keepalive.c


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44

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

const useconds_t 
  minSleepTime = 1,
  maxSleepTime = 1000000; 

int main(int argc, char **argv) {
  if (argc < 2) {
    fprintf(stderr, "supply a program name\n");
    return -1;
  }

  useconds_t sleepTime = minSleepTime;
  time_t td = time(NULL);
  while (1) {
    pid_t pid = fork();
    switch (pid) {
    case 0: // child
      execvp(argv[1], &(argv[1]));
      return -1; // exec failed, stop
    case -1: // fork failed, assume temporary failure
      break;
    default: // parent
      wait(NULL);
    }

    fprintf(stderr, "child exit, restarting\n");

    // apply current and calc new delay
    td = time(NULL) - td;
    if (td > 2) {
      sleepTime = minSleepTime;
    }
    usleep(sleepTime);
    if (td <= 2) {
      sleepTime *= 2;
      if (sleepTime > maxSleepTime)
	sleepTime = maxSleepTime;
    }
    td = time(NULL);
  }
}