A small and simple visualizer built on top of the explicit allocator example from Computer Systems: A Programmer's Perspective (chapter 9 on Virtual Memory).
It allows 2 commands: malloc <bytes> and free <block address> and displays a representation of the heap and the allocator's implicit free list.
It was meant as a learning project to help me get an intuition for the general job of an explicit allocator such as the malloc package.
One can see heap blocks being allocated, freed and coalesced as well the heap being expanded by requesting the kernel for more memory.
Each block has the following structure: |header|payload|footer|. The payload is omitted if its size is zero bytes.
The header and footer carry the same information with the format size:allocated. size includes the both the header and footer (4 bytes each). allocated is 0 if the block is free or 1 if it is allocated.
Blocks obey an 8-byte alignment. For example, calling malloc 6 will result in the allocation of a payload of 8 bytes: |16:1|---8---|16:1|. If we were to call free with the block's address (returned previously by malloc), its allocated bit would be zeroed (|16:0|---8---|16:0|), allowing the block to be allocated again (or coalesced with a neighbouring free block).
The headers and footers allow the allocator to find free blocks without having to do the bookeeping on a dedicated data structure. Thus the name implicit free list.
The heap is initialized with a prologue and an epilogue. Respectively, |8:1||8:1| and |0:1| (special case w/ only a header w/ size set to 0).
It is also given a free block with total 4096 bytes (4KB).
NOTE: all code originally from CSAPP except all of main.c and functions mm_read_num_headers, mm_read_headers, mm_read_size, mm_read_alloc in mm.c.
Just run the precompiled binary (Linux x86_64 machine) ./heap-visualizer if you're feeling lucky, or inspect the code and build it yourself.
