implement and test a complex constrained scheduler
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ansuz
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@ -0,0 +1,173 @@
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var WriteQueue = require("./write-queue");
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var Util = require("./common-util");
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/* This module provides implements a FIFO scheduler
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which assumes the existence of three types of async tasks:
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1. ordered tasks which must be executed sequentially
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2. unordered tasks which can be executed in parallel
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3. blocking tasks which must block the execution of all other tasks
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The scheduler assumes there will be many resources identified by strings,
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and that the constraints described above will only apply in the context
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of identical string ids.
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Many blocking tasks may be executed in parallel so long as they
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concern resources identified by different ids.
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USAGE:
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const schedule = require("./schedule")();
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// schedule two sequential tasks using the resource 'pewpew'
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schedule.ordered('pewpew', function (next) {
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appendToFile('beep\n', next);
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});
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schedule.ordered('pewpew', function (next) {
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appendToFile('boop\n', next);
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});
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// schedule a task that can happen whenever
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schedule.unordered('pewpew', function (next) {
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displayFileSize(next);
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});
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// schedule a blocking task which will wait
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// until the all unordered tasks have completed before commencing
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schedule.blocking('pewpew', function (next) {
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deleteFile(next);
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});
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// this will be queued for after the blocking task
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schedule.ordered('pewpew', function (next) {
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appendFile('boom', next);
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});
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*/
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// return a uid which is not already in a map
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var unusedUid = function (set) {
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var uid = Util.uid();
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if (set[uid]) { return unusedUid(); }
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return uid;
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};
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// return an existing session, creating one if it does not already exist
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var lookup = function (map, id) {
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return (map[id] = map[id] || {
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//blocking: [],
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active: {},
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blocked: {},
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});
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};
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var isEmpty = function (map) {
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for (var key in map) {
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if (map.hasOwnProperty(key)) { return false; }
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}
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return true;
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};
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// XXX enforce asynchrony everywhere
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module.exports = function () {
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// every scheduler instance has its own queue
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var queue = WriteQueue();
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// ordered tasks don't require any extra logic
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var Ordered = function (id, task) {
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queue(id, task);
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};
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// unordered and blocking tasks need a little extra state
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var map = {};
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// regular garbage collection keeps memory consumption low
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var collectGarbage = function (id) {
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// avoid using 'lookup' since it creates a session implicitly
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var local = map[id];
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// bail out if no session
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if (!local) { return; }
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// bail out if there are blocking or active tasks
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if (local.lock) { return; }
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if (!isEmpty(local.active)) { return; }
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// if there are no pending actions then delete the session
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delete map[id];
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};
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// unordered tasks run immediately if there are no blocking tasks scheduled
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// or immediately after blocking tasks finish
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var runImmediately = function (local, task) {
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// set a flag in the map of active unordered tasks
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// to prevent blocking tasks from running until you finish
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var uid = unusedUid(local.active);
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local.active[uid] = true;
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task(function () {
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// remove the flag you set to indicate that your task completed
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delete local.active[uid];
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// don't do anything if other unordered tasks are still running
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if (!isEmpty(local.active)) { return; }
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// bail out if there are no blocking tasks scheduled or ready
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if (typeof(local.waiting) !== 'function') {
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return void collectGarbage();
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}
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local.waiting();
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});
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};
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var runOnceUnblocked = function (local, task) {
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var uid = unusedUid(local.blocked);
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local.blocked[uid] = function () {
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runImmediately(local, task);
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};
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};
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// 'unordered' tasks are scheduled to run in after the most recently received blocking task
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// or immediately and in parallel if there are no blocking tasks scheduled.
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var Unordered = function (id, task) {
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var local = lookup(map, id);
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if (local.lock) { return runOnceUnblocked(local, task); }
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runImmediately(local, task);
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};
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var runBlocked = function (local) {
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for (var task in local.blocked) {
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runImmediately(local, local.blocked[task]);
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}
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};
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// 'blocking' tasks must be run alone.
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// They are queued alongside ordered tasks,
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// and wait until any running 'unordered' tasks complete before commencing.
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var Blocking = function (id, task) {
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var local = lookup(map, id);
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queue(id, function (next) {
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// start right away if there are no running unordered tasks
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if (isEmpty(local.active)) {
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local.lock = true;
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return void task(function () {
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delete local.lock;
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runBlocked(local);
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next();
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});
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}
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// otherwise wait until the running tasks have completed
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local.waiting = function () {
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local.lock = true;
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task(function () {
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delete local.lock;
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delete local.waiting;
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runBlocked(local);
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next();
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});
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};
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});
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};
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return {
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ordered: Ordered,
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unordered: Unordered,
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blocking: Blocking,
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};
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};
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@ -0,0 +1,220 @@
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/* three types of actions:
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* read
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* write
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* append
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each of which take a random amount of time
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*/
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var Util = require("../../lib/common-util");
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var schedule = require("../../lib/schedule")();
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var nThen = require("nthen");
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var rand = function (n) {
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return Math.floor(Math.random() * n);
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};
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var rand_time = function () {
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// between 51 and 151
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return rand(300) + 25;
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};
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var makeAction = function (type) {
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var i = 0;
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return function (time) {
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var j = i++;
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return function (next) {
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console.log(" Beginning action: %s#%s", type, j);
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setTimeout(function () {
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console.log(" Completed action: %s#%s", type, j);
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next();
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}, time);
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return j;
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};
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};
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};
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var TYPES = ['WRITE', 'READ', 'APPEND'];
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var chooseAction = function () {
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var n = rand(100);
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if (n < 50) { return 'APPEND'; }
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if (n < 90) { return 'READ'; }
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return 'WRITE';
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//return TYPES[rand(3)];
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};
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var test = function (script, cb) {
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var uid = Util.uid();
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var TO_RUN = script.length;
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var total_run = 0;
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var parallel = 0;
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var last_run_ordered = -1;
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//var i = 0;
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var ACTIONS = {};
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TYPES.forEach(function (type) {
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ACTIONS[type] = makeAction(type);
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});
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nThen(function (w) {
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setTimeout(w(), 3000);
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// run scripted actions with assertions
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script.forEach(function (scene) {
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var type = scene[0];
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var time = typeof(scene[1]) === 'number'? scene[1]: rand_time();
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var action = ACTIONS[type](time);
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console.log("Queuing action of type: %s(%s)", type, time);
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var proceed = w();
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switch (type) {
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case 'APPEND':
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return schedule.ordered(uid, w(function (next) {
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parallel++;
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var temp = action(function () {
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parallel--;
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total_run++;
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proceed();
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next();
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});
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if (temp !== (last_run_ordered + 1)) {
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throw new Error("out of order");
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}
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last_run_ordered = temp;
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}));
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case 'WRITE':
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return schedule.blocking(uid, w(function (next) {
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parallel++;
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action(function () {
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parallel--;
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total_run++;
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proceed();
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next();
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});
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if (parallel > 1) {
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console.log("parallelism === %s", parallel);
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throw new Error("too much parallel");
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}
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}));
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case 'READ':
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return schedule.unordered(uid, w(function (next) {
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parallel++;
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action(function () {
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parallel--;
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total_run++;
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proceed();
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next();
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});
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}));
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default:
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throw new Error("wut");
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}
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});
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}).nThen(function () {
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// make assertions about the whole script
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if (total_run !== TO_RUN) {
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console.log("Ran %s / %s", total_run, TO_RUN);
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throw new Error("skipped tasks");
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}
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console.log("total_run === %s", total_run);
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cb();
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});
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};
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var randomScript = function () {
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var len = rand(15) + 10;
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var script = [];
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while (len--) {
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script.push([
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chooseAction(),
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rand_time(),
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]);
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}
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return script;
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};
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var WRITE = function (t) {
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return ['WRITE', t];
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};
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var READ = function (t) {
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return ['READ', t];
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};
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var APPEND = function (t) {
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return ['APPEND', t];
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};
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nThen(function (w) {
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test([
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['READ', 150],
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['APPEND', 200],
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['APPEND', 100],
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['READ', 350],
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['WRITE', 400],
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['APPEND', 275],
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['APPEND', 187],
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['WRITE', 330],
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['WRITE', 264],
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['WRITE', 256],
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], w(function () {
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console.log("finished pre-scripted test\n");
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}));
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}).nThen(function (w) {
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test([
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WRITE(289),
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APPEND(281),
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READ(207),
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WRITE(225),
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READ(279),
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WRITE(300),
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READ(331),
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APPEND(341),
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APPEND(385),
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READ(313),
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WRITE(285),
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READ(304),
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APPEND(273),
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APPEND(150),
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WRITE(246),
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READ(244),
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WRITE(172),
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APPEND(253),
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READ(215),
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READ(296),
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APPEND(281),
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APPEND(296),
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WRITE(168),
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], w(function () {
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console.log("finished 2nd pre-scripted test\n");
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}));
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}).nThen(function () {
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var totalTests = 50;
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var randomTests = 1;
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var last = nThen(function () {
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console.log("beginning randomized tests");
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});
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var queueRandomTest = function (i) {
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last = last.nThen(function (w) {
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console.log("running random test script #%s\n", i);
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test(randomScript(), w(function () {
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console.log("finished random test #%s\n", i);
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}));
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});
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};
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while (randomTests <=totalTests) { queueRandomTest(randomTests++); }
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last.nThen(function () {
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console.log("finished %s random tests", totalTests);
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});
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});
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