[dancer-users] Delayed and asynchronous Dancer2

Amelia Ireland aireland at lbl.gov
Tue Oct 6 20:54:06 BST 2015

Hello again,

What are my options for running a potentially lengthy process using Dancer?
I'm adapting old CGI.pm-based code, which uses one of two techniques:

1. the CGI creates a job that it sends to an externally-managed queue;
users have a workspace area where they can check to see if their job has

2. the CGI keeps the connection to the browser open while performing the
process using a hack involving sending small chunks of data from time to

Another common technique (similar to 1 above) is to fork off a child
process and have the browser periodically refresh the page, which triggers
a check to see if the child process has finished (e.g. by checking for the
presence of a results file) and the results can be loaded.

Do Dancer2's delayed / async / non-blocking capabilities offer any
additional ways to deal with long-running processes, or maybe a more
elegant way to do option 2?

Thank you for any information!


On 2 October 2015 at 10:50, Amelia Ireland <aireland at lbl.gov> wrote:

> Hello,
> I'm very interested in using Dancer2's streaming and async capabilities,
> and have a number of questions about using Dancer2 asynchronously:
> - Does the whole app have to be written to be asynchronous / non-blocking?
> (I assume so)
> - Do all apps running from the same .psgi file have to be non-blocking?
> E.g. in app.psgi:
> builder {
>    mount '/app1' => $nonblocking_app;
>    mount '/app2' => $blocking_app;
> };
> - Are hooks safe to use in a non-blocking Dancer2 app or do they introduce
> a blocking element?
> - When I run the drums example in a browser (Safari), it waits until the
> entire drum loop has completed and then prints the content. Is that what is
> expected to happen? I expected the content to be written by the browser as
> it received it. The docs aren't very clear on what Dancer is actually doing
> under the hood -- it would be useful to have more explanation of what's
> going on. I'd be happy to write up something myself, but I don't know
> what's going on. ;-)
> Thanks!
> Amelia.
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