11-06-2009
1. No
2. Depends on what scheduler the kernel uses.
3. Yes, but this has nothing to do with system or concurrent programming, but with counting how much output you already produced and waiting after a certain amount.
5. Sendmail, Postfix, Firefox, FTP, SSH, ... pretty much anything using a network.
6. It doesn't. By the time fork() finishes, there are already 2 separate processes. In the parent process it's returning the PID of the child. In the child it returns 0. If it can't spawn a child for any reason, it returns -1 and sets errno.
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LEARN ABOUT OPENDARWIN
fork
FORK(2) BSD System Calls Manual FORK(2)
NAME
fork -- create a new process
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
pid_t
fork(void);
DESCRIPTION
Fork() causes creation of a new process. The new process (child process) is an exact copy of the calling process (parent process) except for
the following:
o The child process has a unique process ID.
o The child process has a different parent process ID (i.e., the process ID of the parent process).
o The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that,
for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the
child process can affect a subsequent read or write by the parent. This descriptor copying is also used by the shell to establish
standard input and output for newly created processes as well as to set up pipes.
o The child processes resource utilizations are set to 0; see setrlimit(2).
RETURN VALUES
Upon successful completion, fork() returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
ERRORS
Fork() will fail and no child process will be created if:
[EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration-
dependent.
[EAGAIN] The system-imposed limit MAXUPRC (<sys/param.h>) on the total number of processes under execution by a single user would
be exceeded.
[ENOMEM] There is insufficient swap space for the new process.
SEE ALSO
execve(2), wait(2)
HISTORY
A fork() function call appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution