throttle loading outcomes on student grades page

fixes TALLY-228

test plan:
 * Smoke test student grades page with many outcomes
 * Jenkins oughtta be enough

Change-Id: Idc66f8b2cccea29da3a5641eb9ba0776ea623a2f
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/216867
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Tested-by: Jenkins
QA-Review: Gary Mei <gmei@instructure.com>
Product-Review: Spencer Olson <solson@instructure.com>
Reviewed-by: Gary Mei <gmei@instructure.com>
Reviewed-by: Spencer Olson <solson@instructure.com>

app/jsx/outcomes/IndividualStudentMastery/NaiveFetchDispatch.js

@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2019 - present Instructure, Inc.
+ *
+ * This file is part of Canvas.
+ *
+ * Canvas is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Affero General Public License as published by the Free
+ * Software Foundation, version 3 of the License.
+ *
+ * Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Affero General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+const ACTIVE_REQUEST_LIMIT = 12 // naive limit
+
+export default class NaiveFetchDispatch {
+  constructor(options = {}) {
+    this.options = {
+      activeRequestLimit: ACTIVE_REQUEST_LIMIT,
+      ...options
+    }
+    this.requests = []
+  }
+
+  get activeRequestCount() {
+    // Return the count of active requests currently in the queue.
+    return this.requests.filter(request => request.active).length
+  }
+
+  get nextPendingRequest() {
+    // Return the first request in the queue which has not been started.
+    return this.requests.find(request => !request.active)
+  }
+
+  addRequest(request) {
+    this.requests.push(request)
+    this.fillQueue()
+  }
+
+  clearRequest(request) {
+    this.requests = this.requests.filter(r => r !== request)
+    this.fillQueue()
+  }
+
+  fillQueue() {
+    let nextRequest = this.nextPendingRequest
+    while (nextRequest != null && this.activeRequestCount < this.options.activeRequestLimit) {
+      nextRequest.start()
+      nextRequest = this.nextPendingRequest
+    }
+  }
+
+  fetch(...args) {
+    const request = {
+      active: false
+    }
+
+    request.promise = new Promise((resolve, reject) => {
+      request.resolve = resolve
+      request.reject = reject
+    })
+
+    request.start = () => {
+      /*
+       * Update the request as "active" so that it is counted as an active
+       * request in the queue and is not restarted when filling the queue.
+       */
+      request.active = true
+
+      /* eslint-disable promise/catch-or-return */
+      fetch(...args)
+        .then(request.resolve)
+        .catch(request.reject)
+        .finally(() => {
+          this.clearRequest(request)
+        })
+      /* eslint-enable promise/catch-or-return */
+    }
+
+    this.addRequest(request)
+
+    return request.promise
+  }
+}

app/jsx/outcomes/IndividualStudentMastery/__tests__/NaiveFetchDispatch.test.js

@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2019 - present Instructure, Inc.
+ *
+ * This file is part of Canvas.
+ *
+ * Canvas is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Affero General Public License as published by the Free
+ * Software Foundation, version 3 of the License.
+ *
+ * Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Affero General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import fetchMock from 'fetch-mock'
+
+import NaiveFetchDispatch from '../NaiveFetchDispatch'
+
+describe('Outcomes > IndividualStudentMastery > NaiveFetchDispatch', () => {
+  const URL = 'http://localhost/example'
+
+  let dispatch
+
+  beforeEach(() => {
+    dispatch = new NaiveFetchDispatch({activeRequestLimit: 2})
+  })
+
+  describe('#fetch()', () => {
+    let exampleData
+
+    function resourceUrl(resourceIndex) {
+      return `${URL}/?index=${resourceIndex}`
+    }
+
+    function stageRequests(resourceCount) {
+      for (let resourceIndex = 1; resourceIndex <= resourceCount; resourceIndex++) {
+        exampleData[resourceIndex] = {resourceIndex}
+        fetchMock.mock(resourceUrl(resourceIndex), exampleData[resourceIndex])
+      }
+    }
+
+    function fetch(resourceIndex) {
+      return new Promise((resolve, reject) => {
+        dispatch
+          .fetch(resourceUrl(resourceIndex))
+          .then(resolve)
+          .catch(reject)
+      })
+    }
+
+    beforeEach(() => {
+      exampleData = {}
+      stageRequests(4)
+    })
+
+    afterEach(() => {
+      fetchMock.restore()
+    })
+
+    it('sends a request for the resource', async () => {
+      await fetch(1)
+      expect(fetchMock.calls(url => url.match(URL))).toHaveLength(1)
+    })
+
+    it('resolves with the data from the request', async () => {
+      const response = await fetch(1)
+      expect(response.body).toEqual(JSON.stringify(exampleData[1]))
+    })
+
+    it('resolves when flooded with requests', async () => {
+      const requests = [1, 2, 3, 4].map(fetch)
+      await Promise.all(requests)
+      expect(fetchMock.calls(url => url.match(URL))).toHaveLength(4) // 4 resources
+    })
+  })
+})

app/jsx/outcomes/IndividualStudentMastery/__tests__/fetchOutcomes.test.js

@@ -18,6 +18,7 @@
 
 import fetchMock from 'fetch-mock'
 import fetchOutcomes, {fetchUrl} from '../fetchOutcomes'
+import NaiveFetchDispatch from '../NaiveFetchDispatch'
 
 describe('fetchOutcomes', () => {
   afterEach(() => {
@@ -206,6 +207,12 @@ describe('fetchOutcomes', () => {
   })
 
   describe('fetchUrl', () => {
+    let dispatch
+
+    beforeEach(() => {
+      dispatch = new NaiveFetchDispatch({activeRequestLimit: 2})
+    })
+
     const mockRequests = (first, second, third) => {
       fetchMock.mock('/first', {
         body: first,
@@ -233,40 +240,36 @@ describe('fetchOutcomes', () => {
       }
     }
 
-    it('combines result arrays', done => {
+    it('combines result arrays', () => {
       mockRequests([1, 'hello world', {foo: 'bar'}], [2, 'goodbye', {baz: 'bat'}])
-      fetchUrl('/first').then(resp => {
+      return fetchUrl('/first', dispatch).then(resp => {
         expect(resp).toEqual([1, 'hello world', {foo: 'bar'}, 2, 'goodbye', {baz: 'bat'}])
-        done()
       })
     })
 
-    it('combines result objects', done => {
+    it('combines result objects', () => {
       mockRequests({a: 'b', c: ['d', 'e', 'f']}, {g: 'h', c: ['i', 'j', 'k']})
-      fetchUrl('/first').then(resp => {
+      return fetchUrl('/first', dispatch).then(resp => {
         expect(resp).toEqual({a: 'b', c: ['d', 'e', 'f', 'i', 'j', 'k'], g: 'h'})
-        done()
       })
     })
 
-    it('handles three requests', done => {
+    it('handles three requests', () => {
       mockRequests({a: 'b', c: ['d', 'e', 'f']}, {g: 'h', c: ['i', 'j', 'k']}, {a: 'x'})
-      fetchUrl('/first').then(resp => {
+      return fetchUrl('/first', dispatch).then(resp => {
         expect(resp).toEqual({a: 'x', c: ['d', 'e', 'f', 'i', 'j', 'k'], g: 'h'})
-        done()
       })
     })
 
-    it('handles deeply nested objects', done => {
+    it('handles deeply nested objects', () => {
       mockRequests(
         {a: {b: {c: {d: ['e', 'f'], g: ['h', 'i'], j: 'k'}}}},
         {a: {b: {c: {d: ['e2', 'f2'], g: ['h2', 'i2'], j: 'k2'}}}}
       )
-      fetchUrl('/first').then(resp => {
+      return fetchUrl('/first', dispatch).then(resp => {
         expect(resp).toEqual({
           a: {b: {c: {d: ['e', 'f', 'e2', 'f2'], g: ['h', 'i', 'h2', 'i2'], j: 'k2'}}}
         })
-        done()
       })
     })
   })

app/jsx/outcomes/IndividualStudentMastery/fetchOutcomes.js

@@ -19,6 +19,7 @@
 import _ from 'lodash'
 import uuid from 'uuid'
 import parseLinkHeader from 'parse-link-header'
+import NaiveFetchDispatch from './NaiveFetchDispatch'
 
 const deepMerge = (lhs, rhs) => {
   if (lhs === undefined || lhs === null) {
@@ -37,20 +38,25 @@ const combine = (promiseOfJson1, promiseOfJson2) =>
 
 const parse = response => response.text().then(text => JSON.parse(text.replace('while(1);', '')))
 
-export const fetchUrl = url =>
-  fetch(url, {
-    credentials: 'include'
-  }).then(response => {
-    const linkHeader = response.headers.get('link')
-    const next = linkHeader ? parseLinkHeader(linkHeader).next : null
-    if (next) {
-      return combine(parse(response), fetchUrl(next.url))
-    } else {
-      return parse(response)
-    }
-  })
+export function fetchUrl(url, dispatch) {
+  return dispatch
+    .fetch(url, {
+      credentials: 'include'
+    })
+    .then(response => {
+      const linkHeader = response.headers.get('link')
+      const next = linkHeader ? parseLinkHeader(linkHeader).next : null
+      if (next) {
+        return combine(parse(response), fetchUrl(next.url, dispatch))
+      } else {
+        return parse(response)
+      }
+    })
+}
 
 const fetchOutcomes = (courseId, studentId) => {
+  const dispatch = new NaiveFetchDispatch()
+
   let outcomeGroups
   let outcomeLinks
   let outcomeRollups
@@ -58,11 +64,19 @@ const fetchOutcomes = (courseId, studentId) => {
   let outcomeResultsByOutcomeId
   let assignmentsByAssignmentId
 
+  function fetchWithDispatch(url) {
+    return fetchUrl(url, dispatch)
+  }
+
   return Promise.all([
-    fetchUrl(`/api/v1/courses/${courseId}/outcome_groups?per_page=100`),
-    fetchUrl(`/api/v1/courses/${courseId}/outcome_group_links?outcome_style=full&per_page=100`),
-    fetchUrl(`/api/v1/courses/${courseId}/outcome_rollups?user_ids[]=${studentId}&per_page=100`),
-    fetchUrl(`/api/v1/courses/${courseId}/outcome_alignments?student_id=${studentId}`)
+    fetchWithDispatch(`/api/v1/courses/${courseId}/outcome_groups?per_page=100`),
+    fetchWithDispatch(
+      `/api/v1/courses/${courseId}/outcome_group_links?outcome_style=full&per_page=100`
+    ),
+    fetchWithDispatch(
+      `/api/v1/courses/${courseId}/outcome_rollups?user_ids[]=${studentId}&per_page=100`
+    ),
+    fetchWithDispatch(`/api/v1/courses/${courseId}/outcome_alignments?student_id=${studentId}`)
   ])
     .then(([groups, links, rollups, alignments]) => {
       outcomeGroups = groups
@@ -73,7 +87,7 @@ const fetchOutcomes = (courseId, studentId) => {
     .then(() =>
       Promise.all(
         outcomeLinks.map(outcomeLink =>
-          fetchUrl(
+          fetchWithDispatch(
             `/api/v1/courses/${courseId}/outcome_results?user_ids[]=${studentId}&outcome_ids[]=${outcomeLink.outcome.id}&include[]=assignments&per_page=100`
           )
         )