Hypothesis: SVs are owned by the tread in which they were created. When a thread exits, any SVs it owns are freed.

Nice hypothesis!++

By the way, using a string buffer to store a pointer is a waste. An IV is guaranteed to be big enough. Or you can use the PV itself (using SvPV_set) if you set LEN to zero.

Indeed. Or, as RVs and IVs are now aliases for the same thing, skip the intermediary completely, which appears to fix the problems Update: No it doesn't. I was so happy to see the back of the panic, that I missed that the contained value is updated by the thread :(

#! perl -slw
use strict;
package O;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C',  NAME => 'xso', CLEAN_AFTER_BUILD => 0;

typedef struct {
    SV**sv;
} O;

void *mem( size_t size ) {
    void *p;
    Newx( p, size, char );
    return p;
}

SV *new( char *package ) {
    O *o = (O*)mem( sizeof( O ) );
    SV *rv = newRV( o );

    o->sv = mem( sizeof( SV* ) );

    sv_bless( rv, gv_stashpv( package, 0 ) );
    SvREADONLY_on( rv );
    printf( "N:rv:%p o:%p\n", rv, o );
    return rv;
}

int set( SV *rv, SV *in ) {
    O *o = *(O**)SvRV( rv );
    printf( "S:rv;%p o:%p\n", rv, o );
    o->sv = newSVsv( in );
    return 1;
}

SV *get( SV *rv ) {
    O *o = *(O**)SvRV( rv );
    SV *old = newSVsv( o->sv );

    SvREFCNT_inc( old );

    printf( "G:rv;%p o:%p old:%p\n", rv, o, old );
    return old;
}

void DESTROY( SV *rv ) {
    printf( "DESTROY:%s\n", SvPV_nolen( rv ) );
}

void CLONE( SV *rv ) {
    printf( "CLONE:%s\n", SvPV_nolen( rv ) );
}


END_C
package main;
use threads;
use Devel::Peek;

my $o = O->new();
print $o;

$o->set( "abcde" );
print $o->get();

print "\nthreaded\n";

async {
    $o->set( "12345" );
}->join;

print $o->get();

__END__
C:\test>xso
N:rv:000000000025E128 o:00000000040D6738
O=SCALAR(0x40d6738)
S:rv;000000000025E248 o:0000000003CB6088
G:rv;000000000025E248 o:0000000003CB6088 old:00000000002B7980
abcde

threaded

CLONE:O
S:rv;0000000004361010 o:000000000432F5F8
DESTROY:O=SCALAR(0x4361028)
G:rv;000000000025E248 o:0000000003CB6088 old:00000000002B79E0
abcde
DESTROY:O=SCALAR(0x40d6738)
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