Indirect Naming Schemes

• Do not name the process from (to) which message is received (sent), rather use an indirection
• Mailbox (VAX/VMS) - an OS structure independent of both sender and receiver.
  Permits multiple senders and receivers
  Implemented as a queue - bound or circular
  send to and receive from a queue
  
• In mailboxes : asynchronous send
  No receivers = messages queued
  No messages = receiver processes queued
  Synchronous send
  No receivers = sender process queued
  No messages = receiver process queued
• Ports or Sockets (Unix - Berkeley IPC) - data structure associated with a process
• Holds name of source or destination process (usable with any communication primitive)
• Bind(pt1,B) - places name of process in port 1 data structure
  OS picks up name when message is sent

  
Figure 6: VAX Mailboxes

  
Figure 7: Unix sockets