8 ms·

JamVM – A compact Java Virtual Machine

69 points by scriptproof 12y ago

616c 12y ago
For the lazy, the features list is quite impressive. JamVM "Features" For those interested in the design of virtual machines, JamVM includes a number of optimisations to improve speed and reduce foot-print. A list, in no particular order, is given below. Execution engine supports many levels of optimisation from basic switched interpreter to inline-threaded interpreter with stack-caching (equivalent performance to a simple JIT). Uses native threading (posix threads). Full thread implementation including Thread.interrupt() Object references are direct pointers (i.e. no handles) Supports class loaders Efficient thin locks for fast locking in uncontended cases (the majority of locking) without using spin-locking Two word object header to minimise heap overhead (lock word and class pointer) Stop-the-world garbage collector, with separate mark/sweep and mark/compact phases to minimise heap fragmentation Thread suspension uses signals to reduce suspend latency and improve performance (no suspension checks during normal execution) Full object finalisation support within the garbage collector (with finaliser thread) Full support for Soft/Weak/Phantom References (with Reference Handler thread) Full support for class and class-loader garbage-collection and unloading (including associated shared libraries) Garbage collector can run synchronously or asynchronously within its own thread String constants within class files are stored in hash table to minimise class data overhead (string constants shared between all classes) Supports JNI and dynamic loading for use with standard libraries Uses its own lightweight native interface for internal native methods without overhead of JNI VM support for invokedynamic (JSR 292) VM support for type annotations (JSR 308) VM support for lambda expressions (JSR 335) VM support for method parameter reflection JamVM is written in C, with a small amount of platform dependent assembler, and is easily portable to other architectures.
mike_hearn 12y ago
Useful, but how does it compare to Avian? As far as I can tell JamVM is not actually a JIT compiling VM at all, although the features list is optimistically phrased to make that a bit unclear. Avian is also very lightweight but it also manages to be a JIT compiler.
- justinsb 12y ago
  The lack of JIT is interesting to me; JIT does give higher performance, but at a memory cost (because JITted code is not shared between processes). I think the 3 sweet-spots are: * JIT (OpenJDK, Android Dalvik) * AOT compilation (Android ART, RoboVM) * Interpreted (JamVM) I think JamVM is interesting, because there aren't many good options there. It's also presumably much simpler, so if you wanted to experiment (Golang-style lightweight threads is an interest of mine), it would probably be easier.
  - personZ 12y ago
    This is orthogonal, but the AOT versus JIT difference between ART and Dalvik is hugely overstated. Dalvik attempted to AOT compile, and when that wasn't possible it also maintains a pre-compiled cache for subsequent runs. Similarly, while ART attempts AOT, for various reasons it often resorts to JIT with some types of code. They both behave incredibly similarly. ART is a ground-up rewrite of Dalvik. The AOT thing seemed to take root as some sort of differentiating talking point.
    - _delirium 12y ago
      > The AOT thing seemed to take root as some sort of differentiating talking point. I think it took root in part because even end-users who were only casually interested saw a dialog suggesting as much on upgrade. When you upgraded to an Android version that used ART, you got a message telling you that the apps were being precompiled, which took a while to finish.
      - crwll 12y ago
        There is currently no released version of Android that uses ART out of the box. It's available behind the development options in KitKat and as default in the L developer preview, but that's it. The "optimizing applications" screen comes after system upgrades also with Dalvik.
  - pjmlp 12y ago
    > because JITted code is not shared between processes It depends on which JVM you talk about. IBM J9 does it if I am not mistaken. Additionally, the OS/400 JVM is integrated with the kernel JIT used for the bytecode executable format of OS/400 applications (TIMI) http://www.drdobbs.com/new-to-the-as400/184404408 http://www.drdobbs.com/new-to-the-as400/184404408 > I think the 3 sweet-spots are: A few more to your list. These do all three. - IBM Websphere RealTime J9 - Aonix Perc - JamaicaVM - Excelsior JET Sometimes I find a bit sad that many equate JVM == OpenJDK, not understanding how many choices are out there.
alexnewman 12y ago
How does this compare with juanino
- chc 12y ago
  AFAIK, Janino is a compiler — it only replaces javac. Once you've compiled a class with Janino, it needs to be loaded into a JVM. JamVM is a whole Java Virtual Machine — it will actually run your program instead of the traditional Java implementation.
ausjke 12y ago
Used jamvm in some osgi products and it works well. however I never heard about Avian (http://oss.readytalk.com/avian/ http://oss.readytalk.com/avian/ https://github.com/ReadyTalk/avian https://github.com/ReadyTalk/avian) and it does look interesting. a table of all JVMs: http://en.wikipedia.org/wiki/Comparison_of_Java_virtual_machines http://en.wikipedia.org/wiki/Comparison_of_Java_virtual_mach...
sitkack 12y ago
I like jam, but I tried to purchase a license for an embedded product, all I could get was a dial tone.
aninteger 12y ago
The page indicates that JamVM can run on the PowerPC platform yet it requires GNU Classpath which doesn't work on PowerPC architectures... Does anyone use this on PowerPC? Unfortunately the only other alternative Kaffe seems to have been abandoned..
beagle3 12y ago
The PhD of Andreas Gal (now Mozilla CTO) dealt, among other things, with adding a JIT to JamVM called HotPath[0]. The code, unfortunately, is nowhere to be found. [0] https://www.usenix.org/events/vee06/full_papers/p144-gal.pdf https://www.usenix.org/events/vee06/full_papers/p144-gal.pdf

69 points by scriptproof 12y ago

616c 12y ago

For the lazy, the features list is quite impressive. JamVM "Features" For those interested in the design of virtual machines, JamVM includes a number of optimisations to improve speed and reduce foot-print. A list, in no particular order, is given below. Execution engine supports many levels of optimisation from basic switched interpreter to inline-threaded interpreter with stack-caching (equivalent performance to a simple JIT). Uses native threading (posix threads). Full thread implementation including Thread.interrupt() Object references are direct pointers (i.e. no handles) Supports class loaders Efficient thin locks for fast locking in uncontended cases (the majority of locking) without using spin-locking Two word object header to minimise heap overhead (lock word and class pointer) Stop-the-world garbage collector, with separate mark/sweep and mark/compact phases to minimise heap fragmentation Thread suspension uses signals to reduce suspend latency and improve performance (no suspension checks during normal execution) Full object finalisation support within the garbage collector (with finaliser thread) Full support for Soft/Weak/Phantom References (with Reference Handler thread) Full support for class and class-loader garbage-collection and unloading (including associated shared libraries) Garbage collector can run synchronously or asynchronously within its own thread String constants within class files are stored in hash table to minimise class data overhead (string constants shared between all classes) Supports JNI and dynamic loading for use with standard libraries Uses its own lightweight native interface for internal native methods without overhead of JNI VM support for invokedynamic (JSR 292) VM support for type annotations (JSR 308) VM support for lambda expressions (JSR 335) VM support for method parameter reflection JamVM is written in C, with a small amount of platform dependent assembler, and is easily portable to other architectures.

mike_hearn 12y ago

Useful, but how does it compare to Avian? As far as I can tell JamVM is not actually a JIT compiling VM at all, although the features list is optimistically phrased to make that a bit unclear. Avian is also very lightweight but it also manages to be a JIT compiler.

justinsb 12y ago
The lack of JIT is interesting to me; JIT does give higher performance, but at a memory cost (because JITted code is not shared between processes). I think the 3 sweet-spots are: * JIT (OpenJDK, Android Dalvik) * AOT compilation (Android ART, RoboVM) * Interpreted (JamVM) I think JamVM is interesting, because there aren't many good options there. It's also presumably much simpler, so if you wanted to experiment (Golang-style lightweight threads is an interest of mine), it would probably be easier.
- personZ 12y ago
  This is orthogonal, but the AOT versus JIT difference between ART and Dalvik is hugely overstated. Dalvik attempted to AOT compile, and when that wasn't possible it also maintains a pre-compiled cache for subsequent runs. Similarly, while ART attempts AOT, for various reasons it often resorts to JIT with some types of code. They both behave incredibly similarly. ART is a ground-up rewrite of Dalvik. The AOT thing seemed to take root as some sort of differentiating talking point.
  - _delirium 12y ago
    > The AOT thing seemed to take root as some sort of differentiating talking point. I think it took root in part because even end-users who were only casually interested saw a dialog suggesting as much on upgrade. When you upgraded to an Android version that used ART, you got a message telling you that the apps were being precompiled, which took a while to finish.
    - crwll 12y ago
      There is currently no released version of Android that uses ART out of the box. It's available behind the development options in KitKat and as default in the L developer preview, but that's it. The "optimizing applications" screen comes after system upgrades also with Dalvik.
- pjmlp 12y ago
  > because JITted code is not shared between processes It depends on which JVM you talk about. IBM J9 does it if I am not mistaken. Additionally, the OS/400 JVM is integrated with the kernel JIT used for the bytecode executable format of OS/400 applications (TIMI) http://www.drdobbs.com/new-to-the-as400/184404408 http://www.drdobbs.com/new-to-the-as400/184404408 > I think the 3 sweet-spots are: A few more to your list. These do all three. - IBM Websphere RealTime J9 - Aonix Perc - JamaicaVM - Excelsior JET Sometimes I find a bit sad that many equate JVM == OpenJDK, not understanding how many choices are out there.

alexnewman 12y ago

How does this compare with juanino

chc 12y ago
AFAIK, Janino is a compiler — it only replaces javac. Once you've compiled a class with Janino, it needs to be loaded into a JVM. JamVM is a whole Java Virtual Machine — it will actually run your program instead of the traditional Java implementation.

ausjke 12y ago

Used jamvm in some osgi products and it works well. however I never heard about Avian (http://oss.readytalk.com/avian/ http://oss.readytalk.com/avian/ https://github.com/ReadyTalk/avian https://github.com/ReadyTalk/avian) and it does look interesting. a table of all JVMs: http://en.wikipedia.org/wiki/Comparison_of_Java_virtual_machines http://en.wikipedia.org/wiki/Comparison_of_Java_virtual_mach...

sitkack 12y ago

I like jam, but I tried to purchase a license for an embedded product, all I could get was a dial tone.

aninteger 12y ago

The page indicates that JamVM can run on the PowerPC platform yet it requires GNU Classpath which doesn't work on PowerPC architectures... Does anyone use this on PowerPC? Unfortunately the only other alternative Kaffe seems to have been abandoned..

beagle3 12y ago

The PhD of Andreas Gal (now Mozilla CTO) dealt, among other things, with adding a JIT to JamVM called HotPath[0]. The code, unfortunately, is nowhere to be found. [0] https://www.usenix.org/events/vee06/full_papers/p144-gal.pdf https://www.usenix.org/events/vee06/full_papers/p144-gal.pdf