C - 利用multiprocess & message passing實作Fibonacci數列

	/*****************
	程式功能: Fibonacci數列之實作。
	程式流程: 執行此程式後輸入一數字，作為Fibonacci數列之個數，由parent process接收該數值，並利用message passing將數值傳給child process，並於child process內實作此數列，將結果傳回parent process後印出。
	執行方法: ./prog2
	Please enter the size of Fibonacci sequence (m): [value]
	******************/
	#include <sys/types.h>
	#include <sys/msg.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	//message buffer structure, 作為parent&child process間的訊息傳遞物
	struct msgbuf {
	long mtype;
	int size;
	int Fib[100];
	};
	int main ()
	{
	key_t key;
	pid_t pid;
	struct msgbuf buf;
	int i, n, msqid;
	pid = fork(); //create a child process
	//report if fork failed
	if (pid < 0) {
	printf("Fork Failed.\n");
	return 1;
	}
	//Child process
	else if (pid == 0) {
	//setup the message permission key
	if ((key = ftok("prog2.c", 'C')) == -1) {
	printf("ftok failed.\n");
	return 1;
	}
	//set the permissions on the queue to 777
	if ((msqid = msgget(key, 0777 | IPC_CREAT)) == -1) {
	printf("msgget failed.\n");
	return 1;
	}
	//receive the message with the same key from the queue
	if (msgrcv(msqid, &buf, sizeof(struct msgbuf) - sizeof (long), 0, 0) == -1) {
	printf("msgrcv failed.\n");
	return 1;
	}
	//setup the initial value of Fibonacci sequence
	buf.Fib[0] = 0; buf.Fib[1] = 1;
	//計算並儲存Fibonacci數列之值，數列個數為使用者輸入之值
	for (n = 2; n < buf.size; n++) {
	buf.Fib[n] = buf.Fib[n - 1] + buf.Fib[n - 2];
	}
	//send the message with the key to the queue
	if (msgsnd(msqid, &buf, sizeof(struct msgbuf) - sizeof(long), 0) == -1) {
	printf("msgsnd failed.\n");
	return 1;
	}
	}
	//Parent process
	else {
	//setup the permission key
	if ((key = ftok("prog2.c", 'C')) == -1) {
	printf("ftok failed.\n");
	return 1;
	}
	//set the permissions on the queue to 777
	if ((msqid = msgget(key, 0777 | IPC_CREAT)) == -1) {
	printf("msgget failed.\n");
	return 1;
	}
	//ask user to enter the size of fibonacci sequence
	printf("Please enter the size of fibonacci sequence (m): ");
	scanf("%d", &buf.size);
	//Get the next message with an mtype equal to the specified msgtyp.
	buf.mtype = 1;
	//send the message with the key to the queue
	if (msgsnd(msqid, &buf, sizeof(struct msgbuf) - sizeof(long), 0) == -1) {
	printf("msgsnd failed.\n");
	return 1;
	}
	//wait for the child to complete
	wait(NULL);
	//receive the message with the same key from the queue
	if (msgrcv(msqid, &buf, sizeof(struct msgbuf) - sizeof(long), 0, 0) == -1) {
	printf("msgrcv failed.\n");
	return 1;
	}
	//print out the result
	printf("Fibonacci: ");
	for (i = 0; i < buf.size; i++)
	printf("%d ", buf.Fib[i]);
	putchar('\n');
	}
	return 0;
	}

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