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| Linux程式設計-23.共享記憶體(Shared Memory) |
| http://www.openchess.org/noitatsko/programming/ (2001-05-27 14:08:00) |
共享記憶體是指同一塊記憶體區段被一個以上的行程所分享。這是我們所知速度最快的行程間通訊方式。使用共享記憶體在使用多CPU的機器上，會使機器發揮較佳的效能。
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#include
#include
int shmget(key_t key, int size, int shmflg);
char *shmat ( int shmid, char *shmaddr, int shmflg )
int shmdt ( char *shmaddr)
int shmctl(int shmid, int cmd, struct shmid_ds *buf);
struct shmid_ds {
struct ipc_perm shm_perm; /* operation perms */
int shm_segsz; /* size of segment (bytes) */
time_t shm_atime; /* last attach time */
time_t shm_dtime; /* last detach time */
time_t shm_ctime; /* last change time */
unsigned short shm_cpid; /* pid of creator */
unsigned short shm_lpid; /* pid of last operator */
short shm_nattch; /* no. of current attaches */
/* the following are private */
unsigned short shm_npages; /* size of segment (pages) */
unsigned long *shm_pages; /* array of ptrs to frames -> SHMMAX */
struct vm_area_struct *attaches; /* descriptors for attaches */
};
shm_perm
This is an instance of the ipc_perm structure, which is defined for us in
linux/ipc.h. This holds the permission information for the segment,
including the access permissions, and information about the creator of the
segment (uid, etc).
shm_segsz
Size of the segment (measured in bytes).
shm_atime
Time the last process attached the segment.
shm_dtime
Time the last process detached the segment.
shm_ctime
Time of the last change to this structure (mode change, etc).
shm_cpid
The PID of the creating process.
shm_lpid
The PID of the last process to operate on the segment.
shm_nattch
Number of processes currently attached to the segment.
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