Free-List Memory Pool

This is a C99 header library that provides efficient type-generic code to allocate heap memory from the OS for user-defined number of objects. Achieved through the magic of C macros and free lists.

This library is built for situations where programs repeatedly call malloc/calloc/new/etc. for small data structures, followed closely by free/delete. Once a pool is created, getting a pointer from the pool to an unused object costs a couple of machine instructions. Boost memory pools and others are overkill sometimes.

Limitations:

• Memory pools are statically-sized.

Inspired by computer game particles.

Try it now

make; ./bin/perftest

Example

#include "fmpool.h"

/* define a "point" struct with x and y coordinates as doubles */
typedef struct Point_s
{
  double x;
  double y;
} Point_t;

/* macro that initializes fmpool functions that take Point_t structs as
   arguments - compile-time only */
FMPOOL_INIT(Point_t)

#define NUM_POINTS 16

int main()
{
  /* create pool - requests memory from OS */
  fmpool_t(Point_t)* Pool;
  Pool = fmpool_create(Point_t, NUM_POINTS);
  
  /* grab some pointers to allocated memory from the pool */
  Point_t* PointArray[NUM_POINTS] = {NULL};
  for(size_t i = 0; i < NUM_POINTS; i++)
  {
    Point_t* Point = fmpool_get(Point_t, Pool);
    if(Point)
      PointArray[i] = Point;
  }
  /* release some points back to the pool */
  for(size_t i = 0; i < NUM_POINTS - 5; i++)
    fmpool_free(Point_t, PointArray[i], Pool);

  /* destroy pool when done - releases memory to OS */
  fmpool_destroy(Point_t, Pool);
  return 0;
}

Details

FMPool requests a contiguous block of memory once during creation with fmpool_create. Afterwards, pointers to unused objects are provided with fmpool_get. Objects can be released back to the pool with fmpool_free and subsequently re-requested. When finished, the memory is released back to the OS with fmpool_destroy.

Functions

fmpool_create(TYPE, NUM)

Creates a new memory pool. The new pool has NUM objects of type TYPE.

Return Values
On success: returns a pointer to the new fmpool.
On failure: returns a NULL pointer.

fmpool_destroy(TYPE, POOL)

Frees all memory associated with POOL.

Return Values
Returns no value. (mimics C99 standard).

fmpool_get(TYPE, POOL)

Grabs an unused object from the pool.

Return Values
On success: returns a TYPE pointer.
On failure: returns a NULL pointer.

fmpool_free(TYPE, OBJ, POOL)

If OBJ is controlled by POOL, sets it as unused. Does not zero memory.

Return Values
On success: returns true.
On failure: returns false.

License

MIT License