I am trying to make Perl bindings for two C++ objects. In C++, their usage is:

SecurityCredentials *credentials = new SecurityCredentials(service_url
+, some_secret_key);
credentials->IsValid();
credentials->ChangeKey(new_secret_key); // Does occur during a normal 
+program as these change frequently.

AlarmZone zone(credentials, 0);
zone->IsArmed();
zone->SetArmed(true);

AlarmZone another_zone(credentials, 1);
another_zone->IsArmed();
another_zone->SetArmed(true);
[download]

As you can see, a SecurityCredentials object exists in isolation. An AlarmZone object however requires a pointer to a SecurityCredentials throughout its lifetime. Following perlxs (using ExtUtils::MakeMaker, h2xs type tools), I got the SecurityCredentials object working fine; the XS file looks like:

SecurityCredentials*
SecurityCredentials::new(const char* service_url, const char* service_
+credentials)
CODE:
  RETVAL = new SecurityCredentials(service_url, service_credentials);
OUTPUT:
  RETVAL

void
SecurityCredentials::DESTROY()

bool
SecurityCredentials::IsValid()
...
[download]

Now comes the time to implement AlarmZone. I am hoping the usage looks like:

my $security_credentials = SecurityCredentials->new(service_url, some_
+secret_key);
my $zone = AlarmZone->new($security_credentials, 1);
$zone->IsArmed(); # Some time later
[download]

The reference counting of $security_credentials is my problem: For the C++ AlarmZone to work, its pointer to the C++ SecurityCredentials must be valid. However since things are running from Perl land, $security_credentials may go out of scope and be destroyed, prematurely cleaning up the underlying C++ object required by AlarmZones.

For example, in the following example AlarmZone should still work, even though $security_credentials goes out of scope:

sub SillySub {
  my $security_credentials = SecurityCredentials->new(service_url, som
+e_secret_key);
  return AlarmZone->new($security_credentials, 1);
}
[download]

My ideas to fix this so far have been:

• The XS part of AlarmZone::new(SV* security_credentials, int zone) increases the reference count of security_credentials with SvREFCNT_inc() or similar, retains a pointer to the SV*, and decreases the reference count in AlarmZone->DESTROY(). This is the cleanest idea I can think of (reference counting stays in the Perl area of the program, C++ part continues unaware of Perl's existence.). I am stuck working out the details though, in particular where to store the security_credentials pointer (so it can be used later in DESTROY()).
• Each AlarmZone retains a copy of SecurityCredentials (thus no reference counting problems, however extra memory usage and duplication, not possible security_credentials->ChangeKey() - which does happen)
• Bypass reference counting at the Perl level by using some kind of C++ Singleton pattern (but this pattern is generally discouraged)

Any suggestions?

Thanks! :)

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