Add a FileWatcher to base/.

base/file_watcher_inotify.cc

+// Copyright (c) 2009 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/file_watcher.h"
+
+#include <errno.h>
+#include <string.h>
+#include <sys/inotify.h>
+#include <sys/ioctl.h>
+#include <sys/select.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <set>
+#include <utility>
+#include <vector>
+
+#include "base/eintr_wrapper.h"
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "base/hash_tables.h"
+#include "base/lock.h"
+#include "base/logging.h"
+#include "base/message_loop.h"
+#include "base/scoped_ptr.h"
+#include "base/singleton.h"
+#include "base/task.h"
+#include "base/thread.h"
+#include "base/waitable_event.h"
+
+namespace {
+
+class FileWatcherImpl;
+
+// Singleton to manage all inotify watches.
+class InotifyReader {
+ public:
+  typedef int Watch;  // Watch descriptor used by AddWatch and RemoveWatch.
+  static const Watch kInvalidWatch = -1;
+
+  // Watch |path| for changes. |watcher| will be notified on each change.
+  // Returns kInvalidWatch on failure.
+  Watch AddWatch(const FilePath& path, FileWatcherImpl* watcher);
+
+  // Remove |watch|. Returns true on success.
+  bool RemoveWatch(Watch watch, FileWatcherImpl* watcher);
+
+  // Callback for InotifyReaderTask.
+  void OnInotifyEvent(const inotify_event* event);
+
+ private:
+  friend struct DefaultSingletonTraits<InotifyReader>;
+
+  typedef std::set<FileWatcherImpl*> WatcherSet;
+
+  InotifyReader();
+  ~InotifyReader();
+
+  // We keep track of which delegates want to be notified on which watches.
+  base::hash_map<Watch, WatcherSet> watchers_;
+
+  // Lock to protect watchers_.
+  Lock lock_;
+
+  // Separate thread on which we run blocking read for inotify events.
+  base::Thread thread_;
+
+  // File descriptor returned by inotify_init.
+  const int inotify_fd_;
+
+  // Use self-pipe trick to unblock select during shutdown.
+  int shutdown_pipe_[2];
+
+  // Flag set to true when startup was successful.
+  bool valid_;
+
+  DISALLOW_COPY_AND_ASSIGN(InotifyReader);
+};
+
+class FileWatcherImpl : public FileWatcher::PlatformDelegate {
+ public:
+  FileWatcherImpl();
+  ~FileWatcherImpl();
+
+  // Called for each event coming from the watch.
+  void OnInotifyEvent(const inotify_event* event);
+
+  // Start watching |path| for changes and notify |delegate| on each change.
+  // Returns true if watch for |path| has been added successfully.
+  virtual bool Watch(const FilePath& path, FileWatcher::Delegate* delegate,
+                     MessageLoop* backend_loop);
+
+ private:
+  // Delegate to notify upon changes.
+  FileWatcher::Delegate* delegate_;
+
+  // Watch returned by InotifyReader.
+  InotifyReader::Watch watch_;
+
+  // The file we're watching.
+  FilePath path_;
+
+  // Loop where we post file change notifications to.
+  MessageLoop* loop_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileWatcherImpl);
+};
+
+class FileWatcherImplNotifyTask : public Task {
+ public:
+  FileWatcherImplNotifyTask(FileWatcher::Delegate* delegate,
+                            const FilePath& path)
+      : delegate_(delegate), path_(path) {
+  }
+
+  virtual void Run() {
+    delegate_->OnFileChanged(path_);
+  }
+
+ private:
+  FileWatcher::Delegate* delegate_;
+  FilePath path_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileWatcherImplNotifyTask);
+};
+
+class InotifyReaderTask : public Task {
+ public:
+  InotifyReaderTask(InotifyReader* reader, int inotify_fd, int shutdown_fd)
+      : reader_(reader),
+        inotify_fd_(inotify_fd),
+        shutdown_fd_(shutdown_fd) {
+  }
+
+  virtual void Run() {
+    while (true) {
+      fd_set rfds;
+      FD_ZERO(&rfds);
+      FD_SET(inotify_fd_, &rfds);
+      FD_SET(shutdown_fd_, &rfds);
+
+      // Wait until some inotify events are available.
+      int select_result =
+        HANDLE_EINTR(select(std::max(inotify_fd_, shutdown_fd_) + 1,
+                            &rfds, NULL, NULL, NULL));
+      if (select_result < 0) {
+        DPLOG(WARNING) << "select failed";
+        return;
+      }
+
+      if (FD_ISSET(shutdown_fd_, &rfds))
+        return;
+
+      // Adjust buffer size to current event queue size.
+      int buffer_size;
+      int ioctl_result = HANDLE_EINTR(ioctl(inotify_fd_, FIONREAD,
+                                            &buffer_size));
+
+      if (ioctl_result != 0) {
+        DPLOG(WARNING) << "ioctl failed";
+        return;
+      }
+
+      std::vector<char> buffer(buffer_size);
+
+      ssize_t bytes_read = HANDLE_EINTR(read(inotify_fd_, &buffer[0],
+                                             buffer_size));
+
+      if (bytes_read < 0) {
+        DPLOG(WARNING) << "read from inotify fd failed";
+        return;
+      }
+
+      ssize_t i = 0;
+      while (i < bytes_read) {
+        inotify_event* event = reinterpret_cast<inotify_event*>(&buffer[i]);
+        size_t event_size = sizeof(inotify_event) + event->len;
+        DCHECK(i + event_size <= static_cast<size_t>(bytes_read));
+        reader_->OnInotifyEvent(event);
+        i += event_size;
+      }
+    }
+  }
+
+ private:
+  InotifyReader* reader_;
+  int inotify_fd_;
+  int shutdown_fd_;
+
+  DISALLOW_COPY_AND_ASSIGN(InotifyReaderTask);
+};
+
+InotifyReader::InotifyReader()
+    : thread_("inotify_reader"),
+      inotify_fd_(inotify_init()),
+      valid_(false) {
+  shutdown_pipe_[0] = -1;
+  shutdown_pipe_[1] = -1;
+  if (inotify_fd_ >= 0 && pipe(shutdown_pipe_) == 0 && thread_.Start()) {
+    thread_.message_loop()->PostTask(
+        FROM_HERE, new InotifyReaderTask(this, inotify_fd_, shutdown_pipe_[0]));
+    valid_ = true;
+  }
+}
+
+InotifyReader::~InotifyReader() {
+  if (valid_) {
+    // Write to the self-pipe so that the select call in InotifyReaderTask
+    // returns.
+    ssize_t ret = HANDLE_EINTR(write(shutdown_pipe_[1], "", 1));
+    DPCHECK(ret > 0);
+    DCHECK_EQ(ret, 1);
+    thread_.Stop();
+  }
+  if (inotify_fd_ >= 0)
+    close(inotify_fd_);
+  if (shutdown_pipe_[0] >= 0)
+    close(shutdown_pipe_[0]);
+  if (shutdown_pipe_[1] >= 0)
+    close(shutdown_pipe_[1]);
+}
+
+InotifyReader::Watch InotifyReader::AddWatch(
+    const FilePath& path, FileWatcherImpl* watcher) {
+  if (!valid_)
+    return kInvalidWatch;
+
+  AutoLock auto_lock(lock_);
+
+  Watch watch = inotify_add_watch(inotify_fd_, path.value().c_str(),
+                                  IN_CREATE | IN_DELETE |
+                                  IN_CLOSE_WRITE | IN_MOVE);
+
+  if (watch == kInvalidWatch)
+    return kInvalidWatch;
+
+  watchers_[watch].insert(watcher);
+
+  return watch;
+}
+
+bool InotifyReader::RemoveWatch(Watch watch,
+                                FileWatcherImpl* watcher) {
+  if (!valid_)
+    return false;
+
+  AutoLock auto_lock(lock_);
+
+  watchers_[watch].erase(watcher);
+
+  if (watchers_[watch].empty()) {
+    watchers_.erase(watch);
+    return (inotify_rm_watch(inotify_fd_, watch) == 0);
+  }
+
+  return true;
+}
+
+void InotifyReader::OnInotifyEvent(const inotify_event* event) {
+  if (event->mask & IN_IGNORED)
+    return;
+
+  // In case you want to limit the scope of this lock, it's not sufficient
+  // to just copy things under the lock, and then run the notifications
+  // without holding the lock. FileWatcherImpl's dtor removes its watches,
+  // and to do that obtains the lock. After it finishes removing watches,
+  // it's destroyed. So, if you copy under the lock and notify without the lock,
+  // it's possible you'll copy the FileWatcherImpl which is being
+  // destroyed, then it will destroy itself, and then you'll try to notify it.
+  AutoLock auto_lock(lock_);
+
+  for (WatcherSet::iterator watcher = watchers_[event->wd].begin();
+       watcher != watchers_[event->wd].end();
+       ++watcher) {
+    (*watcher)->OnInotifyEvent(event);
+  }
+}
+
+FileWatcherImpl::FileWatcherImpl()
+    : watch_(InotifyReader::kInvalidWatch) {
+}
+
+FileWatcherImpl::~FileWatcherImpl() {
+  if (watch_ == InotifyReader::kInvalidWatch)
+    return;
+
+  Singleton<InotifyReader>::get()->RemoveWatch(watch_, this);
+}
+
+void FileWatcherImpl::OnInotifyEvent(const inotify_event* event) {
+  // Since we're watching the directory, filter out inotify events
+  // if it's not related to the file we're watching.
+  if (path_ != path_.DirName().Append(event->name))
+    return;
+
+  loop_->PostTask(FROM_HERE,
+      new FileWatcherImplNotifyTask(delegate_, path_));
+}
+
+bool FileWatcherImpl::Watch(const FilePath& path,
+                            FileWatcher::Delegate* delegate,
+                            MessageLoop* backend_loop) {
+  // Each FileWatcherImpl can only watch one file.
+  DCHECK(watch_ == InotifyReader::kInvalidWatch);
+
+  // It's not possible to watch a file that doesn't exist, so instead,
+  // watch the parent directory.
+  if (!file_util::PathExists(path.DirName()))
+    return false;
+
+  delegate_ = delegate;
+  path_ = path;
+  loop_ = MessageLoop::current();
+  watch_ = Singleton<InotifyReader>::get()->AddWatch(path.DirName(), this);
+  return watch_ != InotifyReader::kInvalidWatch;
+}
+
+}  // namespace
+
+FileWatcher::FileWatcher() {
+  impl_ = new FileWatcherImpl();
+}