falcor/lib/request/RequestQueueV2.js

A JavaScript library for efficient data fetching.

var RequestTypes = require("./RequestTypes");
var sendSetRequest = require("./sendSetRequest");
var GetRequest = require("./GetRequestV2");
var falcorPathUtils = require("falcor-path-utils");

/**
 * The request queue is responsible for queuing the operations to
 * the model"s dataSource.
 *
 * @param {Model} model -
 * @param {Scheduler} scheduler -
 */
function RequestQueueV2(model, scheduler) {
    this.model = model;
    this.scheduler = scheduler;
    this.requests = this._requests = [];
}

RequestQueueV2.prototype = {
    /**
     * Sets the scheduler, but will not affect any current requests.
     */
    setScheduler: function(scheduler) {
        this.scheduler = scheduler;
    },

    /**
     * performs a set against the dataSource.  Sets, though are not batched
     * currently could be batched potentially in the future.  Since no batching
     * is required the setRequest action is simplified significantly.
     *
     * @param {JSONGraphEnvelope} jsonGraph -
     * @param {number} attemptCount
     * @param {Function} cb
     */
    set: function(jsonGraph, attemptCount, cb) {
        if (this.model._enablePathCollapse) {
            jsonGraph.paths = falcorPathUtils.collapse(jsonGraph.paths);
        }

        if (cb === undefined) {
            cb = attemptCount;
            attemptCount = undefined;
        }

        return sendSetRequest(jsonGraph, this.model, attemptCount, cb);
    },

    /**
     * Creates a get request to the dataSource.  Depending on the current
     * scheduler is how the getRequest will be flushed.
     * @param {Array} requestedPaths -
     * @param {Array} optimizedPaths -
     * @param {number} attemptCount
     * @param {Function} cb -
     */
    get: function(requestedPaths, optimizedPaths, attemptCount, cb) {
        var self = this;
        var disposables = [];
        var count = 0;
        var requests = self._requests;
        var i, len;
        var oRemainingPaths = optimizedPaths;
        var rRemainingPaths = requestedPaths;
        var disposed = false;
        var request;

        if (cb === undefined) {
            cb = attemptCount;
            attemptCount = undefined;
        }

        for (i = 0, len = requests.length; i < len; ++i) {
            request = requests[i];
            if (request.type !== RequestTypes.GetRequest) {
                continue;
            }

            // The request has been sent, attempt to jump on the request
            // if possible.
            if (request.sent) {
                if (this.model._enableRequestDeduplication) {
                    var results = request.add(rRemainingPaths, oRemainingPaths, refCountCallback);

                    // Checks to see if the results were successfully inserted
                    // into the outgoing results.  Then our paths will be reduced
                    // to the complement.
                    if (results[0]) {
                        rRemainingPaths = results[1];
                        oRemainingPaths = results[2];
                        disposables[disposables.length] = results[3];
                        ++count;

                        // If there are no more remaining paths then exit the loop.
                        if (!oRemainingPaths.length) {
                            break;
                        }
                    }
                }
            }

            // If there is an unsent request, then we can batch and leave.
            else {
                request.batch(rRemainingPaths, oRemainingPaths, refCountCallback);
                oRemainingPaths = null;
                rRemainingPaths = null;
                ++count;
                break;
            }
        }

        // After going through all the available requests if there are more
        // paths to process then a new request must be made.
        if (oRemainingPaths && oRemainingPaths.length) {
            request = new GetRequest(self.scheduler, self, attemptCount);
            requests[requests.length] = request;
            ++count;
            var disposable = request.batch(rRemainingPaths, oRemainingPaths, refCountCallback);
            disposables[disposables.length] = disposable;
        }

        // This is a simple refCount callback.
        function refCountCallback(err, data, hasInvalidatedResult) {
            if (disposed) {
                return;
            }

            --count;

            // If the count becomes 0, then its time to notify the
            // listener that the request is done.
            if (count === 0) {
                cb(err, data, hasInvalidatedResult);
            }
        }

        // When disposing the request all of the outbound requests will be
        // disposed of.
        return function() {
            if (disposed || count === 0) {
                return;
            }

            disposed = true;
            var length = disposables.length;
            for (var idx = 0; idx < length; ++idx) {
                disposables[idx]();
            }
        };
    },

    /**
     * Removes the request from the request queue.
     */
    removeRequest: function(request) {
        var requests = this._requests;
        var i = requests.length;
        while (--i >= 0) {
            if (requests[i].id === request.id) {
                requests.splice(i, 1);
                break;
            }
        }
    }
};

module.exports = RequestQueueV2;