Use 'Directory.watch' on Windows in pkg/watcher, instead of pooling.

pkg/watcher/lib/src/directory_watcher/windows.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2014, 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.
 
-library watcher.directory_watcher.mac_os;
+library watcher.directory_watcher.windows;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:stack_trace/stack_trace.dart';
 
 import '../constructable_file_system_event.dart';
 import '../path_set.dart';
 import '../utils.dart';
 import '../watch_event.dart';
 import 'resubscribable.dart';
 
-/// Uses the FSEvents subsystem to watch for filesystem events.
-///
-/// FSEvents has two main idiosyncrasies that this class works around. First, it
-/// will occasionally report events that occurred before the filesystem watch
-/// was initiated. Second, if multiple events happen to the same file in close
-/// succession, it won't report them in the order they occurred. See issue
-/// 14373.
-///
-/// This also works around issues 16003 and 14849 in the implementation of
-/// [Directory.watch].
-class MacOSDirectoryWatcher extends ResubscribableDirectoryWatcher {
-  // TODO(nweiz): remove these when issue 15042 is fixed.
-  static var logDebugInfo = false;
-  static var _count = 0;
-
-  MacOSDirectoryWatcher(String directory)
-      : super(directory, () => new _MacOSDirectoryWatcher(directory, _count++));
+class WindowsDirectoryWatcher extends ResubscribableDirectoryWatcher {
+  WindowsDirectoryWatcher(String directory)
+      : super(directory, () => new _WindowsDirectoryWatcher(directory));
 }
 
-class _MacOSDirectoryWatcher implements ManuallyClosedDirectoryWatcher {
-  // TODO(nweiz): remove these when issue 15042 is fixed.
-  static var _count = 0;
-  final String _id;
-
+class _WindowsDirectoryWatcher implements ManuallyClosedDirectoryWatcher {
   final String directory;
 
   Stream<WatchEvent> get events => _eventsController.stream;
   final _eventsController = new StreamController<WatchEvent>.broadcast();
 
   bool get isReady => _readyCompleter.isCompleted;
 
   Future get ready => _readyCompleter.future;
   final _readyCompleter = new Completer();
 
   /// The set of files that are known to exist recursively within the watched
   /// directory.
   ///
   /// The state of files on the filesystem is compared against this to determine
-  /// the real change that occurred when working around issue 14373. This is
-  /// also used to emit REMOVE events when subdirectories are moved out of the
-  /// watched directory.
+  /// the real change that occurred. This is also used to emit REMOVE events
+  /// when subdirectories are moved out of the watched directory.
   final PathSet _files;
 
   /// The subscription to the stream returned by [Directory.watch].
-  ///
-  /// This is separate from [_subscriptions] because this stream occasionally
-  /// needs to be resubscribed in order to work around issue 14849.
   StreamSubscription<FileSystemEvent> _watchSubscription;
 
+  /// The subscription to the stream returned by [Directory.watch] of the
+  /// parent directory of [directory]. This is needed to detect removal of
+  /// [directory], as Windows will lock the directory when watching.
+  StreamSubscription<FileSystemEvent> _parentWatchSubscription;
+
   /// The subscription to the [Directory.list] call for the initial listing of
   /// the directory to determine its initial state.
   StreamSubscription<FileSystemEntity> _initialListSubscription;
 
   /// The subscription to the [Directory.list] call for listing the contents of
   /// a subdirectory that was moved into the watched directory.
   StreamSubscription<FileSystemEntity> _listSubscription;
 
-  /// The timer for tracking how long we wait for an initial batch of bogus
-  /// events (see issue 14373).
-  Timer _bogusEventTimer;
-
-  _MacOSDirectoryWatcher(String directory, int parentId)
-      : directory = directory,
-        _files = new PathSet(directory),
-        _id = "$parentId/${_count++}" {
+  _WindowsDirectoryWatcher(String directory)
+      : directory = directory, _files = new PathSet(directory) {
     _startWatch();
-
-    // Before we're ready to emit events, wait for [_listDir] to complete and
-    // for enough time to elapse that if bogus events (issue 14373) would be
-    // emitted, they will be.
-    //
-    // If we do receive a batch of events, [_onBatch] will ensure that these
-    // futures don't fire and that the directory is re-listed.
-    Future.wait([
-      _listDir().then((_) {
-        if (MacOSDirectoryWatcher.logDebugInfo) {
-          print("[$_id] finished initial directory list");
-        }
-      }),
-      _waitForBogusEvents()
-    ]).then((_) {
-      if (MacOSDirectoryWatcher.logDebugInfo) {
-        print("[$_id] watcher is ready, known files:");
-        for (var file in _files.toSet()) {
-          print("[$_id]   ${p.relative(file, from: directory)}");
-        }
-      }
-      _readyCompleter.complete();
-    });
+    _startParentWatcher();
+
+    // Before we're ready to emit events, wait for [_listDir] to complete.
+    _listDir().then(_readyCompleter.complete);
   }
 
   void close() {
-    if (MacOSDirectoryWatcher.logDebugInfo) {
-      print("[$_id] watcher is closed\n${new Chain.current().terse}");
-    }
     if (_watchSubscription != null) _watchSubscription.cancel();
+    if (_parentWatchSubscription != null) _parentWatchSubscription.cancel();
     if (_initialListSubscription != null) _initialListSubscription.cancel();
     if (_listSubscription != null) _listSubscription.cancel();
     _watchSubscription = null;
+    _parentWatchSubscription = null;
     _initialListSubscription = null;
     _listSubscription = null;
     _eventsController.close();
   }
 
+  void _startParentWatcher() {

[kasperl, 2014/06/03 13:08:10]

Add a comment that explains why you have a parent watcher.

[Anders Johnsen, 2014/06/03 13:41:56]

Done.

+    var absoluteDir = p.absolute(directory);
+    var parent = p.dirname(absoluteDir);
+    if (FileSystemEntity.identicalSync(parent, directory)) return;
+    var parentStream = Chain.track(
+        new Directory(parent).watch(recursive: false));
+    _parentWatchSubscription = parentStream
+        .listen((event) {

[kasperl, 2014/06/03 13:08:10]

I'd move .listen up to the previous line and use less indentation for the body.

   ... = parentStream.listen((event) {
     ...
   }, onError: (error) {
     ...
   });

[Anders Johnsen, 2014/06/03 13:41:56]

Done.

+          if (!event.path.startsWith(absoluteDir)) {
+            // Only look at events for 'directory'.
+            return;
+          }
+          // Test if the directory is removed.
+          if (FileSystemEntity.typeSync(directory) ==
+              FileSystemEntityType.NOT_FOUND) {
+            for (var path in _files.toSet()) {

[kasperl, 2014/06/03 13:08:10]

Does toSet copy the PathSet? Is it necessary?

[Anders Johnsen, 2014/06/03 13:41:56]

I think it copies, but it does not offer an alternative.

+              _emitEvent(ChangeType.REMOVE, path);
+            }
+            _files.clear();
+            close();
+          }
+        }, onError: (error) {
+          // Ignore errors, simply close the stream.
+          _parentWatchSubscription.cancel();
+          _parentWatchSubscription = null;
+        });
+  }
+
   /// The callback that's run when [Directory.watch] emits a batch of events.
   void _onBatch(List<FileSystemEvent> batch) {
-    if (MacOSDirectoryWatcher.logDebugInfo) {
-      print("[$_id] ======== batch:");
-      for (var event in batch) {
-        print("[$_id]   ${_formatEvent(event)}");
-      }
-
-      print("[$_id] known files:");
-      for (var file in _files.toSet()) {
-        print("[$_id]   ${p.relative(file, from: directory)}");
-      }
-    }
-
-    // If we get a batch of events before we're ready to begin emitting events,
-    // it's probable that it's a batch of pre-watcher events (see issue 14373).
+    // If we get a batch of events before we're ready to begin emitting events.
     // Ignore those events and re-list the directory.
     if (!isReady) {
-      if (MacOSDirectoryWatcher.logDebugInfo) {
-        print("[$_id] not ready to emit events, re-listing directory");
-      }
-
-      // Cancel the timer because bogus events only occur in the first batch, so
-      // we can fire [ready] as soon as we're done listing the directory.
-      _bogusEventTimer.cancel();
-      _listDir().then((_) {
-        if (MacOSDirectoryWatcher.logDebugInfo) {
-          print("[$_id] watcher is ready, known files:");
-          for (var file in _files.toSet()) {
-            print("[$_id]   ${p.relative(file, from: directory)}");
-          }
-        }
-        _readyCompleter.complete();
-      });
       return;
     }
 
     _sortEvents(batch).forEach((path, events) {
       var relativePath = p.relative(path, from: directory);
-      if (MacOSDirectoryWatcher.logDebugInfo) {
-        print("[$_id] events for $relativePath:");
-        for (var event in events) {
-          print("[$_id]   ${_formatEvent(event)}");
-        }
-      }
 
       var canonicalEvent = _canonicalEvent(events);
       events = canonicalEvent == null ?
           _eventsBasedOnFileSystem(path) : [canonicalEvent];
-      if (MacOSDirectoryWatcher.logDebugInfo) {
-        print("[$_id] canonical event for $relativePath: "
-            "${_formatEvent(canonicalEvent)}");
-        print("[$_id] actionable events for $relativePath: "
-            "${events.map(_formatEvent)}");
-      }
 
       for (var event in events) {
         if (event is FileSystemCreateEvent) {
           if (!event.isDirectory) {
-            // Don't emit ADD events for files or directories that we already
-            // know about. Such an event comes from FSEvents reporting an add
-            // that happened prior to the watch beginning.
-            if (_files.contains(path)) continue;
-
             _emitEvent(ChangeType.ADD, path);
             _files.add(path);
             continue;
           }
 
           if (_files.containsDir(path)) continue;
 
           var stream = Chain.track(new Directory(path).list(recursive: true));
           _listSubscription = stream.listen((entity) {

[kasperl, 2014/06/03 13:08:10]

The indentation looks nice here.

[Anders Johnsen, 2014/06/03 13:41:56]

Done.

             if (entity is Directory) return;
             if (_files.contains(path)) return;
 
             _emitEvent(ChangeType.ADD, entity.path);
             _files.add(entity.path);
           }, onError: (e, stackTrace) {
-            if (MacOSDirectoryWatcher.logDebugInfo) {
-              print("[$_id] got error listing $relativePath: $e");
-            }
             _emitError(e, stackTrace);
           }, cancelOnError: true);
         } else if (event is FileSystemModifyEvent) {
           assert(!event.isDirectory);
           _emitEvent(ChangeType.MODIFY, path);
         } else {
           assert(event is FileSystemDeleteEvent);
           for (var removedPath in _files.remove(path)) {
             _emitEvent(ChangeType.REMOVE, removedPath);
           }
         }
       }
     });
-
-    if (MacOSDirectoryWatcher.logDebugInfo) {
-      print("[$_id] ======== batch complete");
-    }
   }
 
   /// Sort all the events in a batch into sets based on their path.
   ///
   /// A single input event may result in multiple events in the returned map;
   /// for example, a MOVE event becomes a DELETE event for the source and a
   /// CREATE event for the destination.
   ///
   /// The returned events won't contain any [FileSystemMoveEvent]s, nor will it
   /// contain any events relating to [directory].
@@ skipping 17 matching lines @@
     isInModifiedDirectory(path) =>
         directories.any((dir) => path != dir && path.startsWith(dir));
 
     addEvent(path, event) {
       if (isInModifiedDirectory(path)) return;
       var set = eventsForPaths.putIfAbsent(path, () => new Set());
       set.add(event);
     }
 
     for (var event in batch) {
-      // The Mac OS watcher doesn't emit move events. See issue 14806.
-      assert(event is! FileSystemMoveEvent);
+      if (event is FileSystemMoveEvent) {
+        FileSystemMoveEvent moveEvent = event;
+        addEvent(moveEvent.destination, event);
+      }
       addEvent(event.path, event);
     }
 
     return eventsForPaths;
   }
 
   /// Returns the canonical event from a batch of events on the same path, if
   /// one exists.
   ///
   /// If [batch] doesn't contain any contradictory events (e.g. DELETE and
@@ skipping 18 matching lines @@
       if (isDir != event.isDirectory) return null;
 
       // Modify events don't contradict either CREATE or REMOVE events. We can
       // safely assume the file was modified after a CREATE or before the
       // REMOVE; otherwise there will also be a REMOVE or CREATE event
       // (respectively) that will be contradictory.
       if (event is FileSystemModifyEvent) {
         hadModifyEvent = true;
         continue;
       }
-      assert(event is FileSystemCreateEvent || event is FileSystemDeleteEvent);
+      assert(event is FileSystemCreateEvent ||
+             event is FileSystemDeleteEvent ||
+             event is FileSystemMoveEvent);
 
       // If we previously thought this was a MODIFY, we now consider it to be a
       // CREATE or REMOVE event. This is safe for the same reason as above.
       if (type == FileSystemEvent.MODIFY) {
         type = event.type;
         continue;
       }
 
       // A CREATE event contradicts a REMOVE event and vice versa.
-      assert(type == FileSystemEvent.CREATE || type == FileSystemEvent.DELETE);
+      assert(type == FileSystemEvent.CREATE ||
+             type == FileSystemEvent.DELETE ||
+             type == FileSystemEvent.MOVE);
       if (type != event.type) return null;
     }
 
     // If we got a CREATE event for a file we already knew about, that comes
     // from FSEvents reporting an add that happened prior to the watch
     // beginning. If we also received a MODIFY event, we want to report that,
     // but not the CREATE.
     if (type == FileSystemEvent.CREATE && hadModifyEvent &&
         _files.contains(batch.first.path)) {
       type = FileSystemEvent.MODIFY;
     }
 
     switch (type) {
       case FileSystemEvent.CREATE:
-        // Issue 16003 means that a CREATE event for a directory can indicate
-        // that the directory was moved and then re-created.
-        // [_eventsBasedOnFileSystem] will handle this correctly by producing a
-        // DELETE event followed by a CREATE event if the directory exists.
-        if (isDir) return null;
-        return new ConstructableFileSystemCreateEvent(batch.first.path, false);
+        return new ConstructableFileSystemCreateEvent(batch.first.path, isDir);
       case FileSystemEvent.DELETE:
         return new ConstructableFileSystemDeleteEvent(batch.first.path, isDir);
       case FileSystemEvent.MODIFY:
         return new ConstructableFileSystemModifyEvent(
             batch.first.path, isDir, false);
+      case FileSystemEvent.MOVE:
+        return null;
       default: assert(false);
     }
   }
 
   /// Returns one or more events that describe the change between the last known
   /// state of [path] and its current state on the filesystem.
   ///
   /// This returns a list whose order should be reflected in the events emitted
   /// to the user, unlike the batched events from [Directory.watch]. The
   /// returned list may be empty, indicating that no changes occurred to [path]
   /// (probably indicating that it was created and then immediately deleted).
   List<FileSystemEvent> _eventsBasedOnFileSystem(String path) {
     var fileExisted = _files.contains(path);
     var dirExisted = _files.containsDir(path);
     var fileExists = new File(path).existsSync();
     var dirExists = new Directory(path).existsSync();
 
-    if (MacOSDirectoryWatcher.logDebugInfo) {
-      print("[$_id] checking file system for "
-          "${p.relative(path, from: directory)}");
-      print("[$_id]   file existed: $fileExisted");
-      print("[$_id]   dir existed: $dirExisted");
-      print("[$_id]   file exists: $fileExists");
-      print("[$_id]   dir exists: $dirExists");
-    }
-
     var events = [];
     if (fileExisted) {
       if (fileExists) {
         events.add(new ConstructableFileSystemModifyEvent(path, false, false));
       } else {
         events.add(new ConstructableFileSystemDeleteEvent(path, false));
       }
     } else if (dirExisted) {
       if (dirExists) {
         // If we got contradictory events for a directory that used to exist and
         // still exists, we need to rescan the whole thing in case it was
         // replaced with a different directory.
         events.add(new ConstructableFileSystemDeleteEvent(path, true));
         events.add(new ConstructableFileSystemCreateEvent(path, true));
       } else {
         events.add(new ConstructableFileSystemDeleteEvent(path, true));
       }
     }
 
     if (!fileExisted && fileExists) {
       events.add(new ConstructableFileSystemCreateEvent(path, false));
     } else if (!dirExisted && dirExists) {
       events.add(new ConstructableFileSystemCreateEvent(path, true));
     }
 
     return events;
   }
 
   /// The callback that's run when the [Directory.watch] stream is closed.
+  /// Note that this is unlikely to happen on Windows, unless the system itself
+  /// closes the handle.
   void _onDone() {
-    if (MacOSDirectoryWatcher.logDebugInfo) print("[$_id] stream closed");
-
     _watchSubscription = null;
 
-    // If the directory still exists and we're still expecting bogus events,
-    // this is probably issue 14849 rather than a real close event. We should
-    // just restart the watcher.
-    if (!isReady && new Directory(directory).existsSync()) {
-      if (MacOSDirectoryWatcher.logDebugInfo) {
-        print("[$_id] fake closure (issue 14849), re-opening stream");
-      }
-      _startWatch();
-      return;
-    }
-
-    // FSEvents can fail to report the contents of the directory being removed
-    // when the directory itself is removed, so we need to manually mark the
-    // files as removed.
+    // Emit remove-events for any remaining files.
     for (var file in _files.toSet()) {
       _emitEvent(ChangeType.REMOVE, file);
     }
     _files.clear();
     close();
   }
 
   /// Start or restart the underlying [Directory.watch] stream.
   void _startWatch() {
     // Batch the FSEvent changes together so that we can dedup events.
     var innerStream =
         Chain.track(new Directory(directory).watch(recursive: true))
         .transform(new BatchedStreamTransformer<FileSystemEvent>());
     _watchSubscription = innerStream.listen(_onBatch,
         onError: _eventsController.addError,
         onDone: _onDone);
   }
 
   /// Starts or restarts listing the watched directory to get an initial picture
   /// of its state.
   Future _listDir() {
     assert(!isReady);
     if (_initialListSubscription != null) _initialListSubscription.cancel();
 
     _files.clear();
     var completer = new Completer();
     var stream = Chain.track(new Directory(directory).list(recursive: true));
-    _initialListSubscription = stream.listen((entity) {
-      if (entity is! Directory) _files.add(entity.path);
-    },
+    _initialListSubscription = stream

[kasperl, 2014/06/03 13:08:10]

I preferred the code as it was.

[Anders Johnsen, 2014/06/03 13:41:56]

Rewrote.

+        .listen((entity) {
+          if (entity is! Directory) _files.add(entity.path);
+        },
         onError: _emitError,
         onDone: completer.complete,
         cancelOnError: true);
     return completer.future;
   }
 
-  /// Wait 200ms for a batch of bogus events (issue 14373) to come in.
-  ///
-  /// 200ms is short in terms of human interaction, but longer than any Mac OS
-  /// watcher tests take on the bots, so it should be safe to assume that any
-  /// bogus events will be signaled in that time frame.
-  Future _waitForBogusEvents() {
-    var completer = new Completer();
-    _bogusEventTimer = new Timer(
-        new Duration(milliseconds: 200),
-        completer.complete);
-    return completer.future;
-  }
-
   /// Emit an event with the given [type] and [path].
   void _emitEvent(ChangeType type, String path) {
     if (!isReady) return;
 
-    if (MacOSDirectoryWatcher.logDebugInfo) {
-      print("[$_id] emitting $type ${p.relative(path, from: directory)}");
-    }
-
     _eventsController.add(new WatchEvent(type, path));
   }
 
   /// Emit an error, then close the watcher.
   void _emitError(error, StackTrace stackTrace) {
-    if (MacOSDirectoryWatcher.logDebugInfo) {
-      print("[$_id] emitting error: $error\n" +
-          "${new Chain.forTrace(stackTrace).terse}");
-    }
     _eventsController.addError(error, stackTrace);
     close();
   }
-
-  // TODO(nweiz): remove this when issue 15042 is fixed.
-  /// Return a human-friendly string representation of [event].
-  String _formatEvent(FileSystemEvent event) {
-    if (event == null) return 'null';
-
-    var path = p.relative(event.path, from: directory);
-    var type = event.isDirectory ? 'directory' : 'file';
-    if (event is FileSystemCreateEvent) {
-      return "create $type $path";
-    } else if (event is FileSystemDeleteEvent) {
-      return "delete $type $path";
-    } else if (event is FileSystemModifyEvent) {
-      return "modify $type $path";
-    } else if (event is FileSystemMoveEvent) {
-      return "move $type $path to "
-          "${p.relative(event.destination, from: directory)}";
-    }
-  }
 }