#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
void die(const char *msg)
{
perror(msg);
exit(1);
}
void child2_do()
{
printf("In child2: execute 'date'\n");
sleep(5);
if (execlp("date", "date", NULL) < 0) {
perror("child2 execlp");
}
}
void child1_do(pid_t child2, char *argv)
{
pid_t pw;
do {
if (*argv == '1') {
pw = waitpid(child2, NULL, 0);
}
else {
pw = waitpid(child2, NULL, WNOHANG);
}
if (pw == 0) {
printf("In child1 process:\nThe child2 process has not exited!\n");
sleep(1);
}
}while (pw == 0);
if (pw == child2) {
printf("Get child2 %d.\n", pw);
sleep(5);
if (execlp("pwd", "pwd", NULL) < 0) {
perror("child1 execlp");
}
}
else {
printf("error occured!\n");
}
}
void father_do(pid_t child1, char *argv)
{
pid_t pw;
do {
if (*argv == '1') {
pw = waitpid(child1, NULL, 0);
}
else {
pw = waitpid(child1, NULL, WNOHANG);
}
if (pw == 0) {
printf("In father process:\nThe child1 process has not exited.\n");
sleep(1);
}
}while (pw == 0);
if (pw == child1) {
printf("Get child1 %d.\n", pw);
if (execlp("ls", "ls", "-l", NULL) < 0) {
perror("father execlp");
}
}
else {
printf("error occured!\n");
}
}
int main(int argc, char *argv[])
{
pid_t child1, child2;
if (argc < 3) {
printf("Usage: waitpid [0 1] [0 1]\n");
exit(1);
}
child1 = fork();
if (child1 < 0) {
die("child1 fork");
}
else if (child1 == 0) {
child2 = fork();
if (child2 < 0) {
die("child2 fork");
}
else if (child2 == 0) {
child2_do();
}
else {
child1_do(child2, argv[1]);
}
}
else {
father_do(child1, argv[2]);
}
return 0;
}
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