RFC 62 (rfc62) - Page 3 of 20

Systems for Interprocess Communication in a Resource Sharing Computer Network

RFC 62                  IPC for Resource Sharing          3 August 1970


   system processes as being locked in core.

   Although they will be of concern later in this study, protection
   considerations are not my concern here: instead I will assume that
   all of the processes are "good" processes which never made any
   mistakes.  If the reader needs a protection structure to keep in mind
   while he reads this note, the capability system developed in
   [1][3][7][8] should be satisfying.

   Of the operations a process can call on the monitor to perform, six
   are of particular interest for providing a capability for
   interprocess communication.

   RECEIVE. This operation allows a specified process to send a message
   to the process executing the RECEIVE. The operation has four
   parameters: the port (defined below) awaiting the message -- the
   RECEIVE port; the port a message will be accepted from -- the SEND
   port; a specification of the buffer available to receive the message;
   and a location to transfer to when the transmission is complete --
   the restart location.

   SEND.  This operation sends a message from the process executing the
   SEND to a specified process.  It has four parameters: a port to send
   the message to -- the RECEIVE port; the port the message is being
   sent from -- the SEND port; a specification of the buffer containing
   the message to be sent; and the restart location.

   RECEIVE ANY.  This operations allows any process to send a message to
   the process executing the RECEIVE ANY.  The operation has four
   parameters: the port awaiting the message -- the RECEIVE port; a
   specification of the buffer available to receive the message; a
   restart location; and a location where the port which sent the
   message may be noted.

   SEND FROM ANY.  This operation allows a process to send a message to
   a process able to receive a message from any process.  It has the
   same four parameters as SEND.  (The necessity for this operation will
   be explained much later).

   SLEEP.  This operation allows the currently running process to put
   itself to sleep pending the completion of an event.  The operation
   has one optional parameter, an event to be waited for.  An example
   event is the arrival of a hardware interrupt.  The monitor never
   unilaterally puts a process to sleep as a result of the process
   executing one of the above four operations; however, if a process is
   asleep when one of the above four operations is satisfied, the
   process is awakened.




Walden