ipc: Move AttachmentBrokerPrivileged singleton logic into ipc/.

ipc/attachment_broker_privileged.cc

 // Copyright 2015 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 "ipc/attachment_broker_privileged.h"
 
 #include <algorithm>
 
+#include "base/lazy_instance.h"
 #include "base/metrics/histogram_macros.h"
 #include "ipc/ipc_endpoint.h"
 
 #if defined(OS_WIN)
 #include "ipc/attachment_broker_privileged_win.h"
 #endif
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
 #include "ipc/attachment_broker_privileged_mac.h"
 #endif
 
 namespace IPC {
 
-AttachmentBrokerPrivileged::AttachmentBrokerPrivileged() {
-  IPC::AttachmentBroker::SetGlobal(this);
-}
+namespace {
 
-AttachmentBrokerPrivileged::~AttachmentBrokerPrivileged() {
-  IPC::AttachmentBroker::SetGlobal(nullptr);
-}
-
-// static
-scoped_ptr<AttachmentBrokerPrivileged>
-AttachmentBrokerPrivileged::CreateBroker() {
+// On platforms that support attachment brokering, returns a new instance of
+// a platform-specific attachment broker. Otherwise returns |nullptr|.
+// The caller takes ownership of the newly created instance, and is
+// responsible for ensuring that the attachment broker lives longer than
+// every IPC::Channel. The new instance automatically registers itself as the
+// global attachment broker.
+scoped_ptr<AttachmentBrokerPrivileged> CreateBroker() {
 #if defined(OS_WIN)
   return scoped_ptr<AttachmentBrokerPrivileged>(
       new IPC::AttachmentBrokerPrivilegedWin);
 #elif defined(OS_MACOSX) && !defined(OS_IOS)
   return scoped_ptr<AttachmentBrokerPrivileged>(
       new IPC::AttachmentBrokerPrivilegedMac);
 #else
   return nullptr;
 #endif
 }
 
+// This class is wrapped in a singleton to ensure that its constructor is only
+// called once. The constructor creates an attachment broker and
+// sets it as the global broker.

[Tom Sepez, 2015/10/21 20:07:38]

Can't lazy instance take care of this for us?

[erikchen, 2015/10/21 21:54:41]

I do use a LazyInstance - I updated the comment to use the word LazyInstance
instead of singleton.

+class AttachmentBrokerMakeOnce {
+ public:
+  AttachmentBrokerMakeOnce() {
+    attachment_broker_.reset(CreateBroker().release());
+  }
+
+ private:
+  scoped_ptr<IPC::AttachmentBrokerPrivileged> attachment_broker_;
+};
+
+base::LazyInstance<AttachmentBrokerMakeOnce>::Leaky
+    g_attachment_broker_make_once = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+AttachmentBrokerPrivileged::AttachmentBrokerPrivileged() {
+  IPC::AttachmentBroker::SetGlobal(this);
+}
+
+AttachmentBrokerPrivileged::~AttachmentBrokerPrivileged() {
+  IPC::AttachmentBroker::SetGlobal(nullptr);
+}
+
+// static
+void AttachmentBrokerPrivileged::CreateBrokerIfNeeded() {
+  g_attachment_broker_make_once.Get();
+}
+
 void AttachmentBrokerPrivileged::RegisterCommunicationChannel(
     Endpoint* endpoint) {
   endpoint->SetAttachmentBrokerEndpoint(true);
   auto it = std::find(endpoints_.begin(), endpoints_.end(), endpoint);
   DCHECK(endpoints_.end() == it);
   endpoints_.push_back(endpoint);
 }
 
 void AttachmentBrokerPrivileged::DeregisterCommunicationChannel(
     Endpoint* endpoint) {
   auto it = std::find(endpoints_.begin(), endpoints_.end(), endpoint);
   if (it != endpoints_.end())
     endpoints_.erase(it);
 }
 
 Sender* AttachmentBrokerPrivileged::GetSenderWithProcessId(base::ProcessId id) {
   auto it = std::find_if(endpoints_.begin(), endpoints_.end(),
                          [id](Endpoint* c) { return c->GetPeerPID() == id; });
   if (it == endpoints_.end())
     return nullptr;
   return *it;
 }
 
 void AttachmentBrokerPrivileged::LogError(UMAError error) {
   UMA_HISTOGRAM_ENUMERATION(
       "IPC.AttachmentBrokerPrivileged.BrokerAttachmentError", error, ERROR_MAX);
 }
 
 }  // namespace IPC