The processes in most systems can execute concurrently, and they may be created and deleted dynamically. Thus, these systems must provide a mechanism for process creation and termination
Process Creation
Most operating systems (including UNIX, Linux, and Windows) identify processes according to a unique process identifier (or pid), which is typically an integer number. The pid provides a unique value for each process in the system, and it can be used as an index to access various attributes of a process within the kernel
Creating a separate process using the UNIX fork() system call
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
pid t pid;
/* fork a child process */
pid = fork();
if (pid < 0) { /* error occurred */
fprintf(stderr, "Fork Failed");
return 1;
}
else if (pid == 0) { /* child process */
execlp("/bin/ls","ls",NULL);
}
else { /* parent process */
/* parent will wait for the child to complete */
wait(NULL);
printf("Child Complete");
}
return 0;
}
Creating a separate process using the Windows API
#include <stdio.h>
#include <windows.h>
int main(VOID)
{
STARTUPINFO si;
PROCESS INFORMATION pi;
/* allocate memory */
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
/* create child process */
if (!CreateProcess(NULL, /* use command line */
"C:\\WINDOWS\\system32\\mspaint.exe", /* command */
NULL, /* don’t inherit process handle */
NULL, /* don’t inherit thread handle */
FALSE, /* disable handle inheritance */
0, /* no creation flags */
NULL, /* use parent’s environment block */
NULL, /* use parent’s existing directory */
&si,
&pi))
{
fprintf(stderr, "Create Process Failed");
return -1;
}
/* parent will wait for the child to complete */
WaitForSingleObject(pi.hProcess, INFINITE);
printf("Child Complete");
/* close handles */
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
}