Track multiple xhrs per URL rather than overriding

It was possible for a url to be overridden then canceled, leaving the
open connection open and forgotten about.

ui/app/adapters/watchable.js

@@ -10,7 +10,27 @@ export default ApplicationAdapter.extend({
   store: service(),
 
   xhrs: computed(function() {
-    return {};
+    return {
+      list: {},
+      track(key, xhr) {
+        if (this.list[key]) {
+          this.list[key].push(xhr);
+        } else {
+          this.list[key] = [xhr];
+        }
+      },
+      cancel(key) {
+        while (this.list[key] && this.list[key].length) {
+          this.remove(key, this.list[key][0]);
+        }
+      },
+      remove(key, xhr) {
+        if (this.list[key]) {
+          xhr.abort();
+          this.list[key].removeObject(xhr);
+        }
+      },
+    };
   }),
 
   ajaxOptions() {
@@ -22,9 +42,9 @@ export default ApplicationAdapter.extend({
       if (previousBeforeSend) {
         previousBeforeSend(...arguments);
       }
-      this.get('xhrs')[key] = jqXHR;
+      this.get('xhrs').track(key, jqXHR);
       jqXHR.always(() => {
-        delete this.get('xhrs')[key];
+        this.get('xhrs').remove(key, jqXHR);
       });
     };
 
@@ -127,10 +147,7 @@ export default ApplicationAdapter.extend({
       return;
     }
     const url = this.urlForFindRecord(id, modelName);
-    const xhr = this.get('xhrs')[url];
-    if (xhr) {
-      xhr.abort();
-    }
+    this.get('xhrs').cancel(url);
   },
 
   cancelFindAll(modelName) {
@@ -142,10 +159,7 @@ export default ApplicationAdapter.extend({
     if (params) {
       url = `${url}?${params}`;
     }
-    const xhr = this.get('xhrs')[url];
-    if (xhr) {
-      xhr.abort();
-    }
+    this.get('xhrs').cancel(url);
   },
 
   cancelReloadRelationship(model, relationshipName) {
@@ -159,10 +173,7 @@ export default ApplicationAdapter.extend({
       );
     } else {
       const url = model[relationship.kind](relationship.key).link();
-      const xhr = this.get('xhrs')[url];
-      if (xhr) {
-        xhr.abort();
-      }
+      this.get('xhrs').cancel(url);
     }
   },
 });

ui/tests/unit/adapters/job-test.js

@@ -257,6 +257,41 @@ test('relationship reloads can be canceled', function(assert) {
   });
 });
 
+test('requests can be canceled even if multiple requests for the same URL were made', function(assert) {
+  const { pretender } = this.server;
+  const jobId = JSON.stringify(['job-1', 'default']);
+
+  pretender.get('/v1/job/:id', () => [200, {}, '{}'], true);
+
+  this.subject().findRecord(null, { modelName: 'job' }, jobId, {
+    reload: true,
+    adapterOptions: { watch: true },
+  });
+
+  this.subject().findRecord(null, { modelName: 'job' }, jobId, {
+    reload: true,
+    adapterOptions: { watch: true },
+  });
+
+  const { request: xhr } = pretender.requestReferences[0];
+  assert.equal(xhr.status, 0, 'Request is still pending');
+  assert.equal(pretender.requestReferences.length, 2, 'Two findRecord requests were made');
+  assert.equal(
+    pretender.requestReferences.mapBy('url').uniq().length,
+    1,
+    'The two requests have the same URL'
+  );
+
+  // Schedule the cancelation before waiting
+  run.next(() => {
+    this.subject().cancelFindRecord('job', jobId);
+  });
+
+  return wait().then(() => {
+    assert.ok(xhr.aborted, 'Request was aborted');
+  });
+});
+
 function makeMockModel(id, options) {
   return assign(
     {