Saturday, February 16, 2013

Process (notes)

 

- a program in execution
- a process contains -> program counter, process stacks & data section.

- process memory layout

Command Line Aruguments

Stack
Stack grows down & Heap grows Up
Heap
Data section (includes BSS)
Text section

    CLA - command line arguments,stored at higher address
    stack - local variables & other info (return info,machine register) stored. In each recursive call, new stack frame is created.
    headp - dynamic memory allocation, shared to all process.
    BSS - Block started by symbol (uninitialized global data)
    data segment - initialized global variables
    text - contains machine instrucitons that cpu executes, shared across various instances of same program. (read only privileges, avoid rewriting)

- process states

process_state_diagram
    new - a process being created
    ready - instructions are executed
    waiting - waiting for some event
    running - waiting to be assigned to processor
    terminate(done) - process has finished

- zombie process – system is referencing the process even if process is  terminated.

- info associated with each process
    Process state
    Program counter
    CPU registers
    CPU scheduling information
    Memory-management information
    Accounting information
    I/O status information

- process queues - job , ready , device
- process scheduler
    - Long term (job) - selects which process to put in ready queue (frequent invoked - very fast)
    - Short term (cpu) - selects which process to execute & allocate CPU (infrequently invoked - very slow)
   
- context switch
    - switching from one process to another, system saves the state of the one process & load the state of new process

- processes can be independent or cooperating
- cooperating process need IPC - shared memory , message passing
    - advantage for co-operating process
        - info sharing
        - computation speedup
        - convenient
        - modularity

    - message passing
        - send /recieve
        - establish connection
        - blocking send / non-blocking
    - shared memory
        - producer consumer problem

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