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Chapter 3 Processes, Implementation of Communication Link - Coggle Diagram

- - - - Function parameters, return addresses, local variables
- - - - Blocking is considered synchronous
        
        Blocking send -- the sender is blocked until the message is received
        
        Blocking receive -- the receiver is blocked until a message is available
      - Non-blocking is considered asynchronous
        
        Non-blocking receive -- the receiver receives:
        
        A valid message, or Null message
        
        Non-blocking send -- the sender sends the message and continue
      - Different combinations possible
        
        If both send and receive are blocking, we have a rendezvous
        
        Producer Consumer Message Passing
        
        Producer
        
        Power Point Chapter 3 Slide 49
        
        Consumer
        
        Power Point Chapter 3 Slide 49
  - - - Power Point Chapter 3 Slide 33-35
    - - 1.
        Suppose that we wanted to provide a solution to the consumer-producer problem that fills all the buffers.
      - 2.
        We can do so by having an integer counter that keeps track of the number of full buffers.
      - 3.
        Initially, counter is set to 0.
      - 4.
        The integer counter is incremented by the producer after it produces a new buffer.
      - 5.
        The integer counter is and is decremented by the consumer after it consumes a buffer.
    - - Power Point Chapter 3 slide 37
    - - Power Point Chapter 3 slide 38
    - - Power Point Chapter 3 slide 39-40
- - - - Establish a communication link between them
      - Exchange messages via send/receive
    - - How many links can there be between every pair of communicating processes?
      - What is the capacity of a link?
      - Can a link be associated with more than two processes?
      - Is the size of a message that the link can accommodate fixed or variable?
      - How are links established?
      - Is a link unidirectional or bi-directional?
- - - - ready
        
        running
        
        terminated
        
        waiting
        
        exit
        
        I/O or event wait
        
        admitted
        
        scheduler dispatch
        
        interrupt
        
        I/O or event completion
- - - - Runs in sandbox restricting disk and network I/O, minimizing effect of security exploits
- - - - Computation speed-up
      - Modularity
      - Information sharing
      - Convenience
  - - - Producer never waits
      - Consumer waits if there is no buffer to consume
    - - Producer must wait if all buffers are full
      - Consumer waits if there is no buffer to consume
- - - - Multiple locations can execute at once
        
        Multiple threads of control -> threads
        
        Must then have storage for thread details, multiple program counters in PCB
- - - - Generally, process identified and managed via a process identifier (pid)
      - Resource sharing options
        
        Children share subset of parent’s resources
        
        Parent and child share no resources
        
        Parent and children share all resources
      - Parent process create children processes, which, in turn create other processes, forming a tree of processes
      - Execution options
        
        Parent and children execute concurrently
        
        Parent waits until children terminate
      - UNIX examples
        
        fork() system call creates new process
        
        exec() system call used after a fork() to replace the process’ memory space with a new program
        
        Parent process calls wait()waiting for the child to terminate
      - Address space
        
        Child duplicate of parent
        
        Child has a program loaded into it
    - - Process executes last statement and then asks the operating system to delete it using the exit() system call.
        
        Returns status data from child to parent (via wait())
        
        Process’ resources are deallocated by operating system
      - Parent may terminate the execution of children processes using the abort() system call. Some reasons for doing so:
        
        Task assigned to child is no longer required
        
        The parent is exiting, and the operating systems does not allow a child to continue if its parent terminates
        
        Child has exceeded allocated resources
      - Some operating systems do not allow child to exists if its parent has terminated. If a process terminates, then all its children must also be terminated.
        
        cascading termination. All children, grandchildren, etc., are terminated.
        
        The termination is initiated by the operating system.
      - The parent process may wait for termination of a child process by using the wait()system call. The call returns status information and the pid of the terminated process
        
        pid = wait(&status);
      - If no parent waiting (did not invoke wait()) process is a zombie
      - If parent terminated without invoking wait(), process is an orphan
- - - - Solutions
        
        Allow only one process at a time to execute a receive operation
        
        Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was.
        
        Allow a link to be associated with at most two processes