fork() is used to create processes; the process that calls
fork() is called the
parent and the new process is called the
child; so, nope, a "father" is not created, only the "son."
Your shell program does this: you type a command and hit the return/ether key and the shell forks and executes your command in a child process, a new process. The parent waits until the child completes (and dies or you kill it with, say, Ctrl-C) returning you to your shell prompt.
In C programming you would use
fork(),
wait() and one of the
exec() functions in a child process in lieu of using the
system() function (it's more efficient to "fork and exec" than to call
system()).
POSIX Threads (pthreads) can be used to implement parallelism; not the same thing. POSIX Threads are most effective on multi-processor or multi-core systems where the process flow can be scheduled to run on another processor thus gaining speed through parallel or distributed processing.
Here's a simple example of "fork and exec;" it is a simple command interpreter (the shell is a command interpreter albeit with a lot more function and capabilities) that prompts for a command the executes it:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <wait.h>
#include <sys/types.h>
void main (void)
{
char line [BUFSIZ];
int process;
for ( ; ; ) {
(void) fprintf (stderr, "cmd: ");
if (gets (line) == (char *) NULL)
exit (EXIT_FAILURE);
/* create new process */
if ((process = fork ()) > 0)
(void) wait ((int *) NULL);
else if (process == 0) { /* child */
/* execute program */
(void) execlp (line, line, NULL);
/* some problem if exec returns */
(void) fprintf (stderr, "can't execute %s\n", line);
exit (errno);
} else if (process == -1) { /* can't create */
(void) fprintf (stderr, "can't fork\n");
exit (errno);
}
}
}
Pretty straight-forward.
Here's and example (from
http://www.yolinux.com/TUTORIALS/Lin...ixThreads.html) that demonstrates thread creation and termination:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
void *print_message_function( void *ptr );
main()
{
pthread_t thread1, thread2;
char *message1 = "Thread 1";
char *message2 = "Thread 2";
int iret1, iret2;
/* Create independent threads each of which will execute function */
iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
/* Wait till threads are complete before main continues. Unless we */
/* wait we run the risk of executing an exit which will terminate */
/* the process and all threads before the threads have completed. */
pthread_join( thread1, NULL);
pthread_join( thread2, NULL);
printf("Thread 1 returns: %d\n",iret1);
printf("Thread 2 returns: %d\n",iret2);
exit(0);
}
void *print_message_function( void *ptr )
{
char *message;
message = (char *) ptr;
printf("%s \n", message);
}
Now, bear in mind that POSIX Threads are useful on multi-core or multi-procesor systems where the operating system schedules and manages the threads (Linux does).
Basically, they're not the same things and each has its uses.
Hope this helps some.