[net/dns] Watch configd notifications to detect DnsConfig changes on Mac.

net/dns/notify_watcher_mac.cc

+// Copyright (c) 2012 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 "net/dns/notify_watcher_mac.h"
+
+#include <notify.h>
+
+namespace net {
+
+NotifyWatcherMac::NotifyWatcherMac() : notify_fd_(-1), notify_token_(-1) {}
+
+NotifyWatcherMac::~NotifyWatcherMac() {
+  Cancel();
+}
+
+bool NotifyWatcherMac::Watch(const char* key, const CallbackType& callback) {
+  DCHECK(key);

[Mark Mentovai, 2012/04/17 16:27:43]

#include "base/logging.h".

+  DCHECK(!callback.is_null());
+  Cancel();
+  uint32_t status = notify_register_file_descriptor(
+      key, &notify_fd_, 0, &notify_token_);
+  if (status != NOTIFY_STATUS_OK)
+    return false;
+  if (!MessageLoopForIO::current()->WatchFileDescriptor(
+          notify_fd_,
+          true,
+          MessageLoopForIO::WATCH_READ,
+          &watcher_,
+          this)) {
+    Cancel();
+    return false;
+  }
+  callback_ = callback;
+  return true;
+}
+
+void NotifyWatcherMac::Cancel() {
+  if (notify_fd_ >= 0) {
+    notify_cancel(notify_token_);  // Also closes |notify_fd_|.
+    notify_fd_ = -1;
+    callback_.Reset();

[Mark Mentovai, 2012/04/17 16:27:43]

Would you need to reset this even if notify_fd_ <= 0?

[szym, 2012/04/17 19:39:31]

This is set in line 34, only after status == NOTIFY_STATUS_OK. I'd add a
DCHECK_GE(notify_fd_, 0); up there.

+    watcher_.StopWatchingFileDescriptor();

[Mark Mentovai, 2012/04/17 16:27:43]

Is this safe if you got to Cancel() because WatchFileDescriptor failed in
Watch(…)?

[szym, 2012/04/17 19:39:31]

This is always safe to call, see message_pump_libevent.h

+  }
+}
+
+void NotifyWatcherMac::OnFileCanReadWithoutBlocking(int /* fd */) {

[Mark Mentovai, 2012/04/17 16:27:43]

No /* */ necessary

+  int token;
+  int status = read(notify_fd_, &token, sizeof(token));

[Mark Mentovai, 2012/04/17 16:27:43]

Always write HANDLE_EINTR around read. #include "base/eintr_wrapper.h".

+  if (status < 0) {
+    Cancel();
+    callback_.Run(false);
+    return;
+  }
+  // Ignoring |token| read to avoid possible endianness mismatch:

[Mark Mentovai, 2012/04/17 16:27:43]

read -> value

+  // http://openradar.appspot.com/8821081
+  callback_.Run(true);
+}
+
+}  // namespace net
+

[Mark Mentovai, 2012/04/17 16:27:43]

No blank line at EOF.

[szym, 2012/04/17 19:39:31]

As before. Lint complained about that.