1. 2.1 Processes process = abstraction of a running program
multiprogramming = CPU switches from running program to running program
pseudoparallelism
each process has its own virtual CPU
each process is considered to be simply sequential
make no assumptions about timing

2. Processes cont’d
critcal real-time requirements = particular events must occur within a specified number of milliseconds
difference between a process and a program

3. Process creation 4 major events causing process creation:
system initialization
running process executes a process creation system call
user requests creation of a new process
initiation of a batch job
daemon = background process to handle some activities (e. g., , telnet, ftp, web server, etc.)

4. Process creation cont’d
win32: use task manager to view process
Unix: ps –edalf command

5. Process creation cont’d
win32: CreateProcess()
10 parameters
creates and loads new process
Unix: fork() + execve() system calls
fork() creates new process (copy of parent)
execve() loads new program

6. Unix process creation: fork()
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main ( const int argc, const char* const argv[] ) {
puts( "forking" );
pid_t ret = fork();
puts( "forked" );
return 0; }

7. fork and exec #include <stdio.h> #include <sys/types.h>
#include <unistd.h>
int main ( const int argc, const char* const argv[] ) {
puts( "parent: forking" );
pid_t ret = fork();
switch (ret) {
case -1: puts( "parent: error: fork failed!" );
break;
case 0: puts( "child: here (before execl)!" );
if (execl( "./child.exe", "./child.exe", 0 )==-1)
perror( "child: execl failed:" );
puts( "child: here (after execl)!" ); //should never get here
default: printf( "parent: child has pid=%d \n", ret ); }
return 0;
fork and exec

8. Child process #include <stdio.h>
int main ( const int argc, const char* const argv[] ) {
printf( "child process %s running with %d arg(s). \n", argv[0], argc );
return 0; }

9. Process termination Conditions: Voluntary: Involuntary: Normal exit
Error exit
Win32: ExitProcess()
Unix: exit()
Involuntary:
Fatal error (e. g., divide by zero, illegal memory access)
Killed by another process

10. Process hierarchies None in win32
Unix maintains a parent/child relationship called a process group.

11. Process states
Running
Ready
Blocked

12. Implementation of processes
Process table = array of structures (process control blocks)

13. Context switch/interrupt service