This is a version of dlmalloc.c ported to V. You can find the original source at ftp://g.oswego.edu/pub/misc/malloc.c

The original source was written by Doug Lea and released to the public domain

Why dlmalloc?

This library does not rely on C code. The primary purpose is for use in freestanding build mode and for WASM target.

dlmalloc is not the most performant allocator. It's main purpose is to be easily portable and easy to learn. Here we have straight port of C and dlmalloc-rs versions of dlmalloc.

fn calloc(size usize) voidptr

Same as malloc, except if the allocation succeeds it's guaranteed to point to size bytes of zeros.

fn free(ptr voidptr)

free deallocates a ptr.

fn get_system_allocator() Allocator

get_system_allocator returns an allocator that uses the system allocator.

fn malloc(size usize) voidptr

malloc allocates size bytes. It returns a null pointer if allocation fails. It returns a valid pointer otherwise.

fn memalign(size usize, align usize) voidptr

memalign allocates size bytes with align align.

Returns a null pointer if allocation fails. Returns a valid pointer otherwise.

fn new(system_allocator Allocator) Dlmalloc

new creates a new instance of Dlmalloc with the given system allocator.

fn realloc(ptr voidptr, oldsize usize, newsize usize) voidptr

realloc reallocates ptr, a previous allocation with old_size and to have new_size.

Returns a null pointer if the memory couldn't be reallocated, but ptr is still valid. Returns a valid pointer and frees ptr if the request is satisfied.

enum Map_flags {
	map_shared          = 0x01
	map_private         = 0x02
	map_shared_validate = 0x03
	map_type            = 0x0f
	map_fixed           = 0x10
	map_file            = 0x00
	map_anonymous       = 0x20
	map_huge_shift      = 26
	map_huge_mask       = 0x3f
}

enum Mm_prot {
	prot_read      = 0x1
	prot_write     = 0x2
	prot_exec      = 0x4
	prot_none      = 0x0
	prot_growsdown = 0x01000000
	prot_growsup   = 0x02000000
}

struct Allocator {
pub:
	alloc            fn (voidptr, usize) (voidptr, usize, u32)         = unsafe { nil }
	remap            fn (voidptr, voidptr, usize, usize, bool) voidptr = unsafe { nil }
	free_part        fn (voidptr, voidptr, usize, usize) bool          = unsafe { nil }
	free_            fn (voidptr, voidptr, usize) bool                 = unsafe { nil }
	can_release_part fn (voidptr, u32) bool = unsafe { nil }
	allocates_zeros  fn (voidptr) bool      = unsafe { nil }
	page_size        fn (voidptr) usize     = unsafe { nil } // not a constant field because some platforms might have different page sizes depending on configs
	data             voidptr
}

In order for dlmalloc to efficiently manage memory, it needs a way to communicate with the underlying platform. This Allocator type provides an interface for this communication.

Why not interface? Interfaces require memory allocation so it is simpler to pass a struct.

struct Dlmalloc {
	system_allocator Allocator
	max_request      usize = 4294901657
mut:
	// bin maps
	smallmap u32 // bin map for small bins
	treemap  u32 // bin map  for tree bins

	smallbins      [66]&Chunk // small bins, it is actually (n_small_bins + 1) * 2
	treebins       [n_tree_bins]&TreeChunk
	dvsize         usize
	topsize        usize
	dv             &Chunk = unsafe { nil }
	top            &Chunk = unsafe { nil }
	footprint      usize
	max_footprint  usize
	seg            Segment
	trim_check     u32
	least_addr     voidptr
	release_checks usize
}

fn (dl &Dlmalloc) calloc_must_clear(ptr voidptr) bool

fn (mut dl Dlmalloc) calloc(size usize) voidptr

calloc is the same as malloc, except if the allocation succeeds it's guaranteed to point to size bytes of zeros.

fn (mut dl Dlmalloc) free_(mem voidptr)

free_ behaves as libc free, but operates within the given space

fn (mut dl Dlmalloc) malloc(size usize) voidptr

malloc allocates a block of memory of the given size.

fn (mut dl Dlmalloc) realloc(oldmem voidptr, bytes usize) voidptr

realloc behaves as libc realloc, but operates within the given space

fn (mut dl Dlmalloc) memalign(alignment_ usize, bytes usize) voidptr

memaligns allocates memory aligned to alignment_. Only call this with power-of-two alignment and alignment > dlmalloc.malloc_alignment