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[英]Establishing shared memory between different processes with limited resources?
[英]Different shared memory values between processes
我通过这个函数创建了一个缓冲区。
int create_buffer(const char *shmem_name, void **shmem_obj)
{
int returnval = 0;
int fd;
fd = shm_open(shmem_name, O_CREAT | O_RDWR, 0666);
ftruncate(fd, sizeof(ShareStruct));
*shmem_obj = (ShareStruct *)mmap(NULL, sizeof(ShareStruct), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (shmem_obj < 0)
{
returnval = -1;
}
return returnval;
}
然后当我在进程 1 中使用指针及其函数时,一切正常。
在进程 2 中,我使用此函数获取缓冲区:
int fetch_buffer(const char *shmem_name, void **shmem_obj)
{
int returnval = 0;
int fd;
fd = shm_open(shmem_name, O_RDWR, 0666);
ftruncate(fd, sizeof(ShareStruct));
*shmem_obj = (ShareStruct *)mmap(NULL, sizeof(ShareStruct), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (shmem_obj < 0)
{
returnval = -1;
}
printf("buffer fetched \n");
return returnval;
}
但是缓冲区的内容不同(奇怪的值)。
我究竟做错了什么?
编辑:
流程1代码:
#define SHMEM_NAME "OS"
int main(void) {
int exitcode = 0;
void *shmem_obj;
/* Initialize the buffer and create the shared memory */
if( create_buffer(SHMEM_NAME, &shmem_obj) != 0) {
fprintf(stderr, "Something went wrong while initializing the buffer.\n");
exitcode = 1;
} else {
printf("Shared buffer created.\n");
initParameters(&shmem_obj);
subscribe(0, &shmem_obj);
printf("\n[PRESS ENTER TO CLOSE THE SHARED BUFFER]");
getchar();
/* unlink the shared memory */
if(destroy_buffer(SHMEM_NAME) != 0) {
fprintf(stderr, "Something went wrong while destroying the buffer.\n");
exitcode = 2;
} else {
printf("Shared buffer closed.\n");
}
}
return exitcode;
}
流程2代码:
#define SHMEM_NAME "OS"
int main(void) {
void *shmem_obj;
/* fetch the buffer from shared memory */
fetch_buffer(SHMEM_NAME, &shmem_obj);
subscribe(1, &shmem_obj);
printf("Subscriber 0 subscribed\n");
}
其他代码:
typedef struct ShareStruct
{
Subscriber subscriberList[20];
int subscriberActiveList[20];
unsigned int writepointer_tail;
unsigned int readpointer_head;
Task taskList[21];
sem_t freePostions;
pthread_mutex_t mutex;
unsigned int subscriberCount;
} ShareStruct;
int initParameters(void *shmem_obj)
{
ShareStruct *shmem = shmem_obj;
int returnval = 0;
shmem->writepointer_tail = 0;
shmem->readpointer_head = 0;
shmem->subscriberCount = 0;
pthread_mutex_init(&shmem->mutex, NULL);
sem_init(&shmem->freePostions, 1, 20);
return returnval;
}
int destroy_buffer(const char *shmem_name)
{
int returnval = 0;
returnval = shm_unlink(shmem_name);
return returnval;
}
int subscribe(subscriber_id subscriber, void *shmem_obj)
{
int returnval = 0;
ShareStruct *shmem = shmem_obj;
int value;
sem_getvalue(&shmem->freePostions, &value);
printf("sem value : %d\n", value);
pthread_mutex_lock(&shmem->mutex);
int freeposition = returnNextFreePosition(shmem_obj);
if (freeposition != -1)
{
printf("subscribe logic");
}
else
{
printf("Subscriber list is full \n");
}
pthread_mutex_unlock(&shmem->mutex);
return returnval;
}
问题是您在指针间接层的数量上不一致,并且您使用void *
而不是更具体的指针类型会阻止编译器意识到并告诉您您正在这样做。 将所有void *
替换为ShareStruct *
s,然后修复编译器给您的结果错误和警告,您的代码将开始工作。
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