Coro, EV and cede

Nick Kostirya has asked for the wisdom of the Perl Monks concerning the following question:

I'd like to try the Coro together with EV.

There are a few code snippets:

async {
    while (1) {
    ...
    cede;
    }
};
[download]

When I use only Coro, everything's fine.

But when I try to connect EV, weird things happen, which can be explained only by the fact cede doesn't pass the control to EV.

It forces me to use cede and Coro::Timer::sleep together:

async {
    while (1) {
    ...
    sleep 0; cede;
    }
};
[download]

Coro::Timer::sleep - it's an explicit call to EV.

Has anyone faced such an issue?

UPDATE:
I was wrong, Coro::AnyEvent::poll really helps.
This is the same as sleep(0).
I was pulling his leg, Coro’s author, shame on me.
I just could not figure it out that Coro can be used without IO in practice And those using IO have Coro::AnyEvent::poll.
Still, I learnt that Marc Lehmann is a patient and very polite person.
I got a good lesson too: don’t make the output on STDIN artificially.

Comment on Coro, EV and cede Select or Download Code

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Re: Coro, EV and cede by ikegami (Patriarch) on Apr 07, 2011 at 15:58 UTC
The docs suggest `async { EV::loop };` [download] That makes me wonder. If that works, then why doesn't `cede` to the main thread?	[reply] [d/l] [select]
Re^2: Coro, EV and cede by Nick Kostirya (Sexton) on Apr 08, 2011 at 06:09 UTC
I've tried this way at once, but it didn't help. Probably cede really doesn't give EV control.	[reply]
Re^3: Coro, EV and cede by ikegami (Patriarch) on Apr 08, 2011 at 17:02 UTC
Just call `sleep` instead of `cede` if it works better. But you may want to consider the output I got from different sleep lengths in the second thread. I changed from printing the length to print `time()`. Using sleep(0), it takes 9s to do a request. first second second second second second second second second second second second second second second second second 1302281756 second first second second second second second second second second second second second second second second second second second 1302281765 Using sleep(1), it takes 2s to do a request. first second second second 1302281791 first second second 1302281793 first second second 1302281795 Using sleep(2), it takes 1s to do a request. first second 1302281819 first second 1302281820 first second 1302281822 first 1302281823 [download]	[reply] [d/l] [select]
Re^3: Coro, EV and cede by ikegami (Patriarch) on Apr 08, 2011 at 15:40 UTC
It gives control to the coro running EventLoop. But of course, that coro is in the `EventLoop` call. What about `async { sleep 60 while 1; }` [download]	[reply] [d/l] [select]
Re: Coro, EV and cede by zwon (Abbot) on Apr 07, 2011 at 10:53 UTC
I don't really understand what you're trying to do. Do you have some complete (but not too big) peace of code that we could run to see the problem?	[reply]
Re^2: Coro, EV and cede by Nick Kostirya (Sexton) on Apr 07, 2011 at 12:01 UTC
`use strict; use warnings; use Coro; use Coro::EV; use Coro::LWP; use LWP::Simple; use Coro::Timer qw(sleep); async { while (1) { CORE::select undef, undef, undef, 0.5; print "first\n"; # my $r = get "http://www.perlmonks.org"; # print length $r, "\n"; # sleep 0; cede; } }; async { while (1) { CORE::select undef, undef, undef, 0.5; print "second\n"; # sleep 0; cede; } }; EV::loop while 1;` [download] output: `first second first second first second ...` [download] When uncomment `my $r = get "http://www.perlmonks.org"; print length $r, "\n";` [download] got output: `first second second second second second second second` [download] Then uncomment "sleep 0" and got output : `first second 76573 second first second 76570 second first second 76597 second first second` [download]	[reply] [d/l] [select]
Re^3: Coro, EV and cede by Corion (Patriarch) on Apr 07, 2011 at 12:12 UTC
Depending on your version of LWP, LWP::Simple might or might not play nice with LWP::Coro. I know that at least for some versions prior to 5.827, LWP::Simple used its own socket factory instead of using what LWP::UserAgent did. You might want to inspect your module versions. Be careful when upgrading to LWP 6.x. If you use HTTPS connections, you will at least also need to install Mozilla::UA, because LWP 6 checks the validity of https certificates.	[reply]
Re^4: Coro, EV and cede by Nick Kostirya (Sexton) on Apr 07, 2011 at 12:36 UTC
Re^3: Coro, EV and cede by zwon (Abbot) on Apr 07, 2011 at 13:00 UTC
The first result shows that `cede` works, as you get your switching. The problem starts after LWP comes in, and looking into Coro::LWP documentation, it looks like it does something rather cumbersome. I don't see it even tries to establish connection with the server. But if I replace CORE::select with just select everything is ok. I'd say you should try something else. I had positive experience with AnyEvent::HTTP, or maybe threads.	[reply] [d/l]
Re^4: Coro, EV and cede by Nick Kostirya (Sexton) on Apr 07, 2011 at 13:22 UTC
Re^5: Coro, EV and cede by zwon (Abbot) on Apr 07, 2011 at 14:20 UTC
Re^2: Coro, EV and cede by Anonymous Monk on Dec 23, 2011 at 00:00 UTC
Sorry to reply on your post, I wish perlmonks had a way to anonymously + reply to postings, but I haven't found it yet. Anyway, Coro::AnyEvent::poll is the right function, and it does work + fine on my box. The output is this: first second second second second second second second second second second second second second second second second second second second second 73246 second first second second second second second The problem the original poster likely runs into is his use of CORE::s +elect - this function blocks the process for half a second each time +it's called, so LWP needs long time to make progress, because it can +only do something twice a second. [download]	[reply] [d/l]
Re^3: Coro, EV and cede by Nick Kostirya (Sexton) on Dec 27, 2011 at 13:59 UTC
I was wrong, Coro::AnyEvent::poll really helps. This is the same as sleep(0). I was pulling his leg, Coro’s author, shame on me. I just could not figure it out that Coro can be used without IO in practice And those using IO have Coro::AnyEvent::poll. Still, I learnt that Marc Lehmann is a patient and very polite person. I got a good lesson too: don’t make the output on STDIN artificially.	[reply]
Re: Coro, EV and cede by Anonymous Monk on Jun 24, 2011 at 19:44 UTC
The Coro::AnyEvent module has a few numbers to implement common forms of "waiting for something", for example Coro::AnyEvent::poll looks as if it were the function you want. Coro only makes thread switches when it must, and will only poll for events when it must - as long as you have a thread to run it will run that one.	[reply]
Re^2: Coro, EV and cede by Nick Kostirya (Sexton) on Nov 15, 2011 at 12:54 UTC
Coro::AnyEvent::poll does not help.	[reply]
Re^3: Coro, EV and cede by Nick Kostirya (Sexton) on Dec 27, 2011 at 13:52 UTC
I was wrong, Coro::AnyEvent::poll really helps. This is the same as sleep(0).	[reply]