cool
Reputation: 89
Process Control Block
My professor asks this question for Homework.
Consult a Linux Manual or a Microsoft Windows manual. Find the actual contents of the Process Control Block (Process Descriptor) in the operating system of your choice.
I know in general PCB contains
Process number or process ID
Process state
Program counter
CPU registers
CPU scheduling information
Memory-management information
Accounting information
I/O status information
I am trying to find manual but I did not see it online. Could anybody help me with this.
Upvotes: 0
Views: 10888
Answers (5)
Mohit Singh
Reputation: 477
PROCESS CONTROL BLOCK
There is a Process Control Block for each process, enclosing all the information about the process. It is a data structure, which contains the following :
Process State - It can be running, waiting etc.
Process ID and parent process ID.
CPU registers and Program Counter. Program Counter holds the address of the next instruction to be executed for that process.
CPU Scheduling information - Such as priority information and pointers to scheduling queues.
Memory Management information - Eg. page tables or segment tables.
Accounting information - user and kernel CPU time consumed, account numbers, limits, etc.
I/O Status information - Devices allocated, open file tables, etc.
to get in details concept i should suggest you to learn from here https://coderworld109.blogspot.in/2017/12/process-control-block-pcb.html https://coderworld109.blogspot.in/2017/12/operating-system-process-management.html
Upvotes: 0
oscar
Reputation: 19
This could help you out. I previously post it but I had to cancel my account for security reasons.
#include <iostream>
#include <sstream>
#include <vector>
#include <list>
#include <string>
#include "proc.h"
#include "rq.h"
using namespace std;
// creates a vector of Queues
void load_queue(vector<rq> &queue, unsigned int num_of_queues)
{
for(int pos=0; pos<num_of_queues; pos++)
{
queue.push_back(rq());
}
}
//returns the biggest queue position in the vector
unsigned int get_biggest_queue_pos(vector<rq> queues)
{
unsigned int queue_pos = 0; // Pos of smaller queue. Default 0.
unsigned int queue_size = queues.at(queue_pos).size(); // Its size
for(unsigned int pos = 0; pos < queues.size(); pos++)
{
if(queues.at(pos).size() > queue_size)
{
queue_pos = pos;
queue_size = queues.at(pos).size();
}
}
return queue_pos; // Return smaller queue position in vector.
}
// Returns the smaller queue position in the vector.
unsigned int get_smaller_queue_pos(vector<rq> queues)
{
unsigned int queue_pos = 0; // Pos of smaller queue. Default 0.
unsigned int queue_size = queues.at(queue_pos).size(); // Its size
for(unsigned int pos = 0; pos < queues.size(); pos++)
{
if(queues.at(pos).size() < queue_size)
{
queue_pos = pos;
queue_size = queues.at(pos).size();
}
}
return queue_pos; // Return smaller queue position in vector.
}
//Searches for a PID in entire system and erases it.
bool get_pid_process(vector<rq> &queue, int id)
{
vector <proc> temp;
proc process(0,0,0);
int check;
int number=id;
int size=queue.size();
/*checks rest of queues, including ready queues and device queues*/
for(int i=0; i<size; i++)
{
temp=queue[i].get_queue();
int size1=temp.size();
for(int j=0; j<size1; j++)
{
process=temp.at(j);
check=process.get_pid();
if(check==number)
{
cout<<"Process found in a queue and being erased..."<<endl;
queue[i].remove_process(j);
float cputime=process.get_burst();
float burstime=process.get_average();
cout<<"Process information:"<<endl;
cout<<"PID: "<<number<<endl<<"Acc CPU time: "<<cputime<<endl<<"Average burst time: "<<burstime<<endl;
cout<<"Process killed"<<endl<<endl;
return true;
}
}
}
/*Checks all CPUs in ready queues*/
for(int k=0; k<size; k++)
{
temp=queue[k].get_cpu();
process=temp.front();
check=process.get_pid();
if(check==number)
{
cout<<"Process found in a CPU and being erased..."<<endl;
float cputime=process.get_burst();
float burstime=process.get_average();
queue[k].clear_cpu();
cout<<"Process information:"<<endl;
cout<<"PID: "<<number<<endl<<"Acc CPU time: "<<cputime<<endl<<"Average burst time: "<<burstime<<endl;
cout<<"Process killed"<<endl<<endl;
return true;//ends if PID is found in CPU and returns true
}
}
return false;
}
int main()
{
cout << "Sys gen starting..."<<endl;
cout<<"Please enter the amount of CPUs (between 1 and 9)"<<endl;
int cpu;
cin>>cpu;
while(cpu<1 || cpu>9)
{
cout<<"Invalid value, please re-enter amount:"<<endl;
cin>>cpu;
}
cout<<"Enter amount of PRINTERs:"<<endl;
int pr;
cin>>pr;
cout<<"Enter amount of DISKs:"<<endl;
int di;
cin>>di;
cout<<"Enter amount of CD/RWs:"<<endl;
int cd;
cin>>cd;
int devices=(cpu*2)+pr+di+cd;//amount of devices(queues and CPU's)
int PID=0;
int PCB=0;
vector<rq> RQ; //vector of ready queues
vector<rq> PQ; //vector of printer queues
vector<rq> DQ; //vector of disk queues
vector<rq> CQ; //vector of CD/RW queues
load_queue(RQ, cpu);
load_queue(PQ, pr); //load printer queues to PQ vector
load_queue(DQ, di); // ...
load_queue(CQ, cd); // ...
cout << "Running section..." <<endl<< endl;
cout<<"Start inputting commands; To terminate program press E or e at any time:"<<endl;
while(true)
{
string device;//for name of device
string enter;//for input
cin>>enter;
int correspond=0;
int smaller;
char num11=enter[0];//1st position character
char input=enter[1];//2nd position char
char num=enter[2];//3rd position char
int num1=num11 -'0';//1st position integer
int n=num -'0';//3rd position int
int inp=input - '0';//2nd position int
int empty;
/*creates a new process and puts it into emptiest Ready Queue*/
if(num11=='A')
{
smaller=get_smaller_queue_pos(RQ); //determines which ready queue has less processes
RQ[smaller].create_process(smaller, PID, PCB);
PID++;
PCB++;
if(RQ[smaller].get_cpu().size() == 0)
{
RQ[smaller].cpu();
}
}
/*terminates a process from a particular CPU*/
else if(input=='t')
{
if(num1>0 && num1<=cpu)
{
RQ[num1-1].terminate();
PCB--;
RQ[num1-1].cpu();
}
else
{
cout<<"Invalid entry"<<endl;
}
}
/*Prints out a snapshot of a particular device Q or the ready queues*/
else if(num11 == 'S')
{
cout << "Select a queue: "<<endl;
char sele;
cin >> sele;
switch(sele)
{
case 'p':
if(pr==0)
{
cout<<"There are no printer queues created."<<endl;
}
else
{
device="Printer";
cout<<"A snapshot of your "<<device<<" queues:"<<endl<<"PCB\tPID\tLENGTH\tLOCATION\tFILE NAME\tUsed CPU time(ms)\tAverage Burst time(ms)"<<endl;
for(int i = 0; i < PQ.size(); i++)
{
cout<<device<<" "<<i+1<<":"<<endl;
PQ.at(i).snapshot(device);
}
}
break;
case 'r':
cout<<endl<<"___A Snapshot of your Ready Queue(s)___"<<endl;
for(int i = 0; i < RQ.size(); i++)
{
cout<<"Ready queue "<<i+1<<":"<<endl;
RQ[i].snapshot();
}
break;
case 'd':
if(di==0)
{
cout<<"There are no disk queues created."<<endl;
}
else
{
device="Disk";
cout<<"A snapshot of your "<<device<<" queues:"<<endl<<"PCB\tPID\tLENGTH\tLOCATION\tFILE NAME\tUsed CPU time(ms)\tAverage Burst time(ms)"<<endl;
for(int i = 0; i < PQ.size(); i++)
{
cout<<device<<" "<<i+1<<":"<<endl;
DQ.at(i).snapshot(device);
}
}
break;
case 'c':
if(cd==0)
{
cout<<"There are no cd/rw queues created."<<endl;
}
else
{
device="Cd/rw";
cout<<"A snapshot of your "<<device<<" queues:"<<endl<<"PCB\tPID\tLENGTH\tLOCATION\tFILE NAME\tUsed CPU time(ms)\tAverage Burst time(ms)"<<endl;
for(int i = 0; i < PQ.size(); i++)
{
cout<<device<<" "<<i+1<<":"<<endl;
CQ.at(i).snapshot(device);
}
}
break;
default:
cout << "No such queue; wrong option." << endl;
break;
}
}
/*moves a process from a particular CPU into a particular printer queue*/
else if(input=='p')
{
if(n>pr)
{
cout<<"You are exceding the amount of queues available for this device."<<endl;
}
else
{
/*start of push */
vector <proc> temp1;
int big;
temp1=RQ[num1-1].get_cpu();
if (temp1.empty())
{
big=get_biggest_queue_pos(RQ);
temp1=RQ[big].get_front();
temp1.at(0).change_q(num1-1);
RQ[num1-1].enter_to_rq(temp1.front());
RQ[num1-1].cpu();
}
/*end of push */
int ind=1;// to determines it's a printer when asking for parameters
vector <proc> temp;
temp=RQ[num1-1].get_cpu();
int nn=temp.at(0).get_first();//to determine if process already has parameters (if nn=1)
if(nn==0)
{
RQ[num1-1].get_info(ind);//input process parameters
RQ[num1-1].bur_info();
temp=RQ[num1-1].get_cpu();
}
else
{
RQ[num1-1].bur_info();
temp=RQ[num1-1].get_cpu();
}
RQ[num1-1].clear_cpu();
proc te(0,0,0);
te=temp.front();
PQ[n-1].enter_to_rq(te);
}
}
/*moves a process from a particular CPU into a particular disk queue*/
else if(input=='d')
{
if(n>di)
{
cout<<"You are exceding the amount of queues available for this device."<<endl;
}
else
{
/*start of push */
vector <proc> temp1;
int big;
temp1=RQ[num1-1].get_cpu();
if (temp1.empty())
{
big=get_biggest_queue_pos(RQ);
temp1=RQ[big].get_front();
temp1.at(0).change_q(num1-1);
RQ[num1-1].enter_to_rq(temp1.front());
RQ[num1-1].cpu();
}
/*end of push */
int ind=0;// to determine it's a printer when asking for parameters
vector <proc> temp;
temp=RQ[num1-1].get_cpu();
int nn=temp.at(0).get_first();//to determine if process already has parameters (if nn=1)
if(nn==0)
{
RQ[num1-1].get_info(ind);//input process parameters
RQ[num1-1].bur_info();
temp=RQ[num1-1].get_cpu();
}
else
{
RQ[num1-1].bur_info();
temp=RQ[num1-1].get_cpu();
}
RQ[num1-1].clear_cpu();
proc te(0,0,0);
te=temp.front();
DQ[n-1].enter_to_rq(te);
}
}
/*moves a process from a particular CPU into a particular cd/rw queue*/
else if(input=='c')
{
if(n>pr)
{
cout<<"You are exceding the amount of queues available for this device."<<endl;
}
else
{
/*start of push */
vector <proc> temp1;
int big;
temp1=RQ[num1-1].get_cpu();
if (temp1.empty())
{
big=get_biggest_queue_pos(RQ);
temp1=RQ[big].get_front();
temp1.at(0).change_q(num1-1);
RQ[num1-1].enter_to_rq(temp1.front());
RQ[num1-1].cpu();
}
/*end of push */
int ind=0;// to determine it's a printer when asking for parameters
vector <proc> temp;
temp=RQ[num1-1].get_cpu();
int nn=temp.at(0).get_first();//to determine if process already has parameters (if nn=1)
if(nn==0)
{
RQ[num1-1].get_info(ind);//input process parameters
RQ[num1-1].bur_info();
temp=RQ[num1-1].get_cpu();
}
else
{
RQ[num1-1].bur_info();
temp=RQ[num1-1].get_cpu();
}
RQ[num1-1].clear_cpu();
proc te(0,0,0);
te=temp.front();
CQ[n-1].enter_to_rq(te);
}
}
/*moves a process from a particular printer queue to it's ready queue*/
else if(num11=='P')
{
if(enter=="P")
{
cout<<"missing values"<<endl;
}
else if(inp>pr)
{
cout<<"Invalid input."<<endl;
}
else if(PQ[inp-1].tamano()==0)
{
cout<<"There are no more processes in the Queue"<<endl;
}
else
{
vector<proc> temp;
temp=PQ[inp-1].get_device();
proc te(0,0,0);
te=temp.front();
correspond=te.get_q();
RQ[correspond].enter_to_rq(te);
}
}
/*moves a process from a particular disk queue to it's ready queue*/
else if(num11=='D')
{
if(enter=="D")
{
cout<<"missing values"<<endl;
}
else if(inp>di)
{
cout<<"Invalid input."<<endl;
}
else if(DQ[inp-1].tamano()==0)
{
cout<<"There are no more processes in the Queue"<<endl;
}
else
{
vector<proc> temp;
temp=DQ[inp-1].get_device();
correspond=DQ[inp-1].queue();
proc te(0,0,0);
te=temp.front();
correspond=te.get_q();
RQ[correspond].enter_to_rq(te);
}
}
/*moves a process from a particular cr/rw queue to it's ready queue*/
else if(num11=='C')
{
if(enter=="C")
{
cout<<"missing values"<<endl;
}
else if(inp>cd)
{
cout<<"Invalid input."<<endl;
}
else if(CQ[inp-1].tamano()==0)
{
cout<<"There are no more processes in the Queue"<<endl;
}
else
{
vector<proc> temp;
temp=CQ[inp-1].get_device();
correspond=PQ[inp-1].queue();
proc te(0,0,0);
te=temp.front();
correspond=te.get_q();
RQ[correspond].enter_to_rq(te);
}
}
/*terminates program*/
else if(num11=='E' || num11=='e')
{
return 0;
}
/*Moves process from CPU to it's ready queue*/
else if(input=='T')
{
if(enter=="T")
{
cout<<"missing values"<<endl;
}
else if (num1>cpu)
{
cout<<"Invalid entry, no such CPU."<<endl;
}
else if (num1==0)
{
cout<<"Invalid entry, no such CPU."<<endl;
}
else
{
vector<proc> temp;
temp=RQ[num1-1].get_cpu();
RQ[num1-1].cpu_clear();
proc te(0,0,0);
te=temp.at(0);
RQ[num1-1].enter_to_rq(te);
RQ[num1-1].clear_cpu();
}
}
/*Kills a process determined by it's PID*/
else if(num11=='K')
{
if(enter=="K")
{
cout<<"missing values"<<endl;
}
else
{
/*Borrowed code to convert a string into an int*/
/*converts the rest of numbers into a separate string*/
int n=enter.length();
char number[n-1];
for (int j=0; j<n; j++)
{
number[j]=enter[j+1];
}
string final=number;
/*end of conversion, final= string containing PID*/
/*convert the string final into an int*/
int id;
stringstream test(final);
test>>id;
/*end of conversion, id= int containing PID*/
/*End of Borrowed code to convert a string into an int*/
if (id > PID)
{
cout<<"Invalid PID, no such process"<<endl;
}
else
{
/*Check if PID is in a Q or CPU and delete process*/
bool buscar;
buscar=get_pid_process(RQ, id);
if(buscar==false)
{
buscar=get_pid_process(PQ, id);
}
if(buscar==false)
{
buscar=get_pid_process(DQ, id);
}
if(buscar==false)
{
buscar=get_pid_process(CQ, id);
}
if(buscar==false)
{
cout<<"Process not found."<<endl;
}
}
}
}
/*If invalid input*/
else
{
cout<<"Invalid input, re-enter command."<<endl<<endl;
}
}
return 0;
}
Upvotes: 0
Nasir
Reputation: 11411
From what I understand in Linux, PCB or Process Descriptors are dynamically allocated by the kernel and cannot directly be read from user-space.
IBM's developerWorks library has a nice article which shows you how to create a kernel module for Linux and access task_struct struct.
http://www.ibm.com/developerworks/linux/library/l-linux-process-management/index.html
Hope this helps.
edit: task_struct as defined in Linux v2.6.37 : http://lxr.linux.no/#linux+v2.6.37/include/linux/sched.h#L1182
Courtesy of google. :)
Upvotes: 5
bjornars
Reputation: 1516
For windows, you can take a look at the user-mode equivalent called the 'PEB'. It can be inspected using WinDbg using '!peb'.
Upvotes: 1
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