操作系统实验六——死锁问题实验
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?
dp.h
#include <iostream>
#include <time.h>
#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>
using namespace std;
typedef union semuns {
int val;
} Sem_uns;
//定义信号量
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
};
//定义锁
class Lock{
public:
Lock(Sema *lock);
~Lock();
void close_lock();
void open_lock();
private:
Sema *sema; //锁使用的信号量
};
//定义条件变量
class Condition {
public:
Condition(Sema *sema1 , Sema *sema2);
~Condition();
void Wait(Lock *conditionLock,int direc); //过路条件不足时阻塞
void Signal( int direc); //唤醒相反方向阻塞车辆
private:
Sema* sema[2]; // 一个方向阻塞队列
Lock* lock; // 进入管程时获取的锁
};
//哲学家管程的定义
class dp{
public:
dp(int rate, int max);
~dp();
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 Leave(int direc); // 车辆通过了单行道
int getNum();
void addNum();
void decNum();
//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,放哲学家状态
char *set_shm(key_t shm_key,int shm_num,int shm_flag);
private:
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 currentDirec; //当前通过的车辆的方向
Condition *con; //通过单行道的条件变量
Lock *lock; //单行道管程锁
int* curDire;//当前的方向
int* isFirst;//是否为第一辆车
int* irnum;//反向的等待的车辆的数量
int* curnum;//当前方向等待的车辆的数量
int* currentCarNum; //当前正在通过的车辆的数量
Sema *mutex;//互斥信号量
};dp.cc
#include "dp.h"
Sema::Sema(int id)
{
sem_id = id;
}
Sema::~Sema(){ }
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;
}
Lock::Lock(Sema * s)
{
sema = s;
}
Lock::~Lock(){ }
//上锁
void Lock::close_lock()
{
sema->down();
}
//开锁
void Lock::open_lock()
{
sema->up();
}
Condition::Condition(Sema *s0, Sema *s1) {
sema[0] = s0;
sema[1] = s1;
}
void Condition::Wait(Lock *lock,int dir)
{
lock->open_lock();
sema[dir]->down();
lock->close_lock();
}
void Condition::Signal(int dir)
{
sema[dir]->up();
}
int dp::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;
}
int dp::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;
}
char * dp::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;
}
//管程构造函数
dp::dp(int r, int max)
{
int ipc_flg = IPC_CREAT | 0644;
int shm_key = 220;
int shm_num = 5;
int sem_key = 120;
int sem_val = 0;
int shm_flg = IPC_CREAT|0644;
int sem_id;
Sema *sema;
Sema *sema1;
Sema *sema2;
rate = r;
maxCars = max;
numCars = 0;
//当前的方向
curDire = (int *) set_shm(shm_key++, 1, shm_flg);
//是否为第一辆车
isFirst = (int *) set_shm(shm_key++, 1, shm_flg);
//反向车辆的数量
irnum = (int *) set_shm(shm_key++, 1, shm_flg);
//当前通过的车辆数
currentCarNum = (int *) set_shm(shm_key++, 1, shm_flg);
//当前方向等待的车辆的数量
curnum = (int *) set_shm(shm_key++, 1, shm_flg);
*curDire=0;
*isFirst=0;
*irnum=0;
*currentCarNum=0;
*curnum=0;
if((sem_id = set_sem(sem_key++,1,ipc_flg)) < 0){
perror("Semaphor create error");
exit(EXIT_FAILURE);
}
sema = new Sema(sem_id);
lock = new Lock(sema);
//为每一个方向建立一个信号量
if((sem_id = set_sem(sem_key++,sem_val,ipc_flg)) < 0){
perror("Semaphor create error");
exit(EXIT_FAILURE);
}
sema1 = new Sema(sem_id);
if((sem_id = set_sem(sem_key++,sem_val,ipc_flg)) < 0){
perror("Semaphor create error");
exit(EXIT_FAILURE);
}
sema2 = new Sema(sem_id);
//管程内的条件
con = new Condition(sema1, sema2);
//共享内存互斥信号量
sem_id = set_sem(sem_key++, 1, ipc_flg);
mutex = new Sema(sem_id);
}
//当车辆到达时
void dp::Arrive(int direc)
{
int count;
lock->close_lock();
mutex->down();
//获取是否为第一辆车
count = *isFirst;
mutex->up();
//如果值为0说明是第一辆车
if(count == 0)
{
mutex->down();
*curDire = direc;
*isFirst = ++count;
mutex->up();
}
if(direc==0)
{
printf("%d号车向东等待单行道\n", getpid());
}else{
printf("%d号车向西等待单行道\n", getpid());
}
mutex->down();
currentDirec = *curDire;
mutex->up();
if(currentDirec != direc) {
mutex->down();
count = *irnum;
*irnum = ++count;
mutex->up();
//等待
con->Wait(lock, direc);
}
sleep(1);
lock->open_lock();
}
//当车辆通过时
void dp::Cross(int direc)
{
int count, i;
lock->close_lock();
//获得当前正在通过的车辆数
numCars = getNum();
if(numCars >= maxCars)
{
mutex->down();
count = *curnum;
*curnum = ++count;
mutex->up();
loop: con->Wait(lock, direc);
sleep(1);
numCars = getNum();
if(numCars >= maxCars)
goto loop;
}
addNum();
//sleep(1);
numCars = getNum();
if(direc==0)
{
printf("%d号车向东通过单行道,道上车数:%d\n", getpid(), numCars);
}else{
printf("%d号车向西通过单行道,道上车数:%d\n", getpid(), numCars);
}
//sleep(1);
lock->open_lock();
}
void dp::Leave(int direc)
{
int count, num;
lock->close_lock();
if(direc==0)
{
printf("%d号车向东离开单行道\n", getpid(), direc);
}else{
printf("%d号车向西离开单行道\n", getpid(), direc);
}
//减少当前车的数量
decNum();
//正在通过道路的车辆的数量
numCars = getNum();
mutex->down();
//反方向的车辆的数量
count = *irnum;
//当前方向等待的车辆的数量
num = *curnum;
//cout<<"-----------当前方向车的数量：-------"<<num<<"\n";
//cout<<"-----------反方向车的数量：-------"<<count<<"\n";
mutex->up();
//反方向的车辆的数量不为0的话，优先唤醒反方向的车辆的数量
if(numCars == 0 && count != 0)
{
//cout<<"-----------maxCars-------"<<maxCars<<"\n";
int i=0;
while(count--)
{
con->Signal(1 - direc);
//cout<<"-----------awake1-------"<<getpid()<<" "<<(1-direc)<<"\n";
i++;
}
mutex->down();
*curDire = 1 - direc;
*irnum = *curnum;
*curnum = 0;
*currentCarNum = 0;
mutex->up();
}
//没有反方向的车的时候唤醒同方向的车
else if(numCars == 0 && num != 0)
{
int i=0;
while(num--)
{
con->Signal(direc);
i++;
}
//cout<<"-----------awake-------"<<getpid()<<"\n";
mutex->down();
*curnum = 0;
*currentCarNum = 0;
mutex->up();
}
lock->open_lock();
}
dp::~dp(){ }
//获取当前正在通过的车辆的数量
int dp::getNum()
{
mutex->down();
int num = *currentCarNum;
mutex->up();
return num;
}
void dp::addNum()
{
mutex->down();
int num = *currentCarNum;
*currentCarNum = ++num;
mutex->up();
}
void dp::decNum()
{
mutex->down();
int num = *currentCarNum;
*currentCarNum = --num;
mutex->up();
}
int main(int argc,char *argv[])
{
dp *tdp;
int cars;
int dir;
int max = 2;
int rate = 2;
cars = (argc > 1) ? atoi(argv[1]) : 5;
max = (argc > 2) ? atoi(argv[2]) : 2;
tdp = new dp(rate, max);
int i;
int pid[cars];
for(i=0;i<cars;i++)
{
pid[i]=fork();
if(pid[i]<0)
{
printf("Create process fail\n");
return -1;
}
if(pid[i]==0)
{
srand(getpid());
dir = rand() % 2;
tdp->Arrive(dir);
tdp->Cross(dir);
tdp->Leave(dir);
exit(0);
}
}
for(i=0;i<cars;i++)
{
waitpid(pid[i],NULL,0);
}
return 0;
}Makefile
head = dp.h
srcs = dp.cc
objs = dp.o
opts = -w -g -c
all: dp
dp: $(objs)
g++ $(objs) -o dp
dp.o: $(srcs) $(head)
g++ $(opts) $(srcs)
clean:
rm dp *.o