C:/systemc-2.2.0/systemc-2.2.0/src/sysc/utils/sc_mempool.cpp

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  set forth in the SystemC Open Source License Version 2.4 (the "License");
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/*****************************************************************************

  sc_mempool.cpp - Memory pools for small objects.

  Original Author: Stan Y. Liao, Synopsys, Inc.

 *****************************************************************************/

/*****************************************************************************

  MODIFICATION LOG - modifiers, enter your name, affiliation, date and
  changes you are making here.

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 *****************************************************************************/
// $Log: sc_mempool.cpp,v $
// Revision 1.1.1.1  2006/12/15 20:31:39  acg
// SystemC 2.2
//
// Revision 1.3  2006/01/13 18:53:10  acg
// Andy Goodrich: Added $Log command so that CVS comments are reproduced in
// the source.
//



//  <sc_mempool> is a class that manages the memory for small objects,
//  of sizes <increment>, 2 * <increment>, ..., <num_pools> *
//  <increment>.  When a memory request of <k> bytes is made through
//  the memory pool, the smallest pool <j> such that <j> * <increment>
//  >= <k> is used.  The default values of <increment> and <num_pools>
//  are 8 and 8, respectively.  Each pool has an allocator, that
//  simply keeps a free list of cells, and allocate new blocks
//  whenever necessary.  We are relying on malloc() to return a
//  properly aligned memory blocks.  Note that the memory blocks
//  allocated by the mempool are never freed.  Thus, if purify is
//  used, we may get MIU (memory-in-use) warnings.  To disable this,
//  set the environment variable SYSTEMC_MEMPOOL_DONT_USE to 1.


static const char* dont_use_envstring = "SYSTEMC_MEMPOOL_DONT_USE";
static bool use_default_new = false;


#include <stdio.h>
#include <cstdlib>
#include "sysc/utils/sc_mempool.h"

namespace sc_core {

//  An allocator is one that handles a particular size.  It keeps a
//  <free_list> from which a cell may be allocated quickly if there
//  is one available.  If no cell is available from <free_list>, then
//  the allocator tries to find whether space is available from the
//  most-recently-allocated block, as pointed to by <next_avail>.  If
//  so, then the cell pointed to by <next_avail> is returned, while
//  <next_avail> is advanced.  If <next_avail> now points beyond
//  the current block, then it's reset to 0.  On the other hand,
//  if <next_avail> was 0 when a request to the block is made, then
//  a new block is allocated by calling system malloc(), and the new
//  block becomes the head of <block_list>.


class sc_allocator {
    friend class sc_mempool;

public:
    sc_allocator( int blksz, int cellsz );
    ~sc_allocator();
    void* allocate();
    void release(void* p);
    
    void display_statistics();

private:
    union link {
        link* next;
        double align;          // alignment required.
    };

    int block_size;            // size of each block in bytes,
                               // including the link
    int cell_size;             // size of each cell in bytes

    char* block_list;
    link* free_list;
    char* next_avail;

    int total_alloc;
    int total_freed;
    int free_list_alloc;
};

sc_allocator::sc_allocator( int blksz, int cellsz )
{
    cell_size = cellsz;
    block_size = sizeof(link) + (((blksz - 1) / cellsz) + 1) * cellsz;
    block_list = 0;
    free_list = 0;
    next_avail = 0;

    total_alloc = 0;
    total_freed = 0;
    free_list_alloc = 0;
}

sc_allocator::~sc_allocator()
{
    // Shouldn't free the block_list, since global objects that use
    // the memory pool may not have been destroyed yet ...
    // Let it leak, let it leak, let it leak ...
}

void*
sc_allocator::allocate()
{
    void* result = 0;
    total_alloc++;
    if (free_list != 0) {
        free_list_alloc++;
        result = free_list;
        free_list = free_list->next;
        return result;
    }
    else if (next_avail != 0) {
        result = next_avail;
        next_avail += cell_size;
        // next_avail goes beyond the block
        if (next_avail >= block_list + block_size)
            next_avail = 0;
        return result;
    }
    else {  // (next_avail == 0)
        link* new_block = (link*) malloc(block_size);  // need alignment?
        new_block->next = (link*) block_list;
        block_list = (char*) new_block;
        result = (block_list + sizeof(link));
        // Assume that the block will hold more than one cell ... why
        // wouldn't it?
        next_avail = ((char*) result) + cell_size;
        return result;
    }
}

void
sc_allocator::release(void* p)
{
    total_freed++;
    ((link*) p)->next = free_list;
    free_list = (link*) p;
}

void
sc_allocator::display_statistics()
{
    int nblocks = 0;
    for (link* b = (link*) block_list; b != 0; b = b->next)
        nblocks++;
    printf("size %3d: %2d block(s), %3d requests (%3d from free list), %3d freed.\n",
           cell_size, nblocks, total_alloc, free_list_alloc, total_freed);
}


static const int cell_sizes[] = {
/* 0 */   0,
/* 1 */   8,
/* 2 */  16,
/* 3 */  24,
/* 4 */  32,
/* 5 */  48,
/* 6 */  64,
/* 7 */  80,
/* 8 */  96,
/* 9 */ 128
};

static const int cell_size_to_allocator[] = {
/*  0 */    0,
/*  1 */    1,
/*  2 */    2,
/*  3 */    3,
/*  4 */    4,
/*  5 */    5,
/*  6 */    5,
/*  7 */    6,
/*  8 */    6,
/*  9 */    7,
/* 10 */    7,
/* 11 */    8,
/* 12 */    8,
/* 13 */    9,
/* 14 */    9,
/* 15 */    9,
/* 16 */    9
};


class sc_mempool_int {
    friend class sc_mempool;

public:
    sc_mempool_int(int blksz, int npools, int incr);
    ~sc_mempool_int();
    void* do_allocate(std::size_t);
    void  do_release(void*, std::size_t);

    void display_statistics();
    
private:
    sc_allocator** allocators;
    int num_pools;
    int increment;
    int max_size;
};


static bool
compute_use_default_new()
{
    const char* e = getenv(dont_use_envstring);
    return (e != 0) && (atoi(e) != 0);
}

sc_mempool_int::sc_mempool_int(int blksz, int npools, int incr)
{
    use_default_new = compute_use_default_new();
    if (! use_default_new) {
        num_pools = npools;
        increment = incr;
        max_size = cell_sizes[sizeof(cell_sizes)/sizeof(cell_sizes[0]) - 1];
        allocators = new sc_allocator*[npools + 1];
        for (int i = 1; i <= npools; ++i)
            allocators[i] = new sc_allocator(blksz, cell_sizes[i]);
        allocators[0] = allocators[1];
    }
}

sc_mempool_int::~sc_mempool_int()
{
    for (int i = 1; i <= num_pools; ++i)
        delete allocators[i];
    delete[] allocators;
}

static sc_mempool_int* the_mempool = 0;

void*
sc_mempool_int::do_allocate(std::size_t sz)
{
    int which_allocator = cell_size_to_allocator[(sz - 1) / increment + 1];
    void* p = allocators[which_allocator]->allocate();
    return p;
}

void
sc_mempool_int::do_release(void* p, std::size_t sz)
{
    int which_allocator = cell_size_to_allocator[(sz - 1) / increment + 1];
    allocators[which_allocator]->release(p);
}

void
sc_mempool_int::display_statistics()
{
    printf("*** Memory Pool Statistics ***\n");
    for (int i = 1; i <= num_pools; ++i)
        allocators[i]->display_statistics();
}

/****************************************************************************/

void*
sc_mempool::allocate(std::size_t sz)
{
    if (use_default_new)
        return ::operator new(sz);

    if (the_mempool == 0) {
        use_default_new = compute_use_default_new();
        if (use_default_new)
            return ::operator new(sz);

        // Note that the_mempool is never freed.  This is going to cause
        // memory leaks when the program exits.
        the_mempool = new sc_mempool_int( 1984, sizeof(cell_sizes)/sizeof(cell_sizes[0]) - 1, 8 );
    }

    if (sz > (unsigned) the_mempool->max_size)
        return ::operator new(sz);

    return the_mempool->do_allocate(sz);
}

void
sc_mempool::release(void* p, std::size_t sz)
{
    if (p) {
        
        if (use_default_new || sz > (unsigned) the_mempool->max_size) {
            ::operator delete(p);
            return;
        }

        the_mempool->do_release(p, sz);
    }
}

void
sc_mempool::display_statistics()
{
    if (the_mempool && !use_default_new) {
        the_mempool->display_statistics();
    } else {
        printf("SystemC info: no memory allocation was done through the memory pool.\n");
    }
}

} // namespace sc_core

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