HPUX shmop[2]

 shmop(2)                                                           shmop(2)





 NAME
      shmat, shmdt - shared memory operations

 SYNOPSIS
      #include <sys/shm.h>

      char *shmat(int shmid, void *shmaddr, int shmflg);

      int shmdt(void *shmaddr);

 DESCRIPTION
      shmat() attaches the shared memory segment associated with the shared
      memory identifier specified by shmid to the data segment of the
      calling process.

      Series 700/800 Systems
           If the shared memory segment is not already attached, shmaddr
           must be specified as zero and the segment is attached at a
           location selected by the operating system.  That location is
           identical in all processes accessing that shared memory object.

           If the shared memory segment is already attached, a non-zero
           value of shmaddr is accepted, provided the specified address is
           identical to the current attach address of the segment.

      Series 300/400 Systems
           shmaddr can be specified as a non-zero value as a machine-
           dependent extension (see DEPENDENCIES below).  However, those
           systems do not necessarily guarantee that a given shared memory
           object appears at the same address in all processes that access
           it, unless the user specifies an address.

           The segment is attached for reading if (shmflg & SHM_RDONLY) is
           ``true''; otherwise it is attached for reading and writing.  It
           is not possible to attach a segment for write only.

      shmdt() detaches from the calling process's data segment the shared
      memory segment located at the address specified by shmaddr.

 RETURN VALUE
      Upon successful completion, the return value is as follows:

           shmat() returns the data segment start address of the attached
           shared memory segment.

           shmdt() returns a value of 0; otherwise, a value of -1 is
           returned and errno is set to indicate the error.

 ERRORS
      shmat() fails and does not attach the shared memory segment if any of
      the following conditions are encountered (see DEPENDENCIES):



 Hewlett-Packard Company            - 1 -     HP-UX Release 9.0: August 1992






 shmop(2)                                                           shmop(2)





           [EINVAL]       shmid is not a valid shared memory identifier.

           [EACCES]       Operation permission is denied to the calling
                          process.

           [ENOMEM]       The available data space is not large enough to
                          accommodate the shared memory segment.

           [EINVAL]       shmaddr is not zero and the machine does not
                          permit non-zero values or shmaddr is not equal to
                          the current attach location for the shared memory
                          segment.

           [EMFILE]       The number of shared memory segments attached to
                          the calling process exceed the system-imposed
                          limit.

      shmdt() fails and returns -1 if the following condition is
      encountered:

           [EINVAL]       shmaddr is not the data segment start address of a
                          shared memory segment.

 EXAMPLES
      The following call to shmat attaches the shared memory segment to the
      process.  This example assumes the process has a valid shmid, which
      can be obtained by calling shmget(2).

           char *shmptr, *shmat();
           shmptr = shmat(myshmid, (char *)0, 0);

      The following call to shmdt() then detaches the shared memory segment.

           shmdt (shmptr);

 DEPENDENCIES
    Series 300/400
      shmaddr can be non-zero, and if it is, the segment is attached at the
      address specified by one of the following criteria:

      If shmaddr is equal to zero, the segment is attached at the first
      available address as selected by the system.  The selected value
      varies for each process accessing that shared memory object.

      If shmaddr is not equal to zero and (shmflg & SHM_RND) is ``true'',
      the segment is attached at the address given by (shmaddr - (shmaddr %
      SHMLBA)).  The character % is the C language modulus operator.

      If shmaddr is not equal to zero and (shmflg & SHM_RND) is ``false'',
      the segment is attached at the address given by shmaddr.




 Hewlett-Packard Company            - 2 -     HP-UX Release 9.0: August 1992






 shmop(2)                                                           shmop(2)





      This form of shmat() fails and does not attach the shared memory
      segment if any of the following conditions are encountered:

           [EACCES]       shmid is the ID of a shared memory segment
                          currently being used by the system to implement
                          other features (see graphics(7) and iomap(7)).

           [EINVAL]       shmaddr is not equal to zero, and the value of
                          (shmaddr - (shmaddr % SHMLBA)) is an illegal
                          address.

           [EINVAL]       shmaddr is not equal to zero, (shmflg & SHM_RND)
                          is ``false'', and the value of shmaddr is an
                          illegal address.

           [ENOMEM]       The calling process is locked (see plock(2)) and
                          there is not sufficient lockable memory to support
                          the process-related data structure overhead.

    Series 700/800
      shmat() fails and returns -1 if the following is encountered:

           [EINVAL]       The calling process is already attached to shmid.

 SEE ALSO
      ipcs(1), exec(2), exit(2), fork(2), shmctl(2), shmget(2), stdipc(3C).

 STANDARDS CONFORMANCE
      shmat(): SVID2 [Series 300/400 only], XPG2, XPG3, XPG4

      shmdt(): SVID2, XPG2, XPG3, XPG4























 Hewlett-Packard Company            - 3 -     HP-UX Release 9.0: August 1992