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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.
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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 ];
