Software Experiment 2 - AndroBenchcsl.skku.edu/uploads/SWE2007F16/8-recitation.pdf · SWE2007:...

Recitation Session

Prof. Jin-Soo Kim (jinsookim@skku.edu)

TA - Dong-Yun Lee (dylee@csl.skku.edu)

Computer Systems Laboratory

Sungkyunkwan University

http://csl.skku.edu

2SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Notice

Some modification in schedule..

• No socket programming

• 1-week break (PA #3 will be uploaded in next week)

Grading

• 10% : Attendance

• 20% : Daily exercise

• 70% : Programming assignment

3SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Notice

Today, we have recitation class

• What we’ve learned and what we’ve missed

• Questions are always welcomed

• However; before calling me, ask yourself

– “Is this work?”

4SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

What We’ve Learned

OS, Unix-like OS, Linux

File I/O, system call, and FIO

Process

• fork, exit, wait

• exec family..

IPC (Inter-Process Communication)

• Signal, pipe, and fifo

• Socket?

5SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

OS Review

What’s OS?

• Provides an execution environment for running

• OS is HW resource manager

– Which process use CPU?

– How processes use Memory?

– How processes issue I/O? (Storage, Network, Mouse, Printer, etc)

• Unix, Linux

– “Everything is a file”

– OS supports it by ‘File System’

6SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

File Review

Q. How can we communicate with files?

• 1. With standard library (fopen, fread, …)

• 2. Unix I/O (system call)

5 basic Unix I/O

• open, close, read, write, lseek

Let’s see together…

7SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

File Review (cont’d)

Q. Why we use Unix I/O instead of library?

Q. What happen in OS if you call ‘open’ and ‘close’

system call?

• ~ table may be created

• ~ table should be created

Q. What happen if you do not close files after use?

8SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Process Review

Q. What is process?

• An instance of a program in execution

Create a new process : fork

• fork is interesting functions; return value is different!

void fork2(){

printf("L0\n");fork();printf("L1\n"); fork();printf("Bye\n");

}L0 L1

L1

Bye

Bye

Bye

Bye

9SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Process Review (cont’d)

Destroying a process : exit

Q. Why is it okay not to call exit explicitly?

Synchronizing processes : wait, waitpid

• If child process is in infinite loop and parent process calls

wait, parent process goes into infinite loop, too

Zombie process

10SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Process Review (cont’d)

Destroying a process : exit

Q. Why is it okay not to call exit explicitly?

Synchronizing processes : wait, waitpid

• If child process is in infinite loop and parent process calls

wait, parent process goes into infinite loop, too

Zombie processlinux> ps -ef6640 ttyp9 00:00:00 forks <defunct>6641 ttyp9 00:00:00 ps

11SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Process Review (cont’d)

Running new program

• Process, Program

• execl, execv, and etc…

There is no “RETURN” if exec function success

• Returning means loading new program is failed

main() {if (fork() == 0) {

execl("/bin/ls", "ls", "/", 0);}wait(NULL);printf("completed\n");exit();

}

main() {char *args[] = {"ls", "/", NULL};if (fork() == 0) {

execv("/bin/ls", args);}wait(NULL);

}

12SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

IPC Review

IPC (Inter-process communication)

Signal

• Small message that notifies a process that an event occure

Let’s see together..

13SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

IPC Review (cont’d)

I/O redirection (<, >)

Pipe

• Close pipe after I/O redirection

• If not, process might not be exit (why?)

Let’s see together

14SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

IPC Review (cont’d)

Let’s see what will happen

• cat < /proc/meminfo | grep –i active | tail –n4 > memory.txt

If your design likes below, what will happen?

cat

grep tail

15SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

IPC Review (cont’d)

Better if

tail

cat grep

16SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Notice

Please consider your algorithm before coding

• Coding is not that important factor!

• Designing is much more important

Questions are always welcomed

• However; before calling me, ask yourself

– “Is this work?”

17SWE2007: Software Experiment 2 | Fall 2016 | Jin-Soo Kim (jinsookim@skku.edu)

Exercise

1. Answer 3 questions in page 7

2. Add some functionality to your mini shell

• Built-in tools

• I/O redirection

• $echo “3+3+3” | bc > result

• $cat < /proc/meminfo | grep –i active | tail –n4 > memory.txt

3. Check your grades..