From fa49500139f365b9f620695af0ef59cd36b57ad7 Mon Sep 17 00:00:00 2001
From: Jur van den Berg <Jurl.berg@gmail.com>
Date: Mon, 3 Jun 2019 10:12:49 +0200
Subject: [PATCH] Switch the global list to Weak based pointers, allowing us to
 actually use rust lifetimes for heaps

---
 src/heap.rs | 46 +++++++++++++++++++++++-----------------------
 src/ops.rs  | 22 ++++++++--------------
 2 files changed, 31 insertions(+), 37 deletions(-)

diff --git a/src/heap.rs b/src/heap.rs
index 26785f0..77cba42 100644
--- a/src/heap.rs
+++ b/src/heap.rs
@@ -1,12 +1,14 @@
 use value::Value;
-use std::rc::Rc;
+use std::rc::{Rc, Weak};
 use std::cell::RefCell;
 
-pub type Heap = Rc<RefCell<Vec<Value>>>;
+pub type HeapInner = RefCell<Vec<Value>>;
+pub type Heap = Rc<HeapInner>;
+pub type WeakHeap = Weak<HeapInner>;
 
 #[derive(Debug,Default)]
 pub struct Heaps {
-    pub heaps: Vec<Heap>
+    pub heaps: Vec<WeakHeap>
 }
 
 impl Heaps {
@@ -20,13 +22,24 @@ impl Heaps {
         self.heaps.len()
     }
 
-    pub fn get(&mut self, i: usize) -> Heap {
-        self.heaps[i].clone()
+    pub fn get(&mut self, i: usize) -> Option<Heap> {
+        if i >= self.len() {
+            return None
+        }
+
+        let weak_ref = self.heaps[i].clone();
+        let possibly_strong = weak_ref.upgrade();
+
+        if possibly_strong.is_none() {
+            self.heaps.remove(i);
+        }
+
+        possibly_strong
     }
 
     pub fn alloc(&mut self, size: usize) -> Heap {
         let heap = Rc::new(RefCell::new(vec![Value::Int(0); size]));
-        self.heaps.push(heap.clone());
+        self.heaps.push(Rc::downgrade(&heap));
         heap
     }
 
@@ -35,23 +48,10 @@ impl Heaps {
     }
 
     pub fn gc(&mut self) {
-        let pre_size = self.len();
-
-        if cfg!(feature = "debug:gc") {
-            for (i, heap) in self.heaps.iter().enumerate() {
-                eprintln!("GC heap {} ref = {}", i, Rc::strong_count(heap));
-            }
-        }
-
-        self.heaps = self.heaps.iter()
-            .filter(|e| Rc::strong_count(e) > 1)
-            .map(|e| Rc::clone(e))
-            .collect();
-
-        let post_size = self.len();
-
-        if cfg!(feature = "debug:gc") {
-            eprintln!("GC reaped {} heaps", pre_size - post_size);
+        println!("GC PRE : {} weaks", self.len());
+        for i in 0..self.len() {
+            println!("\theap: {} = {:?}", i, self.get(i));
         }
+        println!("GC POST: {} weaks", self.len());
     }
 }
diff --git a/src/ops.rs b/src/ops.rs
index 4755621..0f36606 100644
--- a/src/ops.rs
+++ b/src/ops.rs
@@ -267,20 +267,14 @@ fn invokevirtual(machine: &mut Machine) -> Result<()> {
 }
 
 fn ireturn(machine: &mut Machine) -> Result<()> {
-    // Lifetime for prev frame, allows gc to reap into the frame
-    {
-        let mut prev_frame: Frame = match machine.frame.pop() {
-            Some(a) => a,
-            None => return Err("Got no frame... somehow..."),
-        };
-        let result = prev_frame.stack.pop()?;
-        let return_addr: i32 = prev_frame.get(0)?.try_into()?;
-        machine.cur_stack().push(result);
-        machine.block.seek(return_addr as usize)?;
-    }
-
-    machine.heap.gc();
-    Ok(())
+    let mut prev_frame: Frame = match machine.frame.pop() {
+        Some(a) => a,
+        None => return Err("Got no frame... somehow..."),
+    };
+    let result = prev_frame.stack.pop()?;
+    let return_addr: i32 = prev_frame.get(0)?.try_into()?;
+    machine.cur_stack().push(result);
+    machine.block.seek(return_addr as usize)
 }
 
 #[cfg(feature = "extra:sleep")]