Remove ref-counting from FilePathWatcher.

base/files/file_path_watcher_linux.cc

Index: base/files/file_path_watcher_linux.cc
diff --git a/base/files/file_path_watcher_linux.cc b/base/files/file_path_watcher_linux.cc
index d060e49136cbc88dc095b5872d148607af501d39..9589e9b788dce7807ac0b97a011e6012e6b47860 100644
--- a/base/files/file_path_watcher_linux.cc
+++ b/base/files/file_path_watcher_linux.cc
@@ -28,6 +28,8 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "base/memory/weak_ptr.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
@@ -91,6 +93,7 @@ class InotifyReader {
 class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
  public:
   FilePathWatcherImpl();
+  ~FilePathWatcherImpl() override;
 
   // Called for each event coming from the watch. |fired_watch| identifies the
   // watch that fired, |child| indicates what has changed, and is relative to
@@ -105,13 +108,13 @@ class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
                          bool deleted,
                          bool is_dir);
 
- protected:
-  ~FilePathWatcherImpl() override {
-    in_destructor_ = true;
-    CancelOnMessageLoopThreadOrInDestructor();
-  }
-
  private:
+  void OnFilePathChangedOnOriginSequence(InotifyReader::Watch fired_watch,
+                                         const FilePath::StringType& child,
+                                         bool created,
+                                         bool deleted,
+                                         bool is_dir);
+
   // Start watching |path| for changes and notify |delegate| on each change.
   // Returns true if watch for |path| has been added successfully.
   bool Watch(const FilePath& path,
@@ -120,7 +123,6 @@ class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
 
   // Cancel the watch. This unregisters the instance with InotifyReader.
   void Cancel() override;
-  void CancelOnMessageLoopThreadOrInDestructor();
 
   // Inotify watches are installed for all directory components of |target_|.
   // A WatchEntry instance holds:
@@ -185,7 +187,7 @@ class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
   hash_map<InotifyReader::Watch, FilePath> recursive_paths_by_watch_;
   std::map<FilePath, InotifyReader::Watch> recursive_watches_by_path_;
 
-  bool in_destructor_ = false;
+  WeakPtrFactory<FilePathWatcherImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
 };
@@ -312,7 +314,10 @@ void InotifyReader::OnInotifyEvent(const inotify_event* event) {
 }
 
 FilePathWatcherImpl::FilePathWatcherImpl()
-    : recursive_(false) {
+    : recursive_(false), weak_factory_(this) {}
+
+FilePathWatcherImpl::~FilePathWatcherImpl() {
+  DCHECK(!task_runner() || task_runner()->RunsTasksOnCurrentThread());
 }
 
 void FilePathWatcherImpl::OnFilePathChanged(InotifyReader::Watch fired_watch,
@@ -320,22 +325,25 @@ void FilePathWatcherImpl::OnFilePathChanged(InotifyReader::Watch fired_watch,
                                             bool created,
                                             bool deleted,
                                             bool is_dir) {
-  if (!task_runner()->RunsTasksOnCurrentThread()) {
-    // Switch to task_runner() to access |watches_| safely.
-    task_runner()->PostTask(FROM_HERE,
-                            Bind(&FilePathWatcherImpl::OnFilePathChanged, this,
-                                 fired_watch, child, created, deleted, is_dir));
-    return;
-  }
-
-  // Check to see if CancelOnMessageLoopThreadOrInDestructor() has already been
-  // called. May happen when code flow reaches here from the PostTask() above.
-  if (watches_.empty()) {
-    DCHECK(target_.empty());
-    return;
-  }
+  DCHECK(!task_runner()->RunsTasksOnCurrentThread());
+
+  // This method is invoked on the Inotify thread. Switch to task_runner() to
+  // access |watches_| safely. Use a WeakPtr to prevent the callback from
+  // running after |this| is destroyed (i.e. after the watch is cancelled).
+  task_runner()->PostTask(
+      FROM_HERE, Bind(&FilePathWatcherImpl::OnFilePathChangedOnOriginSequence,
+                      weak_factory_.GetWeakPtr(), fired_watch, child, created,
+                      deleted, is_dir));
+}
 
+void FilePathWatcherImpl::OnFilePathChangedOnOriginSequence(
+    InotifyReader::Watch fired_watch,
+    const FilePath::StringType& child,
+    bool created,
+    bool deleted,
+    bool is_dir) {
   DCHECK(task_runner()->RunsTasksOnCurrentThread());
+  DCHECK(!watches_.empty());
   DCHECK(HasValidWatchVector());
 
   // Used below to avoid multiple recursive updates.
@@ -437,41 +445,23 @@ bool FilePathWatcherImpl::Watch(const FilePath& path,
 }
 
 void FilePathWatcherImpl::Cancel() {
-  if (callback_.is_null()) {
-    // Watch was never called, or the message_loop() thread is already gone.
+  if (!callback_) {
+    // Watch() was never called.
     set_cancelled();
     return;
   }
 
-  // Switch to the task_runner() if necessary so we can access |watches_|.
-  if (!task_runner()->RunsTasksOnCurrentThread()) {
-    task_runner()->PostTask(
-        FROM_HERE,
-        Bind(&FilePathWatcherImpl::CancelOnMessageLoopThreadOrInDestructor,
-             this));
-  } else {
-    CancelOnMessageLoopThreadOrInDestructor();
-  }
-}
-
-void FilePathWatcherImpl::CancelOnMessageLoopThreadOrInDestructor() {
-  DCHECK(in_destructor_ || task_runner()->RunsTasksOnCurrentThread());
-
-  if (is_cancelled())
-    return;
+  DCHECK(task_runner()->RunsTasksOnCurrentThread());
+  DCHECK(!is_cancelled());
 
   set_cancelled();
-
-  if (!callback_.is_null())
-    callback_.Reset();
+  callback_.Reset();
 
   for (size_t i = 0; i < watches_.size(); ++i)
     g_inotify_reader.Get().RemoveWatch(watches_[i].watch, this);
   watches_.clear();
   target_.clear();
-
-  if (recursive_)
-    RemoveRecursiveWatches();
+  RemoveRecursiveWatches();
 }
 
 void FilePathWatcherImpl::UpdateWatches() {
@@ -657,7 +647,7 @@ bool FilePathWatcherImpl::HasValidWatchVector() const {
 
 FilePathWatcher::FilePathWatcher() {
   sequence_checker_.DetachFromSequence();
-  impl_ = new FilePathWatcherImpl();
+  impl_ = MakeUnique<FilePathWatcherImpl>();
 }
 
 }  // namespace base