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MBX_$GET_CONDITIONAL              Domain/OS               MBX_$GET_CONDITIONAL


NAME
     mbx_$get_conditional - read a message without waiting

SYNOPSIS (C)
     #include <apollo/base.h>
     #include <apollo/mbx.h>

     void mbx_$get_conditional(
          void *&mbx_handle,
          void *&buffer_pointer,
          long &buffer_length,
          void **return_pointer,
          long *return_length,
          status_$t *status)

SYNOPSIS (Pascal)
     %include '/sys/ins/base.ins.pas';
     %include '/sys/ins/mbx.ins.pas';

     procedure mbx_$get_conditional(
          in mbx_handle: univ_ptr;
          in buffer_pointer: univ_ptr;
          in buffer_length: integer32;
          out return_pointer: univ_ptr;
          out return_length: integer32;
          out status: status_$t);

SYNOPSIS (FORTRAN)
     %include '/sys/ins/base.ins.ftn'
     %include '/sys/ins/mbx.ins.ftn'

           integer*4 mbx_handle, buffer_length, return_length, status

           integer*4 buffer_pointer, return_pointer
           character buffer*32766, ret_buffer*32766

           pointer /buffer_pointer/ buffer
           pointer /return_pointer/ return_buffer

           call mbx_$get_conditional(mbx_handle, buffer_pointer, buffer_length,
          &                          return_pointer, return_length, status)

DESCRIPTION
     Mbx_$get_conditional gets a message from the mailbox on mbx_handle if
     there is one.  If there is no message waiting for the caller,
     mbx_$get_conditional returns immediately with a status of
     mbx_$channel_empty.

     Both servers and clients can call mbx_$get_conditional.  When a server
     uses mbx_$get_conditional, the mailbox manager guarantees fair service to
     each open channel.

     mbx_handle
          A mailbox handle.

     buffer_pointer
          A pointer to the data buffer allocated to receive the message.
          Mbx_$get_conditional does not always use the buffer at
          buffer_pointer, but the caller must provide one.

     buffer_length
          The number of bytes available in the buffer that buffer_pointer
          points to.  Mbx_$get_conditional will not write more than
          buffer_length bytes at buffer_pointer, and cannot write more than
          mbx_$rec_data_max.

     return_pointer
          A pointer to the requested message.  Use this pointer to reference
          the message.  It is not necessarily equivalent to buffer_pointer.

     return_length
          If return_length is positive, it is the number of bytes in the mes-
          sage supplied at return_pointer, and no part of the message remains
          in the channel.  If return_length is negative, it's absolute value
          is the number of bytes from the supplied message remaining in the
          channel, and return_pointer points to only buffer_length bytes of
          the requested message.

          When called by a server, mbx_$get_conditional supplies the 6-byte
          server header each time it gets a portion of a message, so a server
          can always look at the cnt field to find out the total length of a
          message.

     status
          The completion status.