Understanding Processes in Operating Systems
210 likes | 298 Vues
Learn about processes, process creation, termination, hierarchies, states, and implementation in operating systems. Explore differences between process and program, foreground and background processes, and more.
Understanding Processes in Operating Systems
E N D
Presentation Transcript
2.1 Processes • process = abstraction of a running program
2.1 Processes • 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
2.1 Processes Make no assumptions about timing! • Ex. • Start process A. • Start process B. • Which ends first? • Ex. • Start running test.exe. • Start running a second test.exe. • Which ends first? Make no assumptions about timing unless . . .
Processes cont’d • critical real-time requirements = particular events must occur within a specified number of milliseconds • Ex. QNX, VxWorks, RT11 (ancient), Windows Embedded (see http://www.microsoft.com/windowsembedded/en-us/about/solutions/medical-devices-healthcare.mspx?WT.mc_id=HS_search) • http://en.wikipedia.org/wiki/Real-time_operating_system
Processes cont’d • What’s the difference between a process and a program? • process – an activity • = program + input + output + state
Process Types • Foreground – process that interacts with user • Background – not associated with a specific user; specific/dedicated function • daemon = background process to handle some activities (e. g., email, telnet, ftp, web server, etc.)
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
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 <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; }
#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 break; default: printf( "parent: child has pid=%d \n", ret ); break; } return 0; } fork and exec
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; }
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 • Running • Ready • Blocked
Implementation of processes • Process table = array of structures (process control blocks)
Implementation of processes structProcessManagement { inteax, ebx, ecx, …; int pc; inteflags; … };
Implementation of processes structMemoryManagement { char* text; char* data; char* stack; };
Implementation of processes #define MAX_FDS 100 //max open files structFileManagement { char* root; char* working; intfd[ MAX_FDS ]; intuserID; intgroupID; };
Implementation of processes Process table = array of structures (process control blocks) structProcessTable { structProcessManagement pm; structMemoryManagement mm; structFileManagement fm; }; #define MAX_PROCESSES 500 structProcessTable pt[ MAX_PROCESSES ];
