Implement Mutex for Dart.

pkg/analyzer/test/src/dart/analysis/mutex_test.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:analyzer/src/dart/analysis/mutex.dart';
+import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(MutexTest);
+  });
+}
+
+@reflectiveTest
+class MutexTest {
+  test_acquire() async {
+    var values = <int>[];
+    var mutex = new Mutex();
+    await Future.wait([
+      new Future(() async {
+        await mutex.acquire();
+        try {
+          await new Future.delayed(new Duration(milliseconds: 10));
+          values.add(1);
+        } finally {
+          mutex.release();
+        }
+      }),
+      new Future(() async {
+        await mutex.acquire();
+        try {
+          values.add(2);
+        } finally {
+          mutex.release();
+        }
+      }),
+    ]);
+    // The first Future is schedule first, and it acquires the mutex first.
+    // But then it sleeps before adding (1), so if Mutex locking does not work,
+    // the second Future might add (2) first.
+    expect(values, [1, 2]);
+  }
+
+  test_guard() async {
+    var values = <int>[];
+    var mutex = new Mutex();
+    await Future.wait([
+      new Future(() async {
+        await mutex.guard(() async {
+          await new Future.delayed(new Duration(milliseconds: 10));
+          values.add(1);
+        });
+      }),
+      new Future(() async {
+        await mutex.guard(() async {
+          values.add(2);
+        });
+      }),
+    ]);
+    // The first Future is schedule first, and it acquires the mutex first.
+    // But then it sleeps before adding (1), so if Mutex locking does not work,
+    // the second Future might add (2) first.
+    expect(values, [1, 2]);
+  }
+
+  test_release_noLock() {
+    var mutex = new Mutex();
+    expect(() {
+      mutex.release();
+    }, throwsStateError);
+  }
+
+  test_release_noLock_alreadyReleased() async {
+    var mutex = new Mutex();
+    await mutex.acquire();
+    mutex.release();
+    expect(() {
+      mutex.release();
+    }, throwsStateError);
+  }
+}