On Sun Sep 11 07:01:11 2016, pierre.vig...@gmail.com wrote:
> Hi,
>
> i stumbled a across a strange behaviour when playing with Supplier, i
> tried to gulf it down, starting from the documentation of supply. The
> following code, taken from the documentation and slightly modified is
> working as expected:
>
> my $s = Supplier.new;
> my $l = $s.Supply();
> start {
> sleep 1;
> $s.emit(1);
> $s.emit(2);
> $s.done;
> }
> $l.wait;
> say "done";
>
> If i tap the $l variable to display the value that are supplied by the
> supplier, it then hangs indefinitely:
>
> my $s = Supplier.new;
> my $l = $s.Supply();
> $l.tap( -> $v { say "got : $v" } );
> start {
> sleep 1;
> $s.emit(1);
> $s.emit(2);
> $s.done;
> }
> $l.wait;
> say "done";
>
> Pierre
I tried to debug this, but ultimately failed, as I'm getting spectest failures.
There are actually three issues:
1) Supply.sanitize uses a per-instance $!finished attribute and when the first
tap gets closed, no more taps get closed. This is what causes the OP bug.
2) Supply.wait calls Supply.Promise that opens a new tap that keeps/breaks the
Promise on done/quit. However, if this is done on-already finished Supply, that
Promise will never complete, causing in a hang in .wait. This is what causes
the bug if we golf OP's code to get rid of the start {}.
3) To me, it looks like there's a race condition with regards to $!finished,
since one tap can be setting it to `1`, while another is mid-checking it. Not
sure if it matters.
Below is my attempt at fixing it that fixes issues #1 and #2 (where .wait on a
finished supply returns a Nil), however, this has failures in
t/spec/S17-supply/basic.t because I'm not returning a Tap, I think.
I've also no idea why the created supplies go through the .serialize ->
.sanitize chain where both methods look nearly identical. I'm leaving this for
someone more knowledgeable to finish.
----------------------8<-----------------------------------------
diff --git a/src/core/Supply.pm b/src/core/Supply.pm
index d91c3b8..f0fa251 100644
--- a/src/core/Supply.pm
+++ b/src/core/Supply.pm
@@ -197,6 +197,7 @@ my class Supply {
method tap(&emit, &done, &quit) {
my int $cleaned-up = 0;
+ return if $!finished;
my $source-tap = $!source.tap(
-> \value{
emit(value) unless $!finished;
@@ -204,16 +205,16 @@ my class Supply {
done => -> {
unless $!finished {
$!finished = 1;
- done();
self!cleanup($cleaned-up, $source-tap);
}
+ done();
},
quit => -> $ex {
unless $!finished {
$!finished = 1;
- quit($ex);
self!cleanup($cleaned-up, $source-tap);
}
+ quit($ex);
});
Tap.new({ self!cleanup($cleaned-up, $source-tap) })
}
@@ -610,10 +611,11 @@ my class Supply {
my $p = Promise.new;
my $v = $p.vow;
my $final := Nil;
- my $t = self.tap:
+ my $t = self.tap(
-> \val { $final := val },
done => { $v.keep($final) },
- quit => -> \ex { $v.break(ex) };
+ quit => -> \ex { $v.break(ex) },
+ ) or $v.keep(Nil);
$p
}
----------------------8<-----------------------------------------
