CIS-332 -- Principles of Operating Systems

Professor: Franz J. Kurfess

Home page:http://www.cis.njit.edu/franz   E-mail:franz@cis.njit.edu 

Programming Assignment 1 --- Process Control Block

Introduction

This programming assigment is the first of a three-phase project to be implemented in this course. The project consists of writing a program to simulate some general aspects and services of operating systems. Each phase of the project adds to the work done in the previouse phase. Therefore, it is important that you properly document your program and that you write the code in a way that facilitates making modifications if that should become necessary. You have the choice of using Pascal or C/C++ to write your program.

Phase I

A basic structure used thoughout the program is the process control block (PCB). The PCB is a structure which the system creates when a process first arrives and which it maintains throughout the lifetime of the process. The PCB conatins all the relevent information that the system needs to keep track of a process. When a process terminates, the system deallocates its PCB. The type and amount of information stored in a PCB differs among various operating systems. In our case we will define a record type called PCB_Type with fields as shown below. In addition we will define a type called PCB_ptr as a pointer to records of type PCB_Type.

  - Next: A pointer to the next PCB in the linked list.
  - Name: The name of the process (up to 8 characters).
  - Type: A field that indicates whether the PCB is free or in use.
         If the PCB is in use then it should indicate whether it
         represents a system or a user process.

  - State: This field indicates the current state of the process.
         The possible states are: Ready, Running, or Blocked.
  - Suspend : This field indicates whether the process is currently
         suspended or not.
  - Priority: This field stores the priority of the process. This is
         a numerical value in the range  -127 to 127.

The PCB Support Subprograms:

The following seven procedures and functions are the basic operations for manipulating the PCBs. Their use will become clear in the second phase of the project.

   1)  FUNCTION GET_PCB: PCB_ptr;
       This function takes no parameters. When called, the function
       returns a pointer to a free PCB.
   2)  PROCEDURE FREE_PCB (pcb: PCB_ptr);
       This procedure takes a pointer to a PCB that is currently in
       use and deallocates it.
   3)  PROCEDURE BUILD_PCB (pcb: PCB_ptr; name:String8;
                          pcb_type: Proc_Type; pcb_state: Proc_state;
                          pcb_sus: Suspend);
       where the types String8, Proc_Type, Proc_State, and Suspend
       can be defined as follows:
             String8 = Array [1..8] of Char;
             Proc_type = ( FREE, SYSTEM, USER);
             Proc_state = ( READY, RUNNING, BLOCKED);
             Suspend =(SUSPEND, NOT_SUSPENDED);
      The procedure is called to initialize the various fields of a
      PCB to the desired values. The parameter 'pcb' is a pointer to
      the PCB whose fields are to be initialized. The other parameters
      contain the values used for initializing the fields of the PCB.
  4)  PROCEDURE INSERT_PCB(var queue: PCB_ptr; pcb: PCB_ptr;
                            method:Insertion_type)
      This Procedure is called to insert a PCB into a queue. Since there
      are two queues (Ready and I/O queue), a pointer to the queue to
      be used is passed in the parameter 'queue'. The parameter 'pcb'
      is a pointer to the PCB to be inserted into the queue. The parameter
      method specifies whether the PCB to be inserted is added at the rear
      of the queue (FIFO) or according to its priority so as to maintain 
      the queue in decreasing order of priority.
      The type Insertion_Type may be declared as follow:
           Insert_type=(FIFO, PRIORITY);
  5)  FUNCTION REMOVE_PCB(var queue: PCB_ptr): PCB_ptr;
      This function removes the PCB at the head of the queue specified by 
      the parameter 'queue' and returns a pointer to the PCB removed.
  6)  PROCEDURE SET_PRIORITY(pcb: PCB_ptr; prty: integer);
      This procedure sets the priority in the PCB specified by the 
      parameter 'pcb' to the value specified by the parameter 'prty'
  7)  PROCEDURE DISPLAY(queue: PCB_ptr);
      This procedure prints the values assigned to each field of the PCBs
      in the queue specified by the parameter 'queue'. The only purpose of 
      the procedure DISPLAY is to allow you to verify whether the code you
      have written is correctly maintaining the Ready Queue and IO Queue.
      This procedure prints the values assigned to each field of the PCBs
      in the queue specificed by the parameter 'queue'. The only purpose
      of the procedure DISPLAY is to allow you to verify whether the code
      you have written is correctly maintaining the Ready Queue and IO Queue.

Program Main


  Type String8= Array[1..8] of char;

  Proc_type =  (FREE, SYSTEM, USER);
  Proc_state=  (READY, RUNNING, BLOCKED);
  Suspend =    (SUSPENDED, NOT_SUSPENDED);
  Insert_type = (FIFO, PRIORITY);
  PCB_ptr =^PCB;
  PCB = Record
     Next:integer;
     Name:Strings;
     Type:Proc_type;
     ....
  end;
     ....
Var 
   ReadyQueue, IOQueue: PCB_ptr;
   p, q, r :PCB_ptr;
 
  (* The 7 procedures and functions described on the previous pages*)

Begin
  
  ReadyQueue =Nil;
  IoQueue =Nil;

   p:= GET_PCB;
   BUILD_PCB(p, 'Sys1', SYSTEM, READY, NOT_SUSPENDED);
   SET_PRIORITY(p,30);

   q:= GET_PCB;
   BUILD_PCB(q, 'Sys2', SYSTEM, READY, NOT_SUSPENDED);
   SET_PRIORITY(q,55);
  
   INSERT_PCB(ReadyQueue, p,PRIORITY);
   INSERT_PCB(ReadyQueue, q,PRIORITY);

   p:= GET_PCB;
   BUILD_PCB(p, 'user1', USER, READY, SUSPENDED);
   SET_PRIORITY(P,10);

   q:= GET_PCB;
   BUILD_PCB(q, 'user2', USER, READY, NOT_SUSPENDED);
   SET_PRIORITY(q,25);

   r:= GET_PCB;
   BUILD_PCB(r, 'user1', USER, READY, SUSPENDED);
   SET_PRIORITY(r,20);

CIS 332 Principles of Operating Systems Fall 1996 Franz Kurfess.