Throttling fails when multiple calls are made in quick succession

[weiyin]

Hi, thanks for creating an excellent module. I am encountering one issue, where if multiple calls are made before the callbacks settle, then the throttling can fail. Example:

var myThrottle = require('tokenthrottle')({
    rate: 1,
    window: 10 * 1000
});

function getToken() {
    myThrottle.rateLimit('abc', function(err, limited) {
        if (err) console.log(err);
        else console.log(limited);
    });
}

getToken();
getToken();

Expected output:

false
true

Actual output:

false
false

[carlfreeland]

Yup, I ran into this too. The library is not usable for mid-to-high concurrency environments. It doesn't use concurrency-sensitive manipulation of the payload. If there are several concurrent requests in a node server, or multiple servers, they may each fetch the current limit, say, 100, then decrement to 99 and each write back 99 when it should be 97.