potential problem with fork()

[bsder]

Hi,

I m not sure whether the following Perl code is correct with fork().

while (1) {
if (open( FILE, "< $books" ) {
if (!defined($kidpid = fork())) {
die "cannot fork: $!";
}
elsif ($kidpid == 0) { # child
child_func();
}
else # parent.
sleep(1);
}
}

Can anyone please give comment and suggestion of improving it?

Thanks
Sam

 

[Tad McClellan]

I m not sure whether the following Perl code is correct with fork().

while (1) {
if (open( FILE, "< $books" ) {
if (!defined($kidpid = fork())) {
die "cannot fork: $!";
}

Control can never get here if the fork() failed, so...

elsif ($kidpid == 0) { # child

.... you don't need an elsif, just an if would do.

child_func();
}

Control can never get here in the child process, so ...

else # parent.

.... you don't need an else at all.

(and if you did need an else, you would need an opening curly bracket)

sleep(1);
}
}

Can anyone please give comment and suggestion of improving it?

# untested
while (1) {
if (open( FILE, "< $books" ) {
die "cannot fork: $!" unless defined($kidpid = fork());

if ($kidpid == 0) { # child
child_func();
}
# parent
sleep(1);
}
}

 

[xhoster]

Hi,

I m not sure whether the following Perl code is correct with fork().

while (1) {
if (open( FILE, "< $books" ) {

Syntax error, unbalanced parens. Also, you wouldn't you want to do
something more intelligent in case the file can't be opened?

if (!defined($kidpid = fork())) {
die "cannot fork: $!";
}
elsif ($kidpid == 0) { # child
child_func();

child_func() had better never return, or else you are making a fork-bomb.

}
else # parent.
sleep(1);
}
}

Can anyone please give comment and suggestion of improving it?

Without knowing what it is supposed to do?

Xho

 

[Ilya Zakharevich]

[A complimentary Cc of this posting was sent to
Tad McClellan

# untested

while (1) {
if (open( FILE, "< $books" ) {
die "cannot fork: $!" unless defined($kidpid = fork());

if ($kidpid == 0) { # child
child_func();
}
# parent

How should I guess looking on this code that child_func() never
returns? IMO, one should at least move exit() out of child_func()
into the main loop to make the intent clear...

sleep(1);
}
}

Hope this helps,
Ilya

 

[John W. Krahn]

You should use the 3-argument version of open(). You should print why
open did not succeed if it failed. It is usually better to use
variables rather than barewords for file handles:

if ( open( my $file, '<', $books ) ) { ^^^

...
}else{
die("Can't open $books for writing: $!");

^^^^^^^
I'm not suprised that it won't open for writing.


John