Hi,

The demo: 
use warnings;

#use Inline C => Config =>
#    BUILD_NOISY => 1;

use Inline C => <<'EOC';

static int x = 5;

void set_x(int z) {
   x = z;
}

void get_x(char * id) {
   printf("%s %d\n", id, x);
}

EOC

get_x('1st call:');

if($pid = fork()) {
  waitpid($pid,0);
} else {
  set_x(10);
  get_x('2nd call:');
  exit(0);
}
 
get_x('3rd call:');

[download]
On linux that script fulfils my expectations and outputs: 
1st call: 5
2nd call: 10
3rd call: 5

[download]
But on Win32, I get: 
1st call: 5
2nd call: 10
3rd call: 10

[download]
The basic requirement is that the script forks; the child then alters the value of an XS global and exits; that global then still retains its original value.

What options are there that will bring Windows into line with Linux ?
Is there anything that can be done within the C code ?
Perhaps something regarding the way (when/how) the C component is loaded ?

It seems that system() produces a genuine fork, and (as desired) any setting of the global inside a system call is lost when the system call exits.
This is not so straightforward to demo with the Inline::C script, but in the real world scenario I'm dealing with an XS module - and using system instead of fork is one alternative.

But I'm keen to hear what, if any, other options exist - especially any that leave the fork() in place.

Interestingly enough, there's no such problem with *perl* globals. The following script works fine on both Win32 and linux: 
use warnings;

$g = 5;
print "1st call: $g\n";

if($pid = fork()) {
  waitpid($pid,0);
} else {
  $g = 10;
  print "2nd call: $g\n";
  exit(0);
}

print "3rd call: $g\n";

[download]
It yields (as expected and desired): 
1st call: 5
2nd call: 10
3rd call: 5

[download]
Cheers,
Rob

In reply to Win32, fork and XS globals by syphilis

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