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

Processes cont’d  critcal real-time requirements = particular events must occur within a specified number of milliseconds  difference between a process and a program  Process – an activity  = program, input, output, and state

Process Types 1. Foreground – process that interacts with user 2. Background – not associated with a specific user; specific/dedicated function  daemon = background process to handle some activities (e. g., , telnet, ftp, web server, etc.)

Process creation 4 major events causing process creation: 1.system initialization 2.running process executes a process creation system call 3.user requests creation of a new process 4.initiation of a batch job

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

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

Unix process creation: fork() #include int main ( const int argc, const char* const argv[] ) { puts( "forking" ); pid_t ret = fork(); puts( "forked" ); return 0; }

#include 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 break; default:printf( "parent: child has pid=%d \n", ret ); break; } return 0; } fork and exec fork and exec

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

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

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

Process states 1. Running 2. Ready 3. Blocked

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

Context switch/interrupt service