哲学家问题是操作系统中资源分配的经典问题
linux平台下的系统api不同于Windows下的实现
要求：一个正确的哲学家程序（不会发生死锁）
一个错误的哲学家程序（会发生死锁）
系统环境：ElementaryOS
wrong.c
#include<stdio.h>
#include<stdlib.h>
#include<sys/ipc.h>
#include<sys/msg.h>
#include<sys/types.h>
#include<unistd.h>
#include<errno.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<sys/wait.h>
#define DELAY (rand() % 5 + 1)
#define ERR_EXIT(m) \
do { \
perror(m); \
exit(EXIT_FAILURE); \
} while() union semun
{
int val; // Value for SETVAL
struct semid_ds *buf; //Buffer for IPC_STAT, IPC_SET
unsigned short *array; /* Array for GETALL, SETALL */
struct seminfo *__buf; /* Buffer for IPC_INFO (Linux-specific) */
};
//semid ! this is the number of share memory
int semid;
//waiting for fork here
//left and right = the number of sourses
void wait_for_1fork(int no)
{
int left = no;
//system defined struct
//"first":the current number of pro
//"second":resourses -1:wait cannot use;+1:can use
//"thired":?
struct sembuf buf[] =
{
{left, -, },
};
//semop do wait or signal (p/v)
//"first": the number of share memory pro
//"second":the first point of struct
//"third":the number of signal to complete
semop(semid, buf, );
}
void wait_for_2fork(int no)
{
int right = (no + ) % ;
//system defined struct
//"first":the current number of pro
//"second":resourses -1:wait cannot use;+1:can use
//"thired":?
struct sembuf buf[] =
{
{right, -, }
};
//semop do wait or signal (p/v)
//"first": the number of share memory pro
//"second":the first point of struct
//"third":the number of signal to complete
semop(semid, buf, );
}
void free_1fork(int no)
{
int left = no;
//system defined struct
//"first":the current number of pro
//"second":resourses -1:wait cannot use;+1:can use
//"thired":?
struct sembuf buf[] =
{
{left, , },
};
semop(semid, buf, );
}
void free_2fork(int no)
{
int right = (no + ) % ;
//system defined struct
//"first":the current number of pro
//"second":resourses -1:wait cannot use;+1:can use
//"thired":?
struct sembuf buf[] =
{
{right, , }
};
semop(semid, buf, );
}
void philosopere(int num)
{
srand(getpid());
for (; ;)
{
//printf("%d is thinking\n", num);
printf("\033[36m%d is thinking\n\033[0m", num);
if(num!=)
sleep(DELAY);
//printf("%d is hungry\n", num);
wait_for_1fork(num);
//printf("%d pick up left chopsticks\n", num);
printf("\033[31m%d pick up left chopsticks\n\033[0m", num);
sleep(DELAY);
sleep(DELAY);
wait_for_2fork(num);
//printf("%d pick up right chopsticks\n", num);
printf("\033[34m%d pick up right chopsticks\n\033[0m", num);
//printf("%d is eating\n", num);
sleep(DELAY);
free_1fork(num);
//printf("%d return left chopsticks\n", num);
printf("\033[33m%d return left chopsticks\n\033[0m", num);
sleep(DELAY);
free_2fork(num);
//printf("%d return right chopsticks\n", num);
printf("\033[37m%d return right chopsticks\n\033[0m", num);
}
}
int main()
{
//use IPC to connect between processes . A new share memory
//semget() return the number of share memory
//new signal key=0 and never change .So not use key
//"first":use IPC_PRIVATE to share memory between relation processes
//"second":(size_t)naxSize
//"third":(int flag)private:666--read and write ; IPC_CREAT creat new memory
semid = semget(IPC_PRIVATE, , IPC_CREAT | );
if (semid == -)
ERR_EXIT("semget");
union semun su;
su.val = ;
for (int i = ; i < ; i++)
{
//creat a new object on "semid"
//use i to depart 5 processes
semctl(semid, i, SETVAL, su);
}
int no = ;
//pid_t (Process ID _ Type) Just like int
pid_t pid;
for (int i = ; i < ; i++)
{
//use fork() to make a copy of father process named with child pro
//father.pid>0 and child.pid=0
//after for loop will exist a father and five childs(0-4)
pid = fork();
if (pid == -)
ERR_EXIT("fork");
if (pid == )
{
no = i;
//break the child process loop to run the philosopere
break;
}
}
philosopere(no);
return ;
}
right.c
#include<stdio.h>
#include<stdlib.h>
#include<sys/ipc.h>
#include<sys/msg.h>
#include<sys/types.h>
#include<unistd.h>
#include<errno.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<sys/wait.h>
#define DELAY (rand() % 5 + 1)
#define ERR_EXIT(m) \
do { \
perror(m); \
exit(EXIT_FAILURE); \
} while() union semun
{
int val; // Value for SETVAL
struct semid_ds *buf; //Buffer for IPC_STAT, IPC_SET
unsigned short *array; /* Array for GETALL, SETALL */
struct seminfo *__buf; /* Buffer for IPC_INFO (Linux-specific) */
};
//semid ! this is the number of share memory
int semid;
//waiting for fork here
//left and right = the number of sourses
void wait_for_2fork(int no)
{
int left = no;
int right = (no + ) % ;
//system defined struct
//"first":the current number of pro
//"second":resourses -1:wait cannot use;+1:can use
//"thired":?
struct sembuf buf[] =
{
{left, -, },
{right, -, }
};
//semop do wait or signal (p/v)
//"first": the number of share memory pro
//"second":the first point of struct
//"third":the number of signal to complete
semop(semid, buf, );
}
void free_2fork(int no)
{
int left = no;
int right = (no + ) % ;
//system defined struct
//"first":the current number of pro
//"second":resourses -1:wait cannot use;+1:can use
//"thired":?
struct sembuf buf[] =
{
{left, , },
{right, , }
};
semop(semid, buf, );
}
void philosopere(int num)
{
srand(getpid());
for (; ;)
{
//printf("\033[31m Hello\n\033[0m");
//printf("\033[36m Hello\n\033[0m");
//printf("\%d is thinking\n", num);
printf("\033[31m%d is thinking\n\033[0m", num);
sleep(DELAY);
printf("%d pick up two chopsticks\n", num);
printf("\033[36m%d pick up two chopsticks\n\033[0m", num);
wait_for_2fork(num);
//printf("%d is eating\n", num);
printf("\033[34m%d is eating\n\033[0m", num);
sleep(DELAY);
free_2fork(num);
}
}
int main()
{
//use IPC to connect between processes . A new share memory
//semget() return the number of share memory
//new signal key=0 and never change .So not use key
//"first":use IPC_PRIVATE to share memory between relation processes
//"second":(size_t)naxSize
//"third":(int flag)private:666--read and write ; IPC_CREAT creat new memory
semid = semget(IPC_PRIVATE, , IPC_CREAT | );
if (semid == -)
ERR_EXIT("semget");
union semun su;
su.val = ;
for (int i = ; i < ; i++)
{
//creat a new object on "semid"
//use i to depart 5 processes
semctl(semid, i, SETVAL, su);
}
int no = ;
//pid_t (Process ID _ Type) Just like int
pid_t pid;
for (int i = ; i < ; i++)
{
//use fork() to make a copy of father process named with child pro
//father.pid>0 and child.pid=0
//after for loop will exist a father and five childs(0-4)
pid = fork();
if (pid == -)
ERR_EXIT("fork");
if (pid == )
{
no = i;
//break the child process loop to run the philosopere
break;
}
}
philosopere(no);
return ;
}