Witch of Git - ivy/blob - rt/src/lib.rs

   1 use crate::{int::ObjInt, lam::ObjLam};
   2 use std::sync::atomic::{AtomicU32, Ordering};
   3
   4 pub mod int;
   5 pub mod lam;
   6 pub mod sys;
   7
   8 const _STDIN: i32 = 0;
   9 const _STDOUT: i32 = 1;
  10 const STDERR: i32 = 2;
  11
  12 #[macro_export]
  13 macro_rules! trace {
  14     ($fmt:literal $(, $arg:expr)* $(,)?) => {
  15         if std::env::var("IVY_RT_TRACE").is_ok() {
  16             eprintln!($fmt, $($arg),*);
  17         }
  18     }
  19 }
  20
  21 #[repr(u8)]
  22 #[derive(PartialEq, Eq, Clone, Copy)]
  23 pub enum ObjTag {
  24     Lam = 0,
  25     Int = 1,
  26 }
  27
  28 #[repr(C)]
  29 pub struct ObjHeader {
  30     tag: ObjTag,
  31     _pad: [u8; 3],
  32     rc: AtomicU32,
  33 }
  34
  35 #[derive(Clone, Copy)]
  36 #[repr(C)]
  37 pub union Obj {
  38     int: i64,
  39     header: *mut ObjHeader,
  40     box_lam: *mut ObjLam,
  41     box_int: *mut ObjInt,
  42 }
  43
  44 #[no_mangle]
  45 pub unsafe extern "C" fn ivy_debug(obj: Obj) -> Obj {
  46     println!("DEBUG   {:016x}", obj.int);
  47     obj
  48 }
  49
  50 #[no_mangle]
  51 pub unsafe extern "C" fn ivy_abort(msg: *const u8, len: usize) -> ! {
  52     sys::write(STDERR, msg, len);
  53     sys::exit(1);
  54 }
  55
  56 #[no_mangle]
  57 pub unsafe extern "C" fn ivy_exit(code: i32) -> ! {
  58     sys::exit(code)
  59 }
  60
  61 #[no_mangle]
  62 pub unsafe extern "C" fn ivy_free(obj: Obj) {
  63     if !obj.is_box() {
  64         return;
  65     }
  66     sys::free(obj.header as *mut u8)
  67 }
  68
  69 #[no_mangle]
  70 pub unsafe extern "C" fn ivy_incref(obj: Obj) {
  71     obj.incref();
  72 }
  73
  74 #[no_mangle]
  75 pub unsafe extern "C" fn ivy_decref(obj: Obj) {
  76     obj.decref();
  77 }
  78
  79 #[no_mangle]
  80 pub unsafe extern "C" fn ivy_clone(obj: Obj) -> Obj {
  81     if obj.is_null() || !obj.is_box() {
  82         return obj;
  83     }
  84     match obj.tag() {
  85         None => unreachable!(),
  86         Some(ObjTag::Int) => {
  87             unimplemented!("copying boxed integers")
  88         }
  89         Some(ObjTag::Lam) => {
  90             let lam = &*obj.box_lam;
  91             let size = lam.size();
  92             let data = sys::malloc(size);
  93             core::ptr::copy(obj.box_lam as *const u8, data, size);
  94             let box_hdr = data as *mut ObjHeader;
  95             *(*box_hdr).rc.get_mut() = 0;
  96             trace!("COPY    {:016x} {:016x}", obj.int, box_hdr as usize);
  97             let box_lam = data as *mut ObjLam;
  98             Obj { box_lam }
  99         }
 100     }
 101 }
 102
 103 impl Obj {
 104     fn is_null(self) -> bool {
 105         unsafe { self.int == 0 }
 106     }
 107
 108     fn is_box(self) -> bool {
 109         !self.is_null() && unsafe { self.int & 1 == 0 }
 110     }
 111
 112     unsafe fn tag(self) -> Option<ObjTag> {
 113         if self.is_null() {
 114             None
 115         } else if self.is_box() {
 116             Some((*self.header).tag)
 117         } else {
 118             Some(ObjTag::Int)
 119         }
 120     }
 121
 122     unsafe fn incref(self) {
 123         if !self.is_box() {
 124             return;
 125         }
 126         // Ordering::Relaxed is appropriate here, since we assume that each thread with access to a
 127         // reference owns at least one reference (rather than simply borrowing it). Therefore,
 128         // another thread cannot decrement it to 0 while we are performing this increment (since we
 129         // own a reference), so we only need consistency and not ordering.
 130         (*self.header).rc.fetch_add(1, Ordering::Relaxed);
 131     }
 132
 133     unsafe fn decref(self) {
 134         if !self.is_box() {
 135             return;
 136         }
 137         // Ordering::AcqRel is appropriate here. I believe we need the Acquire in order to ensure
 138         // we see all previous increments/decrements, so we can properly see that the decref is
 139         // decrementing to 0, and we need the Release in order to ensure that we see all writes to
 140         // the memory before we deallocate.
 141         // (Check against 1 instead of 0 since we're loading the old refcount.)
 142         if (*self.header).rc.fetch_sub(1, Ordering::AcqRel) == 1 {
 143             self.dealloc();
 144         }
 145     }
 146
 147     unsafe fn dealloc(self) {
 148         if !self.is_box() {
 149             return;
 150         }
 151         match self.tag() {
 152             None | Some(ObjTag::Int) => (),
 153             Some(ObjTag::Lam) => {
 154                 let lam = &mut *self.box_lam;
 155                 for param in lam.params() {
 156                     param.decref();
 157                 }
 158                 for upvar in lam.upvars() {
 159                     upvar.decref();
 160                 }
 161             }
 162         }
 163         sys::free(self.header as *mut u8);
 164     }
 165 }