_array {
-        finalizer_array():m_tail(MSGPACK_NULLPTR), m_end(MSGPACK_NULLPTR), m_array(MSGPACK_NULLPTR) {}
-        void call() {
-            finalizer* fin = m_tail;
-            for(; fin != m_array; --fin) (*(fin-1))();
+        finalizer_array(): m_head(MSGPACK_NULLPTR) {}
+
+        void call(bool clear = false) {
+            finalizer* fin = m_head;
+            finalizer* tmp = nullptr;
+            while(fin) {
+                (*(fin-1))();
+                if (clear) {
+                    tmp = fin;
+                }
+                fin = fin->m_next;
+                if (clear) {
+                    delete tmp;
+                }
+            }
         }
         ~finalizer_array() {
-            call();
-            ::free(m_array);
+            call(true);
         }
         void clear() {
-            call();
-            m_tail = m_array;
+            call(true);
         }
         void push(void (*func)(void* data), void* data)
         {
-            finalizer* fin = m_tail;
-
-            if(fin == m_end) {
-                push_expand(func, data);
-                return;
-            }
-
-            fin->m_func = func;
-            fin->m_data = data;
-
-            ++m_tail;
+            m_head = new finalizer(func, data, m_head);
         }
-        void push_expand(void (*func)(void*), void* data) {
-            const size_t nused = static_cast<size_t>(m_end - m_array);
-            size_t nnext;
-            if(nused == 0) {
-                nnext = (sizeof(finalizer) < 72/2) ?
-                    72 / sizeof(finalizer) : 8;
-            } else {
-                nnext = nused * 2;
-            }
-            finalizer* tmp =
-                static_cast<finalizer*>(::realloc(m_array, sizeof(finalizer) * nnext));
-            if(!tmp) {
-                throw std::bad_alloc();
-            }
-            m_array     = tmp;
-            m_end   = tmp + nnext;
-            m_tail  = tmp + nused;
-            new (m_tail) finalizer(func, data);
-
-            ++m_tail;
+        void pop() {
+            auto n = m_head->m_next;
+            delete m_head;
+            m_head = n;
         }
-        finalizer_array(finalizer_array&& other) noexcept
-            :m_tail(other.m_tail), m_end(other.m_end), m_array(other.m_array)
-        {
-            other.m_tail = MSGPACK_NULLPTR;
-            other.m_end = MSGPACK_NULLPTR;
-            other.m_array = MSGPACK_NULLPTR;
+
+        finalizer_array(finalizer_array&& other) noexcept: m_head(other.m_head) {
+            other.m_head = MSGPACK_NULLPTR;
         }
         finalizer_array& operator=(finalizer_array&& other) noexcept
         {
             this->~finalizer_array();
             new (this) finalizer_array(std::move(other));
             return *this;
         }
-
-        finalizer* m_tail;
-        finalizer* m_end;
-        finalizer* m_array;
+        finalizer* m_head;
 
     private:
         finalizer_array(const finalizer_array&);
@@ -109,69 +87,44 @@ class zone {
         chunk* m_next;
     };
     struct chunk_list {
-        chunk_list(size_t chunk_size)
-        {
-            chunk* c = static_cast<chunk*>(::malloc(sizeof(chunk) + chunk_size));
-            if(!c) {
-                throw std::bad_alloc();
-            }
-
-            m_head = c;
-            m_free = chunk_size;
-            m_ptr  = reinterpret_cast<char*>(c) + sizeof(chunk);
-            c->m_next = MSGPACK_NULLPTR;
-        }
-        ~chunk_list()
-        {
+        chunk_list(size_t chunk_size, char* ptr): m_free(chunk_size), m_ptr(ptr), m_head(MSGPACK_NULLPTR) {}
+        ~chunk_list() {
             chunk* c = m_head;
             while(c) {
                 chunk* n = c->m_next;
                 ::free(c);
                 c = n;
             }
         }
-        void clear(size_t chunk_size)
+        void clear(size_t chunk_size, char* ptr)
         {
             chunk* c = m_head;
-            while(true) {
+            while(c) {
                 chunk* n = c->m_next;
-                if(n) {
-                    ::free(c);
-                    c = n;
-                } else {
-                    m_head = c;
-                    break;
-                }
+                ::free(c);
+                c = n;
             }
             m_head->m_next = MSGPACK_NULLPTR;
             m_free = chunk_size;
-            m_ptr  = reinterpret_cast<char*>(m_head) + sizeof(chunk);
-        }
-        chunk_list(chunk_list&& other) noexcept
-            :m_free(other.m_free), m_ptr(other.m_ptr), m_head(other.m_head)
-        {
-            other.m_head = MSGPACK_NULLPTR;
-        }
-        chunk_list& operator=(chunk_list&& other) noexcept
-        {
-            this->~chunk_list();
-            new (this) chunk_list(std::move(other));
-            return *this;
+            m_ptr  = ptr;
         }
 
         size_t m_free;
         char* m_ptr;
         chunk* m_head;
     private:
+        chunk_list(chunk_list&& other) noexcept = delete;
+        chunk_list& operator=(chunk_list&& other) noexcept = delete;
         chunk_list(const chunk_list&);
         chunk_list& operator=(const chunk_list&);
     };
     size_t m_chunk_size;
-    chunk_list m_chunk_list;
+    chunk_list* m_chunk_list{};
     finalizer_array m_finalizer_array;
 
 public:
     zone(size_t chunk_size = MSGPACK_ZONE_CHUNK_SIZE);
+    ~zone();
 
 public:
     void* allocate_align(size_t size, size_t align = MSGPACK_ZONE_ALIGN);
@@ -223,53 +176,75 @@ class zone {
 
     static char* get_aligned(char* ptr, size_t align);
 
+    chunk_list& get_chank_lst();
+
     char* allocate_expand(size_t size);
 };
 
-inline zone::zone(size_t chunk_size):m_chunk_size(chunk_size), m_chunk_list(m_chunk_size)
+inline zone::zone(size_t chunk_size):m_chunk_size(chunk_size), m_chunk_list(MSGPACK_NULLPTR)
+{
+}
+
+inline zone::~zone()
 {
+    if(m_chunk_list) {
+        m_chunk_list->~chunk_list();
+        ::free(m_chunk_list);
+        m_chunk_list = MSGPACK_NULLPTR;
+    }
 }
 
 inline char* zone::get_aligned(char* ptr, size_t align)
 {
     MSGPACK_ASSERT(align != 0 && (align & (align - 1)) == 0); // align must be 2^n (n >= 0)
     return
-        reinterpret_cast<char*>(
-            reinterpret_cast<uintptr_t>(ptr + (align - 1)) & ~static_cast<uintptr_t>(align - 1)
-        );
+            reinterpret_cast<char*>(
+                reinterpret_cast<uintptr_t>(ptr + (align - 1)) & ~static_cast<uintptr_t>(align - 1)
+            );
+}
+
+inline zone::chunk_list& zone::get_chank_lst()
+{
+    if (!m_chunk_list) {
+        auto ptr = ::malloc(sizeof(chunk_list) + m_chunk_size);
+        if (!ptr)
+            throw std::bad_alloc();
+        m_chunk_list = new (ptr) chunk_list(m_chunk_size, reinterpret_cast<char*>(ptr) + sizeof(chunk_list));
+    }
+    return *m_chunk_list;
 }
 
 inline void* zone::allocate_align(size_t size, size_t align)
 {
-    char* aligned = get_aligned(m_chunk_list.m_ptr, align);
-    size_t adjusted_size = size + static_cast<size_t>(aligned - m_chunk_list.m_ptr);
-    if (m_chunk_list.m_free < adjusted_size) {
+    chunk_list& chank_lst = get_chank_lst();
+    char* aligned = get_aligned(chank_lst.m_ptr, align);
+    size_t adjusted_size = size + static_cast<size_t>(aligned - chank_lst.m_ptr);
+    if (chank_lst.m_free < adjusted_size) {
         size_t enough_size = size + align - 1;
         char* ptr = allocate_expand(enough_size);
         aligned = get_aligned(ptr, align);
-        adjusted_size = size + static_cast<size_t>(aligned - m_chunk_list.m_ptr);
+        adjusted_size = size + static_cast<size_t>(aligned - chank_lst.m_ptr);
     }
-    m_chunk_list.m_free -= adjusted_size;
-    m_chunk_list.m_ptr  += adjusted_size;
+    chank_lst.m_free -= adjusted_size;
+    chank_lst.m_ptr += adjusted_size;
     return aligned;
 }
 
-inline void* zone::allocate_no_align(size_t size)
-{
-    char* ptr = m_chunk_list.m_ptr;
-    if(m_chunk_list.m_free < size) {
+inline void* zone::allocate_no_align(size_t size) {
+    chunk_list& chank_lst = get_chank_lst();
+    char* ptr = chank_lst.m_ptr;
+    if(chank_lst.m_free < size) {
         ptr = allocate_expand(size);
     }
-    m_chunk_list.m_free -= size;
-    m_chunk_list.m_ptr  += size;
+    chank_lst.m_free -= size;
+    chank_lst.m_ptr  += size;
 
     return ptr;
 }
 
 inline char* zone::allocate_expand(size_t size)
 {
-    chunk_list* const cl = &m_chunk_list;
-
+    chunk_list& cl = get_chank_lst();
     size_t sz = m_chunk_size;
 
     while(sz < size) {
@@ -286,10 +261,10 @@ inline char* zone::allocate_expand(size_t size)
 
     char* ptr = reinterpret_cast<char*>(c) + sizeof(chunk);
 
-    c->m_next  = cl->m_head;
-    cl->m_head = c;
-    cl->m_free = sz;
-    cl->m_ptr  = ptr;
+    c->m_next = cl.m_head;
+    cl.m_head = c;
+    cl.m_free = sz;
+    cl.m_ptr  = ptr;
 
     return ptr;
 }
@@ -308,7 +283,9 @@ inline void zone::push_finalizer(msgpack::unique_ptr<T> obj)
 inline void zone::clear()
 {
     m_finalizer_array.clear();
-    m_chunk_list.clear(m_chunk_size);
+    if (m_chunk_list) {
+        m_chunk_list->clear(m_chunk_size, reinterpret_cast<char*>(m_chunk_list) + sizeof(chunk_list));
+    }
 }
 
 inline void zone::swap(zone& o)
@@ -328,10 +305,10 @@ void zone::object_destruct(void* obj)
     static_cast<T*>(obj)->~T();
 }
 
-inline void zone::undo_allocate(size_t size)
-{
-    m_chunk_list.m_ptr  -= size;
-    m_chunk_list.m_free += size;
+inline void zone::undo_allocate(size_t size) {
+    chunk_list& cl = get_chank_lst();
+    cl.m_ptr  -= size;
+    cl.m_free += size;
 }
 
 
@@ -348,7 +325,7 @@ T* zone::allocate(Args... args)
     try {
         return new (x) T(args...);
     } catch (...) {
-        --m_finalizer_array.m_tail;
+        m_finalizer_array.pop();
         undo_allocate(sizeof(T));
         throw;
     }