问题描述
在两个城市南北方向之间存在一条铁路，多列火车可以分别从两个城市的车站排队等待进入车道向对方城市行驶，该铁路在同一时间，只能允许在同一方向上行车，如果同时有相向的火车行驶将会撞车。请模拟实现两个方向行车，而不会出现撞车或长时间等待的情况。您能构造一个管程来解决这个问题吗？
程序实现
dp.h
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#include <sys/msg.h>
#include <sys/wait.h>
/*信号灯控制用的共同体*/
typedef union semuns
{
int val;
} Sem_uns;
//管程中使用的信号量
class Sema
{
public:
Sema(int id);
~Sema();
int down(); //信号量加 1
int up(); //信号量减 1
private:
int sem_id; //信号量标识符
};
//管程中使用的锁
class Lock
{
public:
Lock(Sema *lock);
~Lock();
void close_lock();
void open_lock();
private:
Sema *sema; //锁使用的信号量
};
class Condition
{
public:
Condition(Sema *sema1, Sema *sema2);
~Condition();
void Wait(Lock *conditionLock, int direct); //过路条件不足时阻塞
int Signal (int direc);
//唤醒相反方向阻塞车辆
private:
Sema* sema0; // 一个方向阻塞队列
Sema* sema1; // 另一方向阻塞队列
Lock* lock; // 进入管程时获取的锁
};
class OneWay
{
public:
OneWay (int maxall, int maxcur);
~OneWay();
void Arrive (int direc);
// 车辆准备上单行道,direc 为行车方向
void Cross (int direc);
// 车辆正在单行道上
void Quit (int direc);
// 车辆通过了单行道
int *eastCount;
int *westCount;
int *eastWait;
int *westWait;
int *sumPassedCars;//已经通过的车辆总数
private:
//建立或获取 ipc 信号量的一组函数的原型说明
int get_ipc_id (char *proc_file, key_t key);
int set_sem(key_t sem_key, int sem_val, int sem_flag);
//创建共享内存
char *set_shm(key_t shm_key, int shm_num, int shm_flag);
int rate; //车速
int *maxCars;//最大同向车数
int *numCars; //当前正在通过的车辆数
int *currentDire;//当前通过的车辆的方向
Condition *condition; //通过单行道的条件变量
Lock *lock;//单行道管程锁
};
dp.c
#include "dp.h"
using namespace std;
Sema::Sema(int id)
{
sem_id = id;
}
Sema::~Sema()
{
}
/*
* 信号灯上的 down/up 操作
* semid:信号灯数组标识符
* semnum:信号灯数组下标
* buf:操作信号灯的结构
*/
int Sema::down()
{
struct sembuf buf;
buf.sem_op = -1;
buf.sem_num = 0;
buf.sem_flg = SEM_UNDO;
if ((semop(sem_id, &buf, 1)) < 0)
{
perror("down error ");
exit(EXIT_FAILURE);
}
return EXIT_SUCCESS;
}
int Sema::up()
{
Sem_uns arg;
struct sembuf buf;
buf.sem_op = 1;
buf.sem_num = 0;
buf.sem_flg = SEM_UNDO;
if ((semop(sem_id, &buf, 1)) < 0)
{
perror("up error ");
exit(EXIT_FAILURE);
}
return EXIT_SUCCESS;
}
/*
* 用於单行道管程的互斥执行
*/
Lock::Lock(Sema * s)
{
sema = s;
}
Lock::~Lock()
{
}
//上锁
void Lock::close_lock()
{
sema->down();
}
//开锁
void Lock::open_lock()
{
sema->up();
}
int OneWay::get_ipc_id (char *proc_file, key_t key)
{
#define BUFSZ 256
FILE *pf;
int i, j;
char line[BUFSZ], colum[BUFSZ];
if ((pf = fopen(proc_file, "r")) == NULL)
{
perror("Proc file not open");
exit(EXIT_FAILURE);
}
fgets(line, BUFSZ, pf);
while (!feof(pf))
{
i = j = 0;
fgets(line, BUFSZ, pf);
while (line[i] == ' ')
i++;
while (line[i] != ' ')
colum[j++] = line[i++];
colum[j] = '\0';
if (atoi(colum) != key)
continue;
j = 0;
while (line[i] == ' ')
i++;
while (line[i] != ' ')
colum[j++] = line[i++];
colum[j] = '\0';
i = atoi(colum);
fclose(pf);
return i;
}
fclose(pf);
return -1;
}
/*
*
set_shm 函数建立一个具有 n 个字节 的共享内存区
*
如果建立成功,返回 一个指向该内存区首地址的指针 shm_buf
*
输入参数:
*
shm_key 共享内存的键值
*
shm_val 共享内存字节的长度
*
shm_flag 共享内存的存取权限
*/
char * OneWay::set_shm(key_t shm_key, int shm_num, int shm_flg)
{
int i, shm_id;
char * shm_buf;
//测试由 shm_key 标识的共享内存区是否已经建立
if ((shm_id = get_ipc_id("/proc/sysvipc/shm", shm_key)) < 0)
{
//shmget 新建 一个长度为 shm_num 字节的共享内存
if ((shm_id = shmget(shm_key, shm_num, shm_flg)) < 0)
{
perror("shareMemory set error");
exit(EXIT_FAILURE);
}
//shmat 将由 shm_id 标识的共享内存附加给指针 shm_buf
if ((shm_buf = (char *) shmat (shm_id, 0, 0)) < (char *) 0)
{
perror("get shareMemory error");
exit(EXIT_FAILURE);
}
for (i = 0; i < shm_num; i++)
shm_buf[i] = 0; //初始为 0
}
//共享内存区已经建立,将由 shm_id 标识的共享内存附加给指针 shm_buf
if ((shm_buf = (char *) shmat(shm_id, 0, 0)) < (char *) 0)
{
perror("get shareMemory error");
exit(EXIT_FAILURE);
}
return shm_buf;
}
/*
*
set_sem 函数建立一个具有 n 个信号灯的信号量
*
如果建立成功,返回 一个信号量的标识符 sem_id
*
输入参数:
*
sem_key 信号量的键值
*
sem_val 信号量中信号灯的个数
*
sem_flag 信号量的存取权限
*/
int OneWay::set_sem(key_t sem_key, int sem_val, int sem_flg)
{
int sem_id;
Sem_uns sem_arg;
//测试由 sem_key 标识的信号量是否已经建立
if ((sem_id = get_ipc_id("/proc/sysvipc/sem", sem_key)) < 0)
{
//semget 新建一个信号灯,其标号返回到 sem_id
if ((sem_id = semget(sem_key, 1, sem_flg)) < 0)
{
perror("semaphore create error");
exit(EXIT_FAILURE);
}
}
//设置信号量的初值
sem_arg.val = sem_val;
if (semctl(sem_id, 0, SETVAL, sem_arg) < 0)
{
perror("semaphore set error");
exit(EXIT_FAILURE);
}
return sem_id;
}
Condition::Condition(Sema *semax1, Sema *semax2)
{
sema0 = semax1;
sema1 = semax2;
}
/**
* 看看是否能通过
*/
void Condition::Wait(Lock *lock, int direc)
{
if (direc == 0)
{
cout << getpid() << "east waiting" << "\n";
lock->open_lock();
sema0->down();
lock->close_lock();
}
else if (direc == 1)
{
cout << getpid() << "west waiting" << "\n";
lock->open_lock();
sema1->down();
lock->close_lock();
}
}
int Condition::Signal (int direc)
{
int i;
if (direc == 0)
{
i = sema0->up();
}
else if (direc == 1)
{
i = sema1->up();
}
return i;
}
/*
* get_ipc_id() 从/proc/sysvipc/文件系统中获取 IPC 的 id 号
* pfile: 对应/proc/sysvipc/目录中的 IPC 文件分别为
*
msg-消息队列,sem-信号量,shm-共享内存
* key: 对应要获取的 IPC 的 id 号的键值
*/
Condition::~Condition()
{
}
;
/*
*
set_shm 函数建立一个具有 n 个字节 的共享内存区
*
如果建立成功,返回 一个指向该内存区首地址的指针 shm_buf
*
输入参数:
*
shm_key 共享内存的键值
*
shm_val 共享内存字节的长度
*
shm_flag 共享内存的存取权限
*/
OneWay::OneWay (int maxall, int maxcur)
{
Sema *sema0;
Sema *sema1;
Sema *semaLock;
int ipc_flg = IPC_CREAT | 0644;
maxCars = (int *) set_shm(100, 1, ipc_flg);
numCars = (int *) set_shm(200, 1, ipc_flg);
currentDire = (int *) set_shm(300, 1, ipc_flg);
eastCount = (int *) set_shm(501, 1, ipc_flg);
westCount = (int *) set_shm(502, 1, ipc_flg);
sumPassedCars = (int *) set_shm(700, 1, ipc_flg);
eastWait = (int *) set_shm(801, 1, ipc_flg);
westWait = (int *) set_shm(802, 1, ipc_flg);
int sema0_id = set_sem(401, 0, ipc_flg);
int sema1_id = set_sem(402, 0, ipc_flg);
int semaLock_id = set_sem(601, maxcur, ipc_flg);
*maxCars = maxcur;
*numCars = 0;
*currentDire = 0;
*eastCount = 0;
*westCount = 0;
*sumPassedCars = 0;
*eastWait = 0;
*westWait = 0;
sema0 = new Sema(sema0_id);
sema1 = new Sema(sema1_id);
semaLock = new Sema(semaLock_id);
lock = new Lock(semaLock);
condition = new Condition(sema0, sema1);
}
void OneWay::Arrive (int direc)
{
lock->close_lock();
if ((*currentDire != direc || *numCars >= *maxCars) & *sumPassedCars > 0)
{
if (direc == 0)
{
*eastWait += 1;
}
else if (direc == 1)
{
*westWait += 1;
}
condition->Wait(lock, direc);
}
if (direc == 0) //东 +1
{
*eastWait -= 1;
*eastCount = *eastCount + 1;
cout << getpid() << "east entering\n";
}
else if (direc == 1) //西 +1
{
*westCount = *westCount + 1;
*westWait -= 1;
cout << getpid() << "west entering\n";
}
*numCars = *numCars + 1;
*currentDire = direc;
*sumPassedCars += 1;
lock->open_lock();
}
void OneWay::Cross (int direc)
{
lock->close_lock();
sleep(3);
if (direc == 0)
cout << getpid() << "cross" << *numCars << "\n";
else if (direc == 1)
cout << getpid() << "cross" << *numCars << "\n";
lock->open_lock();
}
void OneWay::Quit (int direc)
{
lock->close_lock();
*numCars -= 1;
if (direc == 0)
{
cout << getpid() << "leave" << "\n";
}
else if (direc == 1)
{
cout << getpid() << "leave" << "\n";
}
if (*numCars == 0)
{
if (direc == 0)
{
if (*westWait > 0)
{
condition->Signal(1);
}
else if (*eastWait > 0)
{
condition->Signal(0);
}
}
else if (direc == 1)
{
if (*eastWait > 0)
{
condition->Signal(0);
}
else if (*westWait > 0)
{
condition->Signal(1);
}
}
}
lock->open_lock();
}
OneWay::~OneWay()
{
delete condition;
}
int main (int argc, char **argv)
{
int maxCars;
int maxSingelDirect;
cout << "请输入总车辆数:";
cin >> maxCars;
cout << "请输入单方向通过的最大车数:";
cin >> maxSingelDirect;
OneWay *oneWay = new OneWay(maxCars, maxSingelDirect);
//建立管程,判断可不可进、决定方向,进入单行道
int i;
int pid[maxCars];
for (i = 0; i < maxCars; i++) //对每一辆车都创建一个子进程
{
pid[i] = fork();
if (pid[i] == 0)
{
sleep(1);
srand(time(NULL));
int direct = rand() % 2;
direct=*oneWay->sumPassedCars%2;
oneWay->Arrive(direct);
oneWay->Cross(direct);
oneWay->Quit(direct);
exit(EXIT_SUCCESS);
}
}
for (i = 0; i < maxCars; i++)
{
waitpid(pid[i], NULL, 0);
}
cout << *(oneWay->eastCount) << "辆列车向东" << *(oneWay->westCount)
<< "辆列车向西,正常通行.\n";
delete oneWay;
return EXIT_SUCCESS;
}
编译
g++ -w -g -c dp.c
g++ dp.o -o dp
编译完成后截图如下：
运行
输入命令
./dp
可以看到运行结果
