I am just wondering whether there would be a significant speed performance advantage relatively on a given set of machines when using JavaCV as opposed to the C/C++ implementation of OpenCV.
Please correct me if I am wrong, but my understanding is that the c/c++ implementation of opencv is closer to the machine where as the Java implementation of OpenCV, JavaC, would have a slight speed performance disadvantage (in milliseconds) as there would be a virtual machine converting your source code to bytecode which then gets converted to machine code. Whereas, with c/c++, it gets converted straight to machine code and thus doesn't carry that intermediary step of the virtual machine overhead.
Please don't kill me here if I made mistakes; I am just learning and would welcome constructive criticism.
Thank you
I'd like to add a couple of things to #ejbs's answer.
First of all, you concerned 2 separate issues:
Java vs. C++ performance
OpenCV vs JavaCV
Java vs. C++ performance is a long, long story. On one hand, C++ programs are compiled to a highly optimized native code. They start quickly and run fast all the time without pausing for garbage collection or other VM duties (as Java do). On other hand, once compiled, program in C++ can't change, no matter on what machine they are run, while Java bytecode is compiled "just-in-time" and is always optimized for processor architecture they run on. In modern world, with so many different devices (and processor architectures) this may be really significant. Moreover, some JVMs (e.g. Oracle Hotspot) can optimize even the code that is already compiled to native code! VM collect data about program execution and from time to time tries to rewrite code in such a way that it is optimized for this specific execution. So in such complicated circumstances the only real way to compare performance of implementations in different programming languages is to just run them and see the result.
OpenCV vs. JavaCV is another story. First you need to understand stack of technologies behind these libraries.
OpenCV was originally created in 1999 in Intel research labs and was written in C. Since that time, it changed the maintainer several times, became open source and reached 3rd version (upcoming release). At the moment, core of the library is written in C++ with popular interface in Python and a number of wrappers in other programming languages.
JavaCV is one of such wrappers. So in most cases when you run program with JavaCV you actually use OpenCV too, just call it via another interface. But JavaCV provides more than just one-to-one wrapper around OpenCV. In fact, it bundles the whole number of image processing libraries, including FFmpeg, OpenKinect and others. (Note, that in C++ you can bind these libraries too).
So, in general it doesn't matter what you are using - OpenCV or JavaCV, you will get just about same performance. It more depends on your main task - is it Java or C++ which is better suited for your needs.
There's one more important point about performance. Using OpenCV (directly or via wrapper) you will sometimes find that OpenCV functions overcome other implementations by several orders. This is because of heavy use of low-level optimizations in its core. For example, OpenCV's filter2D function is SIMD-accelerated and thus can process several sets of data in parallel. And when it comes to computer vision, such optimizations of common functions may easily lead to significant speedup.
JavaCV interfaces to OpenCV, so when you call something OpenCV related there would be some overhead but in general most of the heavy work will still be on the C++ side and therefore there won't be a very large performance penalty.
You would have to do performance benchmarks to find out more.
PS. I'm pretty new here but I'm rather sure that this is not a suitable question for StackOverflow.
i would like to add a few more insights on java as an interface to c++ libraries...
A)developing:
1)while java may be easier to manage large scale projects and compiles extremely fast, it is very very hard, and next to impossible to debug native code from java...
when code crush on native side...or memory leaks( something that happens a lot... ) you feel kind of helpless...
2)unless you build the bindings yourself( not an easy task even with using swig or whatever... ) you are dependent on the good will/health/time of the bindings builder....
so in this case i would prefer the official "desktop java " bindings over javacv...
B)performance.
1) while bindings may be optimized( memory transfer using neobuffer ) as in the javacv case there is still a very very small jni overhead for each native function call -
this is meaningless in our case since most opencv functions consume X100000++ cpu cycles compared to this jni overhead...
2) The BIG-PROBLEM ---- stop the world GARBAGE COLLECTIOR( GC )
java uses a garbage collector that halts all cpu's threads making it UNSUITABLE for REAL-TIME application's , there are work-around's iv'e heard of like redesigning your app not to produce garbage, use a spaciel gc, or use realtime java( cost money... ) they all seem to be extra-work( and all you wanted is a nice easy path to opencv.... )
conclusion - if you want to create a professional real time app - then go with c++
unless you have a huge modular project to manage - just stick with c++ and precompiled headers( make things compile faster... )
while java is a pleasure to work with , when it comes to native binding's HELL breaks loose...i know iv'e been there....
I'm a front end developer that's looking to get into some other languages such as Java or C++. I have an idea for a program and was just looking for an answer to something. What I would like to do is build a program and boot directly to that program. For example I have an old computer and I wipe the hard drive clean. So they is nothing currently on it. Not even an OS. I want to build a program that I can install to the hard drive that will boot straight into the program once started. Would this be considered an OS?
No you don't. Unless you want to spend many years, writing drivers for your graphics card, harddisk controller, usb controller, dma controller and all the other hardware your computer have.
What you want is a minimal operation system, which include just the kernel, and a runtime library and which start your program and nothing else on startup. A minimal Linux such as linux from scratch or bsd would be a good starting point.
First of all you need to decide your your program needs what. I mean should operate in Protected mode or the routine you have is tiny, so it is enough to run before entering protected mode (i.e. in real mode).
Here you can do three things
Modify bootloader to jump the execution to your code . Then Your code can resume normal os initialization.
Modify your os kernel early initialization code So that it executes your code before entering protected mode
I think your code will not be harmed if a bit of os portion is running. So you can write your routine before full kernel initialization.
Now note that for the later two point you need to modify your kernel, which is not easy (not even always possible)
Now the problem in first approach: Nothing will be ready for you, not even a regular c library or divice drivers , so you have to write every raw bit of code by hand which is crude.
This is off course not possible in java. Because the jvm will not be ready for you.
Now practically: there are lot of tiny os available, use one of them and modify as per your need. use this link to get a complete list of what is available for you.
First, Java is right out. You cannot possibly do this in Java without enormous amounts of tool-building. Java is not suited for this task at all.
You can do it in C++ or C. The search terms you are looking for is operating system development. This would probably not technically be considered developing an Operating System since it wouldn't run other programs, but the information about how to get through the boot-up procedure and establish a minimal environment are going to be most easily found in the category of operating system development. Some reasonable starting resources for that can be found at the OS Dev Wiki.
Alternately, you could take an existing small open-source OS and modify what it does after the boot-up sequence completes. If your program is intending to do anything more than just use the keyboard and the screen in text mode, there need to be device drivers. Thus, depending on the project, changing an existing OS may be the easiest route because you won't need to write your own device drivers for any devices you want to use.
Java can't run without Environment. If you want to run you program on you machine without OS, Java is a wrong choice.
C++ program can run without OS, but it's difficult to write a bootable program in C++.
If you want to write your own bootable program, you should use assembly for boot and load function, with some knowledge to use hardware in low level.
You have to have an operating system, so your program would be the operating system (or you would have to use another one and write it for that). It's certainly possible in C++, but it's not really possible to write an operating system in java.
Unless you want write something in (for example) Open Firmware and Forth or say a ROM BASIC. You'll probably qualify as a boot loader. Your application may qualify as an operating system. In my opinion, and a modern context, it entirely depends on how much functionality it provides to hosted applications. I'm not sure that something like FreeDOS would be considered an operating system (no pre-emptive task scheduling or GUI for example) given modern computers (I don't care to argue the point either way).
I never did kernel programming. I am a good programmer in the Java language and frequently use it. Now i feel to do something interesting with kernels. A kernel resides between hardware and OS. It communicates with hardware using system calls. Every programming language require a compiler to compile the code written in high level language and then it generate low level code, which is generally assembly language code. Here comes my doubt, if we have kernel written in C, then should we have a C compiler installed on the machine? At the end, when kernel interacts with hardware it uses assembly language, can i create kernel in Java language? If yes, then what are the requirements for the same? Thank you.
A kernel resides between hardware and OS
Usually, the kernel is considered to be part of the operating system.
It communicates with hardware using system calls
System calls are the interface that is provided by the OS to user applications. The operating system communicates with the hardware through other mechanisms (for example interrupts or memory-mapped registers).
Every programming language require a compiler to compile the code written in high level language and then it generate low level code, which is generally assembly language code.
The compiler output is typically either native machine code or a language-specific bytecode (like in the case of Java). Sometimes, compilers also target another programming language such as C or Javascript (transpilation).
Here comes my doubt, if we have kernel written in C, then should we have a C compiler installed on the machine?
That's not necessary. The C compiler produces output that can execute directly on the hardware without interpretation.
At the end, when kernel interacts with hardware it uses assembly language
The CPU doesn't understand assembly. It understands machine code.
can i create kernel in Java language?
It has been done.
If yes, then what are the requirements for the same?
If you want to write a kernel in Java, then you either have to
compile your entire Java codebase to machine code
get yourself a CPU that can execute Java bytecode
find or build a Java VM and runtime that can run on bare metal and run your Java code in it (if you do it cleverly, you can write much of the runtime and maybe also parts of the VM in Java itself).
Now to the unspoken, almost rhethorical question:
Is this a good idea?
Probably not. Why? First of all, because it would take ages to set up. Second, because you couldn't just code the way you develop an average business application. You'd have to think about performance of very time-critical code (e.g. context switching, which often requires hand-tuned assembly to be fast enough), manual memory management (as in: your MRU might expect you to give it the physical address where the page table lies), system-/hardware-specific mechanisms (how to access a XYZ controller on this particular architecture?), ...
So you would lose many of the advantages that Java has over a low-level language like C in the first place.
Yes a kernel can be written in Java, see the JNode. It would have the advantage of having no problems with: dangling pointers, mix up of pointers and array addresses, unitialised data, and many more features of C.
Introduction
I heard something about writing device drivers in Java (heard as in "with my ears", not from the internet) and was wondering... I always thought device drivers operated on an operating system level and thus must be written in the same language as the OS (thus mostly C I suppose)
Questions
Am I generally wrong with this
assumption? (it seems so)
How can a driver in an "alien"
language be used in the OS?
What are the requirements (from a
programming language point of view)
for a device driver anyway?
Thanks for reading
There are a couple of ways this can be done.
First, code running at "OS level" does not need to be written in the same language as the OS. It merely has to be able to be linked together with OS code. Virtually all languages can interoperate with C, which is really all that's needed.
So language-wise, there is technically no problem. Java functions can call C functions, and C functions can call Java functions. And if the OS isn't written in C (let's say, for the sake of argument that it's written in C++), then the OS C++ code can call into some intermediate C code, which forwards to your Java, and vice versa. C is pretty much a lingua franca of programming.
Once a program has been compiled (to native code), its source language is no longer relevant. Assembler looks much the same regardless of which language the source code was written in before compilation. As long as you use the same calling convention as the OS, it's no problem.
A bigger problem is runtime support. Not a lot of software services are available in the OS. There usually is no Java virtual machine, for example. (There is no reason why there technically couldn't be, but usually, but usually, it's safe to assume that it's not present).
Unfortunately, in its "default" representation, as Java bytecode, a Java program requires a lot of infrastructure. It needs the Java VM to interpret and JIT the bytecode, and it needs the class library and so on.
But there are two ways around this:
Support Java in the kernel. This would be an unusual step, but it could be done.
Or compile your Java source code to a native format. A Java program doesn't have to be compiled to Java bytecode. You could compile it to x86 assembler. The same goes for whatever class libraries you use. Those too could be compiled all the way to assembler. Of course, parts of the Java class library requires certain OS features that won't be available, but then use of those classes could be avoided.
So yes, it can be done. But it's not straightforward, and it's unclear what you'd gain.
Of course another problem may be that Java won't let you access arbitrary memory locations, which would make a lot of hardware communication pretty tricky. But that could be worked around too, perhaps by calling into very simple C functions which simply return the relevant memory areas as arrays for Java to work on.
Writing Solaris Device Drivers in Java covers a A RAM disk device written in Java.
Another one for Linux. Goes more in depth on why you might want a DD in Java as well (since some people were wondering by the looks of the other posts and comments)
A device driver could be a lot of things
I actually write device drivers in java for a living: drivers for industrial devices, such as scales or weighing devices, packaging machines, barcode scanners, weighing bridges, bag and box printers, ... Java is a really good choice here.
Industrial devices are very different from your home/office devices (e.g. scanners, printers). Especially in manufacturing (e.g. food), companies opt more and more for a centralized server which runs an MES application (e.g. developed in Java) The MES server needs to interface with the devices of the production line, but also contains business logic. Java is a language that can do both.
Where your home/office devices are often built-in to your computer or connected with an USB cable, these industrial devices usually use Ethernet or RS232 connectors. So, in essence, pretty much every language could do the job.
There is not much standardisation in this area yet. Most vendors prefer to create their own protocol for their devices. After all they are hardware builders, not software geniuses. The result is that there is a high diversity of protocols. Some vendors prefer simple plain-text protocols, but others prefer complex binary protocols with CRC codes, framing, ... Sometimes they like to stack multiple protocols (e.g. a vendor specific handshaking algorithm on top of an OPC layer). A strong OOP language has a lot of advantages here.
E.g. I've seen java print at a continuous speed of 100ms/cycle. This includes generating a unique label, sending it to the printer, receiving a confirmation, printing it on paper and applying it to the product using air pressure.
In summary, the power of java:
It is useful for both business logic as complex interfacing.
It is just as reliable in communication with sockets as C.
Some drivers can benifit from Java's OOP power.
Java is fast enough.
It's not impossible, but possibly hard and possibly makes not much sense.
Possible is it, because Java is a normal programming language, as long as you have some way to access the data, it's no problem. Normally in a modern OS the kernel has a layer to allow raw access to hardware in some way. Also already exist drivers in userspace, at least the userspace-part should be no problem to implement in Java.
It makes possibly not too much sense, because the kernel has to start a JVM to execute the driver. Also JVM-implementations normally eat up much memory.
You could also use Java-code compiled to be executed natively on the platform (not with the help of a JVM). This is usually not that efficient, but it could be suitable for a device-driver.
The question is, does it make sense to implement the driver in Java? Or stated in another way: What is the benefit you hope for, if you use Java for implementing the driver instead of another alternative? If you can answer this question, you should find a way to make it possible.
At the end the hint to JNode, a project that tries to implement a complete OS purely based on Java.
You have a too narrow view of device drivers.
I have written such device drivers on top of MOST in an automotive application. A more widespread use might be drivers for USB devices if Java ever gets a decent USB library.
In these cases there is a generic low-level protocol which is handled in native code, and the Java driver handles the device specifics (data formats, state machines, ...).
For the motivation, please remember that there is plenty of fast languages which are better than C for programming; they might not be as fast as C, but they are safe languages: if you make a mistake you don't get undefined behavior. And "undefined behavior" includes executing arbitrary code supplied by some attacker which formats your HD.
Many functional languages are usually compiled to native code.
Device drivers contain the most bugs in an OS kernel - I know that for Linux (Linus Torvalds and others keep saying so) and I heard that for Windows. While for a disk or Ethernet driver you need top-notch performance, and while in Linux drivers today are the bottleneck for 10G Ethernet or SSD disks, most drivers don't need that much speed - all computers wait at the same speed.
That's why there are various projects to allow writing drivers which run outside of the kernel, even if that causes a slowdown; when you can do that, you can use whatever language you want; you will just then need Java bindings for the hardware control library you use - if you were writing the driver in C, you would still have a library with C bindings.
For drivers in kernel mode proper, there are two problems that I've not yet seen mentioned:
Garbage Collection, and that's a tough requirement. You need to write an in-kernel Garbage Collector; some GC algorithms rely on Virtual Memory, and you cannot use them. Moreover, you probably need to scan the whole OS memory to find roots for the GC. Finally, I would only trust an algorithm guaranteeing (soft) real-time GC, which would make the overhead even bigger.
Reading the paper which was mentioned about Java Device Drivers on top of Linux, they just give up, and require programmers to manually free memory. They try to argue that this will not compromise safety, but I don't think their argument is convincing - it's not even clear whether they understand that Garbage Collection is needed for a safe language.
Reflection and class loading. A full Java implementation, even when running native code, needs to be able to load new code. This is a library you can avoid, but if you have an interpreter or JIT compiler in kernel (and there's no real reason that makes it technically impossible).
Performance. The paper about a JVM on Linux is very bad, and their performance numbers are not convincing - indeed, they test a USB 1.1 network driver, and then show that performance is not so bad! However, given enough effort something better can surely be done.
Two last things:
I'd like to mention Singularity, which is a complete OS written in a C# variant, with just a Hardware Abstraction Layer in a native language.
About picoJava, it's a bad idea to use it unless your system is a really memory constrained one, like a smart card. Cliff Click already explained why: it gives better performance to write a good JIT, and nowadays even smartphones can support that.
Have you perhaps heard a reference to the JDDK?
Writing a device driver 100% in Java is not possible without native code to provide the interaction between (1) the OS-specific driver entry points and conventions, and (2) the JVM instance. The JVM instance could be started "in-process" (and "in-process" may have different meanings depending on the OS and on whether the driver is a kernel-mode or user-mode driver), or as a separate user-land process with which a thin, native driver adaptation layer can communicate and onto which the said driver adaptation layer can offload actual user-land work.
It is possible to compile java code to hardware native (i.e. not JVM bytecode) instructions. See for instance GCJ. With this in hand, you're a lot closer to being able to compile device drivers than you were before.
I don't know how practical it is, though.
Possible?
Yes but only in special circumstances. Because you can write an operating system in Java and C#, and then, should be able to write device drivers for it. The memory hit to these drivers and operating systems would be substantial.
Probable?
Not likely. Atleast not in the world of Windows or MacOS or even Linux... At least not anytime soon. Because languages like C# and Java depend on the CLR and JVM. The way these languages work means that they cannot effectively be loaded into ring0.
Also, the performance hit would be rather large if managed languages were employed in device drivers.
Device drivers have to be written in a language which can execute in the kernel, either compiled into it, or loaded as a module at runtime. This usually precludes writing device drivers in Java, but I suppose you theoretically could implement a JVM inside a device driver and let it execute Java code. Not that any sane person would want to do that.
On Linux there are several user-land (i.e. non-kernel) implementations of filesystems which uses a common abstraction layer called (fuse) which allows user-land programs to implement things which are typically done in the kernel.
The Windows Driver Foundation (WDF) is a Microsoft API that does allow both User and Kernel mode device drivers to be written. This is being done today, and it is now compatible with w2k and later (used to not have w2k as a supported target). There is no reason that JNI calls can't be made to do some work in the JRE . . . ( assuming that JNI is still the way to call Java from C/C++ . . . my knowledge is dated in that arena). This could be an interesting way to have high level algorithms directly munch on data from a USB pipe for something to that effect . . . cool stuff!
PCIe user space device drivers can be written in Pure Java. See JVerbs for details about memory-based direct hardware access, in the context of OFED. This is a technique that can be used to create very high performance systems.
You can examine the PCI bus to determine the memory regions for a given device, what ports it has, etc. The memory regions can be mapped into the JVM's process.
Of course, you're responsible for implementing everything yourself.
I didn't say easy. I said possible. ;)
See also Device Drivers in User Space, which discusses using the UIO framework to build a user space driver.
First of all, note that I'm not an expert on device drivers (though I wrote a few myself back in the day), much less an expert on Java.
Let's leave the fact that writing device drivers in a high-level language is not a good idea (for performance and possibly many other reasons) aside for a moment, and answer your question.
You can write device drivers in almost any language, at least in theory.
However, most device drivers need to do plenty of low-level stuff like handling interrupts and communicating with the OS using the OS APIs and system calls, which I believe you can't do in Java.
But, if your device communicates using, say, a serial port or USB, and if the OS doesn't necessarily need to be aware of the device (only your application will access the device*), then you can write the driver in any language that provides the necessary means to access the device.
So for example you probably can't write a SCSI card driver in Java, but you can write a driver for a proprietary control device, USB lava lamp, license dongle, etc.
* The obvious question here is, of course, does that count as a driver?