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Saturday the 19th September 2015

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Hi my name is Joakim Nordström, and I'm going to talk about 
Java for Amiga, which is my night time project.

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At daytime I'm a system developer at Telia here in Uppsala

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and at night time I'm trying to get java to work on the Amiga

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The project I'm working is called JAmiga, and I have continued on
an open source project from 2003-2005

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It was started by two Germans, Peter Werno and Andre Dörffler.

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They started creating Java for Amiga.

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and released a version in 2005, and then nothing much happened
until around 2009 when I began looking at it.

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At that time they supported parts of Java 1.4.

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If you know something about Java, you'll get something from this,
and if you know nothing about Java, I hope you'll also get something out of this.

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So hopefully everyone will be happy at the end, 
or everyone will be confused by my ramblings.

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The target architecture is Amiga, and I'm working at the next generation Amiga.

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So it isn't the classic Amiga as seen on the first slide I'm focusing, but rather the next generation Amigas.

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And, believe it or not, Amiga still selling some sort of computers, and then one I have is this with a Power PC processor.

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And if I'm not mistaken, this is the same processor Mac should've used, if they didn't switch to Intel.

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The operating system i s Amiga OS 4.1, the latest release.

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Audience question: can you run old Amiga applications on this new computer?

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Yes, yes you can, AmigaOS emulates the old Amigas, and can also take advantage of the updated functionality.

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Audience question: as an old Amiga user, have they fixed the biggest problem, that the entire file system was corrupted when the machine crashed?

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Yes, there are a few new file systems that aren't as sensitive.

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Audience question: Have they removed the Guru meditation?

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Yes, I'm sorry, they've replaced it with the Grim Reaper.

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So the guru is gone, but problems persist.

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I'm going to start by showing the parts in a typical Java
installation, so we'll get a common ground to start from.

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In essence, it's these four parts. And I'm going to go through them one by one.

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We'll start with the JVM.

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The java Virtual Machine is an executable file, usually java.exe.

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It execute bytecode, and bytecode is the JVM's internal instructions, 
just like an x86 processor has x86 instructions, and PPC has PPC instructions.

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The JVM translates from bytecode to processor instructions.

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In the most simple case, it's relatively easy. 
One instructions have its obvious counterpart.

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Sometimes one bytecode is several processor instructions, and so on.

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It is however a rather slow process, if you take the easy way.

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If you want more a advanced JVM, you have to do various smart things.

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The JVM also handles memory and that stuff.

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Going right we come to the class library.

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And this is basically the Java SE standard.

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The class library are the standard classes you use when youäre developiong Java programs.

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And it's basically Oracle that decides how this should look.

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And if you know your Java, you recognize all the standard classes, in the java packages.

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This is stuff like handling lists, writing to the console, 
open files, and, handling XML and various things.

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In order to for instance open a file, we need to somehow get 
access to the underlying operating system.

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For this we have the native library.

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And this is the way from the class library, which is the same for all JVM's,

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but the native library is different, depending on the operating system.

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When we're on Windows, the native library is a DLL, Unix/Linux uses shared objects, and on AmigaOS its library files.

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And this is basically the parts we have in a JVM.

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And now I'm going to show what alternatives we have for these parts.

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The class library and the native library are closely tied together.

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And there is in essence two choices: OpenJDK from Oracle, and GNU Classpath.

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Open JDK supports the later Java versions 7, 8 and 9.

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In the beginning OpenJDK wasn't "Open"

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Somewhere between Java 6 and 7 that Sun decided to open up JDK and make it open source.

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Before that, around 1998 the JDK was still closed source.

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And then some people started GNU Classpath, which is an open source version of the Java standard.

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They implemented everything in the Java standard from scratch.

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And when OpenJDK became Open, people stopped developing for GNU Classpath.

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A lot of people who started with GNU Classpath, are now developing for OpenJDK.

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Some work at Oracle, and some develop in their spare time.

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A few different JVM options

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What you're probably using today is Oracle's hotspot,

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which is, if I'm not mistaken, a combination of JRockit and HotSpot.

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JRockit is actually a JVM developed by a Swedish company, later bought by Oracle.

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Some of the JRockit developers are like working a t Oracle now.

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Microsoft and MacOS had their own JVMs up until 2001.

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Or rather, Windows had its to 2001, and Mac had its until OSX.

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But then they skipped them, and let people decide themselver

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Then we have onw called "Kaffe".

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Its open source, and it support GNU Classpath

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It also exists for Classic Amigas, i.e. the 68k processor.

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The Jamiga project also has it s own virtual machine, which also can run on Classic Amigas.

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Then there's a nother variant, GCJ, GNU Compiler for Java.

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Which compiles either java code, or bytecode, to machine dependent code.

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So the bytecode is translated to x86 or PPC code.

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So you get a binary which needs to be compiled for each new architecture.

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Then I can also mention Dalvik which is Android's VM.

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And there's a small dispute, if Dalvik isn't in fact JamVM, where 
Google took the JamVM code and called it Dalvik.

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But, lets focus on this VM JamVM.

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It's developed since 2003, written in C, with some assembler.

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It uses Posix threads, and it supports PowerPC.

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So I thought this was good and interesting.

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So instead of continuing JAmiga's VM, I began looking at using JamVM.

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And that is what I've done.

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In teh beginning it only supported GNU Classpath, but then when OpenJDK became open, it supports that aswell.

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So when I'm developing, I'm porting JamVM.

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A small summary. 
The JVM is JamVM

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The class library is GNU Classpath, since that is what original JAmiga supported.

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So I've continnued with that.

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Native libraries are .library, and operating system AmigaOS 4.1.

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I can talk a bit about the interface of GNU Classpath.

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From the class library, via the native library down to the operating system.

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And there's a number of different native libraries.

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And these libraries corresponds to the Java packages.

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Comparing this with OpenJDk, they have one big library for all classes

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A small screen shot over GNU Classpath file structure.

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On the right side we see the Java standard class "java.lang.System".

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This has some connectiosn down to the operating system.

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And those connectiosn can be found in the "java.lang.VMSystm" class.

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And that is a pretty nice connection.

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If we have a Java class, wee know which native class we should look in,
to find connections to the OS.

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In OpenJDK it isn't quite as nice, but I think they're trying to achieve that.

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And now we're going to run some Amiga.

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I'm going to show how it looks when you run a Java program, and what happens in the Java code.

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So, now there's going to be some code.

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Here we have a small Java program.

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And here we have a main method that will print to the console "Hello Uppsala".

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I.e. "Hello World" in Java.

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And we're going to see what happens "under the hood".

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Audience question: is your laptop an Amiga machine?

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No.

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No. Its an Ubuntu.

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The amiga is at home, it's to big to take with me.

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So this is just pictures.

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We begin here in "Java.lang.System"
"System" is a class in the java standard.

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And then we have an object "out" here.

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And if we go to the System class, we'll find that "out" is a PrintStream.

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And if you know your Java, you know that PrintStream has a method "printline",
which print a line to the stream.

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Then we need to look at what "out" is initialised to.

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And then we see this VMSystem class, which has a method "makeStadnardOutputStream".

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So we move along to that class.

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And now, this is VMSystem. I.e not a Java standard class, but a aprt of Gnu CLasspath..

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And here we have a method "makeStandradOutputStream"

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This returns a PrintStream, which wraps around a BufferedOutputStream
that wraps around a FileOutputStream...

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If you know your Java, you know about these streams... 
but we'll ignore that for now.

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The main thing here is the "FileDescriptor.out".

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This is just ordinary Java code.

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But this "FileDescriptor.out" is a bit interesting.

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So we move on that.
We end up in a new class: "FileDescriptor"

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And that has an object named "out" up there.

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And.. that is a FileDescriptor object, which has an 
parameter FileChannelImpl.out, again.

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So we move on to the class "FileChannelImpl".

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And there we find the object "out", somewhere... 
There!

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And if we look here; here we load our library "javanio".

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So when this line is executed we're going to open "javanio.library".
If this was Windows, we would've opened "javanio.dll".

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We continue with "out".

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Down here we see "out=ch". 
And "ch" we previously set to a FileChannelImpl.

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Which is wrapped around a "VMFileChannelImpl.getStandardOut()".

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So we move along to the "VMFileChannelImpl" class

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And then we see the method "getStandardOut()"

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And that methd is here "getStandardOut",
which return a new VMFileChannel

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And calls a method "stdout_fd",
which is here, and it has no method body...

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However, it has a intereseting word here: "native"

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This means, that this call will be made to some sort of native library.

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And now we will go from Java to C.

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So this is C code.

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And this is the function that is executed when we call this native method.

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And, now,m if you know your Amiga,
you might recognize this "IDOS->Output()".

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This is a C function in Amigas SDk, which returns a pointer to the console.

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So the pointer to the console is returned into the Java code,
and going all the way back...

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So, somewhere here in the System.out, there is a small pointer to our C function.

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So this is some explanation to why Java is a bit slow to start up.

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Aroudn 1995-1996 it took a long time to start a JVM,
since all these classes had to be loaded on start-up

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It is also a bit hard to find errors, when you don't know where you are.

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This call.... er... eh

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This call, from Java code to C code,
looks a bit magic.

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And it is a bit magic, 
but not much.

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How does the JVM know which native method it should find?

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From out antive libaray we can export different functions.

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In the Java standard, it is defined that all native 
functions will have a standard name,

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with a prefix, followed by the java package, method name and arguments,
so the VM can find the method.

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And with these small header definitions in the C code,
the compile knows that these functions should be exported

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But this is not how it works on the Amiga.

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In the Amigas native libraries we only export on function "getLibraryContent"

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And that returns a strcture where the JVM can do the lookup.

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So that is one difference in Amiga.

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Then ,some more code.
A different example.

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We're going to look at the class VMSecureRandom.java

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The VM prefix tells us that there might be antive calls in here.

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And this class generates a random seed,
which is used by f.i. cryptography.

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And one of my users that tested Jamiga,
found a small crypto library

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However, when executing it, the entire machine locked up.

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And this is the VMSecureRandom class.
The detalis aren't important.

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But here we have the method "generateSeed",
that generates our seed.

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It does this by starting 8 threads that spins,
and increments a counter,

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and then randomly they will end,
and then we'll end up with a random value.

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And it was here that JVM started 8 threads, got into a (unsolved) race condition.

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however, I managed to shorten this method to this.

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Here we instead open a file from the Amiga device "Random:"

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Which generate random numbers.

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So, this method became much shorter, and a lot faster.

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As an example we have here a variant from a Unix flavor,
wirh a native call to his C code.

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And this is C++, which with its object orientation maps a bit better to Java.

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And just for the fun of it, we can look at the Win32 variant.

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And this just throws an exception, that this 
method isn't supported on Win32.

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Oh no! The Guru meditation!

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Not at all planned.
Oh no. How annoying.

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Another problem i had,
was how these threads are handled.

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I experienced some problem when adding network support

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I started a Java program
which opens a socket

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And this socket should talk to some other server, and send data to it.

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And I thought it might be nice to put in its own thread,
so the main thread can do other stuff.

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We create a socket,
and a new thread.

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And then I try to read from the socket here.

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But then I got this error:
apparently, the socket, isn't a socket!

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Much strange.

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But if you read the Amiga docs...

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You'll find that this socket 
only exists within this process.

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There are ways to circumvent this,
they are bit troublesome.

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So instead I here created a 
new socket process.

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So instead of sending the socket ID, I instead send 
a reference to the process.

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We'll continue with these threads.

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I mentioned that JamVM uses Posix-thread,
where AmigaOS has processes.

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Posix-threads are a bit more lightweight than AmigaOS' processes.

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The AmigaOS processes has a few connections to DOS library and such.

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Audience question: do they still have all that old DOS stuff, like BCPL and processes.

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It's sort of all gone in Amiga OS 4.

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Audience: they had these heavy processes, and then "threads".

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Ah, yes, yes, that's still there.

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An AmigaOS process is a "task", which is more lightweight.
But the Amiga process has connections to DOS.

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And the "tasks" can't be used for disk I/O, so if you need that, you need a "process".

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Here we've started a simple Java class, "Start thread", that actually doesn't start a thread.

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We're going to see how this looks when its running on the Amiga

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Each new JVm instance, has beside the main process,
also have three JamVM specific Amiga processes.

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We have a Reference handler, Finalizer, and Signal handler.

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Reference handler handles garbage collection, i.e. frees created objects.

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The Finalizer runs the "finalize()" method on objects that's been garbage collected.

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And the Signal handler handles signals sent to the program.

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So it kind of looks like this.

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And now I'm going to end this, 
so why not try and end this Java program by pressing Ctrl-C.

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Ctrl-C is handled by the signal handler.

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And when it gets the Ctrl-C it executes the Java method System.exit and VMRuntime.exit().

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And then it also executes the native c-function exit().

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The problem with running exit(), is that only the Signal handler process is ended.

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Like i said, Amiga processes are a bit bigger than Posix-threads.

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If this was Posix-threads, an exit() would've ended the main process,
which would've ended the Posix-threads aswell.

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But not in the Amiga case.

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So instead, we run the Java methods in the Signal handler.

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And then we send the Ctrl-C signal back to the main process.

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Receiving that signal, the main process ends the three subprocesses,
frees memory,closes libraries, and then exists.

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And with that, I'm almost done.

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Current status: Jamiga is at version 1.2, downloadable from http://www.os4depot.net.

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There's also a few automatic updates available.

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Somewhat completet support for Java 1.5,
however no graphics or AWT.

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I also have a small Twitter client,
which uses Twitter4j.jar

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Its very simple, this is a command line tool you can run,

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which creates a small tweet.

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Fantastic! The technology moves forward, even for the Amiga.

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The plan ahead is to support OpenJDK

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And this a small test i ran, which shows that I'm missing java.libraray,
which I must implement.

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JamVM supports OpenJDK, out of the box.

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I'll also try to fix graphics stuff.

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Just to mention a few ways to build OpenJDK.

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You can either build it like Oracle wants you to.

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One though I had was to build OpenJDK, grab the class files, and then just iteratively see what's missing.

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Alternatively, you can build it using IcedTea,
which is a way to build OpenJDK using free GNU tools.

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When you're building using OpenJDK, I think there's still some thing that aren't completely open source.

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If I'm not mistaken.

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With IcedTea, you can also do cross compiles, so i can compile Jamiga-stuff on that.

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Otherwise I have to compile everything on the Amiga, and it actually isn't that fast.

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And that's where I am right now.

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If you want more information, you can follow me on twitter or look at my blog.
If you want info on Amiga, you can go to http://amigaos.se

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That's it. Thank you!
Questions?

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Audience: what was the biggest challenge? Is it this with the threads?

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Currently its cross-compiling OpenJDK, but previously it was...

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... mostly time... to find the time to fix everything.

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Much of the work isn't very advanced, but it's
these sort of bugs that is the hardest part.

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Audience: what is the process model on the new Amiga? Back in the days, 
all memory was shared, and you could peek wherever you wanted.

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It's not possible to do that anymore, if you do that, the Grim Reaper will appear.

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Audience: But wasn't that the case in Os 3.1. You could enable the MMU somehow.

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Eh... er...

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Yes, that's correct.

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Audience: but the model was to send pointers.

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Yes, er, that's still kind of like it is.

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When you allocate memory, you can tell it to be"public" so other processes can reach it.

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But you can also say that it's private, which is the preferred way.

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But when two processes need to talk to each other, the memory needs to be "public".

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Audience: and "public" is globally, shared?

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Yes.

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Audience: Have you found functions not available on Amiga? You mentioned the crypto-secure-random....

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Audience: ...but have you found something where you had to port a third party library.

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no.. no.. well.

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The JVM and GNU Classpath has a few dependencies, but most them are available.

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Or, well, the Posix-threads doesn't exist.

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Or, there is a support for Posix-threads, but that implementation lacks a few things.

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So I made my own Posix-thread implementation which is very Jamiga specific.

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So you can't use anywhere you like, sadly, 
but it works for JAmiga.

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Audience: You mentioned AWT, but why not SWT?

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Er... SWT.... isn't that Swing in the background? Or is that AWT?

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Audience: SWT has its own native libraray, and is nät oart of the java standard.

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Audience: so SWT isn't standard, and that's why you don't mention it?

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Audience: (some discussion on SWT, AWT, etc): SWT is horrible. Don't go there.

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Sounds like I shouldn't bother with SWT... atleast not now.

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Audeince: Do you have any more commiters in the project?

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I had one who helpd with some MorphOS parts, but, no, now its just me.

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And lately, it's not been much from me either.

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Audeince: What about test code. Does Rocale have that?

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Yes... Oracle has some test-sets, JTreg I think its called.
I haven't looked at that much.

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However, GNU Classpath has "Mauve", which is an entire test suite for all Java classes.

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If you look at my blog, I've listed what is tested,
and I think like 80 % is covered.

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But, yes. Test suite exists.

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Thank you!

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A movie by Joel Edberg