笔记

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#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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