Add multi-process notification class.

chrome/common/multi_process_notification_mac.mm

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.

[Mark Mentovai, 2011/01/04 18:19:33]

What will you use this for?

How is it supposed to operate with multiple running Chromes? Consider two
Chromes running out of different profiles in the same user account, or two
Chromes running in different user accounts under fast user switching.

Keep in mind that I’m not going to use your answers to block you from checking
in an incomplete design, I just want to get an idea of how this will be used,
what the constraints are, how it currently deals with those constraints, and how
it might ultimately be able to deal.

[dmac, 2011/01/06 06:06:03]

Sending notifications to the service process.
I have changed the API so the caller and listener can handle those cases.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/common/multi_process_notification.h"
+
+#include <notify.h>

[Mark Mentovai, 2011/01/04 18:19:33]

<notify.h> and <Foundation/Foundation.h> can be in the same group, no need for a
blank line separating them. Once they’re in the same group, F sorts before n.

[dmac, 2011/01/06 06:06:03]

Done.

+
+#import <Foundation/Foundation.h>
+
+#include "base/mac/mac_util.h"
+#include "base/mac/scoped_nsautorelease_pool.h"
+#include "base/message_loop.h"
+#include "base/message_pump_libevent.h"
+#include "base/sys_string_conversions.h"
+#include "base/task.h"
+
+namespace {
+
+std::string PrependBundleID(const std::string& name) {
+  base::mac::ScopedNSAutoreleasePool pool;
+  NSBundle *bundle = base::mac::MainAppBundle();
+  NSString *ns_bundle_id = [bundle bundleIdentifier];
+  std::string bundle_id = base::SysNSStringToUTF8(ns_bundle_id);
+  return bundle_id + "." + name;
+}
+
+}  // namespace
+
+namespace multi_process_notification {
+
+bool Post(const std::string& name) {
+  std::string notification = PrependBundleID(name);
+  uint32_t status = notify_post(notification.c_str());
+  DCHECK_EQ(status, static_cast<uint32_t>(NOTIFY_STATUS_OK));
+  return status == NOTIFY_STATUS_OK;
+}
+
+class ListenerImpl : public base::MessagePumpLibevent::Watcher {
+ public:
+  ListenerImpl(const std::string& name,
+               Listener::Delegate* delegate);
+  virtual ~ListenerImpl();
+
+  virtual bool Start();
+
+  virtual void OnFileCanReadWithoutBlocking(int fd);
+  virtual void OnFileCanWriteWithoutBlocking(int fd);
+
+ private:
+  std::string name_;
+  base::MessagePumpLibevent::FileDescriptorWatcher watcher_;
+  Listener::Delegate* delegate_;
+  int fd_;
+  int token_;
+};
+
+ListenerImpl::ListenerImpl(const std::string& name,
+                           Listener::Delegate* delegate)
+    : name_(name), delegate_(delegate), fd_(-1), token_(-1) {
+}
+
+ListenerImpl::~ListenerImpl() {
+  if (token_ != -1) {
+    uint32_t status = notify_cancel(token_);
+    DCHECK_EQ(status, static_cast<uint32_t>(NOTIFY_STATUS_OK));
+    token_ = -1;
+  }
+}
+
+bool ListenerImpl::Start() {
+  DCHECK_EQ(fd_, -1);
+  DCHECK_EQ(token_, -1);
+  std::string notification = PrependBundleID(name_);
+
+  uint32_t status = notify_register_file_descriptor(notification.c_str(), &fd_,
+                                                    0, &token_);
+  if (status != NOTIFY_STATUS_OK) {
+    return false;
+  }
+
+  MessageLoopForIO *io_loop = MessageLoopForIO::current();
+  return io_loop->WatchFileDescriptor(fd_, true, MessageLoopForIO::WATCH_READ,

[Mark Mentovai, 2011/01/04 18:19:33]

Do you ever need to undo this? watcher_ will disappear when ListenerImpl is
destroyed, but I don’t know whether something else makes io_loop aware of that
or if you need to do it yourself.

[dmac, 2011/01/06 06:06:03]

when watcher_ is destroyed it handles taking care of unregistering itself.

+                                      &watcher_, this);
+}
+
+void ListenerImpl::OnFileCanReadWithoutBlocking(int fd) {
+  DCHECK_EQ(fd, fd_);
+  int token = 0;
+  if (read(fd_, &token, sizeof(token)) >= 0) {

[Mark Mentovai, 2011/01/04 18:19:33]

HANDLE_EINTR from base/eintr_wrapper.h.

[dmac, 2011/01/06 06:06:03]

Done.

+    // Have to swap to native endianness <rdar://problem/5352778>.

[Mark Mentovai, 2011/01/04 18:19:33]

Link to the problem: good.

Link to the problem that I can’t see: bad.

Open Radar and Google Search aren’t fruitful. I’d appreciate a better
description of the problem. Is this something that will be fixed in some future
OS release? If it is, will ntohl stop being the right thing to do? If so, is
there some sort of test we can write so that we’ll be notified pretty quickly if
this workaround (if that’s what it is) becomes obsolete?

[dmac, 2011/01/06 06:06:03]

I copied the rdar link from some Apple source code. I have filed a separate bug
and referenced it, and copied it into openradar.

+    token = static_cast<int>(ntohl(token));
+    if (token == token_) {
+      delegate_->OnNotificationReceived(name_);
+    } else {
+      LOG(WARNING) << "Unexpected value " << token;
+    }
+  }
+}
+
+void ListenerImpl::OnFileCanWriteWithoutBlocking(int fd) {
+  NOTREACHED();
+}
+
+Listener::Listener(const std::string& name, Listener::Delegate* delegate) :
+  impl_(new ListenerImpl(name, delegate)) {
+}
+
+Listener::~Listener() { }

[Mark Mentovai, 2011/01/04 18:19:33]

{} on separate lines, along with whatever other questions and comments I made in
the Linux file that apply to this one too.

[dmac, 2011/01/06 06:06:03]

Done.

+
+bool Listener::Start() {
+  return impl_->Start();
+}
+
+}  // namespace multi_process_notification