IT628 Systems Programming Course Outline

IT628: Systems Programming Course outline, process creation 1 What’s this course all about?  Operating systems provide a set of constructs and well-defined primitives to simplify application development  You will learn how to write applications that exploit...

IT628: Systems Programming Course outline, process creation 1 What’s this course all about?  Operating systems provide a set of constructs and well-defined primitives to simplify application development  You will learn how to write applications that exploit important OS features  Often we will present an OS concept first and then the system calls associated with that concept 2 Main topics we’ll cover  Concurrent programming  processes, signals, pipes, threads, synchronization  Network programming  sockets and servers 3 System calls  A request for the OS to do something on behalf of the user’s program  Example  fork()  exec()  Don’t confuse system calls with libc calls  strcpy() 4 Main categories of system calls  File system  Low-level file I/O  E.g., creat, open, read, write, lseek, close  Multi-tasking mechanisms  Process control  E.g., fork, wait, exec, exit, signal, kill  Inter-process communication  E.g., pipe, dup, dup2 5 Classroom organization  Standard lecture format with exercises sprinkled in for class discussion  We’ll also demo code examples in class  Questions are ALWAYS encouraged (both directions) 6 Classroom Etiquette  Come on time to both class and labs  Talking, cell phones, etc. will not be tolerated 7 Reference books  Keith Haviland, Dina Gray and Ben Salama  “UNIX System Programming”, Addison-Wesley  Randal Bryant and David O’Hallaron  “Computer Systems: A Programmer’s Perspective”, Pearson India  Brian Kernighan and Dennis Ritchie  “The C Programming Language, Second Edition”, Prentice Hall India 8 Grade breakdown  Exams (70%): two insem exams and final  two insems weighted 20%  final weighted 50% (covers entire course)  Lab exercises (checkoffs) and homework (30%)  weighted 20%, 10%  lab attendance is mandatory 9 Processes  A process is the basic unit of execution in an OS  A process is a running instance of a program  Program = static file (image)  Process = executing program = program + execution state  Two processes are said to run concurrently when instructions of one process are interleaved with the instructions of the other process 10 Context switching  Transferring control from the current process to another process is called a context switch  OS saves the state of the current process, restores the state of the other process, and passes control to the new process  From a human observer’s point of view, many processes appear to proceed simultaneously 11 fork()  fork creates a new process  the process created (child) runs the same program as the creating (parent) process  and starts with the same PC,  the same CPU registers,  the same open files, etc. 12  Ppare intntmain(){ fork(); foo(); } OS 13  Ppare intntmain(){ fork(); foo(); } OS 14  Ppare Pchild intntmain(){ int main(){ fork(); fork(); foo(); foo(); } } OS creates 15  Ppare Pchild intntmain(){ int main(){ fork(); fork(); foo(); foo(); } } OS 16  fork(), when called, returns twice (to each process @ the next instruction) int main() { fork(); printf(“Hello world!\n”); } Hello world! Hello world! 17 int main() { fork(); fork(); printf(“Hello world!\n”); } Hello world! Hello world! Hello world! Hello world! 18 int main() { fork(); fork(); fork(); printf(“Hello world!\n”); } Hello world! Hello world! Hello world! Hello world! Hello world! Hello world! Hello world! Hello world! 19 return value of fork() typedef int pid_t; pid_t fork(); system-wide unique process identifier child’s pid (> 0) is returned in the parent sentinel value (0) is returned in the child 20 void fork0() { if (fork()==0) printf(“Hello from Child!\n”); else printf(“Hello from Parent!\n”); } main(){ fork0(); } Hello from Child! Hello from Parent! (or) Hello from Parent! Hello from Child! 21 void fork3() { int i; sum = 0; fork(); for (i=1 ; i