gpu: Reuse transfer buffers more aggresively

gpu/command_buffer/client/cmd_buffer_helper.h

Index: gpu/command_buffer/client/cmd_buffer_helper.h
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.h b/gpu/command_buffer/client/cmd_buffer_helper.h
index a50dc7bfe4e4e73e4bc4ce392bc1cb85e32182be..9cfb6e69d1673f4e721065142af3c6bdc84cecc2 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.h
+++ b/gpu/command_buffer/client/cmd_buffer_helper.h
@@ -83,6 +83,15 @@ class GPU_EXPORT CommandBufferHelper {
   //   shutdown.
   int32 InsertToken();
 
+  // Returns true if the token has passed.
+  // Parameters:
+  //   the value of the token to check whether it has passed
+  bool HasTokenPassed(int32 token) const {
+    if (token > token_)
+      return true;  // we wrapped
+    return last_token_read() >= token;
+  }
+
   // Waits until the token of a particular value has passed through the command
   // stream (i.e. commands inserted before that token have been executed).
   // NOTE: This will call Flush if it needs to block.
@@ -90,6 +99,32 @@ class GPU_EXPORT CommandBufferHelper {
   //   the value of the token to wait for.
   void WaitForToken(int32 token);
 
+  // Inserts a new async token to the command buffer. One can then check if the
+  // token has passed using HasAsyncTokenPassed(). It is guaranteed that the
+  // order of returned async tokens is the same as inserted, but it is
+  // implementation specific when a token is returned.
+  //
+  // NOTE: A async token is asynchronous in a way that Finish():ing the command
+  // buffer does mean it has passed.

[epenner, 2014/01/23 02:52:44]

Nit: 'doesn't'

+  uint32 InsertAsyncToken();
+
+  // Returns true if the async token has passed.
+  //
+  // NOTE: This will detect wrapped async tokens by checking if the most
+  // significant  bit of async token to check is 1 but the last read is 0, i.e.
+  // the uint32 wrapped.
+  //
+  // Parameters:
+  //   the value of the async token to check whether it has passed
+  bool HasAsyncTokenPassed(uint32 token) const {
+    uint32 last_async_token = last_async_token_read();
+    if (token <= last_async_token)
+      return true;
+    if (token & 0x80000000 && !(last_async_token & 0x80000000))
+      return true; // we wrapped
+    return false;
+  }
+
   // Called prior to each command being issued. Waits for a certain amount of
   // space to be available. Returns address of space.
   CommandBufferEntry* GetSpace(uint32 entries);
@@ -244,6 +279,11 @@ class GPU_EXPORT CommandBufferHelper {
   bool AllocateRingBuffer();
   void FreeResources();
 
+  // Get the async token number last read by the command buffer.
+  uint32 last_async_token_read() const {
+    return command_buffer_->GetLastState().async_token;
+  }
+
   CommandBuffer* command_buffer_;
   int32 ring_buffer_id_;
   int32 ring_buffer_size_;
@@ -251,6 +291,7 @@ class GPU_EXPORT CommandBufferHelper {
   CommandBufferEntry* entries_;
   int32 total_entry_count_;  // the total number of entries
   int32 token_;
+  uint32 async_token_;
   int32 put_;
   int32 last_put_sent_;
   int commands_issued_;