我们必须制作一个程序来模拟剧院座位预订系统的功能。我们有 N_cust 客户调用电话中心，还有 N_tel 人员接听电话。每次通话持续时间从 t_seathigh 到 t_seatlow 秒。信用卡支付成功的概率为P_cardsuccess。程序获取的两个参数是客户端数量和rand_r 的种子。每个客户端都有一个线程，客户端必须等待有人打电话。我的问题是程序运行但出现段错误，或者在函数 AwesomeThreadFunction 的第一个循环中陷入无限循环。
我想也许我没有正确处理变量telefoners，因为程序有时会卡在函数的第一个循环中，但我不知道到底是怎么回事。我也不知道为什么会出现这种段错误。我的程序到底在哪里尝试访问未分配的内存。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <pthread.h>
#include "p3170013-p3170115-p3170097-res1.h"
#include <unistd.h>
#define N_seat 250
#define N_tel 8
#define N_seatlow 1
#define N_seathigh 5
#define t_seatlow 5
#define t_seathigh 10
#define P_cardsuccess 0.9
#define C_seat 20.0
#define BILLION 1E9
pthread_mutex_t lock_phone, lock_bank_account,lock_number_of_transfer,lock_wait_time, lock_service_time, lock_plan, lock_screen;
int plan[N_seat];
int phone_count=0,bank_account=0,tid=0,seats=0,telefoners=N_tel;
unsigned int seed;
float avg_wait_time=0,avg_service_time;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
void* AwesomeThreadFunction(void* vargc){
tid=*(int*)vargc;
struct timespec waitStart, waitEnd;
clock_gettime(CLOCK_REALTIME, &waitStart);
avg_wait_time-=(waitStart.tv_sec+waitStart.tv_nsec/BILLION);
pthread_mutex_lock(&lock_screen);
printf("%d\n",telefoners);
pthread_mutex_unlock(&lock_screen);
pthread_mutex_lock(&lock_phone);
while (telefoners == 0) {
pthread_cond_wait(&cond, &lock_phone);
}
telefoners--;
pthread_mutex_unlock(&lock_phone);
pthread_mutex_lock(&lock_screen);
printf("coooooooool\n");
pthread_mutex_unlock(&lock_screen);
clock_gettime(CLOCK_REALTIME, &waitEnd);
avg_wait_time+=(waitEnd.tv_sec+waitEnd.tv_nsec/BILLION);
struct timespec talkStart, talkEnd;
clock_gettime(CLOCK_REALTIME, &talkStart);
int how_many_seats=rand_r(&seed);
seed=how_many_seats;
how_many_seats=how_many_seats%(N_seathigh-N_seatlow)+N_seatlow;
int how_many_seconds=rand_r(&seed);
seed=how_many_seconds;
how_many_seconds=how_many_seconds%(t_seathigh-t_seatlow)+t_seatlow;
sleep(how_many_seconds);
if(seats==N_seat){
pthread_mutex_lock(&lock_screen);
printf("%d Reservation cancelled because the theater is full\n",*(int*)vargc);
pthread_mutex_unlock(&lock_screen);
}else if(seats+how_many_seats>N_seat){
pthread_mutex_lock(&lock_screen);
printf("%d Reservation cancelled because there are not enough seats available\n",*(int*)vargc);
pthread_mutex_unlock(&lock_screen);
}else{
int c=0,i=0;
pthread_mutex_lock(&lock_number_of_transfer);
pthread_mutex_unlock(&lock_number_of_transfer);
pthread_mutex_lock(&lock_plan);
while(c<how_many_seats){
if(!plan[i]){
plan[i]=tid;
c++;
}
i++;
}
seats+=how_many_seats;
pthread_mutex_unlock(&lock_plan);
int card_success=rand_r(&seed);
seed=card_success;
float tempp=(float)card_success/(float)RAND_MAX;
card_success=(tempp<=P_cardsuccess);
if(!card_success){
pthread_mutex_lock(&lock_screen);
printf("%d Reservation cancelled because the transaction with the credit card was not accepted\n",*(int*)vargc);
pthread_mutex_unlock(&lock_screen);
pthread_mutex_lock(&lock_plan);
c=0;i=0;
while(c<how_many_seats){
if(plan[i]==tid){
plan[i]=0;
c++;
}
pthread_mutex_lock(&lock_screen);
pthread_mutex_unlock(&lock_screen);
i++;
}
seats-=how_many_seats;
pthread_mutex_unlock(&lock_plan);
pthread_mutex_lock(&lock_number_of_transfer);
pthread_mutex_unlock(&lock_number_of_transfer);
}else{
pthread_mutex_lock(&lock_screen);
printf("%d Reservation completed successfully.The number of the transaction is %d, your seats are ",*(int*)vargc,*(int*)vargc);
pthread_mutex_unlock(&lock_screen);
c=0;i=0;
pthread_mutex_lock(&lock_plan);
while(c<how_many_seats){
if(plan[i]==*(int*)vargc){
pthread_mutex_lock(&lock_screen);
printf("%d ",i);
pthread_mutex_unlock(&lock_screen);
c++;
}
i++;
}
pthread_mutex_unlock(&lock_plan);
pthread_mutex_lock(&lock_screen);
printf("and the cost of the transaction is %.2f euros\n",how_many_seats*C_seat);
pthread_mutex_unlock(&lock_screen);
pthread_mutex_lock(&lock_bank_account);
bank_account+=how_many_seats*C_seat;
pthread_mutex_unlock(&lock_bank_account);
}
}
//we assume that the client is fully served when we have also printed out his/her result of the try to book seats
clock_gettime(CLOCK_REALTIME, &talkEnd);
double cow = ( talkEnd.tv_sec - talkStart.tv_sec ) + ( talkEnd.tv_nsec - talkStart.tv_nsec ) / BILLION;
pthread_mutex_lock(&lock_service_time);
avg_service_time+=cow;
pthread_mutex_unlock(&lock_service_time);
pthread_mutex_lock(&lock_phone);
telefoners++;
pthread_cond_signal(&cond);
pthread_mutex_unlock(&lock_phone);
pthread_exit(0);
}
int main(int argc,char* argv[]){
int i;
for(i=0;i<N_seat;i++){
plan[i] = 0;
}
//if user did not give the correct number of arguments
if(argc!=3){
printf("Wrong number of arguments\n");
return -1;
}
int N_cust=atoi(argv[1]),tel_available=N_tel,err;
i=0;
seed=atoi(argv[2]);
pthread_t *threads=(pthread_t*)malloc(N_cust*sizeof(pthread_t));
int threadid[N_cust];
//if we can't init one of the mutexes
pthread_mutex_init(&lock_phone, NULL);
pthread_mutex_init(&lock_bank_account, NULL);
pthread_mutex_init(&lock_number_of_transfer, NULL);
pthread_mutex_init(&lock_wait_time, NULL);
pthread_mutex_init(&lock_service_time, NULL);
pthread_mutex_init(&lock_plan, NULL);
pthread_mutex_init(&lock_screen, NULL);
//creating the threads
while(i<N_cust){
threadid[i]=i+1;
err = pthread_create(&(threads[i]), NULL, AwesomeThreadFunction, (void*)&threadid[i]); //func name
if (err){
printf("Thread can't be created :[%s]\n", strerror(err));
}
i++;
}
//join the threads
void *status;
for (i = 0; i < N_cust; i++) {
rc = pthread_join(threads[i], &status);
if (rc != 0) {
printf("ERROR: return code from pthread_join() is %d\n", rc);
exit(-1);
}
printf("Main: Thread %lu finished with status %d.\n", threads[i], *(int *)status);
}
//final output
for(i=0;i<N_seat;++i){
if(plan[i]){
printf("Seat %d / client %d\n",i+1,plan[i]);
}
}
printf("Total revenue from sales:\t%d\n",bank_account);
printf("Average waiting time:\t%f\n",(float)avg_wait_time/(float)N_cust);
printf("Average service time:\t%f\n",(float)avg_service_time/(float)N_cust);
free(threads);
//Destroy mutexes
pthread_mutex_destroy(&lock_phone);
pthread_mutex_destroy(&lock_bank_account);
pthread_mutex_destroy(&lock_number_of_transfer);
pthread_mutex_destroy(&lock_wait_time);
pthread_mutex_destroy(&lock_service_time);
pthread_mutex_destroy(&lock_plan);
pthread_mutex_destroy(&lock_screen);
pthread_cond_destroy(&cond);
return 0;
}
最佳答案
导致段错误的直接问题位于(省略不相关的细节):
if(seats+how_many_seats>N_seat) {
....
} else {
int c=0,i=0;
pthread_mutex_lock(&lock_plan);
while(c<how_many_seats) {
if(!plan[i]){
plan[i]=tid;
c++;
}
i++;
}
seats+=how_many_seats;
pthread_mutex_unlock(&lock_plan);
代码确定它是否可以满足请求，然后愉快地继续预订座位。只有这样才能锁定计划。同时，在测试 seats+how_many_seats>N_seat 之间并锁定计划，另一个线程执行相同的操作并修改计划。之后，可用座位数比第一个线程预期的要少，并且 while(c<how_many_seats)循环访问plan越界。
其余的我没有检查；我预计还有其他类似的问题。非 volatile 全局变量非常可疑。无论如何，帮自己一个忙，使用更多的功能。
关于c - 多线程的段错误(核心转储)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55764603/