Each occurrence of {a:t@ype+} should be changed to {a:type}. E.g.,
extern
fun pop {a:t@ype+}(&stack_t(a) >> _) : Option(a) =
"ext#pop_ats"
should be changed to
extern
fun pop {a:type}(&stack_t(a) >> _) : Option(a) = "ext#pop_ats"
On Sunday, November 17, 2019 at 10:16:11 PM UTC-5, Vanessa McHale wrote:
>
> Hi all,
>
> I am trying to write a concurrent stack. Code is below:
>
> %{
> #include <stdatomic.h>
> #include <stdlib.h>
>
> struct stack_t {
> void *value;
> struct stack_t *next;
> };
>
> void __cats_new(struct stack_t *st) {
> st->value = NULL;
> st->next = NULL;
> }
>
> void __cats_push(struct stack_t *st, void *val) {
> for (;;) {
> struct stack_t old_st = *st;
> struct stack_t new_st = {val, &old_st};
> if (atomic_compare_exchange_strong(st, &old_st, new_st))
> return;
> }
> }
>
> // ignore ABA problem
> void *__cats_pop(struct stack_t *st) {
> for (;;) {
> if (st->next == NULL)
> return NULL;
> struct stack_t *old_st = st;
> struct stack_t xs1 = *(st->next);
> void *x = st->value;
> if (atomic_compare_exchange_strong(st, old_st, xs1))
> return x;
> }
> }
>
> atstype_boxed pop_ats(atstype_ref st) { return __cats_pop(st); }
>
> atsvoid_t0ype new_ats(atstype_ref st) { __cats_new(st); }
>
> atsvoid_t0ype push_ats(atstype_ref st, atstype_var val) {
> __cats_push(st, val);
> }
> %}
>
> typedef stack_t(a: t@ype+) = $extype "struct stack_t"
>
> extern
> fun new {a:t@ype+}(&stack_t(a)? >> _) : void =
> "ext#new_ats"
>
> extern
> fun push {a:t@ype+}(&stack_t(a) >> _, a) : void =
> "ext#push_ats"
>
> extern
> fun pop {a:t@ype+}(&stack_t(a) >> _) : Option(a) =
> "ext#pop_ats"
>
> fn print_str(x : string) : void =
> println!(x)
>
> implement main0 (argc, argv) =
> let
> var st: stack_t(string)
> val () = new(st)
> val () = push(st, "res")
> val () = push(st, "res2")
> val- Some (x) = pop(st)
> val () = print_str(x)
> in end
>
> (This compiles with gcc; I can run it with patscc simple.dats -latomic ;
> ./a.out)
>
> Unfortunately, it immediately segfaults. I know that the offending line
> is the
>
> val () = print_str(x)
>
> because removing it makes the program run fine.
>
> I tried writing an equivalent program in C, viz.
>
> #include <stdio.h>
>
> int main(int argc, char *argv[]) {
>
> struct stack_t *st;
>
> __cats_push(st, "res");
> __cats_push(st, "res2");
>
> char *res;
>
> res = __cats_pop(st);
> printf("%s\n", res);
>
> res = __cats_pop(st);
> printf("%s\n", res);
> }
>
> ...which works as expected. So I believe I am misunderstanding how ATS
> handles FFI and how structures exist in memory.
>
> Any insight is appreciated!
>
> Thanks,
> Vanessa
>
>
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