Java CPUTime

How to calculate CPUTime of a Java function

I've wanted to know the cputime used in java functions, but it turned out that this was a bit too low level for java. Therefore I had to create a JNI (Java Native Interface) function for it. The code for this example is here, or here, and here's how to do it:

First I define it in my class, CPUtest.java:

class CPUtest {
        public static  native long cpuCount();
        static {
                System.loadLibrary("jnicputime");
        }

        public static void main(String[] args) {
                long cputime;
                int i,j;
                cputime = cpuCount();
                for (i=0;i<300000000;i++) j = i*7;
                cputime = cpuCount() - cputime;
                System.out.print("CPUTIME:\t");
        }
}

Compile it javac CPUtest.java, and create a headerfile for the native function javah -jni CPUtest. Then I implement the function defined in CPUtest.h in C using the POSIX times() like this:

/* Let's try to be portable here */
#define _POSIX_SOURCE 1
/* System headers */
#include sys/times.h
#include unistd.h

/* Local headers */
#include "CPUtest.h"

/* Macros */
#define CLK_TCK ((clock_t)(sysconf(_SC_CLK_TCK)))

/* Functions */

JNIEXPORT jlong JNICALL Java_CPUtest_cpuCount (JNIEnv *env, jobject obj)
{
        struct tms tmsbuff;
        times(&tmsbuff);
        return (jlong)tmsbuff.tms_utime/CLK_TCK;
}

Then I create the library with cc -o libjnicputime.so -O -shared cputime.c -I/usr/java/include/ -I/usr/java/include/irix. On linux this line would be something like gcc -o libjnicputime.so -O -shared -fPIC cputime.c -I/usr/java/include/linux, and on solaris it should be gcc -o libjnicputime.so -O -G -fPIC cputime.c -I/usr/java/include/ -I/usr/java/include/solaris.

Then I have to tell the system where to find libjnicputime.so by setenv LD_LIBRARY_PATH . and now I can run my small java program:

java CPUtest
CPUTIME:        13

That's all! Comments? — janfrode@tanso.net