/* usage: memwatch [commandline] */
/* make sure the first argument (the program to run) is given with full
 * path.  This will fork a second process that uses /proc/[pid]/statm to
 * calculate the maximum resident memory size the other process has in
 * his life time.  This only works on Linux. */
#include <unistd.h>
#include <stdio.h>
#include <time.h>

int main(int argc,char* argv[],char* envp[]) {
  char fn[100];
  FILE* f;
  pid_t p=fork();
  unsigned long max=0;
  struct timespec ts,tmp;
  ts.tv_sec=0; ts.tv_nsec=100000000;
  if (p==-1) { perror("fork failed"); return 1; }
  if (p!=0) {	// do the exec in the parent, so time memwatch ls shows ls, not memwatch
    execve(argv[1],argv+1,envp);
    perror("execve failed"); return 1;
    return 0;
  }
  sprintf(fn,"/proc/%u/statm",getppid());
  for (;;) {
    unsigned int a,b,c,d,e,f,g;
    FILE* F=fopen(fn,"r");
    if (!F) break;
// "7773 734 465 297 0 275 0"
    if (fscanf(F,"%u %u %u %u %u %u %u",&a,&b,&c,&d,&e,&f,&g)<6) break;
    fclose(F);
    if (b>max) {
//      fprintf(stderr,"new max %u\n",b);
      max=b;
    }
    nanosleep(&ts,&tmp);
    if (b==0) break;
  }
  fprintf(stderr,"max: %'.3f MB\n",max*4/1024.0); // in K
}