gpu: Thread-safe command buffer state lookup.

gpu/command_buffer/client/cmd_buffer_helper.cc

Index: gpu/command_buffer/client/cmd_buffer_helper.cc
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.cc b/gpu/command_buffer/client/cmd_buffer_helper.cc
index 0304b8f7e5d1ae6d4322bdd889729477746a822c..9a424ffa7576740a4d316edeb9c655f38180b865 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper.cc
@@ -32,6 +32,7 @@ CommandBufferHelper::CommandBufferHelper(CommandBuffer* command_buffer)
       immediate_entry_count_(0),
       token_(0),
       put_(0),
+      last_get_(0),
       last_put_sent_(0),
 #if defined(CMD_HELPER_PERIODIC_FLUSH_CHECK)
       commands_issued_(0),
@@ -71,7 +72,7 @@ void CommandBufferHelper::CalcImmediateEntries(int waiting_count) {
   }
 
   // Get maximum safe contiguous entries.
-  const int32_t curr_get = get_offset();
+  const int32_t curr_get = last_get_;
   if (curr_get > put_) {
     immediate_entry_count_ = curr_get - put_ - 1;
   } else {
@@ -128,6 +129,7 @@ bool CommandBufferHelper::AllocateRingBuffer() {
   // Call to SetGetBuffer(id) above resets get and put offsets to 0.
   // No need to query it through IPC.
   put_ = 0;
+  last_get_ = 0;
   CalcImmediateEntries(0);
   return true;
 }
@@ -143,8 +145,8 @@ void CommandBufferHelper::FreeResources() {
 }
 
 void CommandBufferHelper::FreeRingBuffer() {
-  CHECK((put_ == get_offset()) ||
-      error::IsError(command_buffer_->GetLastState().error));
+  CHECK((put_ == last_get_) ||
+        error::IsError(command_buffer_->GetLastState().error));
   FreeResources();
 }
 
@@ -165,8 +167,10 @@ bool CommandBufferHelper::WaitForGetOffsetInRange(int32_t start, int32_t end) {
   if (!usable()) {
     return false;
   }
-  command_buffer_->WaitForGetOffsetInRange(start, end);
-  return command_buffer_->GetLastError() == gpu::error::kNoError;
+  CommandBuffer::State last_state =
+      command_buffer_->WaitForGetOffsetInRange(start, end);
+  last_get_ = last_state.get_offset;
+  return last_state.error == gpu::error::kNoError;
 }
 
 void CommandBufferHelper::Flush() {
@@ -213,7 +217,7 @@ bool CommandBufferHelper::Finish() {
     return false;
   }
   // If there is no work just exit.
-  if (put_ == get_offset()) {
+  if (put_ == last_get_) {
     return true;
   }
   DCHECK(HaveRingBuffer() ||
@@ -221,7 +225,7 @@ bool CommandBufferHelper::Finish() {
   Flush();
   if (!WaitForGetOffsetInRange(put_, put_))
     return false;
-  DCHECK_EQ(get_offset(), put_);
+  DCHECK_EQ(last_get_, put_);
 
   CalcImmediateEntries(0);
 
@@ -263,7 +267,8 @@ void CommandBufferHelper::WaitForToken(int32_t token) {
   // Return immediately if corresponding InsertToken failed.
   if (token < 0)
     return;
-  if (token > token_) return;  // we wrapped
+  if (token > token_)
+    return;  // we wrapped
   if (last_token_read() >= token)
     return;
   Flush();
@@ -288,13 +293,13 @@ void CommandBufferHelper::WaitForAvailableEntries(int32_t count) {
     // but we need to make sure get wraps first, actually that get is 1 or
     // more (since put will wrap to 0 after we add the noops).
     DCHECK_LE(1, put_);
-    int32_t curr_get = get_offset();
+    int32_t curr_get = last_get_;
     if (curr_get > put_ || curr_get == 0) {
       TRACE_EVENT0("gpu", "CommandBufferHelper::WaitForAvailableEntries");
       Flush();
       if (!WaitForGetOffsetInRange(1, put_))
         return;
-      curr_get = get_offset();
+      curr_get = last_get_;
       DCHECK_LE(curr_get, put_);
       DCHECK_NE(0, curr_get);
     }
@@ -328,7 +333,7 @@ void CommandBufferHelper::WaitForAvailableEntries(int32_t count) {
 }
 
 int32_t CommandBufferHelper::GetTotalFreeEntriesNoWaiting() const {
-  int32_t current_get_offset = get_offset();
+  int32_t current_get_offset = last_get_;
   if (current_get_offset > put_) {
     return current_get_offset - put_ - 1;
   } else {