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// file : examples/cxx/hybrid/allocator/arena.cxx
// author : Boris Kolpackov <boris@codesynthesis.com>
// copyright : not copyrighted - public domain
#include <stdio.h>
#include <string.h> // memcpy
#include "arena.hxx"
arena::
arena (void* memory, size_t size)
: alloc_count_ (0),
realloc_count_ (0),
free_count_ (0),
cur_allocated_ (0),
max_allocated_ (0)
{
head_ = static_cast<block*> (memory);
head_->cap = size - sizeof (block);
head_->next = 0;
head_->used = false;
}
void* arena::
allocate (size_t size)
{
block* b = head_;
while (b != 0)
{
if (!b->used)
{
if (b->cap >= size)
{
// See if it makes sense to fragment this block.
//
if (b->cap - size >= sizeof (block) * 2)
{
block* b1 = reinterpret_cast<block*> (
reinterpret_cast<char*> (b) + sizeof (block) + size);
b1->cap = b->cap - size - sizeof (block);
b1->next = b->next;
b1->used = false;
b->next = b1;
b->cap = size;
}
b->used = true;
b->size = size;
alloc_count_++;
cur_allocated_ += size;
if (cur_allocated_ > max_allocated_)
max_allocated_ = cur_allocated_;
return b + 1;
}
// This block is not big enough. See if we can merge it
// with the next block.
//
if (b->next != 0 && !b->next->used)
{
block* b1 = b->next;
b->cap += b1->cap + sizeof (block);
b->next = b1->next;
// Try the merged block again.
//
continue;
}
}
// This block is either in use or not big enough. Continue
// searching.
//
b = b->next;
}
return 0;
}
void* arena::
reallocate (void* p, size_t size)
{
// If the passed pointer is NULL, reallocate is equivalent to
// allocate.
//
if (!p)
return allocate (size);
block* b = static_cast<block*> (p) - 1;
// If the passed size is NULL, reallocate is equivalent to free.
//
if (size == 0)
{
free (p);
return 0;
}
// If this block is not large enough to satisfy the request, try to
// merge it with the next block(s).
//
while (b->cap < size && b->next != 0 && !b->next->used)
{
block* b1 = b->next;
b->cap += b1->cap + sizeof (block);
b->next = b1->next;
}
// If this block is now large enough then we can reuse the same
// memory region.
//
if (b->cap >= size)
{
realloc_count_++;
cur_allocated_ += size - b->size;
if (cur_allocated_ > max_allocated_)
max_allocated_ = cur_allocated_;
b->size = size;
return p;
}
// Otherwise allocate a new block and copy the data over.
//
void* r = allocate (size);
if (r)
{
memcpy (r, p, b->size);
free (p);
}
return r;
}
void arena::
free (void* p)
{
if (p)
{
block* b = static_cast<block*> (p) - 1;
cur_allocated_ -= b->size;
free_count_++;
b->used = false;
}
}
void arena::
print_statistics ()
{
printf ("\n");
printf ("allocations: %lu\n", alloc_count_);
printf ("reallocations: %lu\n", realloc_count_);
printf ("deallocations: %lu\n", free_count_);
printf ("currently in use: %lu bytes\n", cur_allocated_);
printf ("maximum in use: %lu bytes\n", max_allocated_);
printf ("\n");
}
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