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12-13-2012
Example, with a little humor
A 'fork' is used when there is no dependency related to the fork-ed process; things do not all have to be done sequentially.
Example 1.
you get up
you wake up your son/daughter
you take your keys, start the car, and drive your son/daughter to school
you come back home
you now go on unix.com
*no fork in here as everything is sequential and you do not do the next step until the previous step is complete.
Example 2.
you get up
you wake your spouse up
ask (nicely) your spouse to get son/daughter up and drive to school
* here is the fork *
your spouse wakes up your son/daughter and drives to school
you now go on unix.com
*the fork here allows you to go on unix.com earlier in the day.
However, the 'fork' would serve no real purpose if you could not go on unix.com earlier.
Example 1.
you get up
you wake up your son/daughter
you take your keys, start the car, and drive your son/daughter to school
you come back home
you now go on unix.com
*no fork in here as everything is sequential and you do not do the next step until the previous step is complete.
Example 2.
you get up
you wake your spouse up
ask (nicely) your spouse to get son/daughter up and drive to school
* here is the fork *
your spouse wakes up your son/daughter and drives to school
you now go on unix.com
*the fork here allows you to go on unix.com earlier in the day.
However, the 'fork' would serve no real purpose if you could not go on unix.com earlier.
This User Gave Thanks to joeyg For This Post:
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LEARN ABOUT BSD
fork
FORK(2) System Calls Manual FORK(2) NAME
fork - create a new process SYNOPSIS
pid = fork() int pid; DESCRIPTION
Fork causes creation of a new process. The new process (child process) is an exact copy of the calling process except for the following: The child process has a unique process ID. The child process has a different parent process ID (i.e., the process ID of the parent process). 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. The child processes resource utilizations are set to 0; see setrlimit(2). RETURN VALUE
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 one or more of the following are true: [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) 3rd Berkeley Distribution May 22, 1986 FORK(2)