[Modal] Fix concurrency regression (#13743)

packages/material-ui/src/Modal/Modal.test.js

@@ -1,6 +1,7 @@
 import React from 'react';
 import { assert } from 'chai';
 import { spy, stub } from 'sinon';
+import PropTypes from 'prop-types';
 import keycode from 'keycode';
 import consoleErrorMock from 'test/utils/consoleErrorMock';
 import { createShallow, createMount, getClasses, unwrap } from '@material-ui/core/test-utils';
@@ -514,4 +515,30 @@ describe('<Modal />', () => {
       assert.strictEqual(handleRendered.callCount, 1);
     });
   });
+
+  describe('two modal at the same time', () => {
+    it('should open and close', () => {
+      const TestCase = props => (
+        <React.Fragment>
+          <Modal open={props.open}>
+            <div>Hello</div>
+          </Modal>
+          <Modal open={props.open}>
+            <div>World</div>
+          </Modal>
+        </React.Fragment>
+      );
+
+      TestCase.propTypes = {
+        open: PropTypes.bool,
+      };
+
+      const wrapper = mount(<TestCase open={false} />);
+      assert.strictEqual(document.body.style.overflow, '');
+      wrapper.setProps({ open: true });
+      assert.strictEqual(document.body.style.overflow, 'hidden');
+      wrapper.setProps({ open: false });
+      assert.strictEqual(document.body.style.overflow, '');
+    });
+  });
 });

packages/material-ui/src/Modal/ModalManager.js

@@ -124,7 +124,7 @@ class ModalManager {
     const containerIdx = findIndexOf(this.data, item => item.modals.indexOf(modal) !== -1);
     const data = this.data[containerIdx];
 
-    if (data.modals.length === 1 && this.handleContainerOverflow) {
+    if (!data.style && this.handleContainerOverflow) {
       setContainerStyle(data);
     }
   }