[英]How to use struct in POSIX shared memory?
我希望我的 POSIX 共享內存段符合特定結構。 我認為這段代碼以結構體的形式創建了共享內存段。
(File creating the shared memory segment)
typedef struct {
int cnt;
char buf[segsize];
} shmseg_t;
int shm_fd = shm_open(shm_name, O_CREAT | O_RDWR, 0666);
ftruncate(shm_fd, sizeof(shmseg_t);
void* addr = mmap(NULL, sizeof(shmseg_t), PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
如何將文件中的數據寫入共享內存中結構的不同字段?
(File writing to the shared memory segment)
int shm_fd = shm_open(shm_name, O_WRONLY, 0);
ftruncate(shm_fd, segsize);
void* addr = mmap(NULL, segsize, PROT_WRITE, MAP_SHARED, shm_fd, 0);
// How do I get shmp, which should be a shmseg_t struct?
shmp->cnt = read(fd, shmp->buf, segsize);
以及如何取出寫入共享內存中結構的數據?
(File reading from the shared memory segment)
int shm_fd = shm_open(shm_name, O_RDONLY, 0);
ftruncate(shm_fd, segsize);
void* addr = mmap(NULL, segsize, PROT_READ, MAP_SHARED, shm_fd, 0);
// How to get out shmp->cnt and shmp->buf?
目前還不清楚您是要共享整個結構還是只是buf
。
選項 1:使buf
成為一個指針,並共享它指向的內容。
typedef struct {
int cnt;
char *buf;
} shmseg_t;
ftruncate(shm_fd, segsize);
void* addr = mmap(NULL, segsize,
PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
assert(addr != MAP_FAILED);
shm_seg_t shmp = {
.cnt = ???, // Whatever value of cnt you want.
.buf = addr,
};
選項 2:共享整個結構。
typedef struct {
int cnt;
char buf[segsize];
} shmseg_t;
ftruncate(shm_fd, sizeof(shmseg_t));
void* addr = mmap(NULL, sizeof(shmseg_t),
PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
assert(addr != MAP_FAILED);
shm_seg_t *shmp = addr;
如果以這種方式共享,讀取和寫入並沒有真正不同(但您確實需要使用內存屏障或同步)。
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