How to use the bluebird concurrency option for the map function

bluebird, concurrency, promise

Solution

Short answer: yes , this will limit the number of requests to 5.

Caveat: keep in mind you might still be susceptible to more limits, such as the HTTP client's, or any other pools, modules and services you might be using.

Also, a Mongo connection is meant to be used as a persistent one, so you should probably only open one and then use it rather than open and close one every time.

If `createDatesArray` does not do anything asynchronous, you do not have to Promise.resolve it, you can instead use the static variant of `map` as `Promise.map(datesArray, function(date){ ... })` etc. I would also not nest. Assuming `createDatesArray` is indeed async:

Promise.join(getNames(), createDatesArray(), function(names, dates){
    var tasks = [];
    names.forEach(function(name ){ // create Cartesian product of names * dates
        dates.forEach(function(date){
             tasks.push(function(){ return requestData(name, date); });
        });
    });
    return Promise.map(tasks, function(job){ return job(); } , { concurrency: 5} );
}), then(function(results){
     // do whatever
});

Problem

I am trying to use bluebird's map function with the built-in concurrency control. I want to retrieve a list of names, then make a number of POST requests for each name. For example, I want to make a request for each name for each day of the week. However, I need to throttle the number of concurrent POST requests because the intended server has rate limits. ``` function getNames() { //Open mongodb connection //Get collection and array of names //return array of names in a promise } function createDatesArray() { //Create an array of rates //return array of dates in a promise //Ex. return Promise.resolve(datesArray); } getNames().map(function (name) { return createDatesArray().map(function (date) { return requestData(date, name); }, {concurrency: 5}); }).then(function () { //do something }); ``` Is this the correct way to use bluebird's concurrency? The documentation link is here bluebird documentation.

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