Re: XS: Passing an external library's function a Perl XS callback

For completeness sake, I'm posting the relevant code that now has fixed my original problem. I can now use an external library that has ISR (Interrupt Service Routine) capability.

What I needed to do was allow a user to send in a Perl code reference, and then have the C interrupt handler dynamically call that user-supplied sub when the interrupt occurred.

XS code that sets up the interrupt through the external lib:

void interruptHandler();
int setInterrupt(int pin, int edge, char *callback);

char *perl_callback;
PerlInterpreter *mine;

void interruptHandler(){
    PERL_SET_CONTEXT(mine);

    dSP;
    PUSHMARK(SP);
    PUTBACK;

    call_pv(perl_callback, G_DISCARD|G_NOARGS);

    FREETMPS;
    LEAVE;
}

int setInterrupt(int pin, int edge, char *callback){
    perl_callback = callback;
    int interrupt = wiringPiISR(pin, edge, &interruptHandler);
    return interrupt;
}

# XS

int
setInterrupt(pin, edge, callback)
    int pin
    int edge
    char *callback

void
interruptHandler()
[download]

Perl module code that calls into the XS:

sub set_interrupt {
    shift if @_ == 4;
    my ($pin, $edge, $callback) = @_;
    setInterrupt($pin, $edge, $callback);
}
[download]

...and finally a basic test script:

use warnings;
use strict;

use RPi::WiringPi;
use RPi::WiringPi::Constant qw(:all);

my $pi = RPi::WiringPi->new();
my $pin = $pi->pin(27);

RPi::WiringPi::Core::set_interrupt(
    $pin->num, 
    EDGE_RISING, 
    'pin_27_edge_rise'
);

$pin->mode(INPUT);

sleep 10;

# manually change the pin state here to trigger
# interrupt

$pi->cleanup;

sub pin_27_edge_rise {
    print "pin 27 edge rise callback...\n";
    # do other stuff
}
[download]

Comment on Re: XS: Passing an external library's function a Perl XS callback Select or Download Code

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Re^2: XS: Passing an external library's function a Perl XS callback by RonW (Parson) on Aug 16, 2016 at 20:09 UTC
I see where you declare `PerlInterpreter mine` to hold the Perl context, but where you assign it? In his linked example, BrowserUk has: `void setCallback( SV cb1, SV* cb2, SV cb3, SV cb4 ) { saved = Perl_get_context();` [download] but I don't see an equivalent in your code.	[reply] [d/l] [select]
Re^3: XS: Passing an external library's function a Perl XS callback by pRiVi (Initiate) on Jan 06, 2019 at 00:05 UTC
I can confirm that you have to run `mine = Perl_get_context();` [download] before you can use this. The run of `dSP;` [download] just segfaults if `mine` [download] have not been set via `mine = Perl_get_context();` [download] I call on initialisation of my module a XS function which does does do `mine = Perl_get_context();` [download] and verify that mine is not NULL before trying to call a perl function. All I needed is the following to get it working, and call the function "functionname" within of the module I called "setcallback" from. The use in C: `void dorunperlfunction() { if (mine) { PERL_SET_CONTEXT(mine); dSP; ENTER; SAVETMPS; PUSHMARK(SP); PUTBACK; call_pv("functionname", G_DISCARD\|G_NOARGS); FREETMPS; LEAVE; }` [download] The initialisation in XS(!): `PerlInterpreter * mine = NULL; ... void setcallback() CODE: ... mine = Perl_get_context(); ...` [download]	[reply] [d/l] [select]