Javascript and the jvm – modus create euro to aud chart


When it comes to server-side JavaScript programming, there are other choices besides v8 based solutions like NodeJS, TeaJS, SilkJS, and others. For the longest time, the Rhino JavaScript engine has been around for the JVM, and recently Java 8 was released with a brand new and improved JavaScript engine for the JVM called Nashorn famous quotes about life and death. There is another project called DynJS that shows a lot of promise as well. In this post, I will investigate the benefits of JavaScript running on the JVM and demonstrate how easy it is to integrate with, or script, Java from JavaScript. JavaScript in the JVM

A few years back, I read a blog post by a fellow named Steve Yegge, which talked about JavaScript on the JVM. The post is long, but well worth the read. At one point, he talks about the benefits of scripting on the JVM, and all of what he wrote and talked about back then is still valid today.

First, if there ever has been a computing problem, there is a solution for it in Java. Many times, the Java implementation of some library will be superior to what you might cobble together from other sources (see Apache Lucene). Why not leverage all this prior work? On top of the availability of all this code, in .jar format, it is portable between operating systems and CPUs – it almost runs everywhere.

Second, the JVM itself has a considerable number of man hours of research and development applied to it and it is ongoing. When they figure out how to make something smaller/faster/better for the JVM, it benefits everything that uses the JVM – including JavaScript execution and the libraries we’d call from JavaScript. We also get the benefit of Java’s excellent garbage collection schemes.

Third, the JVM features native threads. This means multiple JVM threads can be executing in the same JavaScript context concurrently. If v8 supported threads in this manner, nobody would be talking about event loops, starving them, asynchronous programming, nested callbacks, etc msn news. Threads trivially allow your application to scale to use all the CPU cores in your system and to share data between the threads.

I’ll add a fourth, that you can compile your JavaScript programs into Java class files and distribute your code like you would any Java code.

Rhino has a few built-in global functions, but I’ll only elaborate on a few. We’ve already seen that the print() function echoes strings to the console window.

Note the hello was printed on what looks like the command line. That was printed from the background thread and I had to hit return to see the next prompt. The Thread[Thread-1,5,main] was the return value of the spawn() method; it is a variable containing a Java Thread instance.

This allows only one thread at a time to enter the foo() method. If a second thread attempts to call the function while a first has entered it (but not returned yet), the second thread will block until the first returns.

Synchronization is vital for multithreaded applications to avoid race conditions where one thread might be modifying a variable/array/object while another thread is trying to examine it. The state of the variable/array/object is inconsistent until the modification is complete.

To recap so far, Rhino provides print(), load(), spawn(), and sync() functions, among others. In practice, I only see the load() and sync() methods being necessary because Rhino and other JVM JavaScript implementations allow us to “script Java” from JavaScript programs. Scripting Java

Rhino makes scripting Java rather easy. It exposes a global variable Packages that is a namespace for every Java package, class, interface, etc., on the CLASSPATH.

The “standard” output stream idr to usd converter. This stream is already open and ready to accept output data. Typically this stream corresponds to display output or another output destination specified by the host environment or user.

What this is showing is that there are a number of implementations of println() in Java with different signatures. Rhino is smart enough to choose the right implementation based upon how we call it. Also note that the types in the println() signatures are Java native types.

Rhino also exposes a global java variable which is identical to – this is a handy way to access the builtin Java classes. A minimal console class

When writing JavaScript, things work as expected. An object is an object, an array is an array, a string is a string, and so on. But when we script Java from JavaScript, our variables often are instances of Java objects. A trivial example:

Note that getBytes() is a method you can call on Java strings, but not on JavaScript strings. Also note that we can cast Java strings to JavaScript strings.

Fortunately, we rarely have to instantiate Java strings, but we will have to deal with binary data when scripting Java. JavaScript has no real native binary type, but we can have our variables refer to instances of Java binary types stock market futures today. Java Byte Arrays

Let’s look at how to read in a text file by scripting Java, and it does look a lot like Java. All the Java classes we use are in the package and you can read up on FileInputStream, BufferedInputStream, and ByteArrayOutputStream binary code translator to english. There are certainly many examples of their use (in Java) on the web.

Maybe this is a bit ugly, but we can encapsulate all the bridging between JavaScript and Java in nice JavaScript classes. Then we only need to call our JavaScript from JavaScript and not care so much about how Java is being called or the conversions between JavaScript native objects and Java ones is being done. One thing for sure is that this seems a lot cleaner and simpler than writing C++ modules to link with NodeJS or other V8 alternatives.

In other words, we only had to write the cat() function once. We can load() it in any or all of our applications from now on and not have to write the interface code to Java again. Threads without spawn()

This version works, but it is not quite perfect. You see, the bumpX() function returned by sync() synchronizes on the this object, which isn’t harmful in this example. However if we had another two threads bumping a y variable with a bumpY() method also synchronized on this, there’d be unnecessary contention among the 4 threads silver chart history. When thread1() calls bumpX(), the remaining 3 threads will be blocked when they call bumpX() or bumpY().

Note the extra argument to sync(), the object we want to synchronize on. Now the callers that call bumpX() will block appropriately, not affecting callers of bumpY(). About synchronization

I wouldn’t count on any JavaScript operation to be atomic. That is, array.pop() could in theory get interrupted by a thread switch interrupt, so if you have two threads manipulating that array, you have a seriously bad race condition. So be aware of thread safety. If you ever expect to have two threads access the same memory, synchronize around the accesses, as I demonstrated. Extending Rhino (3rd party java)

The rhino executable program is really a bash script that starts up the JVM (java command) with the rhino .jar file and passes any additional command line arguments to the rhino java program.

From this we can craft our own command lines, including some that add .jar files to the class path. To see a full description of the java command and all the command line options, enter this at your shell prompt:

We cannot pass a CLASSPATH via -cp flags to the java command if we also specify -jar. So we are going to have to use a form of the java command that specifies CLASSPATH and the initial class/function to call. I dug into the rhino sources and found that the main function is

We can see it is running the REPL as if we ran the rhino shell script. Now we can see if our function is accessible from our JavaScript environment.

You should note that our x variable holds a reference to a Java String, not a JavaScript string. We can pretty much use it like a JavaScript string, and Rhino does the type conversions automagically as needed.

eIt seems intuitive to me that if a directory is part of your CLASSPATH that Java runtime should find .class files as well as .jar files in that directory. But it does not work that way! CLASSPATH may specify a directory where only .class files are considered or it may specify .jar files that basically act like a directory containing only .class files.

In order to run it, I installed the Java 8 JDK on my Mac. I haven’t seen any ill effects yet, so I guess it is safe. There were some negative effects of installing Java 7 on a Mac, particularly that Java 7’s browser plugin is 64-bit only and Google Chrome is 32-bit only; you lose the ability to run Java from WWW sites in Chrome stock market opening times new years eve. I haven’t tested to see if this is true for Java 8, but I haven’t seen any similar warnings.

The installation process is not 100% right. There is a jjs program that we are supposed to be able to run to execute Nashorn scripts (jjs is roughly Nashorn’s version of the rhino command). After installing Java 8, jjs is not in /usr/bin as it should be nyse futures market. A little bit of digging turned up the file here:

There is also a /usr/bin/jrunscript and a manual page for that dated 2006. The jrunscript program appears to launch Nashorn as well. There is also a jrunscript in the same directory as jjs that is different than the one in /usr/bin. A lot of confusion caused by all this, but I will use jjs for the rest of this article.

Instead, Nashorn can figure out that Runnable has only one member (run) and Runnable is required for Thread constructor, so it does the right thing if you pass the constructor a JavaScript function.

One other change I had to make was to call join() on one of the threads started. Without this, jjs exited right away. This is a different behavior from rhino.

Nashorn also features a scripting mode that adds some very non-standard features to the JavaScript language. The concept is a good one if you want to use Nashorn to write shell scripts. The only problem is anything you write using these extensions will not be portable to any other JavaScript environment. For this reason, I won’t go into more depth about this feature the millionaire tv show. Nashorn Performance

I happen to know that Rhino 1.7R4 is notoriously slow at string concatenation. It is much faster to join() an array. So I created a second trial program: javascript

Rhino is the gold standard of JavaScript for the JVM. It simply has been around for a very long time (since the 1990s) and it is feature rich and relatively bug free. Nashorn represents a new code base and new commitment by Oracle to JavaScript for the JVM. It’s brand new, and already appears to be a solid implementation in its own right. It’s only going to get better, too. Rhino is likely to run on any new release of Java for a long time to come, but it’s not as likely to get the attention to improvements as Nashorn.

If I said “EVERY TIME” about the Java implementations, you’d have a point. I specifically mentioned Lucene, which is an outstanding document indexing library that people have tried to port from Java with inferior results.

C++ is out of reach for most JavaScript coders, so they’re not going to have a good time at creating modules that need to link with C/C++ libraries. Scripting Java in Rhino or Nashorn is so trivial, these guys won’t have any issue.

I think you are wrong about threading vs. event loop. Very wrong. There’s an old adage in programming that you can trade memory for speed love quotes tumblr. In this case, memory for thread stacks. What event loop gains you is the ability to handle a huge number of simultaneous connections.

The Nashorn that will be released in 8u40 will have significantly bridged the gap towards native performance and will be on par with v8 on a couple of benchmarks in e.g. the octane suite, and virtually orders of magnitude (no exaggeration) faster than rhino -opt 9 on all of them… Rhino is left way behind.

As Nashorn relies heavily on invoke dynamic, which tends to generate a lot of intermediate methods due to its implementation, warmup will most likely take longer as well as the JVM warms up. We are also working on addressing various warmup issues in Nashorn – adding persistent code stores, class caching and lazy JITting.

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