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Processes (Communication (Communication link (Properties (Link associated…

- - - - Physical
        
        Hardware bus
        
        Network
        
        Shared memory
      - Logical
        
        Synchronous or asynchronous
        
        Automatic or explicit buffering
        
        Direct or indirect
    - - Link associated with exactly one pair of communicating proccesses
      - Between each pair exists only one link
      - Links are established automatically
      - Link may be unidirectional or bi-directional
    - - Each mailbox has a unique id
      - Processes can communicate only if they share a mailbox
    - - Queue of messages attached to the link
      - Implementation
        
        Bounded capacity
        
        Finite length of n messages
        
        Sender must wait if link full
        
        Unbounded capacity
        
        Infinite length
        
        Sender never waits
        
        Zero capacity
        
        No messages are queued on a link
        
        Sender must wait for receiver
  - - - Blocking
        
        Synchronous
        
        Blocking send: sender blocked until message is received
        
        Blocking receive: receiver blocked until message is available
      - Non-blocking
        
        Non-blocking send: sends message and continues
        
        Asynchronous
        
        Non-blocking receive
        
        Valid message
        
        Null message
  - - - System on which process is running
  - - - Client-side proxy for actual procedure on the server
  - - - Unidirectional
      - Parent creates pipe & communicates with a child
      - Can't be accessed from outside the process that created it
    - - Can be accessed without a parent-child relationship
      - Several processes can use it
      - Bidrectional
- - - - Contains temporary data
        
        Return addresses
        
        Local variables
        
        Function parameters
    - - Contains memory dinamically allocated
  - - - Waiting for some event
    - - Waiting to be assigned to a CPU
    - - Instructions are being executed
    - - Finished execution
    - - Being created
  - - - Priorities
      - Scheduling queue pointers
    - - Memory allocated to the process
    - - Content of registers
    - - CPU used
      - Clock time elapsed
      - Time limits
    - - Location of next instruction
    - - Devices
      - Open files
- - - - Ready queue
        
        All processes in main memory
        
        Ready
        
        Waiting
      - Device queues
        
        Processes waiting for an I/O
      - Job queue
        
        All processes in the system
  - - - Selects next process & allocates CPU
      - Sometimes the only scheduler
      - CPU scheduler
      - Invoked frequently
        
        Must be fast
    - - Selects processes for the ready queue
      - Invoked infrequently
      - Job scheduler
      - Controls the degree of multiprogramming
    - - If degree of multiple programming needs to decrease
      - Swapping
        
        Remove process from memory, store on disk, bring back from disk
  - - - Spends more time doing I/O than computations
        
        Short CPU bursts
    - - Spends more time doing computations
        
        Very long CPU bursts
- - - - Save & load state