Comments inline.
On Mon, May 28, 2018 at 2:02 AM, Norman Gaywood <ngayw...@gmail.com> wrote:
> T""his simple program creates a thread to read a directory with dir() and
> place the files on a channel. $N worker threads read that channel and
> "process" (prints) the files. But I'm getting this "An operation first
> awaited:" error.
>
> I've read the traps page about this error several times, but still can't
> make sense of it. Can some explain what's going on here?
>
> The directory contents:
> $ ls
> a b c traverse-dir0.p6
>
> Running the program:
> $ ./traverse-dir0.p6
> traverse-dir0.p6
> a
> b
> c
> An operation first awaited:
> in sub MAIN at ./traverse-dir0.p6 line 24
> in block <unit> at ./traverse-dir0.p6 line 5
>
> Died with the exception:
> Cannot find method 'path': no method cache and no .^find_method
> in block at ./traverse-dir0.p6 line 16
>
> The program:
> $ cat traverse-dir0.p6
> #!/usr/bin/env perl6
> # There is a thread to populate $dir-channel by reading filenames in a
> directory with dir()
> # and $N worker threads to read the filenames from the $dir-channel.
>
> sub MAIN( Str $dir = ".", Int :$N = 4 ) {
>
> my $dir-channel = Channel.new();
> my $dir-read = start {
> $dir-channel.send( $_ ) for dir $dir;
> $dir-channel.close;
> }
>
> my @workers = (^$N).map: {
> start {
> while my $file = $dir-channel.receive() {
> say $file.path;
> }
> CATCH {
> when X::Channel::ReceiveOnClosed { .resume }
------------------------------
What did you expect to happen if you resumed?
Because I expect it to try to run `say $file.path;` with invalid data.
You can just remove the `.resume` and it works.
------------------------------
> }
> }
> }
>
> await $dir-read, @workers;
> }
There is no need to await for $dir-read, as the workers won't finish
until it's done anyway.
---
Anyway I would use a `react` block.
my @workers = (^$N).map: {
start react whenever $dir-channel -> $file {
say $file.path;
}
}
Note that `start` and `react` don't need {}, but you can use them if neccesary.
my @workers = (^$N).map: {
start {
say 'started';
react {
say 'reacting';
whenever Promise.in(½) { say '½ second has elapsed' }
whenever $dir-channel -> $file {
say $file.path;
}
}
}
}
