进程间通讯(六).semaphore and shared（3）

EINVAL：参数size小于SHMMIN或大于SHMMAX

EEXIST：预建立key所指的共享内存，但已经存在

EIDRM：参数key所指的共享内存已经删除

ENOSPC：超过了系统允许建立的共享内存的最大值(SHMALL)

ENOENT：参数key所指的共享内存不存在，而参数shmflg未设IPC_CREAT位

EACCES：没有权限

ENOMEM：核心内存不足

/* Attach shared memory segment.  */
extern void *shmat (int __shmid, __const void *__shmaddr, int __shmflg)
     __THROW;

EACCES：无权限以指定方式连接共享内存

EINVAL：无效的参数shmid或shmaddr

ENOMEM：核心内存不足

/* Get semaphore.  */
extern int semget (key_t __key, int __nsems, int __semflg) __THROW;

EACCESS：没有权限

EEXIST：信号量集已经存在，无法创建

EIDRM：信号量集已经删除

ENOENT：信号量集不存在，同时semflg没有设置IPC_CREAT标志

ENOMEM：没有足够的内存创建新的信号量集

ENOSPC：超出限制

/* Operate on semaphore.  */
extern int semop (int __semid, struct sembuf *__sops, size_t __nsops) __THROW;

E2BIG：一次对信号量个数的操作超过了系统限制

EACCESS：权限不够

EAGAIN：使用了IPC_NOWAIT，但操作不能继续进行

EFAULT：sops指向的地址无效

EIDRM：信号量集已经删除

EINTR：当睡眠时接收到其他信号

EINVAL：信号量集不存在,或者semid无效

ENOMEM：使用了SEM_UNDO，但无足够的内存创建所需的数据结构

ERANGE：信号量值超出范围

/* Detach shared memory segment.  */
extern int shmdt (__const void *__shmaddr) __THROW;

EINVAL：无效的参数shmaddr

/* Semaphore control operation.  */
extern int semctl (int __semid, int __semnum, int __cmd, ...) __THROW;

/* Commands for `semctl'.  */
#define GETPID          11              /* get sempid */
#define GETVAL          12              /* get semval */
#define GETALL          13              /* get all semval's */
#define GETNCNT         14              /* get semncnt */
#define GETZCNT         15              /* get semzcnt */
#define SETVAL          16              /* set semval */
#define SETALL          17              /* set all semval's */

/* The user should define a union like the following to use it for arguments
   for `semctl'.

   union semun
   {
     int val;                           <= value for SETVAL
     struct semid_ds *buf;              <= buffer for IPC_STAT & IPC_SET
     unsigned short int *array;         <= array for GETALL & SETALL
     struct seminfo *__buf;             <= buffer for IPC_INFO
   };

   Previous versions of this file used to define this union but this is
   incorrect.  One can test the macro _SEM_SEMUN_UNDEFINED to see whether
   one must define the union or not.  */

/* Data structure describing a set of semaphores.  */
struct semid_ds
{
  struct ipc_perm sem_perm;             /* operation permission struct */
  __time_t sem_otime;                   /* last semop() time */
  unsigned long int __unused1;
  __time_t sem_ctime;                   /* last time changed by semctl() */
  unsigned long int __unused2;
  unsigned long int sem_nsems;          /* number of semaphores in set */
  unsigned long int __unused3;
  unsigned long int __unused4;
};

struct  seminfo
{
  int semmap;
  int semmni;
  int semmns;
  int semmnu;
  int semmsl;
  int semopm;
  int semume;
  int semusz;
  int semvmx;
  int semaem;
};

/* Shared memory control operation.  */
extern int shmctl (int __shmid, int __cmd, struct shmid_ds *__buf) __THROW;

EACCESS：参数cmd为IPC_STAT，确无权限读取该共享内存

EFAULT：参数buf指向无效的内存地址

EIDRM：标识符为msqid的共享内存已被删除

EINVAL：无效的参数cmd或shmid

EPERM：参数cmd为IPC_SET或IPC_RMID，却无足够的权限执行

/* Control commands for `msgctl', `semctl', and `shmctl'.  */
#define IPC_RMID        0               /* Remove identifier.  */
#define IPC_SET         1               /* Set `ipc_perm' options.  */
#define IPC_STAT        2               /* Get `ipc_perm' options.  */
#ifdef __USE_GNU
# define IPC_INFO       3               /* See ipcs.  */
#endif

/* Data structure describing a shared memory segment.  */
struct shmid_ds
  {
    struct ipc_perm shm_perm;           /* operation permission struct */
    size_t shm_segsz;                   /* size of segment in bytes */
    __time_t shm_atime;                 /* time of last shmat() */
#if __WORDSIZE == 32
    unsigned long int __unused1;
#endif
    __time_t shm_dtime;                 /* time of last shmdt() */
#if __WORDSIZE == 32
    unsigned long int __unused2;
#endif
    __time_t shm_ctime;                 /* time of last change by shmctl() */
#if __WORDSIZE == 32
    unsigned long int __unused3;
#endif
    __pid_t shm_cpid;                   /* pid of creator */
    __pid_t shm_lpid;                   /* pid of last shmop */
    shmatt_t shm_nattch;                /* number of current attaches */
    unsigned long int __unused4;
    unsigned long int __unused5;
  };

/* Data structure used to pass permission information to IPC operations.  */
struct ipc_perm
  {
    __key_t __key;                      /* Key.  */
    __uid_t uid;                        /* Owner's user ID.  */
    __gid_t gid;                        /* Owner's group ID.  */
    __uid_t cuid;                       /* Creator's user ID.  */
    __gid_t cgid;                       /* Creator's group ID.  */
    unsigned short int mode;            /* Read/write permission.  */
    unsigned short int __pad1;
    unsigned short int __seq;           /* Sequence number.  */
    unsigned short int __pad2;
    unsigned long int __unused1;
    unsigned long int __unused2;
  };