sdenter(2XNX)       (XENIX System Compatibility)       sdenter(2XNX)


       NAME
             sdenter, sdleave - (XENIX) synchronize access to a shared data
             segment

       SYNOPSIS
             cc [flag . . . ] flag . . . -lx
             #include <sys/sd.h>
             int sdenter(char *addr, int flags);
             int sdleave(char *addr);

       DESCRIPTION
             sdenter is used to indicate that the current process is about
             to access the contents of a shared data segment.  The actions
             performed depend on the value of flags.  flags values are
             formed by OR-ing together entries from the following list:

             SD_NOWAIT   If another process has called sdenter but not
                         sdleave for the indicated segment, and the segment
                         was not created with the SD_UNLOCK flag set,
                         return an ENAVAIL error instead of waiting for the
                         segment to become free.

             SD_WRITE    Indicates that the process wants to write data to
                         the shared data segment.  A process that has
                         attached to a shared data segment with the
                         SD_RDONLY flag set will not be allowed to enter
                         with the SD_WRITE flag set.

             sdleave is used to indicate that the current process is done
             modifying the contents of a shared data segment.

             Only changes made between invocations of sdenter and sdleave
             are guaranteed to be reflected in other processes.  sdenter
             and sdleave are very fast; consequently, it is recommended
             that they be called frequently rather than leave sdenter in
             effect for any period of time.  In particular, system calls
             should be avoided between sdenter and sdleave calls.

             The fork system call is forbidden between calls to sdenter and
             sdleave if the segment was created without the SD_UNLOCK flag.

          Return Values
             Successful calls return 0.  Unsuccessful calls return -1 and
             set errno to indicate the error.  errno is set to EINVAL if a
             process does an sdenter with the SD_WRITE flag set and the
             segment is already attached with the SD_RDONLY flag set.


                           Copyright 1994 Novell, Inc.               Page 1

      sdenter(2XNX)       (XENIX System Compatibility)       sdenter(2XNX)


            errno is set to ENAVAIL if the SD_NOWAIT flag is set for
            sdenter and the shared data segment is not free.

      REFERENCES
            sdget(2XNX), sdgetv(2XNX)











































                          Copyright 1994 Novell, Inc.               Page 2