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  Java's Unsafe class  (Read 5371 times)
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Offline xfactor973

Senior Newbie




Java games rock!


« Posted 2003-08-14 00:02:51 »

Anyone have experience using sun.misc.Unsafe ?  I tried using it today and it's giving an error when i run it.  

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import sun.misc.*;

public class UnsafeTester {
  private static final Unsafe unsafe = Unsafe.getUnsafe();
  public static void main(String[] args) {
    long ptr = unsafe.allocateMemory(512);
    try{
      unsafe.putChar(ptr,'a');
      unsafe.putChar(ptr,'b');
      System.out.println("Unsafe: " + unsafe.toString());
    }
    finally{
      unsafe.freeMemory(ptr);
    }
  }
}

java.lang.ExceptionInInitializerError
Caused by: java.lang.SecurityException: Unsafe
      at sun.misc.Unsafe.getUnsafe(Unsafe.java:68)
      at garbage.UnsafeTester.<clinit>(UnsafeTester.java:8)
Exception in thread "main"

I'm not sure exactly how I should go about tackling this one so any help would be great.   Wink
Offline AndersDahlberg

Junior Member





« Reply #1 - Posted 2003-08-14 00:05:33 »

Well, don't use it Grin

There was a bug once upon a time Wink when you could actually use it to wrec havoc (first beta1.4.0 or something like that) - they fixed that quite fast Smiley
Offline GergisKhan

Junior Member




&quot;C8 H10 N4 O2&quot;


« Reply #2 - Posted 2003-08-14 00:35:38 »

Ummmm.... what is this class?

why does it curiously remind me of the structs discussion that was occurring in another thread somewhere?

And for future reference, where can I get information about the sun.misc.* classes?

gK

"Go.  Teach them not to mess with us."
          -- Cao Cao, Dynasty Warriors 3
Games published by our own members! Check 'em out!
Legends of Yore - The Casual Retro Roguelike
Offline tortoise

Junior Member




<3 Shmups


« Reply #3 - Posted 2003-08-14 00:49:23 »

Whatever it is, I suspect it is unsafe to use Smiley

You're really not supposed to use any of the sun.* classes for real use. They are subject to change at any moment, and are only available on Sun JVMs.
Offline socketrider

Innocent Bystander




Java games rock!


« Reply #4 - Posted 2003-08-14 10:25:03 »

Check this page: http://www.jguru.com/faq/view.jsp?EID=448031

Cheers
Offline xfactor973

Senior Newbie




Java games rock!


« Reply #5 - Posted 2003-08-14 11:12:54 »

Thanks for your help.  The only reason I was curious about that Unsafe class was my friend wanted to make a stringBuffer class using JNI and it turned out being alot slower than even your normal stringbuffer.  I'm guessing the JNI calls are expensive.  so we went hunting in the nio classes and found no native methods and that lead to the Unsafe class.  Only problem is that security exception that i'm getting.  Guess it's unusable at this point.   :-/
Offline princec

JGO Kernel


Medals: 362
Projects: 3
Exp: 16 years


Eh? Who? What? ... Me?


« Reply #6 - Posted 2003-08-14 11:32:56 »

You should have no need whatsoever to use Unsafe.
Got performance problems? You've written the code wrong. Time to run with the -Xprof flag methinks!

Cas Smiley

Offline xfactor973

Senior Newbie




Java games rock!


« Reply #7 - Posted 2003-08-14 11:39:16 »

yeah this is true.  It was just something i was toying around with.   Grin
Offline xfactor973

Senior Newbie




Java games rock!


« Reply #8 - Posted 2003-08-22 11:57:26 »

When I allocate memory with the Unsafe class what exactly is it doing?  I'm really just experimenting with the class.  And the other thing is that when i call unsafe.addressSize() it always returns 4 for some odd reason.  Anyone know how this class works? Huh
Offline abies

Senior Member





« Reply #9 - Posted 2003-08-22 12:52:14 »

Quote
 And the other thing is that when i call unsafe.addressSize() it always returns 4 for some odd reason.


I suppose that it returns size of native platform pointer in bytes. So on 64-bit system you will probably get 8 as a return.

Artur Biesiadowski
Games published by our own members! Check 'em out!
Legends of Yore - The Casual Retro Roguelike
Offline xfactor973

Senior Newbie




Java games rock!


« Reply #10 - Posted 2003-08-23 13:46:46 »

Good thinking.  Thanks for the help
Offline Jeff

JGO Coder




Got any cats?


« Reply #11 - Posted 2003-09-05 22:23:22 »

Unsafe is the underpinning to Native Byte Buffers

Thats really where you want to hit this.

JK

Got a question about Java and game programming?  Just new to the Java Game Development Community?  Try my FAQ.  Its likely you'll learn something!

http://wiki.java.net/bin/view/Games/JeffFAQ
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