为什么用共享内存编译C代码会报错"undefined reference to 'sem_init' "

Question

我是共享内存的初学者，我实现了一个并行加法器，其中 k 个处理器中的每一个都作为子进程实现。具体来说，给定一组 n 个整数和 k 的值，主程序创建 k 个子进程，分配每个子进程计算其分配的 n/k 个数字上限的总和，等待每个子进程的小计k个子进程，对小计求和，打印每个小计的结果和总计。我没有使用线程。

这个程序是为学院的作业而创建的，他们预计运行在任何部门的计算机中。

此代码在 Kali Linux 上正确编译，但我无法在其他 Linux 版本上编译和运行。当我尝试在 Ubuntu 上编译时，它给出了

的错误

undefined reference to 'sem_init'

我在编译行中使用了-lrt。请帮我解决这个问题。

这是我创建的代码。

#include<stdio.h>
#include<sys/ipc.h>
#include<sys/wait.h>
#include<sys/stat.h>
#include<sys/types.h>
#include<fcntl.h>
#include<errno.h>
#include<semaphore.h>
#include<unistd.h>
#include<math.h>
#include<stdlib.h>

#define BUFFER_SIZE 100
#define BUFFER_SUB 2

typedef struct
{
    int bufMax;
    int datalimit;
    int buff[BUFFER_SIZE];
    sem_t mutex, empty, full;

} shared_inputs;
typedef struct
{
        int sub[BUFFER_SUB];
        sem_t mutex,empty,full;
}sub_tot;

int main(int argc, char *argv[])
{
    int x = 0;
    int data,count,i,j,tot;
    int n;
    int k =atoi(argv[2]);
    int assign_size;
    count = tot =0;




    int segment_id;
        size_t segment_size = sizeof(shared_inputs);
        segment_id = shmget(IPC_PRIVATE,segment_size,IPC_CREAT|0666);
        shared_inputs *shared_memory = shmat(segment_id,NULL,0);

    sem_init(&shared_memory->mutex,1,1);
        sem_init(&shared_memory->empty,1,BUFFER_SIZE);
        sem_init(&shared_memory->full,1,0);



    int segment_idSubs;
        size_t segment_size1 = sizeof(sub_tot);
        segment_idSubs = shmget(IPC_PRIVATE,segment_size1,IPC_CREAT|0666);
        sub_tot *subtotal = shmat(segment_idSubs,NULL,0);

    sem_init(&subtotal->mutex,1,1);
        sem_init(&subtotal->empty,1,BUFFER_SUB);
        sem_init(&subtotal->full,1,0);

    FILE *numFile;
    numFile = fopen(argv[1], "r");



    while(!feof(numFile))
        {
        fscanf(numFile,"%d",&data);
                sem_wait(&shared_memory->empty);
                sem_wait(&shared_memory->mutex);
                shared_memory->buff[x] = data;
                sem_post(&shared_memory->mutex);
                sem_post(&shared_memory->full);
        printf("%d ", shared_memory->buff[x]);
                x++;
        n = x;

        }
    assign_size = ceil((double)n/(double)k);
    printf("\n");
    shared_memory->datalimit = 0;
    shared_memory->bufMax = n-1;
    printf("assigned size : %d \n", assign_size);
    printf("n : %d , k : %d \n",n,k);


    for(i =0; i < k; i++)
    {
        int id;
        int subt = 0;

        id = fork();
        if(id < 0) // error in fork
        {
            perror("Error in fork ");
            exit(300);
        }
        else if(id == 0)//the new child process
        {


            for(j=0;j< assign_size; j++)//getting items from the shared memory
            {

                sem_wait(&shared_memory->full);
                                sem_wait(&shared_memory->mutex);
                                int num = shared_memory->buff[shared_memory->datalimit];
                //printf("%d \n",shared_memory->buff[shared_memory->datalimit]);
                shared_memory->datalimit++;
                                sem_post(&shared_memory->mutex);
                                sem_post(&shared_memory->empty);
                                subt = subt + num;
                if(shared_memory->datalimit == shared_memory->bufMax)
                {
                    break;
                }

            }

            int pid = getpid();
                        sem_wait(&subtotal->empty);
                        sem_wait(&subtotal->mutex);
                        subtotal->sub[0] = pid;
                        subtotal->sub[1] = subt;
                        sem_post(&subtotal->mutex);
                        sem_post(&subtotal->full);
            printf("Sub-total produced by Processor with ID %d: %d \n",pid,subt);

            exit(0);
        }
        else//parent process
        {
            int status;
                        wait(&status);
                        sem_wait(&subtotal->full);
                        sem_wait(&subtotal->mutex);
                        int sub = subtotal->sub[1];
                        sem_post(&subtotal->mutex);
                        sem_post(&subtotal->empty);
                        tot = tot+sub;
        }
    }
    printf("Total: %d \n",tot);


    return 0;

}

Answer 1

编译时需要加上-lpthread，同时使用-lm和-lrt。

Answer 2

您需要添加 #include <pthread.h> 才能使其正常工作

为什么用共享内存编译C代码会报错"undefined reference to 'sem_init' "

Why do I get an error "undefined reference to 'sem_init' " when I compile C code with shared memory

c

shared-memory

semaphore