#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <stdio.h>

/* The iteration count below needs to be in a reasonable range for the
   specific hardware this program is run on.  If you make a change to
   the inner loop that makes it slower (as assigned in the lab), you
   may also want to adjust the iteration count downward. */

#define ITERATIONS 1000000

/* This program runs furiously away in a loop, writing a character to
   a temporary file each time around the loop.  It will stop only when
   interrupted or killed.  Every ITERATIONS times through its loop it
   prints a report of how long (in microseconds) it took to do the
   last ITERATIONS iterations.  The time is elapsed (wall clock) time,
   so that it includes not only time this process spent, but also time
   when the processor is busy running other processes.  The times are
   not actually accurate to the microsecond.  -Max Hailperin
   <max@gac.edu> 1999-08-30 */
   

int main(int argc, char *argv[]){
  FILE *outFile;  /* temporary output file, as high-level FILE* */
  int outFd;      /* same, but as low level file descriptor */

  if((outFile = tmpfile()) == NULL){
    fprintf(stderr, "Couldn't open temporary file.\n");
    exit(1);
  }
  outFd = fileno(outFile);  /* convert to system-level file desciptor */

  while(1){ /* Do the timing test repeatedly until killed. */
    struct timeval start, stop;
    long diff, i;
    char c = 'X'; /* arbitrary character to write. */
    
    if(gettimeofday(&start, 0) < 0){ /* Get starting time. */
      perror("gettimeofday");
      exit(1);
    }
    for(i = ITERATIONS; i > 0; i--){ /* the actual test */
      if(write(outFd, &c, 1) < 0){ /* write the 'X' out from c to temp file */
        perror("write");
      }
      /* The above write not only outputs the character, but also advances
         the file position by one byte.  Thus if repeated, we would wind
         up with a very long file of Xs, and chew up the disk.  So to avoid
         that, we want to back up and do the next X on top of this one.
         The lseek system call below does this, by setting the file position
         back to the beginning. */
      if(lseek(outFd, 0, SEEK_SET) < 0){
        perror("lseek");
      }
    }
    if(gettimeofday(&stop, 0) < 0){ /* Get ending time. */
      perror("gettimeofday");
      exit(1);
    }
    diff = stop.tv_sec - start.tv_sec;
    diff *= 1000000; /* microseconds per second */
    diff += stop.tv_usec - start.tv_usec;
    printf("%ld\n", diff); /* Print elapsed time. */
  }
}