On Sat Dec 05 11:13:54 2015, b...@abrij.org wrote:
>
> 16:18 skids I think the Supply work may have made
> $fh.watch.Promise not fire anymore.
> 16:20 watch.tap still works.
> 16:21 jnthn The semantics of Supply.Promise changed
> 16:21 You'll need $fh.watch.head(1).Promise to get the
> original ones
> 16:21 skids Ah that would explain it. jnthn++
> 16:22 Hrm that doesn't seem to do it though.
> 2 more elements. Show/hide.
> 16:34 jnthn Hm, head doesn't seem to be filing the "done"
>
> These work:
>
> $ perl6 -e 'my $f = Supplier.new; my $s = $f.head(1).Supply; my $t =
> $s.tap(-> $ { 42.say }, done => {43.say} ); start { for 0..3 {
> $f.emit(42) }; $f.done(); }; await $s.Promise; 44.say; '
> 42
> 43
> 44
>
> $ perl6 -e 'my $f = Supplier.new; my $s = $f.head(1).Supply; my $t =
> $s.tap(-> $ { 42.say }, done => {43.say} ); start { for 0..3 {
> $f.emit(42) }; }; await $s.Promise; 44.say; '
> 42
> 43
> 44
>
>
> This neither sends a done nor fulfills a .Promise (input echoed into
> file from another terminal):
>
> $ perl6 -e 'my $fh = open("/tmp/foo.txt", :create); my $s =
> $fh.watch.head(1); my $t = $s.tap(-> $ { 42.say }, done => {43.say} );
> await $s.Promise; 44.say'
> 42
> ^C
>
This works reliably now, and so could do with a test. Probably thanks to one of
the many Supply fixes over the last months.
> ...and when the .head is off a Supply instead of a Supplier, a done
> from the original Supply propagates but the Promise never unhooks:
>
> $ perl6 -e 'my $f = Supplier.new; my $s = $f.Supply.head(1); my $t =
> $s.tap(-> $ { 42.say }, done => {43.say} ); start { for 0..3 {
> $f.emit(42) }; $f.done(); }; await $s.Promise; 44.say; '
> 42
> 43
> ^C
>
> $ perl6 -e 'my $f = Supplier.new; my $s = $f.Supply.head(1); my $t =
> $s.tap(-> $ { 42.say }, done => {43.say} ); start { for 0..3 {
> $f.emit(42) }; }; await $s.Promise; 44.say; '
> 42
> ^C
This code is vulnerable to a race condition, thus it sometimes works, sometimes
not. If you add a `sleep 1` before the `await` then it reliably hangs. The
reason is that a Supplier is a live supply; if you miss the events (emit/done)
then they're gone for good. (Note that `.Promise` taps the supply separately
from the `.tap` that is already taking place.) For this to reliably work, the
`Promise` should be obtained prior to setting off the `start` block. This works
reliably, every time:
my $f = Supplier.new;
my $s = $f.Supply.head(1);
my $t = $s.tap(-> $ { 42.say }, done => {43.say} );
my $p = $s.Promise;
start {
for 0..3 {
$f.emit(42)
};
$f.done();
}
await $p;
44.say;
Tagging testneeded for the part that deserves a test.
/jnthn
