monitorProc.c

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <unistd.h>
#include <time.h>

#define PERIOD 100000

// Substrings string s from nth occurence of char c
const char *nth_strchr(const char *s, int c, int n) 
{
  const char *nth = s;
  assert(c != '\0');

  for (int i = 0; i < n; i++)
  {
    if ((nth = strchr(nth, c)) == 0)
      break;
    nth++;
  }

  return nth;
}

// Gets the sum of first n numbers in string
int sumOfn(char *s, int n) 
{
  int sum = 0;
  int cache = 0;
  char *line = s;

  for (int i = 0; i < n; i++)
  {
    sscanf(line, "%d", &cache);
    if ((line = strchr(line, ' ')) == 0) 
      break;

    sum+=cache;
    line++;
  }

  return sum;
}

void getPidStats(char *argv[], int argc)
{
  int procCount = !strcmp(argv[argc-1], "p") ? argc-2 : argc-1;
  char procPath[procCount][32];
   
  int pastNonIdleUsage;
  int nonIdleUsage;

  int userTimes[procCount];
  int pastUserTimes[procCount];

  int sysTimes[procCount];
  int pastSysTimes[procCount];

  int totalTimes[procCount+1];
  int pastTotalTimes[procCount+1];

  struct timespec ts;

  FILE *fa[procCount];
  FILE *ft = fopen("resultsTOTAL.csv", "w");
  fprintf(ft, "Timestamp,Util\n");

  for(int i = 1; i < procCount+1; i++)
  { 
    char saveLoc[32];

    // Treats 1st argument as parent thread, all other listed threads get polled as tasks
    snprintf(saveLoc, sizeof saveLoc, "results%s.csv", argv[i]);
    if (i == 1 || !strcmp(argv[argc-1], "p")) {
	snprintf(procPath[i-1], sizeof procPath[i-1], "/proc/%s/stat", argv[i]);
    } else {
	snprintf(procPath[i-1], sizeof procPath[i-1], "/proc/%s/task/%s/stat", argv[1], argv[i]);
    }

    fa[i-1] = fopen(saveLoc, "w");
    fprintf(fa[i-1], "Timestamp,Util\n");
  }
  
  for (;;)
  {
    for(int i = 0; i < procCount; i++)
    {
      static char buf[128];
      FILE *fd=fopen(procPath[i],"r");
      fgets(buf, sizeof buf, fd);
      fclose(fd);

      strcpy(buf, nth_strchr(buf, ' ', 13)); // 13 refers to the 13th index of /proc/PID/stat, which is usertime followed by systime
      sscanf(buf, "%d %d", &userTimes[i], &sysTimes[i]);

      FILE *fg=fopen("/proc/stat", "r");
      fgets(buf, sizeof buf, fg);
      fclose(fg);

      totalTimes[i] = sumOfn(buf, 32);
      nonIdleUsage = sumOfn(buf, 3);
      
      clock_gettime(CLOCK_MONOTONIC, &ts);

      if(pastTotalTimes[i] && totalTimes[i] > pastTotalTimes[i]) 
      {
        if(!i) {
            float totalUtil = 100 * (nonIdleUsage - pastNonIdleUsage) / (totalTimes[i] - pastTotalTimes[argc-1]);
            fprintf(ft, "%d.%02ld,%.2f\n", ts.tv_sec, ts.tv_nsec/10000000, totalUtil);
        } 
        float sumUtil = 100 * ((userTimes[i] - pastUserTimes[i]) + (sysTimes[i] - pastSysTimes[i])) / (totalTimes[i] - pastTotalTimes[i]);
        fprintf(fa[i], "%d.%02ld,%.2f\n", ts.tv_sec, ts.tv_nsec/10000000, sumUtil); 

        pastTotalTimes[argc-1] = totalTimes[i];
      }

      pastUserTimes[i] = userTimes[i];
      pastSysTimes[i] = sysTimes[i];
      pastTotalTimes[i] = totalTimes[i];
      pastNonIdleUsage = nonIdleUsage;

      // Performs flush to guarantee that lines are written to file
      fflush(fa[i]);
      fflush(ft);
    }
    usleep(PERIOD);
  }
}

int main(int argc, char *argv[]) {
  if(argc >= 2) {
    getPidStats(argv, argc);
  } else {
    printf("Not enough arguments");
  }
}