Refactor CommandBufferHelper to use Jump to loop...

gpu/command_buffer/client/cmd_buffer_helper.h

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file contains the command buffer helper class.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 #define GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 
 #include <string.h>
@@ skipping 184 matching lines @@
              shared_memory_id,
              shared_memory_offset);
   }
 
  private:
   // Waits until get changes, updating the value of get_.
   void WaitForGetChange();
 
   // Returns the number of available entries (they may not be contiguous).
   int32 AvailableEntries() {
-    return (get_ - put_ - 1 + entry_count_) % entry_count_;
+    return (get_ - put_ - 1 + usable_entry_count_) % usable_entry_count_;
   }
 
   // Synchronize with current service state.
   void SynchronizeState(CommandBuffer::State state);
 
   CommandBuffer* command_buffer_;
   Buffer ring_buffer_;
   CommandBufferEntry *entries_;
-  int32 entry_count_;
+  int32 total_entry_count_;  // the total number of entries
+  int32 usable_entry_count_;  // the usable number (ie, minus space for jump)
   int32 token_;
   int32 last_token_read_;
   int32 get_;
   int32 put_;
 
   friend class CommandBufferHelperTest;
   DISALLOW_COPY_AND_ASSIGN(CommandBufferHelper);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_