20180917
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What is a process?
A running program, including its machine state

What's part of a process's machine state?
Process state
PID
Address space - the memory the process
Registers
* Program counter
* Stack pointer
* Frame pointer

With time sharing (multiprogramming), the OS switches between processes every 10-100 millisecond
Pseudo-parallelism
True parallelism requires a multi-processors system

What is the API in the OS for a process:
-----------
Create
Destroy
Wait
Control
+ Kill
+ Suspend
+ Etc.
Status

Process Creation
~~~~~~~~~~~~~~~~~~~~~~
Processes are created when:
1) System initialization
2) The user requests a new process 
3) A running process wants help (e.g., using fork())
4) Starting a batch job (only on mainframes)

OS steps to run a program
-----------
Load (from disk) the code and any static data (initialized variables) into memory
Allocate memory for the stack
Initialize the stack (with argc and argv)
Allocate some memory for the heap
Setup file descriptors (stdin, stdout, stderr)
Start executing main()

Process Hierarchies
-----------
UNIX: init starts running after booting, a new process for each terminal, builds a process tree
Windows: No process hierarchy, but a parent process is given a special token (handle) to control the child process

Process Termination
-----------
Processes are terminated when:
1) Normal completion
   exit() or ExitProcess()
2) Error
3) Fatal error (involuntary)
4) Killed (involuntary)
   kill() or TerminateProcess()

Process States
~~~~~~~~~~~~~~~~~~~~~~
Exercise

Process Table
~~~~~~~~~~~~~~~~~~~~~~
OS tracks processes in the process table (aka Process Control Block (PCB))
Stores a process's
+ Program counter
+ Stack pointer
+ Memory allocation
+ Open files
+ Scheduling information
+ etc.

Process API
~~~~~~~~~~~~~~~~~~~~~~
How many lines will be printed?

#include <stdio.h>
#include <unistd.h>
int main(){

    fork();
    fork();
    fork();

    fprintf(stderr, "All done!\n");
    return 0;
}


20180919
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UNIX Commands: ../unixCommands.txt


Process API
~~~~~~~~~~~~~~~~~~~~~~

fork()
-----------
Makes a clone of the current process (with the same memory image, environment strings and open files)
Memory is mapped so that it only makes a copy when the child writes to (changes) its memory
The child generally calls exec() and replaces the memory