Fix LockingCache expiry behaviour. #44

[rcoup]

Fix #44, make the cache actually cache for the specified timeout rather than until initial callbacks happen.

Also adds some tests around LockingCache.

[rcoup]

hmm, just found #16
will think on it a bit more

[rcoup]

ok, updated request special-cases timeout=0 to do the instant-purge behaviour, and makes tilelive-mapnik use it like that. If someone else is using lockingcache (/cough/ me /cough/) then non-0 timeouts work a bit more as expected.

I can't find anything else that uses lockingcache, but I'm happy to revise further if it helps.

[rcoup]

@kkaefer yeah, and timeout=0 maintains that behaviour (and that's what _createMetatileCache() now uses)

[springmeyer]

@rcoup - thanks for the patch. reviewing now, but seeing:

   grid.test.js getGrid() with invalid layer: AssertionError: false == true
    at exports.getGrid() with invalid layer (/Users/dane/projects/tilelive-mapnik/test/grid.test.js:85:16)
    at Test.runParallel (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:961:13)
    at Test.EventEmitter.emit (events.js:93:17)
    at process.<anonymous> (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:892:18)
    at process.EventEmitter.emit (events.js:126:20)
    at process.emit (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:1053:10)
    at report (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:992:13)
    at process.emit (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:1050:9)


   lockingcache.test.js later requests get a cached response: AssertionError: 2 == 3
    at exports.later requests get a cached response (/Users/dane/projects/tilelive-mapnik/test/lockingcache.test.js:148:16)
    at Test.runParallel (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:961:13)
    at Test.EventEmitter.emit (events.js:93:17)
    at process.<anonymous> (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:892:18)
    at process.EventEmitter.emit (events.js:126:20)
    at process.emit (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:1053:10)
    at report (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:992:13)
    at process.emit (/Users/dane/projects/tilelive-mapnik/node_modules/expresso/bin/expresso:1050:9)

[springmeyer]

@rcoup - running this inside the tilelive-mapnik master directory hangs:

var assert = require('assert')
var tilelive = require('./lib/mapnik_backend');
var coords = [0,0,0];
var uri = 'mapnik://./test/data/invalid_interactivity_1.xml'
var ddd = new tilelive(uri, function(err, source) {
    if (err) throw err;
    source.getGrid(coords[0], coords[1], coords[2], function(err, tile, headers) {
        // never gets here, just hangs with patch from #57
        assert.ok(err);
        source.close(function(){});
        console.log('worked!')
    })
});

[springmeyer]

Okay, thanks, all tests passing for me now. I will merge since this maintains the current behavior.

Next up I think we need to 1) move tests to mocha to ensure we are more able to catch possible bugs, and 2) potentially expose options to control the locking cache behavior by options passed to the MapnikSource constructor.