Refactor CommandBufferHelper to use Jump to loop...

gpu/command_buffer/client/cmd_buffer_helper.cc

 // 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 implementation of the command buffer helper class.
 
 #include "../client/cmd_buffer_helper.h"
 #include "../common/command_buffer.h"
 
 namespace gpu {
 
 CommandBufferHelper::CommandBufferHelper(CommandBuffer* command_buffer)
     : command_buffer_(command_buffer),
       entries_(NULL),
-      entry_count_(0),
+      total_entry_count_(0),
+      usable_entry_count_(0),
       token_(0),
       last_token_read_(-1),
       get_(0),
       put_(0) {
 }
 
 bool CommandBufferHelper::Initialize(int32 ring_buffer_size) {
   ring_buffer_ = command_buffer_->GetRingBuffer();
   if (!ring_buffer_.ptr)
     return false;
 
   CommandBuffer::State state = command_buffer_->GetState();
   entries_ = static_cast<CommandBufferEntry*>(ring_buffer_.ptr);
   int32 num_ring_buffer_entries = ring_buffer_size / sizeof(CommandBufferEntry);
   if (num_ring_buffer_entries > state.num_entries) {
     return false;
   }
-  entry_count_ = num_ring_buffer_entries;
+
+  const int32 kJumpEntries =
+      sizeof(cmd::Jump) / sizeof(*entries_);  // NOLINT
+
+  total_entry_count_ = num_ring_buffer_entries;
+  usable_entry_count_ = total_entry_count_ - kJumpEntries;
   put_ = state.put_offset;
   SynchronizeState(state);
   return true;
 }
 
 CommandBufferHelper::~CommandBufferHelper() {
 }
 
 bool CommandBufferHelper::Flush() {
   CommandBuffer::State state = command_buffer_->Flush(put_);
@@ skipping 48 matching lines @@
     }
     // Do not loop forever if the flush fails, meaning the command buffer reader
     // has shutdown.
     if (!Flush())
       return;
   }
 }
 
 // Waits for available entries, basically waiting until get >= put + count + 1.
 // It actually waits for contiguous entries, so it may need to wrap the buffer
-// around, adding noops. Thus this function may change the value of put_.
-// The function will return early if an error occurs, in which case the
-// available space may not be available.
+// around, adding a jump. Thus this function may change the value of put_. The
+// function will return early if an error occurs, in which case the available
+// space may not be available.
 void CommandBufferHelper::WaitForAvailableEntries(int32 count) {
-  CHECK(count < entry_count_);
-  if (put_ + count > entry_count_) {
+  CHECK(count < usable_entry_count_);
+  if (put_ + count > usable_entry_count_) {
     // There's not enough room between the current put and the end of the
-    // buffer, so we need to wrap. We will add noops all the way to the end,
-    // 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).
+    // buffer, so we need to wrap. We will add a jump back to the start, 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 jump).
     DCHECK_LE(1, put_);
     Flush();
     while (get_ > put_ || get_ == 0) {
       // Do not loop forever if the flush fails, meaning the command buffer
       // reader has shutdown.
       if (!Flush())
         return;
     }
-    // Insert Noops to fill out buffer.
-    int32 num_entries = entry_count_ - put_;
-    while (num_entries > 0) {
-      int32 num_to_skip = std::min(CommandHeader::kMaxSize, num_entries);
-      cmd::Noop::Set(&entries_[put_], num_to_skip);
-      put_ += num_to_skip;
-      num_entries -= num_to_skip;
-    }
+    // Insert a jump back to the beginning.
+    cmd::Jump::Set(&entries_[put_], 0);
     put_ = 0;
   }
   // If we have enough room, return immediatly.
   if (count <= AvailableEntries()) return;
   // Otherwise flush, and wait until we do have enough room.
   Flush();
   while (AvailableEntries() < count) {
     // Do not loop forever if the flush fails, meaning the command buffer reader
     // has shutdown.
     if (!Flush())
       return;
   }
 }
 
 CommandBufferEntry* CommandBufferHelper::GetSpace(uint32 entries) {
   WaitForAvailableEntries(entries);
   CommandBufferEntry* space = &entries_[put_];
   put_ += entries;
-  DCHECK_LE(put_, entry_count_);
-  if (put_ == entry_count_) {
+  DCHECK_LE(put_, usable_entry_count_);
+  if (put_ == usable_entry_count_) {
+    cmd::Jump::Set(&entries_[put_], 0);
     put_ = 0;
   }
   return space;
 }
 
 error::Error CommandBufferHelper::GetError() {
   CommandBuffer::State state = command_buffer_->GetState();
   SynchronizeState(state);
   return static_cast<error::Error>(state.error);
 }
 
 void CommandBufferHelper::SynchronizeState(CommandBuffer::State state) {
   get_ = state.get_offset;
   last_token_read_ = state.token;
 }
 
 }  // namespace gpu