The design and evaluation of a high-performance smalltalk system

The speed of message dispatching is an important issue in the overall performance of object-oriented programs. We have developed an algorithm for constructing efficient dispatch functions that combines novel algorithms for efficient single dispatching, multiple dispatching, and predicate dispatching. Our algorithm first reduces methods written in the general predicate dispatching model (which generalizes single dispatching, multiple dispatching, predicate classes and classifiers, and pattern-matching) into ones written using a simpler multimethod dispatching model. Our algorithm then computes a strategy for implementing multiple dispatching in terms of sequences of single dispatches, representing the strategy as a lookup DAG. Finally, our algorithm computes an implementation strategy separately for each of the single dispatches, producing for each dispatch a dispatch tree, which is a binary decision tree blending class identity tests, class range tests, and table lookups. Our algorithm exploits any available static information (from type declarations or class analysis) to prune unreachable paths from the lookup DAG, and uses any available dynamic profile information to minimize the expected time to search the dispatch trees. We measure the effectiveness of our dispatching algorithms on a collection of large Cecil programs, compiled by the Vortex optimizing compiler, showing improvements of up to 30% over already heavily optimized baseline versions.

http://www-inf.int-evry.fr/~defude/P2P/PAPIERS/chambers99.pdf

Efficient multiple and predicated dispatching

Object-oriented programming represents an original implementation issue due to its philosophy of making the program behavior depend on the dynamic type of objects. This is expressed by the late binding mechanism, aka message sending. The underlying principle is that the address of the actually called procedure is not statically determined at compile-time, but depends on the dynamic type of a distinguished parameter known as the receiver. A similar issue arises with attributes, because their position in the object layout may also depend on the object's dynamic type. Furthermore, subtyping introduces another original feature (i.e., runtime subtype checks). All three mechanisms need specific implementations and data structures. In static typing, late binding is generally implemented with so-called virtual function tables. These tables reduce method calls to pointers to functions via a small fixed number of extra indirections. It follows that object-oriented programming yields some overhead, as compared to the usual procedural languages. The different techniques and their resulting overhead depend on several parameters. First, inheritance and subtyping may be single or multiple, and even a mixing is possible, as in Java and dNET which present single inheritance for classes and multiple subtyping for interfaces. Multiple inheritance is a well-known complication. Second, the production of executable programs may involve various schemes, from global compilation, which implies the closed-world assumption (CWA), as the whole program is known at compile time, to separate compilation and dynamic loading, where each program unit is compiled and loaded independently of any usage, hence under the open-world assumption (OWA). Global compilation is well-known to facilitate optimization. This article reviews the various implementation techniques available in static typing and in the three cases of single inheritance, multiple inheritance, and multiple subtyping. This language-independent survey focuses on separate compilation and dynamic loading, as they represent the most commonly used and the most demanding framework. However, many works have been undertaken in the global compilation framework, mostly for dynamically typed languages, but also applied to the EIFFEL language. Hence, we also examine global techniques and how they can improve implementation efficiency. Finally, mixed frameworks that combine open and closed world assumptions are considered. For instance, just-in-time (JIT) compilers work under provisional CWA, at the expense of possible recompilations. In contrast, we present an experimental compiler-linker, where separate compilation implies the OWA, whereas the whole program is finally linked under the CWA.

/pdf/implementing-statically-typed-object-oriented-programming-2b66au909w.pdf

Implementing statically typed object-oriented programming languages

1 Introduction Current object oriented programming languages (OOPLs) rely on mono-method dispatching. Recent research has identified multi-methods as a new, powerful feature to be added to OOPLs, and several experimental OOPLs now have multi-methods. Their ultimate success and impact in practice depends, among other things, on whether multi-method dispatching can be supported efficiently. We show that the multi-method dispatching problem can be transformed to a geometric problem on multi-dimensional integer grids, for which we then develop a data structure that uses near-linear space and has log-logarithmic query time. This gives a solution whose performance almost matches that of the best known algorithm for mono-method dispatching. In this paper we study problems from two different areas: the multi-method dispatching problem for object-oriented (00) languages and two string matching problems. It turns out that these problems are surprisingly similar: we prove that they can all be reduced to the same problem on multi-dimensional integer grids-see below for a description of this geometric problem. We present an efficient data structure for this problem, which allows various trade-offs between space and query time. This leads to significantly improved solutions to the multi-method dispatching problem and the string matching problems. In the rest of this introduction, as well as in the remainder of the paper, we lirst focus on the multi-method dispatching problem and then turn our attention to the string matching problems. Our geometric data structure has other applications as well, namely in two string matching problems: matching multiple rectangular patterns against a rectangular query text, and approximate dictionary matching with edit distance at most one. Our results for the former, long-standing open problem are substantially improved, near-linear time bounds. For the latter problem, which has applications in checking password security and the design of filtering tools, we obtain a near-linear solution as well. The multi-method dispatching problem Object-oriented languages. The 00.paradigm is becoming the norm for software development; languages such as Java, C++, and Smalltalk that embody some of the basic tenets of the 00.paradigm are highly popular. Recent research has identified new, powerful features that can enhance the current 00.technology, and the focus now is on understanding the implication of adding these features-their power and their cost in terms of the additional complexity. One such feature is the concept of multi-methods found in the new generation 00-languages such as CommonLoops [BK+86], CLOS [BD+88], Poly-Glot [AQl], Kea [MHHSl], Cecil [ChSZ] and Dylan [Ap94]. …

Multi-method dispatching: a geometric approach with applications to string matching problems

The dispatching problem can be solved very efficiently in the single-inheritance~(SI) setting. In this paper we show how to extend one such solution to the multiple-inheritance~(MI) setting. This generalization comes with an increase to the space requirement by a small factor of κ This factor can be thought of as a metric of the complexity of the topology of the inheritance hierarchy.On a data set of~35 hierarchies totaling some~64 thousand types, our dispatching data structure, based on a novel type slicing technique, exhibits very significant improvements over previous dispatching techniques, not only in terms of the time for creating the underlying data structure, but also in terms of total space used.The cost is in the dispatching time, which is no longer constant, but doubly logarithmic in the number of types. Conversely, by using a simple binary search, dispatching time is logarithmic in the number of different implementations. In practice dispatching uses one indirect branch and, on average, only~2.5 binary branches.Our results also have applications to the space-efficient implementation of the more general problem of dispatching multi-methods.A by-product of our type slicing technique is an incremental algorithm for constant-time subtyping tests with favorable memory requirements. (The incremental version of the subtyping problem is to maintain the subtyping data structure in presence of additions of types to the inheritance hierarchy.)

Fast algorithm for creating space efficient dispatching tables with application to multi-dispatching

The efficiency of dynamic dispatch is a major impediment to the adoption of multimethods in object-oriented languages In this article, we propose a simple multimethod dispatch scheme based on compressed dispatch tables This scheme is applicable to any object-oriented language using a method precedence order that satisfies a specific monotonous property (eg, as Cecil and Dylan) and guarantees that dynamic dispatch is performed in constant time, the latter being a major requirement for some languages and applications We provide efficient algorithms to build the dispatch tables, provide their worst-case complexity, and demonstrate the effectiveness of our scheme by real measurements performed on two large object-oriented applications Finally, we provide a detailed comparison of our technique with other existing techniques

https://hal.inria.fr/inria-00073721/document

Fast algorithms for compressed multimethod dispatch table generation

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Fast algorithms for compressed multimethod dispatch table generation