[Dancer-users] Follow-up: mysterious behavior putting Dancer app in production on Starman

[Mr. Puneet Kishor]

Following with more investigation and observation (please see below) --

On Jul 15, 2011, at 9:07 AM, Mr. Puneet Kishor wrote:

> 
> On Jul 14, 2011, at 8:55 PM, Mr. Puneet Kishor wrote:
> 
>> Check out the following [http://teststrata.geology.wisc.edu/macromap]. It should be working -- it should show a Google map backdrop with a bunch of polygons and a few points. As you pan and zoom, polys and points for the new viewport should be retrieved.
>> 
>> The polys and points are retrieved via ajax from [http://teststrata.geology.wisc.edu/mstrat/] that is serving them from a MySQL db as a REST service.
>> 
>> Both apps are Dancer based, and are running on Starman using the following invocation
>> 
>> $ plackup -p <port> -E production -s Starman -w 10 -a bin/app.pl
>> 
>> The first app (macromap) also has the -D switch added to the above plackup command so plackup runs in the background as a daemon (or a faceless app, or whatever is the correct terminology).
>> 
>> Here is the interesting thing -- if I add the -D switch to the second app as well, it fails to return the polys and the points. It fails with the error
>> 
>> {"error":"Warning caught during route execution: DBD::mysql::st fetchall_arrayref failed: fetch() without execute() at <path/to>/macrostrat.pm line 79.\n"}
>> 
>> The offending lines are
>> 
>> 	71> my $sql = qq{
>> 	72> 	..
>> 	73>
>> 	74>
>> 	75> };
>> 	76> 
>> 	77> my $sth = $dbh->prepare($sql);
>> 	78> $sth->execute();
>> 	79> my $res = $sth->fetchall_arrayref({});
>> 
>> The above could be just correlation rather than causal, but it definitely seems to be a pattern. First, this is bizarre, and why so? And, two... this is totally bogus... how can execute() not take place above? Perl doesn't have a habit of jumping over lines, does it?
>> 
>> Absolutely mystified in Madison.
>> 
> 
> 
> Following Paul Findlay's advice, I launched my offending app with the following invocation
> 
> 	$DBI_TRACE=2=logs/dbi.log plackup -E production -p 5001 -s Starman -w 10 -a bin/app.pl
> 
> And, following is what stood out to me as the potential culprit in the log file
> 
> 	> Handle is not in asynchronous mode error 2000 recorded: Handle is 
> 	> not in asynchronous mode
> 	>    !! ERROR: 2000 CLEARED by call to fetch method
> 
> 
> (I am shooting in the dark here) I believe Dancer uses a lot of global variables. Would that be connected to this error? On occasion, I am also seeing another mysterious behavior, so mysterious that I feel I am smoking something --
> 
> One request to the web server pulls in points, and another request pulls in polys. They are called like so
> 
> 	http://webserver/points.json
> 	http://webserver/polys.json
> 
> They are both separate asynchronous requests, sent via separate $.ajax() jQuery calls from the browser. On occasion, and I swear I am not making this up, I see points json stream returned via the polys request. Of course, because points.json returns different data than polys.json, I get an error.
> 
> For what its worth, and this is highly unscientific, this doesn't happen if plackup is in `-E development` mode. It only happens in the `-E production -D` mode. But, I could be wrong about this as I don't have a large enough sample set to confirm this finding conclusively.
> 
> Thoughts?
> 

A simple script like so works like a champ... no async nonsense, no errors. All 1000 requests are effortlessly returned by the same set up.

    use LWP::UserAgent;

    my $BBOX = "-96.09299316406248+38.96034339396338%2C+83.39279785156248+38.96034339396338%2C+-83.39279785156248+44.33256692562997%2C+96.09299316406248+44.33256692562997%2C+-96.09299316406248+38.96034339396338";

    for (1 .. 1000) {
	open my $fh, ">>", 'foo.txt';
	
	my $ua = LWP::UserAgent->new;
	$ua->agent("MyApp/0.1 ");
	
	my $req = HTTP::Request->new(GET => "http://localhost:5001/points.json?callback=foo&BBOX=$BBOX");
	my $res = $ua->request($req);
	
	# Check the outcome of the response
	if ($res->is_success) {
		say $fh $res->content;
	}
	else {
		say $fh $res->status_line;
	}
	
	close $fh;
    }

So, it seems that both MySQL and Starman are very capable of handling this. The only element missing here is Dancer, and the browser. Thoughts anyone? I am just interested in finding out the issues here, and creating a robust, workable app.

Many thanks in advance.

Puneet.