題目：有一個盤子，父親放入蘋果，母親放入桔子，女兒取出蘋果，兒子取出桔子。

同步關係：父親放蘋果和女兒取蘋果 && 母親放桔子和兒子取桔子

互斥關係：父親放蘋果和母親放桔子

下面是原始碼：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/sem.h>
#include <sys/shm.h>		
#include <errno.h>

union semun {
	int 			val;
	struct 			semid_ds *buf;
	unsigned short 	*array;
};

int main(int argc, char *argv[])
{
	struct sembuf P, V;
	union semun arg;

	if (argc != 3) {				//命令列引數個數必須為3
		printf("usage: ./sem <APPLE> <ORANGE>\n");
		exit(1);
	}
	
	int	APPLE = atoi(argv[1]);		//父親放入的蘋果數
	int	ORANGE = atoi(argv[2]);		//母親放入的桔子數

	int getappleid = shmget(IPC_PRIVATE, sizeof(int), IPC_CREAT|0666);		//申請共享記憶體
	int getorangeid = shmget(IPC_PRIVATE, sizeof(int), IPC_CREAT|0666);

	int *getapple = (int*) shmat(getappleid, 0, 0);			//繫結共享記憶體
	int *getorange = (int*) shmat(getorangeid, 0, 0);
	
	*getapple = 0;			//初始化取出蘋果數為0
	*getorange = 0;			//初始化取出桔子數為0
	
	int empty = semget(IPC_PRIVATE, 1, IPC_CREAT|0666);		//盤子是否為空的訊號量
	int apple = semget(IPC_PRIVATE, 1, IPC_CREAT|0666);		//盤子中是否有蘋果的訊號量
	int orange = semget(IPC_PRIVATE, 1, IPC_CREAT|0666);	//盤子中是否有桔子的訊號量
	int mutex = semget(IPC_PRIVATE, 1, IPC_CREAT|0666);		//放入盤子和取出盤子的互斥訊號量

	arg.val = 1;
	if (semctl(empty, 0, SETVAL, arg) == -1)				//設定訊號量
		perror("semctl setval error");
	arg.val = 0;
	if (semctl(apple, 0, SETVAL ,arg) == -1)
		perror("semctl setval error");
	arg.val = 0;
	if (semctl(orange, 0, SETVAL, arg) == -1)
		perror("semctl setval error");
	arg.val = 1;
	if (semctl(mutex, 0, SETVAL, arg) == -1)
		perror("semctl setval error");

	P.sem_num = 0;					//定義P、V操作
	P.sem_op = -1;
	P.sem_flg = SEM_UNDO;
	V.sem_num = 0;
	V.sem_op = 1;
	V.sem_flg = SEM_UNDO;

	if (fork() == 0) {					//父親程序
		int i = 0;
		for (; i < APPLE; i++) {		//迴圈放入蘋果
			semop(empty, &P, 1);
			semop(mutex, &P, 1);
			printf("Father put APPLE\n");
			semop(mutex, &V, 1);
			semop(apple, &V, 1);
		}
		sleep(2);
		printf("Father is over!\n");
		exit(0);
	} else {
		if (fork() == 0) {				//母親程序
			int i = 0;
			for (; i < ORANGE; i++) {	//迴圈放入桔子
				semop(empty, &P, 1);
				semop(mutex, &P, 1);
				printf("Mother put ORANGE\n");
				semop(mutex, &V, 1);
				semop(orange, &V, 1);
				sleep(1);
			}
			printf("Mother is over!\n");
			exit(0);
		} else {
			if (fork() == 0) {			//女兒程序
				while (1) {				//取出蘋果
					if (*getapple == APPLE) break;
					semop(apple, &P, 1);
					semop(mutex, &P, 1);
					printf("\tDaughter get APPLE!\n\n");
					(*getapple)++;
					semop(mutex, &V, 1);
					semop(empty, &V, 1);
					sleep(1);
				}
				printf("\tDaughter get all APPLE!\n\n");
				exit(0);
			} else {
				if (fork() == 0) {		//兒子程序
					while (1) {			//取出桔子
						if (*getorange == ORANGE) break;
						semop(orange, &P, 1);
						semop(mutex, &P, 1);
						printf("\tSon get ORANGE!\n\n");
						(*getorange)++;
						semop(mutex, &V, 1);
						semop(empty, &V, 1);
						sleep(1);
					}
					printf("\tSon get all ORANGE!\n\n");
					exit(0);
				}
			}
		}
	}
	wait(0);			//等待子程序結束
	wait(0);
	wait(0);
	wait(0);
	
	printf("\nAll processor end!\n\n");

	shmdt(getapple);							//釋放共享記憶體
	shmctl(getappleid, IPC_RMID, 0);
	shmdt(getorange);
	shmctl(getorangeid, IPC_RMID, 0);
	
	semctl(empty, IPC_RMID, 0);					//釋放訊號量
	semctl(apple, IPC_RMID, 0);
	semctl(orange, IPC_RMID, 0);
	semctl(mutex, IPC_RMID, 0);
	exit(0);
}
 

上面的程式碼是最終能在所有Linux下執行的版本。之前因為標頭檔案是 linux/sem.h 和 linux/shm.h 導致無法在部分linux下執行。我看見Unix高階程式設計上面用的 sys/sem.h 和 sys/shm.h，並結合下面的文章對之前的程式碼進行了修改。