c - Implementing your own malloc/free with mmap and munmap

C - Implementing your own malloc/free with mmap and munmap

Implementing your own memory allocator using mmap and munmap in C involves creating a custom memory management system that allocates and deallocates memory from the operating system. This can be a good exercise to understand how memory management works at a lower level.

Here's a basic implementation outline for creating your own malloc and free functions using mmap and munmap:

1. Include Necessary Headers

You'll need to include headers for memory management and system calls:

#include <unistd.h> #include <sys/mman.h> #include <stddef.h> // For size_t #include <stdint.h> // For uintptr_t

2. Define Data Structures

Define data structures to manage memory blocks. A common approach is to use a linked list of blocks where each block contains metadata about its size and status (free or allocated).

typedef struct Block { size_t size; // Size of the block struct Block *next; // Pointer to the next block int free; // Free or allocated status } Block; #define BLOCK_SIZE sizeof(Block)

3. Implement Memory Allocation

To implement malloc, you need to find a free block that fits the requested size, or if none is available, request more memory from the OS using mmap.

#define INITIAL_HEAP_SIZE (1024 * 1024) // 1 MB for initial heap // Global pointer to the first block static Block *heap_start = NULL; void *my_malloc(size_t size) { if (size <= 0) return NULL; // Align size to block boundary size = (size + BLOCK_SIZE - 1) & ~(BLOCK_SIZE - 1); Block *current = heap_start; Block *prev = NULL; // Search for a suitable free block while (current != NULL) { if (current->free && current->size >= size) { // Split the block if it's too big if (current->size > size + BLOCK_SIZE) { Block *new_block = (Block *)((uintptr_t)current + BLOCK_SIZE + size); new_block->size = current->size - size - BLOCK_SIZE; new_block->next = current->next; new_block->free = 1; current->size = size; current->next = new_block; } current->free = 0; return (void *)((uintptr_t)current + BLOCK_SIZE); } prev = current; current = current->next; } // No suitable block found, request more memory size_t total_size = size + BLOCK_SIZE; void *ptr = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (ptr == MAP_FAILED) { return NULL; } Block *new_block = (Block *)ptr; new_block->size = size; new_block->free = 0; new_block->next = NULL; if (prev != NULL) { prev->next = new_block; } else { heap_start = new_block; } return (void *)((uintptr_t)new_block + BLOCK_SIZE); }

4. Implement Memory Deallocation

For free, you need to mark the block as free and potentially merge it with adjacent free blocks.

void my_free(void *ptr) { if (ptr == NULL) return; Block *block = (Block *)((uintptr_t)ptr - BLOCK_SIZE); block->free = 1; // Merge adjacent free blocks Block *current = heap_start; while (current != NULL) { if (current->free) { Block *next = current->next; if (next && next->free) { current->size += BLOCK_SIZE + next->size; current->next = next->next; } } current = current->next; } }

5. Deallocate Memory on Shutdown

Ensure that you unmap the memory allocated by mmap when the program terminates or no longer needs it. This is typically handled in a cleanup function:

void cleanup_memory() { Block *current = heap_start; while (current != NULL) { Block *next = current->next; if (!current->free) { munmap(current, current->size + BLOCK_SIZE); } current = next; } }

6. Use and Test

Use my_malloc and my_free in your program as you would with standard malloc and free. Make sure to test thoroughly for edge cases, memory leaks, and performance.

Summary

  1. Include Headers: Include necessary headers for system calls and data types.
  2. Define Data Structures: Create structures to manage blocks of memory.
  3. Implement my_malloc: Allocate memory using mmap if needed and manage free blocks.
  4. Implement my_free: Free memory and merge adjacent free blocks.
  5. Cleanup: Unmap memory using munmap to prevent leaks.

This is a basic implementation and can be enhanced with additional features like better memory alignment, error handling, and more efficient memory management algorithms.

Examples

  1. "C custom malloc and free using mmap"

    • Description: Implement malloc and free using mmap to allocate and deallocate memory.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #define MEMORY_SIZE (1024 * 1024) // 1MB for example static void *memory = NULL; void *custom_malloc(size_t size) { if (memory == NULL) { memory = mmap(NULL, MEMORY_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } return memory; } void custom_free(void *ptr) { // For simplicity, this implementation does not handle deallocation } int main() { void *ptr = custom_malloc(100); custom_free(ptr); return 0; }

  2. "C mmap based memory allocator implementation"

    • Description: Use mmap to create a simple memory allocator with malloc and free functions.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> static void *base = NULL; void *custom_malloc(size_t size) { if (base == NULL) { base = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } return base; } void custom_free(void *ptr) { if (ptr == base) { munmap(base, 1024 * 1024); base = NULL; } } int main() { void *ptr = custom_malloc(200); custom_free(ptr); return 0; }

  3. "C implementing malloc with mmap and custom free"

    • Description: Create a custom malloc and free using mmap and handle memory deallocation.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> typedef struct Block { size_t size; struct Block *next; } Block; static Block *free_list = NULL; void *custom_malloc(size_t size) { size += sizeof(Block); if (free_list == NULL) { void *mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (mem == MAP_FAILED) return NULL; Block *block = (Block *)mem; block->size = size; block->next = NULL; return (void *)(block + 1); } // Implement free list management here return NULL; } void custom_free(void *ptr) { if (ptr == NULL) return; Block *block = (Block *)ptr - 1; munmap(block, block->size); } int main() { void *ptr = custom_malloc(100); custom_free(ptr); return 0; }

  4. "C memory allocator with mmap example"

    • Description: Example of a simple memory allocator using mmap for memory management.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> void *custom_malloc(size_t size) { return mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } void custom_free(void *ptr, size_t size) { munmap(ptr, size); } int main() { void *ptr = custom_malloc(256); custom_free(ptr, 256); return 0; }

  5. "C custom memory management using mmap and munmap"

    • Description: Implement memory management using mmap and munmap with custom allocation and deallocation.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> void *custom_malloc(size_t size) { return mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } void custom_free(void *ptr, size_t size) { munmap(ptr, size); } int main() { void *ptr = custom_malloc(128); custom_free(ptr, 128); return 0; }

  6. "C creating custom allocator with mmap and munmap"

    • Description: Create a custom memory allocator using mmap and munmap with dynamic memory management.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> static void *memory_pool = NULL; void *custom_malloc(size_t size) { if (memory_pool == NULL) { memory_pool = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } return memory_pool; } void custom_free(void *ptr) { if (ptr == memory_pool) { munmap(memory_pool, 1024 * 1024); // Assuming 1MB pool memory_pool = NULL; } } int main() { void *ptr = custom_malloc(500); custom_free(ptr); return 0; }

  7. "C mmap for custom malloc implementation"

    • Description: Use mmap for implementing a custom malloc function.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> void *custom_malloc(size_t size) { return mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } void custom_free(void *ptr, size_t size) { munmap(ptr, size); } int main() { void *ptr = custom_malloc(512); custom_free(ptr, 512); return 0; }

  8. "C implementing memory allocation using mmap and munmap"

    • Description: Implement a custom memory allocator using mmap and munmap functions for dynamic memory allocation.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> void *custom_malloc(size_t size) { return mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } void custom_free(void *ptr, size_t size) { munmap(ptr, size); } int main() { void *ptr = custom_malloc(1024); custom_free(ptr, 1024); return 0; }

  9. "C custom memory allocator with mmap"

    • Description: Create a custom memory allocator using mmap to allocate memory and munmap to deallocate it.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> void *custom_malloc(size_t size) { return mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } void custom_free(void *ptr) { // Assuming we know the size of the allocated memory size_t size = 1024; // Example size munmap(ptr, size); } int main() { void *ptr = custom_malloc(256); custom_free(ptr); return 0; }

  10. "C using mmap to implement malloc and free"

    • Description: Use mmap to implement custom malloc and free functions, handling memory allocation and deallocation.
    • Code:
      #include <sys/mman.h> #include <unistd.h> #include <stddef.h> #include <stdio.h> static void *pool = NULL; void *custom_malloc(size_t size) { if (pool == NULL) { pool = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); } return pool; } void custom_free(void *ptr) { if (ptr == pool) { munmap(pool, 1024 * 1024); // Example size pool = NULL; } } int main() { void *ptr = custom_malloc(128); custom_free(ptr); return 0; }

More Tags

missingmethodexception limit singlestore decorator checkboxfor laravel-5.6 turkish srand ansi-c bearing

More Programming Questions

More Various Measurements Units Calculators

More Everyday Utility Calculators

More Entertainment Anecdotes Calculators

More Biology Calculators