ipc: Use a global for the process's attachment broker.

content/common/child_process_host_impl.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 "content/common/child_process_host_impl.h"
 
 #include <limits>
 
 #include "base/atomic_sequence_num.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/hash.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/numerics/safe_math.h"
 #include "base/path_service.h"
 #include "base/process/process_metrics.h"
 #include "base/rand_util.h"
 #include "base/strings/stringprintf.h"
+#include "base/synchronization/lock.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "content/common/child_process_messages.h"
 #include "content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.h"
 #include "content/public/common/child_process_host_delegate.h"
 #include "content/public/common/content_paths.h"
 #include "content/public/common/content_switches.h"
 #include "ipc/ipc_channel.h"
 #include "ipc/ipc_logging.h"
 #include "ipc/message_filter.h"
 
 #if defined(OS_LINUX)
 #include "base/linux_util.h"
 #elif defined(OS_WIN)
 #include "content/common/font_cache_dispatcher_win.h"
 #include "ipc/attachment_broker_privileged_win.h"
 #endif  // OS_LINUX
 
+namespace {
+
 #if defined(OS_WIN)
 base::LazyInstance<IPC::AttachmentBrokerPrivilegedWin>::Leaky
     g_attachment_broker = LAZY_INSTANCE_INITIALIZER;
+base::LazyInstance<base::Lock>::Leaky
+    g_attachment_broker_lock = LAZY_INSTANCE_INITIALIZER;
+static bool g_attachment_broker_initialized = false;
 #endif  // defined(OS_WIN)
 
-namespace {
+#if USE_ATTACHMENT_BROKER
+IPC::AttachmentBrokerPrivileged* GetAttachmentBroker() {
+  if (!g_attachment_broker_initialized) {
+    base::AutoLock l(g_attachment_broker_lock.Get());
+    if (!g_attachment_broker_initialized) {
+      IPC::AttachmentBroker::SetGlobal(&g_attachment_broker.Get());
+      g_attachment_broker_initialized = true;
+    }
+  }
+  return &g_attachment_broker.Get();

[Avi (use Gerrit), 2015/09/11 23:24:40]

What? This is literally a double-checked lock, and it's an antipattern.

https://en.wikipedia.org/wiki/Double-checked_locking

If you need a singleton (base::Singleton) then use one; don't build one
yourself.

[erikchen, 2015/09/12 01:06:31]

What I need is a cross-platform version of pthread_once, but I didn't see any in
the Chrome source code. I changed the code to perform the relevant logic in the
constructor of a base::LazyInstance. What do you think?

+}
+#endif  // USE_ATTACHMENT_BROKER
 
 // Global atomic to generate child process unique IDs.
 base::StaticAtomicSequenceNumber g_unique_id;
 
 }  // namespace
 
 namespace content {
 
 int ChildProcessHost::kInvalidUniqueID = -1;
 
@@ skipping 22 matching lines @@
     child_path = base::FilePath(base::kProcSelfExe);
 #endif
 
   // On most platforms, the child executable is the same as the current
   // executable.
   if (child_path.empty())
     PathService::Get(CHILD_PROCESS_EXE, &child_path);
   return child_path;
 }
 
-// static
-IPC::AttachmentBrokerPrivileged* ChildProcessHost::GetAttachmentBroker() {
-#if USE_ATTACHMENT_BROKER
-  return &g_attachment_broker.Get();
-#else
-  return nullptr;
-#endif  // USE_ATTACHMENT_BROKER
-}
-
 ChildProcessHostImpl::ChildProcessHostImpl(ChildProcessHostDelegate* delegate)
     : delegate_(delegate),
       opening_channel_(false) {
 #if defined(OS_WIN)
   AddFilter(new FontCacheDispatcher());
 #endif
 }
 
 ChildProcessHostImpl::~ChildProcessHostImpl() {
 #if USE_ATTACHMENT_BROKER
-  g_attachment_broker.Get().DeregisterCommunicationChannel(channel_.get());
+  GetAttachmentBroker()->DeregisterCommunicationChannel(channel_.get());
 #endif
   for (size_t i = 0; i < filters_.size(); ++i) {
     filters_[i]->OnChannelClosing();
     filters_[i]->OnFilterRemoved();
   }
 }
 
 void ChildProcessHostImpl::AddFilter(IPC::MessageFilter* filter) {
   filters_.push_back(filter);
 
   if (channel_)
     filter->OnFilterAdded(channel_.get());
 }
 
 void ChildProcessHostImpl::ForceShutdown() {
   Send(new ChildProcessMsg_Shutdown());
 }
 
 std::string ChildProcessHostImpl::CreateChannel() {
   channel_id_ = IPC::Channel::GenerateVerifiedChannelID(std::string());
-  channel_ =
-      IPC::Channel::CreateServer(channel_id_, this, GetAttachmentBroker());
+  channel_ = IPC::Channel::CreateServer(channel_id_, this);
   if (!channel_->Connect())
     return std::string();
 #if USE_ATTACHMENT_BROKER
-  g_attachment_broker.Get().RegisterCommunicationChannel(channel_.get());
+  GetAttachmentBroker()->RegisterCommunicationChannel(channel_.get());
 #endif
 
   for (size_t i = 0; i < filters_.size(); ++i)
     filters_[i]->OnFilterAdded(channel_.get());
 
   // Make sure these messages get sent first.
 #if defined(IPC_MESSAGE_LOG_ENABLED)
   bool enabled = IPC::Logging::GetInstance()->Enabled();
   Send(new ChildProcessMsg_SetIPCLoggingEnabled(enabled));
 #endif
@@ skipping 170 matching lines @@
 }
 
 void ChildProcessHostImpl::OnDeletedGpuMemoryBuffer(
     gfx::GpuMemoryBufferId id,
     uint32 sync_point) {
   // Note: Nothing to do here as ownership of shared memory backed
   // GpuMemoryBuffers is passed with IPC.
 }
 
 }  // namespace content