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pub use libc::c_void;
use std::alloc::{alloc_zeroed, dealloc, Layout};
use std::ptr::{drop_in_place, null_mut, NonNull};
use super::vm::Vm;
#[derive(Debug, PartialEq)]
enum GcNodeColor {
White,
Gray,
Black,
}
pub struct GcNode {
next: *mut GcNode,
size: usize,
color: GcNodeColor,
native_refs: usize,
tracer: GenericTraceFunction,
finalizer: GenericFunction,
}
impl GcNode {
pub fn alloc_size<T: Sized>() -> usize {
use std::mem::size_of;
size_of::<GcNode>() + size_of::<T>()
}
}
type GenericFunction = unsafe fn(*mut c_void);
const INITIAL_THRESHOLD: usize = 4096;
const USED_SPACE_RATIO: f64 = 0.7;
pub struct GcManager {
first_node: *mut GcNode,
last_node: *mut GcNode,
bytes_allocated: usize,
gray_nodes: Vec<*mut GcNode>,
threshold: usize,
enabled: bool,
}
impl GcManager {
pub fn new() -> GcManager {
GcManager {
first_node: null_mut(),
last_node: null_mut(),
bytes_allocated: 0,
gray_nodes: Vec::new(),
threshold: INITIAL_THRESHOLD,
enabled: false,
}
}
unsafe fn malloc_raw<T: Sized + GcTraceable>(
&mut self, vm: &Vm, x: T, finalizer: GenericFunction,
) -> *mut T {
let size = GcNode::alloc_size::<T>();
let node: *mut GcNode = self.cycle(vm, size).unwrap_or_else(|| {
let layout = Layout::from_size_align(size, 2).unwrap();
NonNull::new(alloc_zeroed(layout) as *mut GcNode).unwrap()
}).as_ptr();
if self.first_node.is_null() {
self.first_node = node;
self.last_node = node;
(*node).next = null_mut();
} else {
(*self.last_node).next = node;
(*node).next = null_mut();
self.last_node = node;
}
(*node).native_refs = 1;
(*node).tracer = std::mem::transmute(T::trace as *mut c_void);
(*node).finalizer = finalizer;
(*node).size = size;
self.bytes_allocated += (*node).size;
(*node).color = GcNodeColor::Gray;
self.gray_nodes.push(node);
std::mem::forget(std::mem::replace(&mut *(node.add(1) as *mut T), x));
node.add(1) as *mut T
}
pub fn malloc<T: Sized + GcTraceable>(&mut self, vm: &Vm, val: T) -> Gc<T> {
Gc {
ptr: NonNull::new(unsafe {
self.malloc_raw(vm, val, |ptr| drop_in_place::<T>(ptr as *mut T))
})
.unwrap(),
}
}
pub unsafe fn push_gray_body(&mut self, ptr: *mut c_void) {
push_gray_body(&mut self.gray_nodes, ptr)
}
pub fn enable(&mut self) {
self.enabled = true;
}
pub fn disable(&mut self) {
self.enabled = false;
}
unsafe fn cycle(&mut self, vm: &Vm, size: usize) -> Option<NonNull<GcNode>> {
if !self.enabled || self.bytes_allocated < self.threshold {
return None;
}
let gray_nodes = std::mem::replace(&mut self.gray_nodes, Vec::new());
for node in gray_nodes.iter() {
let body = node.add(1) as *mut c_void;
(**node).color = GcNodeColor::Black;
((**node).tracer)(body, std::mem::transmute(&mut self.gray_nodes));
}
if self.gray_nodes.is_empty() {
let mut prev: *mut GcNode = null_mut();
let mut node = self.first_node;
let mut first_fitting_node: Option<NonNull<GcNode>> = None;
while !node.is_null() {
let next: *mut GcNode = (*node).next;
let mut freed = false;
if (*node).native_refs == 0 && (*node).color == GcNodeColor::White {
freed = true;
let body = node.add(1);
if prev.is_null() {
self.first_node = (*node).next;
} else {
(*prev).next = (*node).next;
}
if (*node).next.is_null() {
self.last_node = prev;
}
self.bytes_allocated -= (*node).size;
let finalizer = (*node).finalizer;
finalizer(body as *mut c_void);
if (*node).size == size && first_fitting_node.is_none() {
std::ptr::write_bytes(node as *mut u8, 0, (*node).size);
first_fitting_node = Some(NonNull::new_unchecked(node));
} else {
let layout = Layout::from_size_align((*node).size, 2).unwrap();
dealloc(node as *mut u8, layout);
}
} else if (*node).native_refs != 0 {
self.gray_nodes.push(node);
} else {
(*node).color = GcNodeColor::White;
}
if !freed {
prev = node;
}
node = next;
}
vm.trace(&mut self.gray_nodes);
if ((self.bytes_allocated as f64) / (self.threshold as f64)) > USED_SPACE_RATIO {
self.threshold = (self.bytes_allocated as f64 / USED_SPACE_RATIO) as usize;
}
first_fitting_node
} else {
None
}
}
}
impl std::ops::Drop for GcManager {
fn drop(&mut self) {
unsafe {
let mut node: *mut GcNode = self.first_node;
while !node.is_null() {
let next: *mut GcNode = (*node).next;
let body = node.add(1);
let finalizer = (*node).finalizer;
finalizer(body as *mut c_void);
let layout = Layout::from_size_align((*node).size, 2).unwrap();
dealloc(node as *mut u8, layout);
node = next;
}
}
}
}
#[repr(transparent)]
pub struct Gc<T: Sized + GcTraceable> {
ptr: NonNull<T>,
}
impl<T: Sized + GcTraceable> Gc<T> {
pub unsafe fn from_raw(ptr: *mut T) -> Gc<T> {
let node: *mut GcNode = (ptr as *mut GcNode).sub(1);
(*node).color = GcNodeColor::Black;
(*node).native_refs += 1;
Gc {
ptr: NonNull::new(ptr).unwrap(),
}
}
pub fn to_raw(&self) -> *const T {
self.ptr.as_ptr()
}
pub unsafe fn into_raw(self) -> *mut T {
self.ptr.as_ptr()
}
pub fn as_mut(&self) -> &mut T {
unsafe { &mut *self.ptr.as_ptr() }
}
}
impl<T: Sized + GcTraceable> std::ops::Drop for Gc<T> {
fn drop(&mut self) {
unsafe {
ref_dec(self.ptr.as_ptr() as *mut libc::c_void);
}
}
}
impl<T: Sized + GcTraceable> std::convert::AsRef<T> for Gc<T> {
fn as_ref(&self) -> &T {
unsafe { self.ptr.as_ref() }
}
}
impl<T: Sized + GcTraceable> std::clone::Clone for Gc<T> {
fn clone(&self) -> Self {
Gc {
ptr: unsafe {
ref_inc(self.ptr.as_ptr() as *mut libc::c_void);
self.ptr
},
}
}
}
impl<T: Sized + GcTraceable> std::cmp::PartialEq for Gc<T> {
fn eq(&self, other: &Self) -> bool {
std::ptr::eq(self.ptr.as_ptr(), other.ptr.as_ptr())
}
}
pub trait GcTraceable {
unsafe fn trace(&self, manager: &mut Vec<*mut GcNode>);
}
type GenericTraceFunction = unsafe fn(*mut c_void, *mut c_void);
use super::nativeval::NativeValue;
impl GcTraceable for Vec<NativeValue> {
unsafe fn trace(&self, gray_nodes: &mut Vec<*mut GcNode>) {
for val in self.iter() {
if let Some(ptr) = val.as_gc_pointer() {
push_gray_body(gray_nodes, ptr);
}
}
}
}
pub unsafe fn ref_inc(ptr: *mut c_void) {
if ptr.is_null() {
return;
}
let node: *mut GcNode = (ptr as *mut GcNode).sub(1);
(*node).native_refs += 1;
}
pub unsafe fn ref_dec(ptr: *mut c_void) {
if ptr.is_null() {
return;
}
let node: *mut GcNode = (ptr as *mut GcNode).sub(1);
(*node).native_refs -= 1;
}
pub unsafe fn push_gray_body(gray_nodes: &mut Vec<*mut GcNode>, ptr: *mut c_void) {
let node: *mut GcNode = (ptr as *mut GcNode).sub(1);
if (*node).color == GcNodeColor::Black || (*node).color == GcNodeColor::Gray {
return;
}
(*node).color = GcNodeColor::Gray;
gray_nodes.push(node);
}