Use FSEvents for recursive file watch on Mac

base/files/file_path_watcher_fsevents.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/files/file_path_watcher_fsevents.h"
+
+#include <list>
+
+#include "base/bind.h"
+#include "base/file_util.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/mac/libdispatch_task_runner.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/message_loop/message_loop.h"
+
+namespace base {
+
+namespace {
+
+// The latency parameter passed to FSEventsStreamCreate().
+const CFAbsoluteTime kEventLatencySeconds = 0.3;
+
+class FSEventsTaskRunner : public mac::LibDispatchTaskRunner {
+ public:
+   FSEventsTaskRunner()
+       : mac::LibDispatchTaskRunner("org.chromium.FilePathWatcherFSEvents") {
+   }
+
+ protected:
+   virtual ~FSEventsTaskRunner() {}
+};
+
+static LazyInstance<FSEventsTaskRunner>::Leaky g_task_runner =
+    LAZY_INSTANCE_INITIALIZER;
+
+// Resolve any symlinks in the path.
+FilePath ResolvePath(const FilePath& path) {
+  const unsigned kMaxLinksToResolve = 255;
+
+  std::vector<FilePath::StringType> component_vector;
+  path.GetComponents(&component_vector);
+  std::list<FilePath::StringType>
+      components(component_vector.begin(), component_vector.end());
+
+  FilePath result;
+  unsigned resolve_count = 0;
+  while (resolve_count < kMaxLinksToResolve && !components.empty()) {
+    FilePath component(*components.begin());
+    components.pop_front();
+
+    FilePath current;
+    if (component.IsAbsolute()) {
+      current = component;
+    } else {
+      current = result.Append(component);
+    }
+
+    FilePath target;
+    if (ReadSymbolicLink(current, &target)) {
+      if (target.IsAbsolute())
+        result.clear();
+      std::vector<FilePath::StringType> target_components;
+      target.GetComponents(&target_components);
+      components.insert(components.begin(), target_components.begin(),
+                        target_components.end());
+      resolve_count++;
+    } else {
+      result = current;
+    }
+  }
+
+  if (resolve_count >= kMaxLinksToResolve)
+    result.clear();
+  return result;
+}
+
+// The callback passed to FSEventStreamCreate().
+void FSEventsCallback(ConstFSEventStreamRef stream,
+                      void* event_watcher, size_t num_events,
+                      void* event_paths, const FSEventStreamEventFlags flags[],
+                      const FSEventStreamEventId event_ids[]) {
+  FilePathWatcherFSEvents* watcher =
+      reinterpret_cast<FilePathWatcherFSEvents*>(event_watcher);
+  DCHECK(g_task_runner.Get().RunsTasksOnCurrentThread());
+
+  bool root_changed = watcher->ResolveTargetPath();
+  std::vector<FilePath> paths;
+  FSEventStreamEventId root_change_at = FSEventStreamGetLatestEventId(stream);
+  for (size_t i = 0; i < num_events; i++) {
+    if (flags[i] & kFSEventStreamEventFlagRootChanged)
+      root_changed = true;
+    if (event_ids[i])
+      root_change_at = std::min(root_change_at, event_ids[i]);
+    paths.push_back(FilePath(
+        reinterpret_cast<char**>(event_paths)[i]).StripTrailingSeparators());
+  }
+
+  // Reinitialize the event stream if we find changes to the root. This is
+  // necessary since FSEvents doesn't report any events for the subtree after
+  // the directory to be watched gets created.
+  if (root_changed) {
+    // Resetting the event stream from within the callback fails (FSEvents spews
+    // bad file descriptor errors), so post a task to do the reset.
+    g_task_runner.Get().PostTask(
+        FROM_HERE,
+        Bind(&FilePathWatcherFSEvents::UpdateEventStream, watcher,
+             root_change_at));
+  }
+
+  watcher->OnFilePathsChanged(paths);
+}
+
+}  // namespace
+
+FilePathWatcherFSEvents::FilePathWatcherFSEvents() : fsevent_stream_(NULL) {
+}
+
+void FilePathWatcherFSEvents::OnFilePathsChanged(
+    const std::vector<FilePath>& paths) {
+  if (!message_loop()->BelongsToCurrentThread()) {
+    message_loop()->PostTask(
+        FROM_HERE,
+        Bind(&FilePathWatcherFSEvents::OnFilePathsChanged, this, paths));
+    return;
+  }
+
+  DCHECK(message_loop()->BelongsToCurrentThread());
+  if (resolved_target_.empty())
+    return;
+
+  for (size_t i = 0; i < paths.size(); i++) {
+    if (resolved_target_.IsParent(paths[i]) || resolved_target_ == paths[i]) {
+      callback_.Run(target_, false);
+      return;
+    }
+  }
+}
+
+bool FilePathWatcherFSEvents::Watch(const FilePath& path,
+                                    bool recursive,
+                                    const FilePathWatcher::Callback& callback) {
+  DCHECK(resolved_target_.empty());
+  DCHECK(MessageLoopForIO::current());
+  DCHECK(!callback.is_null());
+
+  // This class could support non-recursive watches, but that is currently
+  // left to FilePathWatcherKQueue.
+  if (!recursive)
+    return false;
+
+  set_message_loop(MessageLoopProxy::current());
+  callback_ = callback;
+  target_ = path;
+
+  FSEventStreamEventId start_event = FSEventsGetCurrentEventId();
+  g_task_runner.Get().PostTask(
+      FROM_HERE,
+      Bind(&FilePathWatcherFSEvents::StartEventStream, this, start_event));
+  return true;
+}
+
+void FilePathWatcherFSEvents::Cancel() {
+  if (callback_.is_null()) {
+    // Watch was never called, so exit.
+    set_cancelled();
+    return;
+  }
+
+  // Switch to the dispatch queue thread if necessary, so we can tear down
+  // the event stream.
+  if (!g_task_runner.Get().RunsTasksOnCurrentThread()) {
+    g_task_runner.Get().PostTask(
+        FROM_HERE,
+        Bind(&FilePathWatcherFSEvents::CancelOnMessageLoopThread, this));
+  } else {
+    CancelOnMessageLoopThread();
+  }
+}
+
+void FilePathWatcherFSEvents::CancelOnMessageLoopThread() {
+  // For all other implementations, the "message loop thread" is the IO thread,
+  // as returned by message_loop(). This implementation, however, needs to
+  // cancel pending work on the Dipatch Queue thread.
+  DCHECK(g_task_runner.Get().RunsTasksOnCurrentThread());
+
+  set_cancelled();
+  if (fsevent_stream_) {
+    DestroyEventStream();
+    callback_.Reset();
+    target_.clear();
+    resolved_target_.clear();
+  }
+}
+
+void FilePathWatcherFSEvents::UpdateEventStream(
+    FSEventStreamEventId start_event) {
+  DCHECK(g_task_runner.Get().RunsTasksOnCurrentThread());
+
+  // It can happen that the watcher gets canceled while tasks that call this
+  // function are still in flight, so abort if this situation is detected.
+  if (is_cancelled() || resolved_target_.empty())
+    return;
+
+  if (fsevent_stream_)
+    DestroyEventStream();
+
+  ScopedCFTypeRef<CFStringRef> cf_path(CFStringCreateWithCString(
+      NULL, resolved_target_.value().c_str(), kCFStringEncodingMacHFS));
+  ScopedCFTypeRef<CFStringRef> cf_dir_path(CFStringCreateWithCString(
+      NULL, resolved_target_.DirName().value().c_str(),
+      kCFStringEncodingMacHFS));
+  CFStringRef paths_array[] = { cf_path.get(), cf_dir_path.get() };
+  ScopedCFTypeRef<CFArrayRef> watched_paths(CFArrayCreate(
+      NULL, reinterpret_cast<const void**>(paths_array), arraysize(paths_array),
+      &kCFTypeArrayCallBacks));
+
+  FSEventStreamContext context;
+  context.version = 0;
+  context.info = this;
+  context.retain = NULL;
+  context.release = NULL;
+  context.copyDescription = NULL;
+
+  fsevent_stream_ = FSEventStreamCreate(NULL, &FSEventsCallback, &context,
+                                        watched_paths,
+                                        start_event,
+                                        kEventLatencySeconds,
+                                        kFSEventStreamCreateFlagWatchRoot);
+  FSEventStreamSetDispatchQueue(fsevent_stream_,
+                                g_task_runner.Get().GetDispatchQueue());
+
+  if (!FSEventStreamStart(fsevent_stream_))
+    message_loop()->PostTask(FROM_HERE, Bind(callback_, target_, true));
+}
+
+bool FilePathWatcherFSEvents::ResolveTargetPath() {
+  DCHECK(g_task_runner.Get().RunsTasksOnCurrentThread());
+  FilePath resolved = ResolvePath(target_).StripTrailingSeparators();
+  bool changed = resolved != resolved_target_;
+  resolved_target_ = resolved;
+  if (resolved_target_.empty())
+    message_loop()->PostTask(FROM_HERE, Bind(callback_, target_, true));
+  return changed;
+}
+
+void FilePathWatcherFSEvents::DestroyEventStream() {
+  FSEventStreamStop(fsevent_stream_);
+  FSEventStreamInvalidate(fsevent_stream_);
+  FSEventStreamRelease(fsevent_stream_);
+  fsevent_stream_ = NULL;
+}
+
+void FilePathWatcherFSEvents::StartEventStream(
+    FSEventStreamEventId start_event) {
+  DCHECK(g_task_runner.Get().RunsTasksOnCurrentThread());
+  ResolveTargetPath();
+  UpdateEventStream(start_event);
+}
+
+FilePathWatcherFSEvents::~FilePathWatcherFSEvents() {}
+
+}  // namespace base