wcmentor161log.txt

<ishaan> : Hello! I am Ishaan. 1st Year
<ankit> : please introduce yourself till everyone joins 
<Pavana> : I am Pavana.2nd year
<ankit> : What about rest of you? 
<ankit> : introduction people
<omkarp> : Omkar Prabhu first year CS
<Anirudh> : I'm Anirudh. 1st Year
<Mahim> : Mahim Agrawal 1st year mech
<Samvid> : Samvid 2nd year CS
<tushaar_> : 204:540d:ce8e:d117:4613:90e7:9873 PRIVMSG #wcmentor16 :Tushaar, 2nd Year IT.
<shreyansh_> : Hii this is shreyansh : 2nd Year IT
<shruthi> : Shruthi , 2nd year
<ankit> : So should we wait for others?
<ankit> : or should we start?
<Mahim> : lets start
<ankit> : ok cool 
<ankit> : So what is this session about?
<tushaar_> : 204:540d:ce8e:d117:4613:90e7:9873 PRIVMSG #wcmentor16 :OS.
<tushaar_> : 204:540d:ce8e:d117:4613:90e7:9873 PRIVMSG #wcmentor16 :Right?
<ishaan> : Operating Systems
<ankit> : You tell me Tushaar,  you joined right?
<tushaar_> : 204:540d:ce8e:d117:4613:90e7:9873 PRIVMSG #wcmentor16 :Yes!
<tushaar_> : 204:540d:ce8e:d117:4613:90e7:9873 PRIVMSG #wcmentor16 :Operating Systems.
<ankit> : Cool so everyone name your favourite operating system
<ishaan> : Android!
<tushaar_> : 204:540d:ce8e:d117:4613:90e7:9873 PRIVMSG #wcmentor16 :Linux.
<niharock69> : hi i m nihar 1st year IT
<niharock69> : sorry for joining late
<Mahim> : windows
<Anirudh> : Android
<niharock69> : Android
<shreyansh_> : Linux and android
<Pavana> : Windows
<ankit> : No problem, everyone is naming their favourite os
<ankit> : done?
<ankit> : Cool, whoever said android, it built on linux, so you can say you like linux too
<ishaan> : cool
<ankit> : So, this session is gonna be a informal one, feel free to interrupt me anywhere 
<ankit> : Can someone tell me what can be a definition of OS?
<Anirudh> : Like Andriod is iOS also based on some other OS
<ankit> : iOS is based on unix but Apple has customised it a lot 
<niharock69> : operating system is a software which acts as an interface between us and other programs
<ankit> : so what are these other programs?
<ishaan> : applications?
<niharock69> : other programs meaning other softwares like google chrome
<ankit> : ok yea that's the most basic definition of OS
<ankit> : I won't talk much about the history of OS, lets start with processes
<niharock69> : ok
<ishaan> : ok!
<ankit> : So anyone knows what is a process?
<niharock69> : no
<ishaan> : no
<puneet> : any program currently running?
<ankit> : correct Puneet 
<puneet> : like in task manager there are processes running and we 'end' them.
<tushaar> : A program in execution.
<ankit> : so what is a program 
<tushaar> : Sequence of instructions.
<ishaan> : set of codes?
<Anirudh> : Set of instructions
<niharock69> : sequence of codes which run according to instructions
<ankit> : yea, all are more or less the same thing and basic definition of program 
<ankit> : and a program under execution is process
<puneet> : yolo! could you tell me how you log chats!
<ankit> : so how many processes are running on your system right now?
<Anirudh> : about 50 to 60 ?
<Mahim> : 134
<ishaan> : around 80
<ankit> : linux users do a cat /proc/stat and tell me the first number 
<ankit> : cat /proc/stat
<Samvid> : 145
<niharock69> : 2901
<ankit> : how are you seeing these numbers like 134/145?
<niharock69> : is it something unusual to get such a huge number ? :P
<Mahim> : task manager under processes tab
<Mahim> : summed up the apps, windows processes and background processes
<ankit> : 53894 that's mine currently 
<ankit> : Task manager will show you the count of processes which you can handle without screwing up your system 
<ankit> : so yea the first job of an OS is process management 
<ankit> : let's consider a single core system for the ease of discussion cool?
<ishaan> : okay
<niharock69> : ok :)
<puneet> : ok
<Pavana> : Ok
<Anirudh> : ok
<ankit> : so what did you understand from that? 
<shreyansh_> : what does core actually mean?
<ankit> : @shreyansh good, I was expecting that question 
<ankit> : so you can take core as a synonym for CPU 
<shreyansh_> : i know only types of core  mean dual,quad like that
<ankit> : currently you would hear words like dual, quad, hexa, octa etc
<ankit> : infront of cores
<niharock69> : yea
<shreyansh_> : okk fine !
<ishaan> : yeah
<suhasbs> : Single core means the CPU can only handle one process at a time?
<ankit> : it just means those systems has that many processing unit 
<ankit> : https://www.d.umn.edu/~gshute/os/images/process-diagram.png
<ankit> : see that image 
<ankit> : it shows life cycle of a process 
<ankit> : saw?
<ishaan> : yes
<puneet> : yep
<Vilas> : Yes
<Pavana> : Yes
<Anirudh> : yes
<ankit> : so a single core system means only one process can be in the running state at a time 
<suhasbs> : Yes
<ishaan> : what happens to the process after it has been terminated?
<ujdcodr> : it dies
<suhasbs> : It is said to be dead
<ankit> : its destructor is called, its memort is deallocated 
<ankit> : memory*
<ishaan> : ok :)
<suhasbs> : What does the ps command actually show?
<ankit> : so in an os, there are many process queues 
<ankit> : ps shows process in that space
<suhasbs> : Ooh OK.
<ankit> : so you see the state ready?
<ankit> : in the image?
<ishaan> : yes
<puneet> : yes
<niharock69> : yes
<Pavana> : Yes
<ankit> : every OS has something called a ready queue 
<ankit> : ready queue contains processes which are ready to run 
<ankit> : Anyone heard about process control block? (PCB)
<ishaan> : no
<omkarp> : no
<Pavana> : No
<shreyansh_> : Nope
<ankit> : so a PCB stores all the information about a process 
<ishaan> : ok!
<ankit> : like the memory address currently used by the process 
<ankit> : can someone tell me difference in memory allocation of local variable and global variable?
<niharock69> : the address of local variable can be used only inside the function
<niharock69> : but for globall it can be used throughpout the program
<ankit> : how many competitive programmers here?
<puneet> : Vilas!
<Vilas> : me. global variables are stored in the heap while local in the stack i guess
<ankit> : yes 
<ankit> : what are these stack and heap?
<omkarp> : data structures
<Vilas> : stack is allocated to a specific program. 
<ankit> : ok that is one, but stack is the memory allocated in RAM and heap is allocated in the main memory 
<ankit> : heap is dynamically allocated during run time 
<ankit> : if any word is unclear, please ask?
<niharock69> : clear
<ishaan> : then what about stack?
<niharock69> : :)
<ankit> : stack is statically allocated to every process 
<ishaan> : ok! :)
<ankit> : That's why Vilas will ask everyone to store large arrays as a global variable :P
<ankit> : because stack can run out of space but heap will keep getting more memory 
<ankit> : That is where "stack overflow" happens 
<puneet> : hey, aren't main memory and ram the same?
<ankit> : Oh I mean Stack is in the memory already allocated to the process in beginning 
<ankit> : Yea my bad they are same 
<niharock69> : so the only differenece is stack is created while compiling and heap while runtime is it so?
<ankit> : yes 
<niharock69> : ok!
<ankit> : so yea back to PCB, a PCB stores all these information 
<ankit> : what is memory range of stack, what is of heap and so on 
<ishaan> : ok!
<ankit> : so say you run a program 
<ankit> : it runs as a process and it first enters the ready state and hence in a ready queue 
<ankit> : and from there is no process running currently, the head of ready queue starts running 
<ujdcodr> : can you clarify again where the heap and stack are respectively stored?
<ankit> : ok so when you run your program, based on the compile time information, stack is allocated the memory 
<ankit> : and then when your program starts running, when it encounters something like a malloc, it gets memory in malloc 
<ankit> : http://static.duartes.org/img/blogPosts/linuxFlexibleAddressSpaceLayout.png
<ankit> : check that image 
<ankit> : that is how they are allocated 
<ankit> : stack has a limited expansion space denoted by Rlimit 
<ankit> : but heap can expand (till you have memory theoritically)
<ankit> : ujjwal clear?
<niharock69> : whats Rlimit?
<ankit> : its just the memory limit of stack 
<ujdcodr> : yep
<ankit> : you stack can't be larger than that 
<niharock69> : ok
<ankit> : so yea 
<ankit> : so the way you send process from ready queue to run is called scheduling 
<ankit> : Has anyone heard of different process scheduling techniques?
<niharock69> : no
<tushaar> : Scheduling jobs?
<ishaan> : no
<puneet> : nope
<Pavana> : No
<ankit> : nope Tushaar just algorithms 
<ankit> : so the simplest scheduling technique is FIFO 
<tushaar> : First come first serve?
<ankit> : what do you think that will be 
<puneet> : thats a queue?
<ankit> : yea first come first serve 
<niharock69> : first in first out
<ankit> : so the first process which comes in the queue gets to run first 
<ankit> : like a simple queue 
<ankit> : what do you think is a problem with this?
<tushaar> : Time.
<Vilas> : Priorities are neglected 
<Samvid> : the processes with higher priorities have to wait if they start after the ones with lower priorites
<niharock69> : suppose a small process comes later and before that theres a very huge process the small process has to wait for a very large amount of time
<tushaar> : If the first job takes lot of time, all other jobs must stall.
<ankit> : yes nihar 
<niharock69> : :)
<ankit> : priorities is also a problem but nihar's answer is a bigger problem 
<ankit> : that is called convoy effect 
<ankit> : what is a convoy?
<ankit> : english meaning 
<tushaar> : A group of ships, travelling together.
<tushaar> : for protection.
<ankit> : yea, its like a large group 
<ankit> : so when a small ship is trying to dock behind a convoy what will happen 
<ankit> : same things happens in FCFS 
<shreyansh_> : FCFS???
<ankit> : first come first serve 
<ishaan> : first come first serve
<shreyansh_> : okay got it
<ankit> : see a simple example, if a person in atm line goes in with 5 cards ahead of you when you just need 100 bucks 
<ishaan> : lol. yeah :P
<ankit> : as for the priority problem, it was solved by bringing in a priority fifo 
<ankit> : in priority fifo, when a process with higher priority comes, a smaller priority process is preempted 
<ankit> : clear?
<ishaan> : yes
<ankit> : so what is a problem with priority fifo which was not there in fifo 
<ishaan> : it is not order based?
<puneet> : incoming process's priority must be checked with all the processes presently in the queue this taking some time?
<ankit> : that is one puneet but not a big one 
<niharock69> : processes quitting before completion because of priority issues?
<ankit> : consider you are in an ATM line and whenever you come in first of line, the MLA, the MP and even the PM comes to same ATM (hypothetically)
<ishaan> : it is not based on the order
<ankit> : you will never get your cash 
<tushaar> : It is not-fair for lower priority jobs, inspite of them arriving first?
<tushaar> : :)
<niharock69> : oh yeaaaaaaa
<ankit> : same happens with the low priority process as Tushaar said 
<ankit> : its called starvation 
<ankit> : similarly there are a few more scheduling algorithms, which you should read by yourself 
<ankit> : Now I will talk a bit about parallelisation 
<niharock69> : ok
<ishaan> : ok
<ankit> : first practical aspect, how do you create a process in C?
<ankit> : anyone?
<suhasbs> : Fork()
<ankit> : yes, how does fork work?
<ankit> : like what do you see
<ankit> : not the kernel level detail 
<suhasbs> : It returns a process id
<puneet> : it creates a copy of the currently running process and runs it parralelly?
<ankit> : yes, it copies the instructions from the point it was called 
<ankit> : printf("hi");
<ankit> : fork();
<ankit> : printf("hello");
<ankit> : what do you think will be the output 
<puneet> : hihihello?
<puneet> : hihellohello*
<ankit> : hihellohello is correct 
<ankit> : is it clear to everyone why that happened?
<niharock69> : no
<niharock69> : y does iyt happen
<niharock69> : it shld just print hihello  ryt
<ankit> : ok so
<ankit> : when you encounter fork, a new process is created, which executes all the statements after fork 
<ankit> : this process is called child process 
<ankit> : so your parent process prints hi 
<niharock69> : ohh
<ankit> : then there are two process running cause there is a fork 
<ankit> : then one process first prints hello 
<ankit> : and then second prints hello 
<niharock69> : got it :)
<suhasbs> : So something like a new thread is created and everything below fork is like as though its inside the run method?
<ankit> : ok yea that reminds me, what is a thread and what is a process
<suhasbs> : Was about to ask that question!
<ankit> : ok so threads are used for smaller tasks 
<ankit> : threads are created by processes and all the threads of one process shares the same memory space 
<ankit> : but this does not happen with process 
<ankit> : every process has a memory space independent of each other 
<niharock69> : ok
<ankit> : now back to fork, how many process do you think will be created by fork();fork();fork();
<niharock69> : 3! ?
<niharock69> : that is 6?
<ankit> : others?
<tushaar> : 8.
<suhasbs> : 1
<ankit> : everyone logic behind your answers 
<tushaar> : 2 - 2 + 2 - 2+2 2+2.
<niharock69> : first fork will create 1 process inside that one more process inside that one more process
<niharock69> : and all these returning will caause 3! processes
<ankit> : suhas?
<ankit> : ok Tushaar answered correct 
<suhasbs> : Just guessed
<ankit> : after first fork - 2 process 
<puneet> : is it 7 + 1 parent? or 8 children?
<ankit> : 7+1
<puneet> : okay. got it.
<ankit> : both these process will execute second fork, hence 2*2 = 4 
<ankit> : and all these 4 processes will execute the last fork so 4*2 = 8
<ishaan> : ok!
<niharock69> : so basically 2^n processes?
<suhasbs> : Ooh OK
<ankit> : yes nihar 
<ankit> : 2^n -1  children and 1 parent
<niharock69> : ok :)
<ankit> : apart from fork there is something called openmp, which can create parallelisation in C 
<ankit> : check that out 
<ankit> : I think I will conduct two more sessions on OS, I will end this session with a question 
<niharock69> : okkk
<puneet> : okay!
<Pavana> : Ok
<ishaan> : ok!
<ankit> : before that one more concept I forgot 
<ishaan> : ohh
<ankit> : How do processes communicate with each other 
<ankit> : there are two methods 
<ankit> : 1) shared memory
<ankit> : 2) message passing 
<ankit> : Message passing is similar to a socket communication of networks 
<ankit> : puneet explain what's that :P
<puneet> : :D, okay.
<puneet> : basically, a socket is end point of a communication channel.
<ishaan> : ok...
<ankit> : so yea 
<puneet> : so, a host who wants to create a server creates a socket, binds the socket to its address.
<puneet> : then listens in the socket for incoming connections.
<niharock69> : okkk
<puneet> : meanwhile, a client opens a socket and connects to a existing host in the network
<ankit> : a process can create a socket for itself and let other processes talk to it, or two processes can create use something call mailboxes and talk to each other by passing messages 
<suhasbs> : A socket is basically a combination of a port and IP address, for those who are wondering what socket is!
<puneet> : your explanations are better ankit :p
<ankit> : in a local system its just the port 
<ankit> : message passing is similar to sending and receiving letters 
<ankit> : socket and mailboxes are just the address where letter can be sent 
<shreyansh_> : port?? :(
<ankit> : read about network port, its a computer network based concept 
<ankit> : you can just think of it as an identifier 
<ankit> : in your system for network communication 
<ankit> : like if message comes with port number 8080, send it to your browser 
<niharock69> : yeaaaa
<ankit> : so the second method is shared memory 
<ankit> : shared memory is how you talk to your benchmate in the class of a strict prof :P
<ankit> : now you tell me how you do it 
<puneet> : is forking a way to do shared memory communication?
<tushaar> : Whisper.
<ankit> : no forking is just process creation 
<puneet> : write it down in a paper would be better tushaar :p
<ankit> : you can communicate in either way between those processes 
<ankit> : exactly at puneet 
<tushaar> : Oh yeah!
<ankit> : the paper is a shared medium 
<ankit> : you write, "I am feeling so sleepy" and he replies with "me too"
<niharock69> : so in shared medium we need a medium for communication
<niharock69> : ubt in message sharing we did not require
<ankit> : so similar happens in shared memory, OS allocates a chunk of memory to two process 
<ankit> : and they communicate by putting information in this shared space so other can read from here 
<ishaan> : ohhh
<ankit> : so back to my question 
<ishaan> : cool
<ankit> : say two processes share a variable, and one process is increasing it and other is decreasing it, what kind of problems may arise and how can they be solved?
<puneet> : in message sharing, we did use a medium @niharock69. thats why it needed a socket.
<tushaar> : Synchronization can solve.
<ankit> : tushaar thats the assignment :P
<niharock69> : okkk
<tushaar> : Okay :)
<puneet> : okay.
<ankit> : find out different methods 
<ankit> : there are at least 7 common ones 
<ankit> : first identify the problem 
<ankit> : cool? I will pass the message when I schedule the next one 
<tushaar> : Awesome!
<puneet> : yep!
<ishaan> : cool!
<ankit> : Thank you 
<Pavana> : Ok
<niharock69> : ok
<niharock69> : thank u :)
<ishaan> : Thank You
<niharock69> : very nice session
<Pavana> : Thank you
<omkarp> : thank you for the session
<puneet> : thanks!
<ankit> : I will on this channel for 10 15 min if anyone has doubts 
<shreyansh_> : 'a host who wants to create a server creates a socket, binds the socket to its address then listens in the socket for incoming connections"....i didnt get it completely
<ankit> : ok you will get that if you actually write a socket program yourself 
<shreyansh_> : okay!
<ankit> : A client server architecture is a request response architecture, where client makes a request and server responds with the replies with the answer. Implementation goes like:
<ankit> : Server side:
<ankit> : Server is alloted a port number to listen to
<ankit> : Server waits for a client to connect 
<ankit> : When a client requests connection on the listening port, server allots a new port to the client and server goes back to listen on the listening port
<ankit> : Client and server talk on the other port
<ankit> : Client side:
<ankit> : Client is alloted a port
<ankit> : It makes a connection request to the server and talks on the port given by the server
<ankit> : The kind of communication which sockets provide is called message passing. It's a common method of remote communication. The other prominent kind of communication is shared memory, which is used by operating systems for inter process communication within same system. 
<ankit> : Other concepts you will need to know before is loopback address (127.0.0.1), its the IP address of your local system. 
<ankit> : Also, as we mentioned before first 1024 ports are reserved, you can't start a connection using any of these port number. 
<ankit> : Also, the reason I made "no python" rule was because it will be a 3 line code and you will not learn anything. I will discuss more socket concept informally on whatsapp. Please be proactive with your doubts.
<ankit> : Log of session: https://github.com/adeepkit01/logger/blob/master/wcnetworkslog.txt
<ankit> : Tutorials:
<ankit> : http://www.cs.rpi.edu/~moorthy/Courses/os98/Pgms/socket.html
<ankit> : http://www.javaworld.com/article/2077322/core-java/core-java-sockets-programming-in-java-a-tutorial.html
<ankit> : Thanks, 
<ankit> : Ankit
<ankit> : That's something you can refer