Inter Process Communication

• Inter-process Communication (IPC)


  Processes executing concurrently in the operating system may be either independent processes or cooperating processes
• Independent process


  Does not share data with any other processes executing in the system
• Cooperating process


  Can affect or be affected by the other processes executing in the system
• Reasons for Process Cooperation

  • Information sharing
  • Computation speedup
  • Modularity
  • Convenience
• Shared memory


  A region of memory that is shared by the cooperating processes
• Message passing


  Provides a mechanism to allow processes to communicate and to synchronize their actions without sharing the same address space
• Producer-Consumer Problem


  1. Producer process produces information that is consumed by a consumer process

  2. Shared memory is one solution to the producer-consumer problem
• Issues with Producer-Consumer Model
• Message Passing


  Provides at least two operations: send(message) and receive(message)
• Methods for implementing communication link in message passing

  • Direct communication
  • Indirect communication
• Direct communication


  Each process that wants to communicate must explicitly name the recipient or sender of the communication
• Indirect communication


  Messages are sent to and received from mailboxes, or ports
• If processes P1, P2, and P3 all share mailbox A, and P1 sends a message to A while both P2 and P3 execute a receive() from A, the system may define an algorithm for selecting which process will receive the message
• Blocking send


  The sending process is blocked until the message is received by the receiving process or by the mailbox
• Nonblocking send


  The sending process sends the message and resumes operation
• Blocking receive


  The receiver blocks until a message is available
• Nonblocking receive


  The receiver retrieves either a valid message or a null
• Ways to implement message queues

  • Zero capacity
  • Bounded capacity
  • Unbounded capacity
• Message Passing in Windows OS

  Windows provides support for multiple operating environments, or subsystems, and application programs communicate with these subsystems via a message-passing mechanism
• Advanced local procedure calls (ALPC) in Windows

  Used for communication between two processes on the same machine, similar to remote procedure call (RPC) but optimized for Windows
• When an ALPC channel is created, one of three message-passing techniques is chosen: 1) For small messages, the port's message queue is used, 2) Larger messages must be passed through a section object, 3) For very large data, an API is available to allow server processes to read and write directly into the address space of a client