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lectures/25_garbage_collection/README.md

@@ -77,14 +77,11 @@ root: 105
 
 1. Split memory in half (working memory and copy memory).
 2. When out of working memory, stop computation and begin garbage collection.
-(a) Place scan and free pointers at the start of the copy memory.
+  (a) Place scan and free pointers at the start of the copy memory.  
-(b) Copy the root to copy memory, incrementing free. Whenever a node is copied from working memory,
+  (b) Copy the root to copy memory, incrementing free. Whenever a node is copied from working memory, leave a forwarding address to its new location in copy memory in the left address slot of its old location.  
-leave a forwarding address to its new location in copy memory in the left address slot of its old location.
+  (c) Starting at the scan pointer, process the left and right pointers of each node. Look for their locations in working memory. If the node has already been copied (i.e., it has a forwarding address), update the reference. Otherwise, copy the location (as before) and update the reference.  
-(c) Starting at the scan pointer, process the left and right pointers of each node. Look for their locations
+  (d) Repeat until scan == free.  
-in working memory. If the node has already been copied (i.e., it has a forwarding address), update the
+  (e) Swap the roles of the working and copy memory.
-reference. Otherwise, copy the location (as before) and update the reference.
-(d) Repeat until scan == free.
-(e) Swap the roles of the working and copy memory.
 
 ## 25.7 Stop and Copy Exercise
 
@@ -118,12 +115,12 @@ free:
 2. Keep a free pointer to the head of the free list.
 3. When memory runs out, stop computation, clear the mark bits and begin garbage collection.
 4. Mark
-(a) Start at the root and follow the accessible structure (keeping a stack of where you still need to go).
+  (a) Start at the root and follow the accessible structure (keeping a stack of where you still need to go).  
-(b) Mark every node you visit.
+  (b) Mark every node you visit.  
-(c) Stop when you see a marked node, so you don’t go into a cycle.
+  (c) Stop when you see a marked node, so you don’t go into a cycle.  
 5. Sweep
-(a) Start at the end of memory, and build a new free list.
+  (a) Start at the end of memory, and build a new free list.  
-(b) If a node is unmarked, then it’s garbage, so hook it into the free list by chaining the left pointers.
+  (b) If a node is unmarked, then it’s garbage, so hook it into the free list by chaining the left pointers.
 
 ## 25.9 Mark-Sweep Exercise
 
@@ -146,9 +143,9 @@ stack:
 ## 25.10 Garbage Collection Comparison
 
 - Reference Counting:
-  + fast and incremental  
+  - + fast and incremental  
-  – can’t handle cyclical data structures!  
+  - – can’t handle cyclical data structures!  
-  ? requires ∼33% extra memory (1 integer per node)  
+  - ? requires ∼33% extra memory (1 integer per node)  
 - Stop & Copy:
   – requires a long pause in program execution  
   + can handle cyclical data structures!  
@@ -171,9 +168,13 @@ enormous beast of a programming language (but that doesn’t stop people from tr
 we can do? Yes, we can use Smart Pointers to gain some of the features of garbage collection.
  Some examples below are modified from these nice online references:
 [http://ootips.org/yonat/4dev/smart-pointers.html](http://ootips.org/yonat/4dev/smart-pointers.html)
+
 [http://www.codeproject.com/KB/stl/boostsmartptr.aspx](http://www.codeproject.com/KB/stl/boostsmartptr.aspx)
+
 [http://en.wikipedia.org/wiki/Smart_pointer](http://en.wikipedia.org/wiki/Smart_pointer)
+
 [http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/smart_ptr.htm](http://www.boost.org/doc/libs/1_48_0/libs/smart_ptr/smart_ptr.htm)
+
 [http://www.acodersjourney.com/2016/05/top-10-dumb-mistakes-avoid-c-11-smart-pointers/](http://www.acodersjourney.com/2016/05/top-10-dumb-mistakes-avoid-c-11-smart-pointers/)
 
 ## 25.12 What’s a Smart Pointer?