wait2.c

/* wait2.c  */
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include  <string.h>
#include  <sys/types.h>
#
#define   MAX_COUNT  200
#define   BUF_SIZE   100

void  ChildProcess(char [], char []);    /* child process prototype  */
void  ParentProcess(void);               /* parent process prototype */

void  main(void)
{
	pid_t   pid1, pid2, pid;
	int     status;
	int     i;
	char    buf[BUF_SIZE];

	printf("*** Parent is about to fork process 1 ***\n");
	if ((pid1 = fork()) < 0) {
		printf("Failed to fork process 1\n");
		exit(1);
	}
	else if (pid1 == 0) 
		ChildProcess("First", "   ");

	printf("*** Parent is about to fork process 2 ***\n");
	if ((pid2 = fork()) < 0) {
		printf("Failed to fork process 2\n");
		exit(1);
	}
	else if (pid2 == 0) 
		ChildProcess("Second", "      ");

	ParentProcess();
	sprintf(buf, "*** Parent enters waiting status .....\n");
	write(1, buf, strlen(buf));
	pid = wait(&status);
	sprintf(buf, "*** Parent detects process %d was done ***\n", pid);
	write(1, buf, strlen(buf));
	pid = wait(&status);
	printf("*** Parent detects process %d is done ***\n", pid);
	printf("*** Parent exits ***\n");
	exit(0);
}

#define  QUAD(x)  (x*x*x*x)

void  ParentProcess(void)
{
	int  a, b, c, d;
	int  abcd, a4b4c4d4;
	int  count = 0;
	char buf[BUF_SIZE];

	sprintf(buf, "Parent is about to compute the Armstrong numbers\n");
	write(1, buf, strlen(buf));
	for (a = 0; a <= 9; a++)
		for (b = 0; b <= 9; b++)
			for (c = 0; c <= 9; c++)
				for (d = 0; d <= 9; d++) {
					abcd     = a*1000 + b*100 + c*10 + d;
					a4b4c4d4 = QUAD(a) + QUAD(b) + QUAD(c) + QUAD(d);
					if (abcd == a4b4c4d4) {
						sprintf(buf, "From parent: "
								"the %d Armstrong number is %d\n",
								++count, abcd);
						write(1, buf, strlen(buf));
					}
				}
	sprintf(buf, "From parent: there are %d Armstrong numbers\n", count);
	write(1, buf, strlen(buf));
}

void  ChildProcess(char *number, char *space)
{
	pid_t  pid;
	int    i;
	char   buf[BUF_SIZE];

	pid = getpid();
	sprintf(buf, "%s%s child process starts (pid = %d)\n", 
			space, number, pid);
	write(1, buf, strlen(buf));
	for (i = 1; i <= MAX_COUNT; i++) {
		sprintf(buf, "%s%s child's output, value = %d\n", 
				space, number, i); 
		write(1, buf, strlen(buf));
	}
	sprintf(buf, "%s%s child (pid = %d) is about to exit\n", 
			space, number, pid);
	write(1, buf, strlen(buf));
	exit(0);
}