I am currently working on updating the SDL bindings for Perl. I need to do some callbacks for functions that need function pointers as parameters. Some functions do not need threaded callbacks and I have been able to get these to work. SDL_EventFilter implementation .

/* Static Memory for event filter call back */
static SV * eventfiltersv;

int eventfilter_cb( const void * event)
{

    dSP;
    int count;
    int filter_signal;
    SV * eventref = newSV( sizeof(SDL_Event *) );
    void * copyEvent = safemalloc( sizeof(SDL_Event) );
    memcpy( copyEvent, event, sizeof(SDL_Event) );
    ENTER;
    SAVETMPS;
    PUSHMARK(SP);
    
    XPUSHs( sv_setref_pv( eventref, "SDL::Event", (void *)copyEvent) )
+;
    PUTBACK;
    
    count = call_sv(eventfiltersv, G_SCALAR);

    SPAGAIN;

    if (count != 1 ) croak("callback returned more than 1 value\n");  
+  

    filter_signal = POPi;

    FREETMPS;
    LEAVE;

    return filter_signal;
}

void
events_set_event_filter(callback)
    SV* callback
    CODE:
    eventfiltersv = callback;
    
    SDL_SetEventFilter( (SDL_EventFilter *)eventfilter_cb);
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However this same method falls apart for functions which may be threaded. The Threaded callbacks are used in time_set_timer and time_add_timer. This is what I have tried

#ifndef aTHX_
#define aTHX_
#endif


#ifdef USE_THREADS
#define HAVE_TLS_CONTEXT
#endif

/* For windows  */
#ifndef SDL_PERL_DEFINES_H
#define SDL_PERL_DEFINES_H

#ifdef HAVE_TLS_CONTEXT
PerlInterpreter *parent_perl = NULL;
extern PerlInterpreter *parent_perl;
#define GET_TLS_CONTEXT parent_perl =  PERL_GET_CONTEXT;
#define ENTER_TLS_CONTEXT \
        PerlInterpreter *current_perl = PERL_GET_CONTEXT; \
            PERL_SET_CONTEXT(parent_perl); { \
                            PerlInterpreter *my_perl = parent_perl;
#define LEAVE_TLS_CONTEXT \
                            } PERL_SET_CONTEXT(current_perl);
#else
#define GET_TLS_CONTEXT         /* TLS context not enabled */
#define ENTER_TLS_CONTEXT       /* TLS context not enabled */
#define LEAVE_TLS_CONTEXT       /* TLS context not enabled */
#endif

#endif



#include <SDL.h>

SV* set_timersv;


Uint32 set_timer_cb( Uint32 interval)
{
    Uint32 retval;
    int back;
    SV* cmd;
    ENTER_TLS_CONTEXT
    dSP;

    cmd = (SV*)set_timersv;

    ENTER;
    SAVETMPS;
    PUSHMARK(SP);
    XPUSHs(sv_2mortal(newSViv(interval)));
    PUTBACK;

    if (0 != (back = call_sv(cmd,G_SCALAR))) {
        SPAGAIN;
        if (back != 1 ) Perl_croak (aTHX_ "Timer Callback failed!");
        retval = POPi;    
    } else {
        Perl_croak(aTHX_ "Timer Callback failed!");
    }

    FREETMPS;
    LEAVE;

    LEAVE_TLS_CONTEXT
    
    return retval;

}

int
time_set_timer ( interval, callback )
    Uint32 interval
    SV* callback
    CODE:
        set_timersv = callback;
        RETVAL = SDL_SetTimer(interval, set_timer_cb);
        
    OUTPUT:
        RETVAL
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To build the new SDL Perl redesign code please refer to this link . My goal is to be able to do this

use SDL;
use SDL::Time;

SDL::init(SDL_INIT_TIMER);
my $time = 0;
SDL::Timer::set_timer(100, sub { $time++; return $_[0]} );
print 'this will not print!'
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Currently this will die silently even with valgrind.