Extract PerformanceLogger from AnalysisDriver.

pkg/front_end/lib/src/base/performace_logger.dart

+// Copyright (c) 2016, 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';
+
+/// This class is used to gather and print performance information.
+class PerformanceLog {
+  final StringSink sink;
+  int _level = 0;
+
+  PerformanceLog(this.sink);
+
+  /// Enter a new execution section, which starts at one point of code, runs
+  /// some time, and then ends at the other point of code.
+  ///
+  /// The client must call [PerformanceLogSection.exit] for every [enter].
+  PerformanceLogSection enter(String msg) {
+    writeln('+++ $msg.');
+    _level++;
+    return new PerformanceLogSection(this, msg);
+  }
+
+  /// Return the result of the function [f] invocation and log the elapsed time.
+  ///
+  /// Each invocation of [run] creates a new enclosed section in the log,
+  /// which begins with printing [msg], then any log output produced during
+  /// [f] invocation, and ends with printing [msg] with the elapsed time.
+  T run<T>(String msg, T f()) {
+    Stopwatch timer = new Stopwatch()..start();
+    try {
+      writeln('+++ $msg.');
+      _level++;
+      return f();
+    } finally {
+      _level--;
+      int ms = timer.elapsedMilliseconds;
+      writeln('--- $msg in $ms ms.');
+    }
+  }
+
+  /// Return the result of the function [f] invocation and log the elapsed time.
+  ///
+  /// Each invocation of [run] creates a new enclosed section in the log,
+  /// which begins with printing [msg], then any log output produced during
+  /// [f] invocation, and ends with printing [msg] with the elapsed time.
+  Future<T> runAsync<T>(String msg, Future<T> f()) async {
+    Stopwatch timer = new Stopwatch()..start();
+    try {
+      writeln('+++ $msg.');
+      _level++;
+      return await f();
+    } finally {
+      _level--;
+      int ms = timer.elapsedMilliseconds;
+      writeln('--- $msg in $ms ms.');
+    }
+  }
+
+  /// Write a new line into the log.
+  void writeln(String msg) {
+    if (sink != null) {
+      String indent = '\t' * _level;
+      sink.writeln('$indent$msg');
+    }
+  }
+}
+
+/**
+ * The performance measurement section for operations that start and end
+ * at different place in code, so cannot be run using [PerformanceLog.run].
+ *
+ * The client must call [exit] for every [PerformanceLog.enter].
+ */
+class PerformanceLogSection {
+  final PerformanceLog _logger;
+  final String _msg;
+  final Stopwatch _timer = new Stopwatch()..start();
+
+  PerformanceLogSection(this._logger, this._msg);
+
+  /**
+   * Stop the timer, log the time.
+   */
+  void exit() {
+    _timer.stop();
+    _logger._level--;
+    int ms = _timer.elapsedMilliseconds;
+    _logger.writeln('--- $_msg in $ms ms.');
+  }
+}