Dr. Ing. Jan Kurš

Článek

10.1016/j.scico.2017.12.001

Katedra softwarového inženýrství

Parser combinators offer a universal and flexible approach to parsing. They follow the structure of an underlying grammar, are modular, well-structured, easy to maintain, and can recognize a large variety of languages including context-sensitive ones. However, these advantages introduce a noticeable performance overhead mainly because the same powerful parsing algorithm is used to recognize even simple languages. Time-wise, parser combinators cannot compete with parsers generated by well-performing parser generators or optimized hand-written code. Techniques exist to achieve a linear asymptotic performance of parser combinators, yet there is a significant constant multiplier. The multiplier can be lowered to some degree, but this requires advanced meta-programming techniques, such as staging or macros, that depend heavily on the underlying language technology. In this work we present a language-agnostic solution. We optimize the performance of parsing combinators with specializations of parsing strategies. For each combinator, we analyze the language parsed by the combinator and choose the most efficient parsing strategy. By adapting a parsing strategy for different parser combinators we achieve performance comparable to that of hand-written or optimized parsers while preserving the advantages of parsers combinators.

Článek

10.1016/j.scico.2013.10.011

Katedra teoretické informatiky
Katedra softwarového inženýrství

After decades of development in programming languages and programming environments, Smalltalk is still one of few environments that provide advanced features and is used in the industry. However, as Java became prevalent, the ability to call a Java code from Smalltalk became important. A traditional approach to integrate the Java and Smalltalk languages is through low-level communication between separate Java and Smalltalk virtual machines. To our best knowledge there is no other project attempting to execute and integrate the Java language directly in the Smalltalk environment. A direct integration allows for a very tight integration of the languages and their objects within a single environment. Yet integration and language interoperability impose challenging issues related to method naming conventions, method overloading, exception handling and thread-locking mechanisms. In this paper we describe ways to overcome these challenges and to integrate Java into the Smalltalk environment. We focus on a possibility to call a Java code from Smalltalk using standard Smalltalk idioms while the semantics of both languages remains preserved. We present stx:libjava – an implementation of a Java virtual machine within Smalltalk/X – as a validation of our approach.

Stať ve sborníku

Katedra teoretické informatiky
Katedra softwarového inženýrství

Runtime Code Update is a technique to update a program while it is running. Such a feature is often used so the developer can modify an application without the necessity to restart the application and recover desired state after restart. This saves time and lowers costs. Furthermore, there are applications which cannot be stopped, such as air traffic control systems or telephone switches. Current virtual machines for Java programming language do not support non-trivial updates to the running code. We have modified STX:LIBJAVA -- an implementation of Java virtual machine within Smalltalk/X -- to support arbitrary changes to the running code. Beside changes to the fields and methods which are already supported by the tools such as JRebel or Javaleon, we also support unrestricted changes to the class and interface hierarchy. Our Runtime Code Updates scheme has been integrated into the Smalltalk/X IDE, thus providing interactive environment where a developer can modify a Java application while it is running.

Stať ve sborníku

10.1007/978-3-642-30561-0_10

Katedra softwarového inženýrství

Programming languages are still evolving, and programming languages and language features are being designed and implemented every year. Since it is not a trivial task to provide a runtime system for a new language, existing runtime systems such as the Java Virtual Machine or the Common Language Runtime are used to host the new language. However, most of the high-performance runtime systems were designed for a specific language with a specific semantics. Therefore, if the new language semantics differs from the semantics hard-coded in a runtime system, it has to be emulated on top of features supported by the runtime. The emulation causes performance overhead. To overcome the limitations of an emulation, a runtime system may provide a meta-object protocol to alter the runtime semantics. The protocol should fulfill opposing goals: it should be flexible, easy to use, fast and easy to implement at the same time. We propose a simple meta-object protocol for customization of a method lookup in Smalltalk. A programmer may define his own custom method lookup routine in Smalltalk and let the runtime system to call it when needed. Therefore there is no need to modify the runtime system itself. Our solution provides reasonable performance thanks to low-level support in a runtime system, nevertheless the changes to the runtime system are small and local. At the same time, it provides the flexibility to implement a wide range of features present in modern programming languages. The presented approach has been implemented and validated on a Smalltalk virtual machine.

Stať ve sborníku

10.1145/2448963.2448968

Katedra teoretické informatiky
Katedra softwarového inženýrství

After decades of development in programming languages and programming environments, Smalltalk is still one of few environments that provide advanced features and is still widely used in the industry. However, as Java became preva- lent, the ability to call Java code from Smalltalk and vice versa becomes important. Traditional approaches to inte- grate the Java and Smalltalk languages are through low-level communication between separate Java and Smalltalk virtual machines. We are not aware of any attempt to execute and integrate the Java language directly in the Smalltalk en- vironment. A direct integration allows for very tight and almost seamless integration of the languages and their ob- jects within a single environment. Yet integration and lan- guage interoperability impose challenging issues related to method naming conventions, method overloading, exception handling and thread-locking mechanisms. In this paper we describe ways to overcome these chal- lenges and to integrate Java into the Smalltalk environment. Using techniques described in this paper, the programmer can call Java code from Smalltalk using standard Smalltalk idioms while the semantics of each language remains pre- served. We present STX : LIBJAVA — an implementation of Java virtual machine within Smalltalk/X — as a validation of our approach.

Stať ve sborníku

Katedra softwarového inženýrství

Software programs are often written in more than one programming language as the emergence of domain specific languages testifies. Language in- terpreters are easily embeddable and performances are usually satisfactory. How- ever, inter-language interaction remains a field tarnished by poor performances. The reason is that alien objects are wrapped, implying the use of expensive for- warding and converting mechanism. We propose to represent alien objects as the set of different states and behaviors it may have by moving between languages, thus avoiding wrapping and conversion. We have validated our solution on integration of Java and Smalltalk programming languages.

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Katedra softwarového inženýrství

XQuery is generic, widely adopted language for querying and manipulating XML data. Many of currently available native XML databases are using XQuery as its primary query language. The XQuery specification requires each XML node to belong to exactly one XML tree. In case of the XML subtree is appended into a new XML structure, the whole subtree has to be copied and afterwards the copy is appended to the new structure. This may lead into excessive and unnecessary data copying and duplication. In this paper, we present a new XML node copying scheme that defers the node data copy operation unless necessary. We will show that this schemes significantly reduces the XML node copy operations required during the query processing.