Posts

Observability of the Java Virtual Machine

-
Image
The JVM is one of the most observable runtimes. It provides us lots of tools for troubleshooting a JVM application in production. 1. Thread observability Threads are how the JVM actually does work. When something is wrong in production, the symptom is almost always a thread: stopped, blocked, leaking etc. Thread dumps work on any JVM with no  instrumentation, no agents, no restarts. <Example project link with /threaddump endpoint>         // (1) Deadlock — two threads grab the same pair of locks in opposite order.         new Thread(() -> grab(LOCK_A, LOCK_B), "deadlock-A-then-B").start();         new Thread(() -> grab(LOCK_B, LOCK_A), "deadlock-B-then-A").start(); http://localhost:8080/actuator/threaddump To list the JVMS, we can use the command below. PS C:\observe-jvm> jps -lv 25296 jdk.jcmd/sun.tools.jps.Jps -Dapplication.home=C:\Program Files\Microsoft\jdk-21.0.3.9-hotspot -Xms8m -Djdk.module.main=...
Post a Comment
Read more

Interpreter for a Subset of Java Language (J-)

-
In this post we will have a look at the interpreter part of my project. Before interpreting the source code, following things happened: • Lexer built the tokens from source code. • AST (Abstract Syntax Tree) was created. • Parser traversed the AST and populated our Symbol Table Interpreter should once again traverse the AST and execute the statements. private Object exec(CommonTree statement) { switch (statement.getType()) { case ProgramWalker.BLOCK: case ProgramWalker.MAINMETHOD: block(statement); break; case ProgramWalker.PRINT: print(statement); sendSourceLineMessage(statement); break; case ProgramWalker.VARDECL: currentSpace.put(statement.getChild(1).getText(), null); sendSourceLineMessage(statement); case ProgramWalker.METHOD: break; case ProgramWalker.INT: ret...
Post a Comment
Read more

A Code Analyzer for a Subset of Java Language (J-) Using ANTLR - PART 2

-
As we know, semantic analysis of a compiler includes checking the types of expressions. To do that, we have to maintain a Symbol Table which maps variable names to their types and locations. There maybe many variables with the same name which are in different scopes. This is legal in most languages and we have to handle this situation. We have to know when following scopes are entered in: - class scope - method scope - no inner block scopes (my language does not support this currently) We will do type-checking in two phases. First we'll populate the Symbol Table and it will contain the symbols with their scopes. Then, we'll check the types of symbols that are subject to addition operation by querying the symbol table. ANTLR allows us to inject code in different places of the generated parser. We need to know when a class/method scope is entered and the end of any scope is reached. Below is some grammar code from the project : classDecl @init {visitor.beforeClass(); System.out.p...
Post a Comment
Read more

A Code Analyzer for a Subset of Java Language (J-) Using ANTLR - PART 1

-
Our goal is to write a code analyzer for a language that is called "J minus". Source code of the whole project can be found here: https://code.google.com/p/j-minus/ Lets start with the language definition: Lexical Rules: Identifiers: Sequence of letters. Integer literals: A sequence of decimal digits. Binary operators: && Grammar Rules: Program -> MainClass ClassDecl* MainClass -> class id { public static void main (String [] id) { Statement* }} ClassDecl -> class id { VarDecl* MethodDecl* } VarDecl -> Type id ; MethodDecl -> public Type id ( ( formalParameter (, formalParameter)* )? ) { varDecl* statement* return exp; } FormalParameter -> Type id Statement -> id = Exp; Exp -> AdditionExp | SimpleExp SimpleExp -> id | int AdditionExp -> SimpleExp + SimpleExp Type: 'int' | 'boolean' ; We must pass following steps to reach our goal: 1) Implement the lexer and parser for the language. (use ANTLR) 2) Build the Abs...
Post a Comment
Read more

"Parsing" Konusu ile ilgili Temel Kavramlar

-
--Halen yazım aşamasında-- Regular expressions yardımıyla bir programın "lexical" yapısını ifade edebildiğimizi görmüştük. Aynı şeyi dildeki cümleler için yapmak mümkün mü? Dildeki cümlelerin yapısını ifade etmek için "context free grammar" kavramı kullanılmakta. Dildeki karmaşık yapıları oluşturmak için "production" yaparak ilerlemek gerekiyor. Aşağıda 5 tane production ile ifade edilen bir dili inceleyelim: S -> S ; S S -> ID = E E -> E + E E -> ID E -> NUM Bu kuralları kullanarak bir cümle üretmeye çalışalım: S ; S ID = E ; ID = E ID = E + E; ID = E ID = ID + NUM; ID = NUM Burada ürettiğimiz cümlenin kaynak kodu (lexer ele almadan önce) şöyle olabilirdi: var = i + 4; j = 5 Burada tokenlerin değerleri: var, i, j, 4, 5 Token türleri: ID, NUM, "+", ";", "=" Gramer ifadesinde sağ tarafta bulunamayan sonlanmış semboller dikkati çekiyor. Bunlara "terminal symbol" deniliyor. Terminal semboller, token tür...
Post a Comment
Read more

ANTLR ile Lexer Generation

-
Java platformunda bir lexer oluşturmak istediğimizde elimizdeki seçenekler JavaCC, SableCC ve ANTLR olarak karşımıza çıkıyor. ANTLR ile elimizdeki dil için bir lexer oluşturmaya çalışalım. Lexer için kullanacağımız dilin token kuralları: Identifier: Harf ile başlar. Harf, rakam ve alt çizgilerden oluşan stringdir. Büyük haft – küçük harf farklı olarak değerlendirilir. Integer constant: Rakamlardan oluşan string. Binary operator: Aşağıdakilerden biri: + - * / && Yorum: İki türlü yorum olabilir: Blok tipi yorum: /* */ Satır tipi yorum: // ANTLR kurulumu için yapılması gerekenler: Antlrworks'ü indir ve üzerine tıkla. En sevdiğin kafeinli içecek de dahil olmak üzere bilgilerini göndermeyi kabul et. ;) Yeni gramer dökümanı mı oluşturmak istiyorsun? Evet Grammar name: MyLexer Type: Lexer Lexical items: Identifier, Integer, Comments (single line + multiline), Whitespace Oluşturacağımız lexer için belirlenen kuralları ana pencerede görüyoruz: ID : ('a'..'z...
Post a Comment
Read more

"REGULAR EXPRESSIONS" KONUSUNU TAM OLARAK VE KOLAYCA ANLAMAK

-
Herhangi bir dilde yazılmış bilgisayar programının derlenebilmesi veya yorumlanabilmesi için öncelikle "lexical analysis" denilen aşamadan geçmesi gerekiyor. Bu aşamada program kelimelere veya "token" denilen yapıtaşlarına ayrılıyor. Programlama dilinin sentaksı, tokenlerin türleri hakkında bilgi verir. Örneğin birçok dilde yer alan bazı token türleri: ID Örnek: price calculateRate lastItem NUM Örnek: 73 0 REAL Örnek: 12.5 0.23 COMMA , IF if Bir lexical analyser (lexer) yazabilmek için herhangi bir programlama dili kullanılabilir. Fakat özellikle "regular expressions" dili bu iş için kullanıma uygun. Regular Expressions Dil (language), bir string kümesi olarak tanımlansın. Örneğin Java dili, legal java programı oluşturabilecek tüm string lerin kümesidir. Bu durumda Java dili sonsuz elemana sahip bir küme. Peki bir dili (belki sonsuz elemana sahip), nasıl sonlu ifadelerle (açıklamalarla) tanımlayabiliriz? İşte burad...
Post a Comment
Read more

nijhof2axon

-
Axon framework kullanıcılarına katkıda bulunmak amacıyla paylaştığım proje ile ilgili yorum ve sorular gelmeye başladı. http://code.google.com/p/nijhof2axon/ >>You share the Data between the Domain and the Query Model? When a command is dispatched, a CommandHandler uses the aggregate root to handle the command. Aggregate root fires DomainEvents. => Query layer related code listens to domain events and updates the query model. (Example: ClientTableUpdater) Domain entities are first class objects but Query Model classes are just DTOs with getters and setters. We have Client as entity and ClientDetailsEntry as DTO. >>The (generated?) table domainevententry looks like you can not replay events? missing the event data? To observe how events are replayed by the framework, you can follow these steps: Click on sample client change name stop server start server put a breakpoint to EventSourcingRepository.doLoad() method put a breakpoint to Client.handleClientNameChangedEvent() me...
Post a Comment
Read more

Popular posts from this blog

The WeakReference class, monitoring memory leak and garbage collection in a Java application

-
Image
 Below is a Stack implementation that uses an internal resizeable array structure.  public class MyStack< T > implements Stack< T > { private static final int CAPACITY = 100 ; private Object[] array ; private int pos = 0 ; public MyStack () { this . array = new Object[ CAPACITY ] ; } @Override public void push ( T item) { if ( pos >= array . length / 2 ) { Object[] newArray = new Object[ pos * 2 ] ; System. arraycopy ( array , 0 , newArray , 0 , array . length ) ; array = newArray ; } array [ pos ++] = item ; } @Override public T pop () { if (isEmpty()) { throw new RuntimeException( "empty stack" ) ; } @SuppressWarnings ( "unchecked" ) T item = ( T ) array [ pos - 1 ] ; pos -= 1 ; return item ; } @Override @SuppressWarnings ( "unchecked" ) public T peek...
Read more

Simplescalar Simulator - Part 2: sim-outorder.c

-
sim-outorder implements a very detailed out-of-order issue superscalar processor with a two-level memory system and speculative execution support. This simulator is a performance simulator, tracking the latency of all pipeline operations. Let's have a look at SimpleScalar simulator's code related to iTLB. (Instruction Translation Lookaside Buffer) First, there are simulator options related to iTLB: /* register simulator-specific options */ void sim_reg_options(struct opt_odb_t *odb) { /* TLB options */ opt_reg_string(odb, "-tlb:itlb", "instruction TLB config, i.e., { |none}", &itlb_opt, "itlb:16:4096:4:l", /* print */TRUE, NULL); opt_reg_int(odb, "-tlb:lat", "inst/data TLB miss latency (in cycles)", &tlb_miss_lat, /* default */30, /* print */TRUE, /* format */NULL); } /* check simulator-specific option values */ void  sim_check_options(... ) { /* sim-outorder.c  line: 1098*/   /* u...
Read more

Kotlin Language Features Related to Null Handling

-
Any software engineer with a Java background would find the null handling features in the Kotlin language interesting. Let's summarize this topic with some examples. Nullable types: In Kotlin, types are non-nullable by default. If you want a variable to be able to hold a null value, you need to explicitly declare its type as nullable using the Type? syntax. For example, String? denotes a nullable string, while String represents a non-nullable string. Safe calls (?.): Kotlin introduces the safe call operator (?.) for handling nullable types. It allows you to safely invoke a method or access a property on a nullable object. If the object is null, the expression returns null instead of throwing a NullPointerException. Example: data class Person(val name: String, val age: Int, val address: String?) fun main() {     // Create a person with a nullable address     val person1 = Person("John Doe", 25, "123 Main Street")     val person2 = Person("Jane Doe", 30,...
Read more