content/gpu: Simplify gpu channel message handling.

content/common/gpu/gpu_channel_manager.cc

Index: content/common/gpu/gpu_channel_manager.cc
diff --git a/content/common/gpu/gpu_channel_manager.cc b/content/common/gpu/gpu_channel_manager.cc
index 0359393f1ae0f1075585f4c21ffdf04b4248641a..42df9046f6ebf6dd8720f3721a6c9e060268bfc8 100644
--- a/content/common/gpu/gpu_channel_manager.cc
+++ b/content/common/gpu/gpu_channel_manager.cc
@@ -107,7 +107,7 @@ void GpuChannelManager::RemoveRoute(int32 routing_id) {
   router_.RemoveRoute(routing_id);
 }
 
-GpuChannel* GpuChannelManager::LookupChannel(int32 client_id) {
+GpuChannel* GpuChannelManager::LookupChannel(int32 client_id) const {
   const auto& it = gpu_channels_.find(client_id);
   return it != gpu_channels_.end() ? it->second : nullptr;
 }
@@ -251,7 +251,17 @@ void GpuChannelManager::OnLoadedShader(std::string program_proto) {
     program_cache()->LoadProgram(program_proto);
 }
 
-uint32_t GpuChannelManager::ProcessedOrderNumber() {
+uint32_t GpuChannelManager::GetNextUnprocessedOrderNum() {
+  base::AutoLock lock(order_num_lock_);

[David Yen, 2015/09/10 22:42:06]

Is the new scheduler also going to use this? Seems like we exchanged a lock on
all the channels during pre-emption, for a lock on every IPC message, which is
better is hard to tell. 

Should we just use an Atomic32?

[sunnyps, 2015/09/10 23:38:36]

On second thought I'm keeping this as is for now - it's likely that the schedule
will be in charge of idle work anyway.

[David Yen, 2015/09/11 16:47:20]

per your comment yesterday, I think you are right. We can detect idle by simply
using the the highest current order number. We can even have a global one stored
in the GpuChannelManager which is updated as they are being handled and we
wouldn't even need to loop through the gpu channels.

+  return ++unprocessed_order_num_;
+}
+
+uint32_t GpuChannelManager::GetCurrentUnprocessedOrderNum() const {
+  base::AutoLock lock(order_num_lock_);
+  return unprocessed_order_num_;
+}
+
+uint32_t GpuChannelManager::GetProcessedOrderNum() const {
   uint32_t processed_order_num = 0;
   for (auto& kv : gpu_channels_) {
     processed_order_num =
@@ -260,15 +270,6 @@ uint32_t GpuChannelManager::ProcessedOrderNumber() {
   return processed_order_num;
 }
 
-uint32_t GpuChannelManager::UnprocessedOrderNumber() {
-  uint32_t unprocessed_order_num = 0;
-  for (auto& kv : gpu_channels_) {
-    unprocessed_order_num =
-        std::max(unprocessed_order_num, kv.second->GetUnprocessedOrderNum());
-  }
-  return unprocessed_order_num;
-}
-
 void GpuChannelManager::LoseAllContexts() {
   for (auto& kv : gpu_channels_) {
     kv.second->MarkAllContextsLost();