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

content/common/child_process_host_impl.cc

Index: content/common/child_process_host_impl.cc
diff --git a/content/common/child_process_host_impl.cc b/content/common/child_process_host_impl.cc
index 2341db13083705eb14995038787566d4bf9e5c02..b3f3764a6f54d6f33c92dfd3bf22b65f61cecf16 100644
--- a/content/common/child_process_host_impl.cc
+++ b/content/common/child_process_host_impl.cc
@@ -18,6 +18,7 @@
 #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"
@@ -35,12 +36,28 @@
 #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;
@@ -83,15 +100,6 @@ base::FilePath ChildProcessHost::GetChildPath(int flags) {
   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) {
@@ -102,7 +110,7 @@ ChildProcessHostImpl::ChildProcessHostImpl(ChildProcessHostDelegate* delegate)
 
 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();
@@ -123,12 +131,11 @@ void ChildProcessHostImpl::ForceShutdown() {
 
 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)