1717// This program imitates work of 3 processes (parent and 2 childs) with some file with flock-blocking, which means
1818// that 2 processes cannot both write into file, but can both read file in the same time. However it cannot write and read in the same time.
1919
20+ void kill_child_handler (int sig )
21+ {
22+ int status ;
23+ pid_t done = waitpid (-1 , // Any child
24+ & status ,
25+ 0 ); // Blocked mode.
26+ if (done == -1 )
27+ {
28+ printf ("No more child processes.\n" );
29+ }
30+ else
31+ {
32+ short isNormalTermination = WIFEXITED (status );
33+ if (!isNormalTermination ||
34+ // WEXITSTATUS should be used only if normal termination = true.
35+ (isNormalTermination && WEXITSTATUS (status ) != 0 ))
36+ {
37+ printf ("Zombie for PID -- %d failed.\n" , done );
38+ exit (EXIT_FAILURE );
39+ }
40+ else
41+ {
42+ printf ("Zombie for PID -- %d successfully removed.\n" , done );
43+ }
44+ }
45+ }
46+ 2047int lock_write ()
2148{
2249 int fd ;
@@ -61,12 +88,24 @@ int lock_read(pid_t pid)
6188 return 1 ;
6289}
6390
64- void main ()
91+ int main ()
6592{
6693 pid_t main_pid = getpid ();
6794
6895 printf ("Start of process %d\n" , main_pid );
6996
97+ // Handle child process killing.
98+ struct sigaction kill_child_signal ;
99+ kill_child_signal .sa_handler = kill_child_handler ;
100+ sigemptyset (& kill_child_signal .sa_mask );
101+ kill_child_signal .sa_flags = SA_RESTART ; // Permanent handler.
102+ 103+ if (sigaction (SIGCHLD , & kill_child_signal , 0 ) == -1 )
104+ {
105+ perror ("Error of calling sigaction" );
106+ exit (EXIT_FAILURE );
107+ }
108+ 70109 // Lock file for writing.
71110 if (lock_write ())
72111 {
@@ -89,12 +128,11 @@ void main()
89128 if ((next_child_pid = fork ()) > 0 )
90129 {
91130 printf ("Start of child process %d.\n" , next_child_pid );
92- 93131 printf ("Parent process %d sleeps 5 seconds.\n" , getpid ());
94132 sleep (5 );
95133 }
96134 }
97- 135+
98136 printf ("Process %d tries to access the file...\n" , getpid ());
99137
100138 int canread = 0 ;
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