Saturday May 31, 2008
Monday May 19, 2008
By john.rose on May 19, 2008
Update: There are some good conversations going on about the EDR at the jvm-languages Google group. Here are some rough changes to the EDR I will be proposing in response; the EG may choose to make these changes (or something like them) official with an EDR update pushed through the JCP (Java Community Process).
Saturday May 10, 2008
By john.rose on May 10, 2008
In other news, today (May 10th) is National Train Day. On this day 139 years ago, a ceremonial golden spike was driven at Promontory Summit, Utah, joining the Central Pacific and Union Pacific railways into a single transcontinental line. The continent was very suddenly smaller, because people, goods, and mail could be moved more quickly from coast to coast, a task which was previously done with wagons, horses, and boats. In the years leading up to this watershed event, two railroads were built, with great difficulty and ingenuity, from each coast, to meet at Promontory Summit.
There is a Promontory Summit and a golden spike in our future also... [Read More]
Wednesday May 07, 2008
By john.rose on May 07, 2008
invokedynamicinstruction in one form or another. The problem has been with picking the one form that simultaneously enables a good range of use cases, addresses several architectural challenges in the JVM, and can be optimized by a variety of commercial JVMs. It has been a restless search for “one bytecode to rule them all”.
The EG has decided to propose an answer, providing a hook which refers all important decisions at a dynamic call site out of the JVM and into Java code. This note builds on a previous blog entry, giving more concrete details and use cases. The current design makes heavy use of method handles, which greatly reduces complexity and clarifies the various roles of language implementors and the JVM. [Read More]
Tuesday May 06, 2008
By john.rose on May 06, 2008
Monday May 05, 2008
By john.rose on May 05, 2008
Interface injection (in the JVM) is the ability to modify old classes just enough for them to implement new interfaces which they have not encountered before. Here are the key design points, in brief... [Read More]
Sunday May 04, 2008
By john.rose on May 04, 2008
Or, anything worth starting is anything worth starting is anything worth starting is anything worth starting is ...
A continuation, simply put, is a reference to the rest of some program P, as of some given point in the midst of P. It is an interesting design problem to introduce continuations into the JVM. I don't know of a full design for JVM continuations, yet, but it's possible to observe both the easy and the hard parts, and to survey some of the reasons we should care. [Read More]
Wednesday Apr 16, 2008
By john.rose on Apr 16, 2008
Wednesday Apr 09, 2008
By john.rose on Apr 09, 2008
Kudos to Vladimir Sizikov for a nice collection of follow-up links. I was very glad for the introduction to Ulrich Drepper’s paper. He also refers to a new wiki on Hotspot implementation, inspired by and serving the OpenJDK, in which I and others are collecting information to help language and JVM implementors understand how Hotspot works, how to make it better, and how to byte-compile for performance.
Finally, if like me you’ve heard but never quite believed the story about how functional languages fix all the problems with side effects and you laugh at the funny papers, you’ll like this little fable about the perils of mutability, in programming languages. It provides an arresting, hard-hitting, and ultimately crushing new perspective on Hindley-Milner type checkers.
Wednesday Mar 12, 2008
By john.rose on Mar 12, 2008
Language-specific VMs often use pseudo-pointers with an immediate “payload” to represent a commonly used subset of numbers, and also “headerless” representations for small but ever-present types like Lisp’s cons cell. The JVM can support fixnums and other headerless objects for the sake of these languages, and even for Java. The idea is to make ordinary object pointers (sometimes called oops) coexist with more specialized formats for headerless objects, which we will call iops and xops. The techniques are mature and well-known, and the overheads (of extra tag checking before pointer usage) can be controlled by optimizations already used widely in JVMs.
We will examine low-level encoding techniques, and investigated how to integrate these concepts into the JVM. Although a language implementor might prefer to try these techniques in the closed environment of a from-scratch, specialized VM, it is probably more profitable in the end to incorporate them into an optimized, mature JIT and GC, such as the Open JDK project. [Read More]
Friday Feb 01, 2008
By john.rose on Feb 01, 2008
Why am I suddenly excited about Microsoft technology? Two or three reasons. First, the DLR (with IronPython and IronRuby) is another evidence that we are in some sort of renaissance or resurgence of programming language design. The second thing that excited me at Redmond was a striking case of parallel evolution between the DLR over the CLR on one hand and the Da Vinci Machine over the JVM on the other side... The final reason is that I am excited for the customers of the JVM, because they will also enjoy the new languages in an expansive open-source community, and on their choice of blazingly fast Java virtual machines. [Read More]
Wednesday Jan 23, 2008
By john.rose on Jan 23, 2008
The JVM uses symbolic names to link together the many hundreds of classes that make up an application. Symbols in the JVM are represented in a uniform syntax, a counted sequence of Unicode characters. The JVM can readily accept class, package, method, field, and type names which could be any string, not just the strings accepted by the Java compiler. Let's call such names “exotic names”.
The JVM originally inherited symbol spelling restrictions from the Java language, but in recent years it has removed most restrictions. This note describes how to remove the remaining restrictions, by presenting a universal mangling convention to encode arbitrary spelling strings. (Updated 9/01/2012.)[Read More]
Tuesday Jan 22, 2008
By john.rose on Jan 22, 2008
One pain point in dynamic language implementation is managing code dynamically. While implementor’s focus is on the body of a method, and the linkage of that body to some desired calling sequence, there is a host of surrounding details required by the JVM to properly place that code. These details add noise to the implementor’s task, and often enough they cause various execution overheads. Anonymous classes can partially address these problems... [Read More]
Thursday Dec 13, 2007
By john.rose on Dec 13, 2007
In a previous post I enumerated the various parts that go into a call site in the JVM. In order to support the program structure of other languages, especially dynamic languages, the JVM must extend the present schemes of method definition, invocation, and linkage.
The key new requirements are dynamic relinking, programmable linkage, programmable guards, descriptor polymorphism, and method handles.
- dynamic relinking allows dynamic linkage decisions to be revoked
- programmable linkage allows dynamic linkage decisions to be made reflectively by “bootstrap methods”
- programmable guards allows call sites to select among overloaded methods according to language-specific rules
- descriptor polymorphism allows call sites and adapters to be managed and connected generically
- method handles let bootstrap code and call sites refer directly to bytecoded methods
Tuesday Nov 13, 2007
By john.rose on Nov 13, 2007
Here are some bits from the conversation that stick in my memory...[Read More]
John R. Rose
Java maven, HotSpot developer, Mac user, Scheme refugee.
Once Sun and present Oracle engineer.