创建了两个子进程.父进程应该执行，直到一个子进程终止.如何用c编写此程序

Question

两个子进程通过不同的方法执行排序。我希望父进程等待至少一个子进程终止。这段代码没有给我所需的输出。

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
pid_t pid1, pid2;
int status;
pid1 = fork();
pid2 = fork();
if(pid1==0 && pid2 !=0)
{
//first child performing selection sort
exit(0);
}
if(pid1>0 && pid2 > 0)
{
wait(&status);
if(WIFEXITED(status))
{
printf("Parent process executed %dn",WEXITSTATUS(status));
}
}
if(pid1>0 && pid2 ==0)
{
//second child performing bubble sort

exit(0);
}

}

Answer 1

pid2 = fork()由父级和从pid1 = fork()创建的第一个子级执行，这不是您在问题描述中想要的。

你可能想要这样的

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
pid_t pid1, pid2;
int status;
pid1 = fork();
if(pid1 == 0) {
//first child performing selection sort
exit(0);
}
if(pid1 > 0) {
pid2 = fork();
if(pid2 == 0) {
//second child performing bubble sort

exit(0);
}
if(pid2 > 0) {
wait(&status);
if(WIFEXITED(status)) {
printf("Parent process executed %dn",WEXITSTATUS(status));
}
}
}
}

Answer 2

执行fork()时，会有一个新的子进程与父进程在同一点开始运行。因此，您应该确保只有父进程调用第二个fork()。

密钥：fork()将在子进程上返回0。

方法如下：

代码

#include <stdio.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
int main(void)
{
int status;
pid_t ret, pid1, pid2;
pid1 = fork();
if (pid1 == 0) {
// First child performing selection sort
printf("Do selection sort here...n");
sleep(5);
printf("Selection sort finishedn");
exit(0);
}

pid2 = fork();
if (pid2 == 0) {
// Second child performing bubble sort
printf("Do bubble sort here...n");
sleep(2);
printf("Bubble sort finishedn");
// The parent must get exit code 100 from this
exit(100);
}

// Parent process waits until at least one child process terminates
do {
status = 0;
ret = wait(&status);
if (WIFEXITED(status)) {
printf("Child process %d has exited with exit code: %dn",
ret, WEXITSTATUS(status));
break;
}
if (ret < 0) {
printf("wait() error: %sn", strerror(errno));
break;
}
/* If we reach here, child may be traced or continued. */
} while (1);
printf("Parent has finished its waiting state...n");
return 0;
}

编译并运行

ammarfaizi2@integral:/tmp$ gcc -Wall -Wextra test.c -o test
ammarfaizi2@integral:/tmp$ ./test
Do bubble sort here...
Do selection sort here...
Bubble sort finished
Child process 143748 has exited with exit code: 100
Parent has finished its waiting state...
ammarfaizi2@integral:/tmp$ Selection sort finished

在这种情况下，当子进程终止(至少一个(时，父进程将停止等待。所以你看到"；选择排序完成"；在父进程终止后，因为我们将选择排序模拟为5秒的工作，将冒泡排序模拟为3秒的工作。