1 #include <sys/eventfd.h>
2 int eventfd(unsigned int initval, int flags);

 1 #include <sys/eventfd.h>
 2 #include <unistd.h>
 3 #include <stdio.h>
 4 #include <stdint.h>
 5 #include <stdlib.h>
 6 #include <errno.h>
 7
 8 #define handle_error(msg) \
 9     do { perror(msg); exit(1); } while (0)
10
11 int main( int argc, char **argv )
12 {
13     uint64_t u;
14     ssize_t s;
15     int j;
16     if ( argc < 2 ) {
17         fprintf(stderr, "input <num> in command argument");
18         exit(1);
19     }
20
21     int efd;
22     if ( (efd = eventfd(0, EFD_NONBLOCK)) == -1 )
23             handle_error("eventfd failed");
24
25
26     switch (fork()) {
27         case 0:
28             for( j = 1; j < argc; j ++ ) {
29                 printf("Child writing %s to efd\n", argv[j] );
30
31                 u = strtoull(argv[j], NULL, 0);  /* analogesly atoi */
32                 s = write(efd, &u, sizeof(uint64_t)); /* append u to counter */
33                 if ( s != sizeof(uint64_t) )
34                     handle_error("write efd failed");
35
36             }
37             printf("child completed write loop\n");
38
39             exit(0);
40         default:
41             sleep (2);
42
43             printf("parent about to read\n");
44             s = read(efd, &u, sizeof(uint64_t));
45             if ( s != sizeof(uint64_t) ) {
46                 if (errno = EAGAIN) {
47                     printf("Parent read value %d\n", s);
48                     return 1;
49                 }
50                 handle_error("parent read failed");
51             }
52             printf("parent read %d , %llu (0x%llx) from efd\n",
53                     s, (unsigned long long)u, (unsigned long long) u);
54             exit(0);
55
56         case -1:
57             handle_error("fork ");
58     }
59     return 0;
60 }