从/向c中的共享内存读写int

Question

我正在尝试制作一个程序，其中一个线程将一个整数写入共享内存位置，然后另一个线程读取并打印该整数。我面临的问题是第二个线程不断读取整数为-1。这是我的代码：

#include <stdio.h> 
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h> 
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <string.h>


struct args {
    void* memptr;
    sem_t* semptr;
};

void *p1(void *vargp) 
{
    void* memory = ((struct args*)vargp)->memptr;
    sem_t* semaphore = ((struct args*)vargp)->semptr;
    //sem_wait(semaphore);
    //sleep(0.5);
    for(int i=0; i<=10; i++)
    {
        if (!sem_wait(semaphore)) {
            printf("got in if p1\n");
            sprintf(memory, "%d", i);
            sem_post(semaphore);
            sleep(1);
        }
    }
    if (!sem_wait(semaphore)) {
        sprintf(memory, "%d", 0);
        sem_post(semaphore);
        sleep(1);
    }
    sleep(0.1);
}

void *p2(void *vargp) 
{
    void* memory = ((struct args*)vargp)->memptr;
    sem_t* semaphore = ((struct args*)vargp)->semptr;
    sleep(0.1);
    while(1)
    {
        if (!sem_wait(semaphore)) {
            printf("got in if p2\n");
            if((int)memory == 0){
                break;
            }
            printf("%d\n", (int)memory);
            sem_post(semaphore);
            sleep(1);
        }
    }
} 

const int ByteSize = 4;
const char* SharedName = "memNameTest";
const char* SemaphoreName = "semNameTest";


int main() 
{   
    int fd = shm_open(SharedName, O_RDWR, 0644);
    ftruncate(fd, ByteSize);
    void* memptr = mmap(0, ByteSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    sem_t* semptr = sem_open(SemaphoreName, O_CREAT, 0644, 0);
    sem_post(semptr);
    struct args *Share = (struct args *)malloc(sizeof(struct args));
    Share->memptr = memptr;
    Share->semptr = semptr;

    pthread_t thread1, thread2; 
    printf("Before Thread\n"); 
    pthread_create(&thread1, NULL, p1, (void*)Share);
    pthread_create(&thread2, NULL, p2, (void*)Share);
    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);
    printf("After Thread\n");



    munmap(memptr, ByteSize);
    close(fd);
    sem_close(semptr);
    unlink(SharedName);
    return 0;
    exit(0); 
}

我曾尝试将(int)memory更改为*((int*)memory)，但导致分段错误。

（编辑）按照建议，我在单线程程序中对此进行了尝试，并使其如下工作：

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h> 
#include <unistd.h>
#include <string.h>

int main()
{

    /* the size (in bytes) of shared memory object */
    const int SIZE = 4;
    /* name of the shared memory object */
    const char* SharedName = "memoryInt";
    /* create the shared memory object */
    int shm_fd = shm_open(SharedName, O_CREAT | O_RDWR, 0644);
    /* configure the size of the shared memory object */
    ftruncate(shm_fd, SIZE);
    /* memory map the shared memory object */
    void* memptr = mmap(0, SIZE, PROT_WRITE, MAP_SHARED, shm_fd, 0); 

    for(int i=1; i<=10; i++){
        /* write to the shared memory object */
        //sprintf(memptr, "%d", i);
        memcpy(memptr, &i, sizeof(int));
        printf("%d\n", *((int*)memptr));
        sleep(1);
    }

    return 0;
}

尽管这在多线程程序中仍然不起作用，因为出现分段错误。这是输出：

Before Thread
got in if p1
Segmentation fault

Answer 1

首先，您必须在编译程序时显示终端上发生的情况。其次，函数sprintf具有以下声明：

sprintf(char *str, const char *format, ...);

这意味着p1将写入以null结尾的字符串。在您的代码中，我不明白为什么您使用空指针memory而不是使用char指针作为描述。在应用到多线程之前，应该使用单线程来验证读/写功能。