shithub: mc

ref: 3cdb85952401e2284ecd285742174b8f774bf18b
dir: /lib/std/alloc.myr/

use "die"
use "extremum"
use "memops"
use "syswrap"
use "threadhooks"
use "types"
use "units"
use "bytealloc"

/*
The allocator implementation here is based on Bonwick's slab allocator.

For small allocations (up to Bktmax), it works by requesting large,
power of two aligned chunks from the operating system, and breaking
them into a linked list of equal sized chunks. Allocations are then
satisfied by taking the head of the list of chunks. Empty slabs
are removed from the freelist.

The data structure looks something like this:
   Bkts:
	[16  byte] -> [slab hdr | chunk -> chunk -> chunk] -> [slab hdr | chunk -> chunk -> chunk]
	[32  byte] -> Zslab
	[64  byte] -> [slab hdr | chunk -> chunk]
	...
	[32k byte] -> ...

Large allocations are simply satisfied by mmap().

*/

pkg std =
	generic alloc	: (		-> @a#)
	generic zalloc	: (		-> @a#)
	generic free	: (v:@a#	-> void)

	generic slalloc	: (len : size	-> @a[:])
	generic slzalloc	: (len : size	-> @a[:])
	generic slgrow	: (sl : @a[:]#, len : size	-> @a[:])
	generic slzgrow	: (sl : @a[:]#, len : size	-> @a[:])
	generic slfree	: (sl : @a[:]	-> void)
;;

type slheader = struct
	cap	: size	/* capacity in bytes */
	magic	: size	/* magic check value */
;;

/* Allocates an object of type @a, returning a pointer to it. */
generic alloc = {-> @a#
	-> (bytealloc(sizeof(@a)) : @a#)
}

generic zalloc = {-> @a#
	-> (zbytealloc(sizeof(@a)) : @a#)
}

/* Frees a value of type @a */
generic free = {v:@a# -> void
	bytefree((v : byte#), sizeof(@a))
}

/* allocates a slice of 'len' elements. */
generic slalloc = {len
	var p, sz

	if len == 0
		-> [][:]
	;;
	sz = len*sizeof(@a) + align(sizeof(slheader), Align)
	p = bytealloc(sz)
	p = inithdr(p, sz)
	-> (p : @a#)[0:len]
}

generic slzalloc = {len
	var p, sz

	if len == 0
		-> [][:]
	;;
	sz = len*sizeof(@a) + align(sizeof(slheader), Align)
	p = zbytealloc(sz)
	p = inithdr(p, sz)
	-> (p : @a#)[0:len]
}

const inithdr = {p, sz
	var phdr, prest

	phdr = (p : slheader#)
	phdr.cap = allocsz(sz) - align(sizeof(slheader), Align)
	phdr.magic = (0xdeadbeefbadf00d : size)

	prest = (p : size) + align(sizeof(slheader), Align)
	-> (prest : byte#)
}

const checkhdr = {p
	var phdr, addr

	addr = (p : size)
	addr -= align(sizeof(slheader), Align)
	phdr = (addr : slheader#)
	iassert(phdr.magic == (0xdeadbeefbadf00d : size), "corrupt memory\n")
}

/* Frees a slice */
generic slfree	 = {sl
	var head

	if (sl : byte#) == Zsliceptr
		-> void
	;;

	checkhdr((sl : byte#))
	head = ((sl : byte#) : size)
	head -= align(sizeof(slheader), Align)
	bytefree((head : byte#), slcap((sl : byte#)))
}

/* Grows a slice */
generic slgrow = {sl : @a[:]#, len
	var cap
	var new
	var n

	/* if the slice doesn't need a bigger bucket, we don't need to realloc. */
	cap = 0
	if (sl# : byte#) != Zsliceptr
		cap = slcap((sl# : byte#))
	;;
	if cap >= allocsz(len*sizeof(@a))
		sl# = (sl# : @a#)[:len]
		-> sl#
	;;

	/* grow in factors of 1.5 */
	cap = max(Align, cap)
	while cap < len
		cap += (cap >> 1)
	;;

	new = slalloc(cap)
	n = min(len, sl#.len)
	for var i = 0; i < n; i++
		new[i] = sl#[i]
	;;
	if sl#.len > 0
		slfree(sl#)
	;;
	sl# = new[:len]
	-> sl#
}

/* Grows a slice, filling new entries with zero bytes */
generic slzgrow = {sl : @a[:]#, len
	var oldlen
	var base

	oldlen = sl#.len
	slgrow(sl, len)
	base = ((sl# : byte#) : intptr)
	if oldlen < len
		memfill((sl#[oldlen:] : byte#), 0, (len - oldlen)*sizeof(@a))
	;;
	-> sl#
}

const slcap = {p
	var phdr

	phdr = ((p : size) - align(sizeof(slheader), Align) : slheader#)
	std.iassert(phdr.magic == (0xdeadbeefbadf00d : size), "corrupt memory\n")
	-> phdr.cap
}