Re: Why is Java so slow????

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 19 Nov 2007 16:38:55 -0500

Message-ID:

<boydnYli0Zjtn9_anZ2dnUVZ_ruqnZ2d@comcast.com>

Java Performance Export wrote:

I'm wondering if anyone can help me understand why my Java is being
very slow compared to an equivalent program written in "C".

I'm simply trying to print out the first N integers like

"This is line <nnnn>"

as a simple benchmark.

My Java version is over 60 times slower than my "C" version and I
would like to establish a lower bound on how long the very fastest
Java version could take, by applying every possible performance
speedup availalbe in the Java environment.

I've profiled with "-Xrunhprof" and looked at the output (below) and
was surprised by what I saw. Over 50 different methods are involved
before I arrive at the point where 80% of the cumulative CPU usage for
the run is accounted for! What the heck is this stuff?????

Is this really happening, and is there a way to get around it?

My client is threatening to implement in "C" and I am trying to talk
him out of it.

I'd be very curious to see how this equivalent benchmark peforms on
others' environments.

I modified the Java benchmark in accordance with others' suggestions and for
five million lines of output came up with:

Java:
$ java -server -cp build/classes testit.TimePrin
Elapsed: 93.966 secs.

C program:
$ ./timepr
Elapsed: 88.000000 secs.

A far cry from 60:1, eh?

AMD-64 ~2 GHz, 1 GB RAM, Linux Fedora 7, the usual mix of other programs
running. 32-bit Java.

Code with my variations follows.
<sscce name="TimePrin.java">
package testit;
public class TimePrin
{
   private static final int LIM = 5000000;

   public static void main( String [] args)
   {
     int lim;
     if ( args.length < 1 )
     {
       lim = LIM;
     }
     else
     {
       try
       {
         lim = Integer.parseInt( args [0] );
       }
       catch ( NumberFormatException ex )
       {
         lim = LIM;
       }
     }

     long start = new Date().getTime();
     for ( int i=0; i < lim; i++)
     {
       System.out.print( "This is line " + i +"\n" );
     }
     long end = new Date().getTime();

     double elapsed = (end - start) / 1000.0;
     System.out.println( "Elapsed: "+ elapsed +" secs." );
   }
}
</sscce>

<sscce name="timepr.c" build="gcc -O4 -o timepr timepr.c" >
#include <stdio.h>
#include <time.h>

#define LIM 5000000

int main(int argc, char ** argv)
{
   int lim;
   if ( argc < 2 )
   {
     lim = LIM;
   }
   else
   {
     lim = atoi(argv[1]);
     if ( lim <= 1000 )
     {
       lim = LIM;
     }
   }

   int i;
   time_t start = time( NULL );
   for ( i=1; i <= lim; i++ )
   {
     printf("this is line %d\n", i);
   }
   time_t end = time( NULL );

   printf( "Elapsed: %f secs.\n", difftime( end, start ));
}
</sscce>

--
Lew