Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: fork function
Top Forums UNIX for Dummies Questions & Answers fork function Post 46848 by Perderabo on Tuesday 27th of January 2004 09:00:42 PM
Old 01-27-2004
Let's take:

int main()
{int pid = fork();
exit(0);
}

as an example. Let's say that it is compiled and is sitting on disk as a file called forktest.

And let's say that forktest starts to run. This means that it must have a pid, let's say that it is pid 25021.

Well, pid 25021 will quickly invoke fork(). This means that the kernel must create a second process. The second process will be the child of process 25021. Let's say that the second process gets a pid of 25079. So now we have two processes: 25021 which is the original and 25079 which is the child.

Now both processes can run. If the system has two cpu's, they can literally run at the same time. But neither process restarts from the beginning. They both continue from where process 25021 was.

Both processes seem to be returning from fork. And both must store a value in pid. Now they do not share a common variable called pid. Each process has a private copy. The variable called pid in process 25021 gets a value of 25079. The variable called pid in process 25079 gets a zero.

Next both processes continue with the next statement. So both processes now exit.

The end.

Now the situation that you are worrying about can occur. And it is a nightmare. But it requires a bug like:

while(1) fork();

Here both processes are in an infinite loop. So both will fork again resulting in 4 processes. Then all 4 processes will fork again. Then all 8 processes will fork again. And so it goes until fork fails. So please don't do that.
 

10 More Discussions You Might Find Interesting

1. Programming

how to use function fork() in Windows NT

Hello, I need to make a gateway from Ethernet to RS-485. I am using stream socket, and I am programming in windows nt. I would like to know how could I use some functions from unix in windows nt. I would like to use the function fork(). Which library it uses and how can I get it? Can I... (1 Reply)
Discussion started by: danieljorge
1 Replies

2. Shell Programming and Scripting

Endless loop - Fork function failed?

I need a quick script that will serve as a sort of "real time monitor" for watching some log files. I am using Bourne shell in HP-UX 10.20. I have basically created a script that never ends, unless of course I manually terminate it. Here's the script (it's called qhistory): clear echo "REAL... (3 Replies)
Discussion started by: cdunavent
3 Replies

3. Shell Programming and Scripting

Passing global variable to a function which is called by another function

Hi , I have three funcions f1, f2 and f3 . f1 calls f2 and f2 calls f3 . I have a global variable "period" which i want to pass to f3 . Can i pass the variable directly in the definition of f3 ? Pls help . sars (4 Replies)
Discussion started by: sars
4 Replies

4. Shell Programming and Scripting

Return a value from called function to the calling function

I have two scripts. script1.sh looks -------------------------------- #!/bin/bash display() { echo "Welcome to Unix" } display ----------------------------- Script2.sh #!/bin/bash sh script1.sh //simply calling script1.sh ------------------------------ (1 Reply)
Discussion started by: mvictorvijayan
1 Replies

5. Shell Programming and Scripting

SHELL SCRIPT Function Calling Another Function Please Help...

This is my function which is creating three variables based on counter & writing these variable to database by calling another function writeRecord but only one record is getting wrote in DB.... Please advise ASAP...:confused: function InsertFtg { FTGSTR="" echo "Saurabh is GREAT $#" let... (2 Replies)
Discussion started by: omkar.sonawane
2 Replies

6. AIX

Fork Function Failed on 4GB ?

Hello, I am running Oracle Database and after a while I keep getting this message whenever I execute any command. I cannot execute any command even shutdown, whenever I execute any command , I get this message /usr/bin/ksh: 0403-031 The fork function failed. There is not enough memory... (7 Replies)
Discussion started by: filosophizer
7 Replies

7. Shell Programming and Scripting

Help to Modify File Name in each function before calling another function.

I have a script which does gunzip, zip and untar. Input to the script is file name and file directory (where file is located) I am reading the input parameters as follows: FILENAME=$1 FILEDIR=$2 I have created 3 functions that are as follows: 1) gunzip file 2) unzip file... (2 Replies)
Discussion started by: pinnacle
2 Replies

8. Shell Programming and Scripting

Will files, creaetd in one function of the same script will be recognized in another function?

Dear All. I have a script, which process files one by one. In the script I have two functions. one sftp files to different server the other from existing file create file with different name. My question is: Will sftp function recognize files names , which are created in another... (1 Reply)
Discussion started by: digioleg54
1 Replies

9. Shell Programming and Scripting

Need help on awk for printing the function name inside each function

Hi, I am having script which contains many functions. Need to print each function name at the starting of the function. Like below, functionname() { echo "functionname" commands.... } I've tried like below, func=`grep "()" scriptname | cut -d "(" -f1` for i in $func do nawk -v... (4 Replies)
Discussion started by: Sumanthsv
4 Replies

10. Shell Programming and Scripting

Function - Make your function return an exit status

Hi All, Good Day, seeking for your assistance on how to not perform my 2nd, 3rd,4th etc.. function if my 1st function is in else condition. #Body function1() { if then echo "exist" else echo "not exist" } #if not exist in function1 my all other function will not proceed.... (4 Replies)
Discussion started by: meister29
4 Replies

LEARN ABOUT OSF1

ppmtosixel

ppmtosixel(1)						      General Commands Manual						     ppmtosixel(1)

NAME

       ppmtosixel - convert a portable pixmap into DEC sixel format

SYNOPSIS

       ppmtosixel [-raw] [-margin] [ppmfile]

DESCRIPTION

       Reads  a  portable  pixmap  as input.  Produces sixel commands (SIX) as output.	The output is formatted for color printing, e.g. for a DEC
       LJ250 color inkjet printer.

       If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled.  A printer control header and a color assignment table
       begin the SIX file.  Image data is written in a compressed format by default.  A printer control footer ends the image file.

OPTIONS

       -raw   If  specified,  each  pixel  will  be explicitly described in the image file.  If -raw is not specified, output will default to com-
	      pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands.  A raw file is often an order	of  magni-
	      tude larger than a compressed file and prints much slower.

       -margin
	      If  -margin  is not specified, the image will be start at the left margin (of the window, paper, or whatever).  If -margin is speci-
	      fied, a 1.5 inch left margin will offset the image.

PRINTING

       Generally, sixel files must reach the printer unfiltered.  Use the lpr -x option or cat filename > /dev/tty0?.

BUGS

       Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion.  If the original PPM maxval was
       greater	than  100,  rescaling  also reduces the image depth.  While the actual RGB values from the ppm file are more or less retained, the
       color palette of the LJ250 may not match the colors on your screen.  This seems to be a printer limitation.

SEE ALSO

       ppm(5)

AUTHOR

       Copyright (C) 1991 by Rick Vinci.

								   26 April 1991						     ppmtosixel(1)
All times are GMT -4. The time now is 10:17 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy