Fork
In this task, the goal is to spawn a new process which can run simultaneously with, and independently of, the original parent process.
You are encouraged to solve this task according to the task description, using any language you may know.
ALGOL 68
<lang> main: (
INT pid; IF (pid:=fork)=0 THEN print("This is new process") ELIF pid>0 THEN print("This is the original process") ELSE print("ERROR: Something went wrong") FI
) </lang> Output:
This is new process This is the original process
C
<lang c>#include<stdio.h>
- include<unistd.h>
int main(void) {
pid_t pid;
if((pid=fork())==0) { printf("This is new process\n"); } else if(pid>0) { printf("This is the original process\n"); } else { printf("ERROR: Something went wrong\n"); }
return 0;
}</lang>
Erlang
-module(fork). -export([start/0]). start() -> spawn(fork,child,[]), io:format("This is the original process~n"). child() -> io:format("This is the new process~n").
Then you can compile your code and execute it:
c(fork). fork:start().
OCaml
<lang ocaml>#load "unix.cma";; let pid = Unix.fork ();; if pid > 0 then
print_endline "This is the original process"
else
print_endline "This is the new process";;</lang>
Perl
In the child code, you may have to re-open database handles and such.
<lang perl>FORK: if ($pid = fork()) {
# parent code
} elsif (defined($pid)) {
setsid; # tells apache to let go of this process and let it run solo # disconnect ourselves from input, output, and errors close(STDOUT); close(STDIN); close(STDERR); # re-open to /dev/null to prevent irrelevant warn messages. open(STDOUT, '>/dev/null'); open(STDIN, '>/dev/null'); open(STDERR, '>>/home/virtual/logs/err.log'); # child code exit; # important to exit
} elsif($! =~ /emporar/){
warn '[' . localtime() . "] Failed to Fork - Will try again in 10 seconds.\n"; sleep(10); goto FORK;
} else {
warn '[' . localtime() . "] Unable to fork - $!"; exit(0);
}</lang>
Obviously you could do a Fork in a lot less lines, but this code covers all the bases
Pop11
lvars ress; if sys_fork(false) ->> ress then ;;; parent printf(ress, 'Child pid = %p\n'); else printf('In child\n'); endif;
Python
<lang python>import os
pid = os.fork() if pid > 0:
# parent code
else:
# child code</lang>
Ruby
<lang ruby>pid = fork if pid
# parent code
else
# child code
end</lang> or <lang ruby>fork do
# child code
end
- parent code</lang>
Smalltalk
<lang smalltalk>'Here I am' displayNl. |a| a := [
(Delay forSeconds: 2) wait . 1 to: 100 do: [ :i | i displayNl ]
] fork. 'Child will start after 2 seconds' displayNl. "wait to avoid terminating first the parent;
a better way should use semaphores"
(Delay forSeconds: 10) wait.</lang>
Toka
needs shell getpid is-data PID [ fork getpid PID = [ ." Child PID: " . cr ] [ ." In child\n" ] ifTrueFalse ] invoke
UnixPipes
Demonstrating a subshell getting forked, and running concurrently with the original process
(echo "Process 1" >&2 ;sleep 5; echo "1 done" ) | (echo "Process 2";cat;echo "2 done")