Java vs. C

Several people have told me recently that Java runs as fast as C. After repeating this information somewhat, I decided to test it for computer forensics.

The test I constructed a test file of 4238912226 bytes. The test involved reading the file 4K byte blocks at a time and computing the SHA1 hash of each block.

Here is the C program I used:

#include <stdio.h>
#include <stdlib.h>
#include <openssl/sha.h>

int main(int argc,char **argv)
{
    
    FILE *f = 0;
    if(argc!=2){
	fprintf(stderr,"usage: %s - compute block hashes (but don't print them)\n");
    }
    f = fopen(argv[1],"r");
    if(!f) {
	perror(argv[1]);
	exit(1);
    }
    while(!feof(f)){
	char buf[4096];
	unsigned char md[20];
	size_t count = fread(buf,1,sizeof(buf),f);
	SHA_CTX c;
	SHA_Init(&c);
	SHA_Update(&c,buf,count);
	SHA_Final(md,&c);
    }
    fclose(f);
}

I ran the test 3 times on my Mac Pro (2x2.66 Ghz Dual-Core Intel Xeons, 12GB 667 Mhz DDR2 FB-DIMM memory, 1TB hard drive)

12:59 PM m:~/nps/speedtest$ time ./ctest /realistic.aff 

real	0m53.443s
user	0m25.459s
sys	0m6.113s
01:00 PM m:~/nps/speedtest$ time ./ctest /realistic.aff 

real	0m31.137s
user	0m25.327s
sys	0m5.650s
01:01 PM m:~/nps/speedtest$ time ./ctest /realistic.aff 

real	0m31.694s
user	0m25.392s
sys	0m5.920s
01:02 PM m:~/nps/speedtest$

The first time the file was being read off the disk, the second two trials the file was in memory.

Interestingly, the entire file can be read in around 8 seconds on this hardware:

time dd if=/realistic.aff of=/dev/null bs=4096
1034890+1 records in
1034890+1 records out
4238912226 bytes transferred in 7.786416 secs (544398372 bytes/sec)

real	0m7.979s
user	0m1.455s
sys	0m6.335s
01:22 PM m:~/nps/speedtest$ 

So how fast is Java? Here is my first Java program:

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.io.*;
//import System.currentTimeMillis;

	
public class jtest {
    public static void main(String[] args){
	long t0 = System.currentTimeMillis();
	try {
	    System.out.println("Start");
	    FileInputStream fis = new FileInputStream(new File(args[0]));
	    while(true){
		MessageDigest md = MessageDigest.getInstance("SHA");
		byte[] buf = new byte[4096];
		int count = fis.read(buf);
		if(count==-1) break; /*throw new Exception("Done");*/
		md.update(buf);
		byte[] f = md.digest();
	    }
	    System.out.println("Done");
	}
	catch (IOException e){
	    System.out.println(e);
	}
	catch (NoSuchAlgorithmException e){
	    System.out.println(e);
	}
	long t1 = System.currentTimeMillis();
	System.out.printf("Miliseconds to execute: %d\n",t1-t0);
    }
}

Notice that I have the program report how long it takes to run the benchmark, so we can factor out the cost of JVM startup.

01:14 PM m:~/nps/speedtest$ time java jtest  /realistic.aff 
Start
Done
Miliseconds to execute: 97843

real	1m39.227s
user	1m29.803s
sys	0m7.687s
01:15 PM m:~/nps/speedtest$ time java jtest  /realistic.aff 
Start
Done
Miliseconds to execute: 95853

real	1m36.944s
user	1m28.722s
sys	0m7.189s
01:18 PM m:~/nps/speedtest$ 

So those are pretty interesting numbers. Java seems to be running 3x slower.