Region-based Memory Management Research Articles

Region inference for an object-oriented language

Region-based memory management offers several important potential advantages over garbage collection, including real-time performance, better data locality, and more efficient use of limited memory. Researchers have advocated the use of regions for functional, imperative, and object-oriented languages. Lexically scoped regions are now a core feature of the Real-Time Specification for Java (RTSJ)[5].Recent research in region-based programming for Java has focused on region checking, which requires manual effort to augment the program with region annotations. In this paper, we propose an automatic region inference system for a core subset of Java. To provide an inference method that is both precise and practical, we support classes and methods that are region-polymorphic, with region-polymorphic recursion for methods. One challenging aspect is to ensure region safety in the presence of features such as class subtyping, method overriding, and downcast operations. Our region inference rules can handle these object-oriented features safely without creating dangling references.

Memory Management for Real-Time Java: An Efficient Solution using Hardware Support*

This paper addresses the issue of improving the performance of memory management for real-time Java applications, building upon the real-time specification for Java (RTSJ) from the Real-Time Java Expert Group. In a first step, a collecting dynamic memory solution including both a real-time garbage collector and region-based memory management, is proposed. A thorough analysis of the parameters influencing the performance of write barriers in memory management, together with ways of improvement are then presented. Finally, the implementation of a memory management solution compliant with the RTSJ and integrating the proposed improvements is sketched.

Ownership types for safe region-based memory management in real-time Java

The Real Time Specification for Java (RTSJ) allows a program to create real-time threads with hard real-time constraints. Real-time threads use region-based memory management to avoid unbounded pauses caused by interference from the garbage collector. The RTSJ uses runtime checks to ensure that deleting a region does not create dangling references and that real-time threads do not access references to objects allocated in the garbage-collected heap. This paper presents a static type system that guarantees that these runtime checks will never fail for well-typed programs. Our type system therefore 1) provides an important safety guarantee for real-time programs and 2) makes it possible to eliminate the runtime checks and their associated overhead.Our system also makes several contributions over previous work on region types. For object-oriented programs, it combines the benefits of region types and ownership types in a unified type system framework. For multithreaded programs, it allows long-lived threads to share objects without using the heap and without memory leaks. For real-time programs, it ensures that real-time threads do not interfere with the garbage collector. Our experience indicates that our type system is sufficiently expressive and requires little programming overhead, and that eliminating the RTSJ runtime checks using a static type system can significantly decrease the execution time of real-time programs.

Type-safe multithreading in cyclone

We extend Cyclone, a type-safe polymorphic language at the C level of abstraction, with threads and locks. Data races can violate type safety in Cyclone. An extended type system statically guarantees their absence by enforcing that thread-shared data is protected via locking and that thread-local data does not escape the thread that creates it. The extensions interact smoothly with parametric polymorphism and region-based memory management. We present a formal abstract machine that models the need to prevent races, a polymorphic type system for the machine that supports thread-local data, and a corresponding type-safety result.

Garbage collection safety for region-based memory management

In this paper, we prove the safety of integrating region-based memory management and Cheney-style copying garbage collection. The safety property relies on a refinement of the region typing rules that forbids dangling pointers during evaluation.To accommodate the triggering of garbage collection at any step in the evaluation process, we base our type-safety result for the region-based system on a small-step contextual semantics and show that whenever a well-typed expression reduces to another expression, possibly by deallocating a region, then no dangling pointer is introduced. Because there are no dangling pointers in the initial heap, no dangling pointers appear during evaluation.Although in principle, the refinement of the region typing rules leads to less flexibility and can cause worse memory behavior than when dangling pointers are permitted, experiments show that, for a range of benchmark programs, the refinement has little effect on overall memory behavior.

Analysis issues for cyclone

Cyclone [1, 2] is an experimental, type-safe programming language based upon the syntax, semantics, and spirit of C. The primary goal of the language is to provide a type-safe environment that is close enough to C in both appearance and functionality, that systems programmers will find it attractive and useful.The most challenging aspect of the design is capturing the spirit of C without compromising type-safety. In particular, systems programmers expect to have good control over data representations, memory management, and performance. Yet, these features are usually absent from high-level, type-safe languages (e.g., Java). Another challenge is validating a sufficiently wide set of idioms that are in fact type-safe, but which conventional type systems reject.To address these issues, we have used a novel combination of typing features in conjunction with some interesting inference and dataflow techniques. The most novel typing feature is the support for region-based memory management which was summarized in an earlier paper [1]. However, this paper did not discuss the inference techniques we use to validate the regions and effects.In this talk, I will briefly summarize the Cyclone type system and then focus on the analysis issues that arise in its implementation, including (a) kind and type inference, (b) region and effect inference, and (c) dataflow analysis for validating initialization, array subscripts, and linear pointers.

Region-based memory management in cyclone

Cyclone is a type-safe programming language derived from C. The primary design goal of Cyclone is to let programmers control data representation and memory management without sacrificing type-safety. In this paper, we focus on the region-based memory management of Cyclone and its static typing discipline. The design incorporates several advancements, including support for region subtyping and a coherent integration with stack allocation and a garbage collector. To support separate compilation, Cyclone requires programmers to write some explicit region annotations, but a combination of default annotations, local type inference, and a novel treatment of region effects reduces this burden. As a result, we integrate C idioms in a region-based framework. In our experience, porting legacy C to Cyclone has required altering about 8% of the code; of the changes, only 6% (of the 8%) were region annotations.

Combining region inference and garbage collection

This paper describes a memory discipline that combines region-based memory management and copying garbage collection by extending Cheney's copying garbage collection algorithm to work with regions. The paper presents empirical evidence that region inference very significantly reduces the number of garbage collections; and evidence that the fastest execution is obtained by using regions alone, without garbage collection. The memory discipline is implemented for Standard ML in the ML Kit compiler and measurements show that for a variety of benchmark programs, code generated by the compiler is as efficient, both with respect to execution time and memory usage, as programs compiled with Standard ML of New Jersey, another state-of-the-art Standard ML compiler.

Language support for regions

Region-based memory management systems structure memory by grouping objects in regions under program control. Memory is reclaimed by deleting regions, freeing all objects stored therein. Our compiler for C with regions, RC, prevents unsafe region deletions by keeping a count of references to each region. Using type annotations that make the structure of a program's regions more explicit, we reduce the overhead of reference counting from a maximum of 27% to a maximum of 11% on a suite of realistic benchmarks. We generalise these annotations in a region type system whose main novelty is the use of existentially quantified abstract regions to represent pointers to objects whose region is partially or totally unknown. A distribution of RC is available at http://www.cs.berkeley.edu/~dgay/rc.tar.gz.

A region-based memory manager for prolog

We extend Tofte and Talpin's region-based model for memory management to support backtracking and cuts, which makes it suitable for use with Prolog and other logic programming languages. We describe how the extended model can be implemented and report on the performance of a prototype implementation. The prototype implementation performs well when compared to a garbage-collecting Prolog implementation using comparable technology for non-memory-management issues.

Typed memory management via static capabilities

Region-based memory management is an alternative to standard tracing garbage collection that makes operation such as memory deallocation explicit but verifiably safe. In this article, we present a new compiler intermediate language, called the Capability Language (CL), that supports region-based memory management and enjoys a provably safe type systems. Unlike previous region-based type system, region lifetimes need not be lexically scoped, and yet the language may be checked for safety without complex analyses. Therefore, our type system may be deployed in settings such as extensible operating systems where both the performance and safety of untrusted code is important. The central novelty of the language is the use of static capabilities to specify the permissibility of various operations, such as memory access and deallocation. In order to ensure capabilities are relinquished properly, the type system tracks aliasing information using a form of bounded quantification. Moreover, unlike previous work on region-based type systems, the proof of soundness of our type system is relatively simple, employing only standard syntactic techniques. In order to show how our language may be used in practice, we show how to translate a variant of Tofte and Talpin's high-level type-and-effects system for region-based memory management into our language. When combined with known region inference algorithms, this translation provides a way to compile source-level languages to CL.

Combining Region-based Memory Management with Conventional Garbage Collection

Combining Region-based Memory Management with Conventional Garbage Collection

A brief introduction to regions

The paper gives an overview of region-based memory management. The emphasis of the paper is on the dynamic aspects of execution, specifically memory management. We illustrate how three static program analyses can be used for inferring memory management directives. They are region inference, physical size inference , and storage mode analysis . We describe these analyses for a skeletal language inspired by Standard ML. We also describe a region-based runtime system for the skeletal language, based on the runtime system of the ML Kit with Regions.

Memory management with explicit regions

Much research has been devoted to studies of and algorithms for memory management based on garbage collection or explicit allocation and deallocation. An alternative approach, region-based memory management, has been known for decades, but has not been well-studied. In a region-based system each allocation specifies a region, and memory is reclaimed by destroying a region, freeing all the storage allocated therein. We show that on a suite of allocation-intensive C programs, regions are competitive with malloc/free and sometimes substantially faster. We also show that regions support safe memory management with low overhead. Experience with our benchmarks suggests that modifying many existing programs to use regions is not difficult.