Allow gpu ringbuffer to wrap around.

The ringbuffer was unwilling to wrap around unless the last block filled it up completely - otherwise it would have to wait until it was completely empty. Fix this in the most straightforward way by filling the ringbuffer up with a padding block if necessary.

BUG=80946
TEST=

Review URL: http://codereview.chromium.org/6901138

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@83924 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 27 insertions, 13 deletions

diff --git a/gpu/command_buffer/client/ring_buffer.cc b/gpu/command_buffer/client/ring_buffer.cc
index 835f430..762f834 100644
--- a/gpu/command_buffer/client/ring_buffer.cc
+++ b/gpu/command_buffer/client/ring_buffer.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -29,8 +29,11 @@ RingBuffer::~RingBuffer() {
 void RingBuffer::FreeOldestBlock() {
   GPU_DCHECK(!blocks_.empty()) << "no free blocks";
   Block& block = blocks_.front();
-  GPU_DCHECK(block.valid) << "attempt to allocate more than maximum memory";
-  helper_->WaitForToken(block.token);
+  GPU_DCHECK(block.state != IN_USE)
+      << "attempt to allocate more than maximum memory";
+  if (block.state == FREE_PENDING_TOKEN) {
+    helper_->WaitForToken(block.token);
+  }
   in_use_offset_ += block.size;
   if (in_use_offset_ == size_) {
     in_use_offset_ = 0;
@@ -45,7 +48,7 @@ void RingBuffer::FreeOldestBlock() {
 
 RingBuffer::Offset RingBuffer::Alloc(unsigned int size) {
   GPU_DCHECK_LE(size, size_) << "attempt to allocate more than maximum memory";
-  GPU_DCHECK(blocks_.empty() || blocks_.back().valid)
+  GPU_DCHECK(blocks_.empty() || blocks_.back().state != IN_USE)
       << "Attempt to alloc another block before freeing the previous.";
   // Similarly to malloc, an allocation of 0 allocates at least 1 byte, to
   // return different pointers every time.
@@ -56,8 +59,14 @@ RingBuffer::Offset RingBuffer::Alloc(unsigned int size) {
     FreeOldestBlock();
   }
 
+  if (size + free_offset_ > size_) {
+    // Add padding to fill space before wrapping around
+    blocks_.push_back(Block(free_offset_, size_ - free_offset_, PADDING));
+    free_offset_ = 0;
+  }
+
   Offset offset = free_offset_;
-  blocks_.push_back(Block(offset, size));
+  blocks_.push_back(Block(offset, size, IN_USE));
   free_offset_ += size;
   if (free_offset_ == size_) {
     free_offset_ = 0;
@@ -74,10 +83,10 @@ void RingBuffer::FreePendingToken(RingBuffer::Offset offset,
         ++it) {
     Block& block = *it;
     if (block.offset == offset) {
-      GPU_DCHECK(!block.valid)
+      GPU_DCHECK(block.state == IN_USE)
           << "block that corresponds to offset already freed";
       block.token = token;
-      block.valid = true;
+      block.state = FREE_PENDING_TOKEN;
       return;
     }
   }
@@ -97,8 +106,8 @@ unsigned int RingBuffer::GetLargestFreeSizeNoWaiting() {
       return 0;
     }
   } else if (free_offset_ > in_use_offset_) {
-    // It's free from free_offset_ to size_
-    return size_ - free_offset_;
+    // It's free from free_offset_ to size_ and from 0 to in_use_offset_
+    return std::max(size_ - free_offset_, in_use_offset_);
   } else {
     // It's free from free_offset_ -> in_use_offset_;
     return in_use_offset_ - free_offset_;
diff --git a/gpu/command_buffer/client/ring_buffer.h b/gpu/command_buffer/client/ring_buffer.h
index b7194bb..b40c446 100644
--- a/gpu/command_buffer/client/ring_buffer.h
+++ b/gpu/command_buffer/client/ring_buffer.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -61,18 +61,23 @@ class RingBuffer {
   }
 
  private:
+  enum State {
+    IN_USE,
+    PADDING,
+    FREE_PENDING_TOKEN
+  };
   // Book-keeping sturcture that describes a block of memory.
   struct Block {
-    Block(Offset _offset, unsigned int _size)
+    Block(Offset _offset, unsigned int _size, State _state)
         : offset(_offset),
           size(_size),
           token(0),
-          valid(false) {
+          state(_state) {
     }
     Offset offset;
     unsigned int size;
     unsigned int token;  // token to wait for.
-    bool valid;  // whether or not token has been set.
+    State state;
   };
 
   typedef std::deque<Block> Container;