Fork
You are encouraged to solve this task according to the task description, using any language you may know.
In this task, the goal is to spawn a new process which can run simultaneously with, and independently of, the original parent process.
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>
Standard ML
<lang sml>case Posix.Process.fork () of
SOME pid => print "This is the original process\n" | NONE => print "This is the new process\n";
</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")