Re: Do you use a garbage collector?

From:
"Chris Thomasson" <cristom@comcast.net>
Newsgroups:
comp.lang.c++
Date:
Sun, 13 Apr 2008 18:11:06 -0700
Message-ID:
<RrGdnZr1EfRYPZ_VnZ2dnUVZ_qOknZ2d@comcast.com>
"Razii" <DONTwhatevere3e@hotmail.com> wrote in message
news:r84504tsla9563r79shakgbg4r37ju4vjs@4ax.com...

On Sun, 13 Apr 2008 23:41:29 +0200, "Bo Persson" <bop@gmb.dk> wrote:

Isn't that what I said? The new and delete operators are not used very
often in the code. Perhaps only once each in std::allocator, where
they don't allocate int-sized objects, and never 10 million times in a
loop.


std::vector has new and delete. They are still there and must be there
every time memory is allocated dynamically.

That's why the benchmark is silly - you would never do anything like
that in real C++ code.


It's not silly. It's a benchmark that tests dynamic memory allocation
and GC performance.


Let me go ahead and try to quickly augment your test using a VERY simple
caching allocator:

<this should compile...>
____________________________________________________________________
#include <new>
#include <cstddef>

template<typename T>
class cache_allocator {
  union node_type {
    T m_obj;
    node_type* m_next;
  };

  node_type* m_head;
  std::size_t m_depth;
  std::size_t const m_max_depth;

public:
  cache_allocator(
   std::size_t const max_depth = 1024
  ): m_head(NULL),
     m_depth(0),
     m_max_depth(max_depth) {
  }

  ~cache_allocator() throw() {
    node_type* node = m_head;
    while (node) {
      node_type* const next = node->m_next;
      ::operator delete(node);
      node = next;
    }
  }

  void sys_destroy(node_type* const node) throw() {
    if (m_depth < m_max_depth) {
      node->m_next = m_head;
      m_head = node;
      ++m_depth;
    } else {
      ::operator delete(node);
    }
  }

public:
  T* create_ctor() {
    node_type* node = m_head;
    if (! node) {
      node = new (::operator new(sizeof(*node))) node_type;
      return &node->m_obj;
    }
    m_head = node->m_next;
    --m_depth;
    return new (&node->m_obj) T;
  }

  void destroy_dtor(T* const obj) {
    node_type* node = reinterpret_cast<node_type*>(obj);
    try {
      obj->~T();
      sys_destroy(node);
    } catch(...) {
      sys_destroy(node);
      throw;
    }
  }

public:
  T* create_raw() {
    node_type* node = m_head;
    if (! node) {
      node = new (::operator new(sizeof(*node))) node_type;
      return &node->m_obj;
    }
    m_head = node->m_next;
    --m_depth;
    return &node->m_obj;
  }

  void destroy_raw(T* const obj) throw() {
    sys_destroy(reinterpret_cast<node_type*>(obj));
  }
};

// Your Test...
#include <ctime>
#include <iostream>

#define TREE_CREATE_CACHE_CTOR g_tree_malloc.create_ctor
#define TREE_CREATE_CACHE_RAW g_tree_malloc.create_raw
#define TREE_CREATE_NEW new Tree
#define TREE_DESTROY_CACHE_CTOR(ptr) g_tree_malloc.destroy_dtor(ptr)
#define TREE_DESTROY_CACHE_RAW(ptr) g_tree_malloc.destroy_raw(ptr)
#define TREE_DESTROY_NEW(ptr) delete ptr

#define TREE_CREATE TREE_CREATE_CACHE_RAW
#define TREE_DESTROY TREE_DESTROY_CACHE_RAW

struct Tree
{
 Tree *left;
 Tree *right;
};

static cache_allocator<Tree> g_tree_malloc;

Tree *CreateTree(int n)
{
 if(n <= 0) return NULL;
 Tree *t = TREE_CREATE();
 t->left = CreateTree(n - 1);
 t->right = CreateTree(n - 1);
 return t;
}

void DeleteTree(Tree *t)
{
 if(t)
 {
  TREE_DESTROY(t->left);
  TREE_DESTROY(t->right);
  TREE_DESTROY(t);
 }
}

int main(int argc, char *argv[])
{
 clock_t start=clock();
 for(int i = 0;i < 15;i++) DeleteTree(CreateTree(22));
 clock_t endt=clock();
 std::cout <<"Time: " <<
 double(endt-start)/CLOCKS_PER_SEC * 1000 << " ms\n";
 return 0;
}

____________________________________________________________________

What numbers do you get? Does that improve anything?

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