Update Java Bridge to use its own thread in the browser process

content/browser/renderer_host/java/java_bridge_dispatcher_host.cc

Index: content/browser/renderer_host/java/java_bridge_dispatcher_host.cc
diff --git a/content/browser/renderer_host/java/java_bridge_dispatcher_host.cc b/content/browser/renderer_host/java/java_bridge_dispatcher_host.cc
index 51335e092418918cef8988adc1ab8b4b3d4d4642..d07dd3b9ca1cd9334f81ced0dd72eb7b964b57ee 100644
--- a/content/browser/renderer_host/java/java_bridge_dispatcher_host.cc
+++ b/content/browser/renderer_host/java/java_bridge_dispatcher_host.cc
@@ -5,7 +5,8 @@
 #include "content/browser/renderer_host/java/java_bridge_dispatcher_host.h"
 
 #include "base/bind.h"
-#include "content/browser/renderer_host/browser_render_process_host.h"
+#include "base/lazy_instance.h"
+#include "base/threading/thread.h"
 #include "content/browser/renderer_host/java/java_bridge_channel_host.h"
 #include "content/browser/renderer_host/render_view_host.h"
 #include "content/common/child_process.h"
@@ -17,6 +18,19 @@
 
 using content::BrowserThread;
 
+namespace {
+struct ThreadLazyInstanceTraits
+    : public base::DefaultLazyInstanceTraits<base::Thread> {
+  static base::Thread* New(void* instance) {
+    base::Thread* thread = new (instance) base::Thread("Java Bridge");

[joth, 2011/12/09 16:26:09]

nit: "JavaBridge"
some tools may not be so smart with whitespace; anyway we generally seem to
avoid it in thread names

[Steve Block, 2011/12/09 17:36:27]

Done.

+    thread->Start();
+    return thread;
+  }
+};

[joth, 2011/12/09 16:26:09]

my own preference would be to make your own Thread subclass that calls Start
from the c'tor.
This way it's easy to add Init() & CleanUp() overrides if needed in future.

[Steve Block, 2011/12/09 17:36:27]

Done.

+base::LazyInstance<base::Thread, ThreadLazyInstanceTraits> g_background_thread =
+    LAZY_INSTANCE_INITIALIZER;

[joth, 2011/12/09 16:26:09]

I wasn't clear in my previous comment, but lazy instance might not be ideal for
this as it is only destroyed when the AtExitManager runs, which is in general a
bit hairy as the thread may still be running using other things that are
destroyed before it in the AtExitManager queue (e.g. MessageLoop::current()
depends on AtExitManager not having run yet but may get cleaned up before this
thread is stopped.)

afaict this "shouldn't" be the case here as by the time we exit we should have
disconnected the renderers and so have no pending sync calls into the bridge,
right?

(conceptually, what happens if the java-side is in an inf. loop when the
renderer is shutdown? somewhere along the line either some one will block on a
thread join that never returns or we need to send an interrupt into the VM for
that thread. either way that's certainly not something to fully handle in this
CL.. just trying to get a model on the relationship between the parts)



another thing occurs to me I have no idea the answer to: this will mean multiple
pages accessing the bridge will end up serialized on this one thread - is that
OK? I guess the alternative - one thread per dispatcher host - requires the
java-side to be fully thread safe. That may well not be the case, in general, I
guess.

[Steve Block, 2011/12/09 17:36:27]

re AtExitManager - yes, the JavaBridge should be gracefully shutdown when the
renderer is disconnected, so this won't be a problem.

re serialization onto a single thread - note that this isn't changed by this CL
and must remain the case for backwards compatibility.

+}  // namespace
+
 JavaBridgeDispatcherHost::JavaBridgeDispatcherHost(
     RenderViewHost* render_view_host)
     : RenderViewHostObserver(render_view_host),
@@ -62,13 +76,7 @@ bool JavaBridgeDispatcherHost::OnMessageReceived(const IPC::Message& msg) {
 }
 
 void JavaBridgeDispatcherHost::OnGetChannelHandle(IPC::Message* reply_msg) {
-  if (RenderProcessHost::run_renderer_in_process()) {
-    // TODO(steveblock): Fix Java Bridge with in-process renderer. See
-    // http://code.google.com/p/chromium/issues/detail?id=106838
-    CHECK(false) << "Java Bridge does not support in-process renderer";
-  }
-  BrowserThread::PostTask(
-      BrowserThread::WEBKIT,
+  g_background_thread.Get().message_loop()->PostTask(
       FROM_HERE,
       base::Bind(&JavaBridgeDispatcherHost::GetChannelHandle, this, reply_msg));
 }
@@ -85,11 +93,11 @@ void JavaBridgeDispatcherHost::GetChannelHandle(IPC::Message* reply_msg) {
 
 void JavaBridgeDispatcherHost::CreateNPVariantParam(NPObject* object,
                                                     NPVariant_Param* param) {
-  // The JavaBridgeChannelHost needs to be created on the WEBKIT thread, as
+  // The JavaBridgeChannelHost needs to be created on the background thread, as
   // that is where Java objects will live, and CreateNPVariantParam() needs the
   // channel to create the NPObjectStub. To avoid blocking here until the
   // channel is ready, create the NPVariant_Param by hand, then post a message
-  // to the WEBKIT thread to set up the channel and create the corresponding
+  // to the background thread to set up the channel and create the corresponding
   // NPObjectStub. Post that message before doing any IPC, to make sure that
   // the channel and object proxies are ready before responses are received
   // from the renderer.
@@ -101,8 +109,7 @@ void JavaBridgeDispatcherHost::CreateNPVariantParam(NPObject* object,
   param->npobject_routing_id = route_id;
 
   WebKit::WebBindings::retainObject(object);
-  BrowserThread::PostTask(
-      BrowserThread::WEBKIT,
+  g_background_thread.Get().message_loop()->PostTask(
       FROM_HERE,
       base::Bind(&JavaBridgeDispatcherHost::CreateObjectStub, this, object,
                  route_id));
@@ -110,8 +117,7 @@ void JavaBridgeDispatcherHost::CreateNPVariantParam(NPObject* object,
 
 void JavaBridgeDispatcherHost::CreateObjectStub(NPObject* object,
                                                 int route_id) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::WEBKIT));
-
+  DCHECK_EQ(g_background_thread.Get().message_loop(), MessageLoop::current());
   if (!channel_) {
     channel_ = JavaBridgeChannelHost::GetJavaBridgeChannelHost(
         render_view_host()->process()->id(),