Region Inference for an Object-Oriented Language

1
Region Inference for an Object-Oriented Language

• Wei Ngan Chin1,2
• Joint work with
• Florin Craciun1, Shengchao Qin1,2, Martin Rinard3
• 1 National University of Singapore
• 2 Singapore-MIT Alliance 3 MIT

2
Background

• Basic problem
• how to recover memory of dead objects?
• Two Approaches
• garbage collection
• explicit memory management
• Our Focus
• Explicit memory regions with different lifetimes

3
Current Status

• Region Inference for a functional language
• ?-Calculus Tofte-Talpin POPL94
• Previous Works on Region Type Checkers
• Java DIKU98,
• Real-Time Java MIT-PLDI03,
• Cyclone Cornell-PLDI02.

Our Goal automatic region inference for
object-oriented programs
4
Two Major Assumptions
top (younger)

• Lexically-Scoped Regions
• Stack-like lifetimes
• construct for local region
• letreg r in e

r4
r3

• No Dangling References
• Regions of components should have longer
  lifetimes than its object.

r2
r1
bottom (older)
5
Main Contributions

• Region Inference for Core-Java
• Constraint-Based Type System.
• Region Polymorphism Region Subtyping
• Handles Inheritance, Overriding, Downcast
• Implementation

6
Region-Annotated Core-Java
7
Inferring for Class
Step 4 Inherit constraint of superclass.
8
Inferring for Class

Step 1 Reserve first region for the receiver
object (this).
Step 2 Keep regions of fields distinct for
precision.
Step 3 No dangling requirement as class
invariant.
9
Inferring for Methods
10
Outline

• Background
• Key Techniques
• Inferring Class
• Inferring Methods
• Region Subtyping
• Region Inference
• Method Overriding Downcast
• Experimental Results

11
(Object) Region Subtyping
concept pioneered in Cyclone PLDI02 an object
w of type cltr,..gt can be passed to a location v
of type clts,..gt provided r