Kill a NIF's process

[Robert Harris]

Hi Sverker,

> On 21 Apr 2021, at 17:37, Sverker Eriksson <sverker.eriksson@REDACTED> wrote:
>
> At process termination the deallocation of the heap is delayed until a running dirty NIF has returned. This to make sure the dirty NIF can safely continue read its arguments.

That makes things somewhat simpler;  thank you.

> The firing of links and monitors (including NIF monitor down calls), on the other hand, are not delayed by a running dirty NIF.

Is enif_monitor_process() serialised with respect to the delivery of
an exit signal by a concurrent thread?  I.e. if the function returns zero
and the caller is later killed then is it guaranteed that its down
callback will be invoked?  I am wondering if (absent any documentation
to the contrary) there might exist a race condition in which process A
might kill process B at exactly the time that the latter calls
enif_monitor_process(), e.g. in the (untested) code below.

Regards,

Robert



/* resource object */
typedef struct foo {
int abort;
...
} foo_t;

void
down(ErlNifEnv *env, void *obj, ErlNifPid *pid, ErlNifMonitor *mon)
{
((foo_t *)obj)->abort = 1;
}

ERL_NIF_TERM
some_dirty_nif(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[])
{
foo_t *foop;
ErlNifPid pid;
ErlNifMonitor monitor;

enif_get_resource(env, argv[0], foo_resource, (void **)&foop));
foop->abort = 0;

enif_self(env, &pid);
if (enif_monitor_process(env, foop, pid, &monitor) > 0)
/* process already dead;  abort */

/* lost a signal here? */

while (/* some very long loop */) {
if (foop->abort) {
/* process waiting to die;  abort */
...
}
/* do stuff */
}

/* no longer care about being directed to abort */
enif_demonitor_process(env, foop, &monitor);
/* return */
...
}
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