Revert "Revert 113250 - Add CommandBuffer::SetGetBuffer"

This reverts commit bd45bd252aeb8babac62547a5c605fbf64287cd3.

TEST=ran webkit tests in DRT and webgl tests in chrome
BUG=103989

Review URL: http://codereview.chromium.org/8758026

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113479 0039d316-1c4b-4281-b951-d872f2087c98

23 files changed, 368 insertions, 269 deletions

diff --git a/gpu/command_buffer/client/cmd_buffer_helper.cc b/gpu/command_buffer/client/cmd_buffer_helper.cc
index 6328923..d43efc3 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper.cc
@@ -17,6 +17,8 @@ const double kFlushDelay = 1.0 / (5.0 * 60.0);
 
 CommandBufferHelper::CommandBufferHelper(CommandBuffer* command_buffer)
     : command_buffer_(command_buffer),
+      ring_buffer_id_(-1),
+      ring_buffer_size_(0),
       entries_(NULL),
       total_entry_count_(0),
       usable_entry_count_(0),
@@ -27,14 +29,25 @@ CommandBufferHelper::CommandBufferHelper(CommandBuffer* command_buffer)
       last_flush_time_(0) {
 }
 
-bool CommandBufferHelper::Initialize(int32 ring_buffer_size) {
-  ring_buffer_ = command_buffer_->GetRingBuffer();
+bool CommandBufferHelper::AllocateRingBuffer() {
+  int32 id = command_buffer_->CreateTransferBuffer(ring_buffer_size_, -1);
+  if (id < 0) {
+    return false;
+  }
+
+  ring_buffer_ = command_buffer_->GetTransferBuffer(id);
   if (!ring_buffer_.ptr)
     return false;
 
+  ring_buffer_id_ = id;
+  command_buffer_->SetGetBuffer(id);
+
+  // TODO(gman): Do we really need to call GetState here? We know get & put = 0
+  // Also do we need to check state.num_entries?
   CommandBuffer::State state = command_buffer_->GetState();
   entries_ = static_cast<CommandBufferEntry*>(ring_buffer_.ptr);
-  int32 num_ring_buffer_entries = ring_buffer_size / sizeof(CommandBufferEntry);
+  int32 num_ring_buffer_entries =
+      ring_buffer_size_ / sizeof(CommandBufferEntry);
   if (num_ring_buffer_entries > state.num_entries) {
     return false;
   }
@@ -48,6 +61,11 @@ bool CommandBufferHelper::Initialize(int32 ring_buffer_size) {
   return true;
 }
 
+bool CommandBufferHelper::Initialize(int32 ring_buffer_size) {
+  ring_buffer_size_ = ring_buffer_size;
+  return AllocateRingBuffer();
+}
+
 CommandBufferHelper::~CommandBufferHelper() {
 }
 
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.h b/gpu/command_buffer/client/cmd_buffer_helper.h
index b6f45e2..5fbf462 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.h
+++ b/gpu/command_buffer/client/cmd_buffer_helper.h
@@ -214,6 +214,10 @@ class CommandBufferHelper {
     return command_buffer_;
   }
 
+  Buffer get_ring_buffer() const {
+    return ring_buffer_;
+  }
+
  private:
   // Waits until get changes, updating the value of get_.
   void WaitForGetChange();
@@ -224,9 +228,13 @@ class CommandBufferHelper {
         usable_entry_count_;
   }
 
+  bool AllocateRingBuffer();
+
   CommandBuffer* command_buffer_;
+  int32 ring_buffer_id_;
+  int32 ring_buffer_size_;
   Buffer ring_buffer_;
-  CommandBufferEntry *entries_;
+  CommandBufferEntry* entries_;
   int32 total_entry_count_;  // the total number of entries
   int32 usable_entry_count_;  // the usable number (ie, minus space for jump)
   int32 token_;
diff --git a/gpu/command_buffer/client/cmd_buffer_helper_test.cc b/gpu/command_buffer/client/cmd_buffer_helper_test.cc
index 3b314c4..216bb60 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper_test.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper_test.cc
@@ -66,15 +66,9 @@ class CommandBufferHelperTest : public testing::Test {
         .WillRepeatedly(Return(error::kNoError));
 
     command_buffer_.reset(new CommandBufferService);
-    command_buffer_->Initialize(kCommandBufferSizeBytes);
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
+    command_buffer_->Initialize();
 
-    parser_ = new CommandParser(ring_buffer.ptr,
-                                ring_buffer.size,
-                                0,
-                                ring_buffer.size,
-                                0,
-                                api_mock_.get());
+    parser_ = new CommandParser(api_mock_.get());
 
     do_jump_command_.reset(new DoJumpCommand(parser_));
     EXPECT_CALL(*api_mock_, DoCommand(cmd::kJump, _, _))
@@ -90,6 +84,12 @@ class CommandBufferHelperTest : public testing::Test {
 
     helper_.reset(new CommandBufferHelper(command_buffer_.get()));
     helper_->Initialize(kCommandBufferSizeBytes);
+
+    // Note: parser->SetBuffer would normally be called through
+    // helper_->Initialize but currently it needs a GpuCommandBufferStub as the
+    // CommandBuffer instead of the CommandBufferService for that to happen.
+    Buffer ring_buffer = helper_->get_ring_buffer();
+    parser_->SetBuffer(ring_buffer.ptr, ring_buffer.size, 0, ring_buffer.size);
   }
 
   virtual void TearDown() {
diff --git a/gpu/command_buffer/client/fenced_allocator_test.cc b/gpu/command_buffer/client/fenced_allocator_test.cc
index 417b26a..ebd8ff6 100644
--- a/gpu/command_buffer/client/fenced_allocator_test.cc
+++ b/gpu/command_buffer/client/fenced_allocator_test.cc
@@ -45,15 +45,9 @@ class BaseFencedAllocatorTest : public testing::Test {
                               Return(error::kNoError)));
 
     command_buffer_.reset(new CommandBufferService);
-    command_buffer_->Initialize(kBufferSize);
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
+    command_buffer_->Initialize();
 
-    parser_ = new CommandParser(ring_buffer.ptr,
-                                ring_buffer.size,
-                                0,
-                                ring_buffer.size,
-                                0,
-                                api_mock_.get());
+    parser_ = new CommandParser(api_mock_.get());
 
     gpu_scheduler_.reset(new GpuScheduler(
         command_buffer_.get(), NULL, parser_));
@@ -64,6 +58,12 @@ class BaseFencedAllocatorTest : public testing::Test {
 
     helper_.reset(new CommandBufferHelper(command_buffer_.get()));
     helper_->Initialize(kBufferSize);
+
+    // Note: parser->SetBuffer would normally be called through
+    // helper_->Initialize but currently it needs a GpuCommandBufferStub as the
+    // CommandBuffer instead of the CommandBufferService for that to happen.
+    Buffer ring_buffer = helper_->get_ring_buffer();
+    parser_->SetBuffer(ring_buffer.ptr, ring_buffer.size, 0, ring_buffer.size);
   }
 
   int32 GetToken() {
diff --git a/gpu/command_buffer/client/gles2_implementation_unittest.cc b/gpu/command_buffer/client/gles2_implementation_unittest.cc
index 5ce2a8b..4c6013d 100644
--- a/gpu/command_buffer/client/gles2_implementation_unittest.cc
+++ b/gpu/command_buffer/client/gles2_implementation_unittest.cc
@@ -15,34 +15,30 @@
 #define GLES2_SUPPORT_CLIENT_SIDE_ARRAYS
 #endif
 
+using testing::_;
+using testing::DoAll;
+using testing::InSequence;
+using testing::Invoke;
+using testing::Mock;
+using testing::Sequence;
+using testing::Truly;
+using testing::Return;
+
 namespace gpu {
 
 class GLES2MockCommandBufferHelper : public CommandBuffer {
  public:
-  static const int32 kTransferBufferId = 0x123;
+  static const int32 kTransferBufferBaseId = 0x123;
+  static const int32 kMaxTransferBuffers = 6;
 
   GLES2MockCommandBufferHelper() { }
   virtual ~GLES2MockCommandBufferHelper() { }
 
   // CommandBuffer implementation:
-  virtual bool Initialize(int32 size) {
-    ring_buffer_.reset(new CommandBufferEntry[size]);
-    ring_buffer_buffer_.ptr = ring_buffer_.get();
-    ring_buffer_buffer_.size = size;
-    state_.num_entries = size / sizeof(ring_buffer_[0]);
-    state_.token = 10000;  // All token checks in the tests should pass.
+  virtual bool Initialize() {
     return true;
   }
 
-  virtual bool Initialize(base::SharedMemory* buffer, int32 size) {
-    GPU_NOTREACHED();
-    return false;
-  }
-
-  virtual Buffer GetRingBuffer() {
-    return ring_buffer_buffer_;
-  }
-
   virtual State GetState() {
     return state_;
   }
@@ -58,28 +54,57 @@ class GLES2MockCommandBufferHelper : public CommandBuffer {
   virtual State FlushSync(int32 put_offset, int32 last_known_get) {
     state_.put_offset = put_offset;
     state_.get_offset = put_offset;
-    OnFlush(transfer_buffer_buffer_.ptr);
+    // Warning: This is a hack. We just happen to know that the default
+    // transfer buffer will be the first transfer buffer.
+    OnFlush(transfer_buffer_buffers_[0].ptr);
     return state_;
   }
 
+  virtual void SetGetBuffer(int transfer_buffer_id) {
+    ring_buffer_buffer_ = GetTransferBuffer(transfer_buffer_id);
+    ring_buffer_ = static_cast<CommandBufferEntry*>(ring_buffer_buffer_.ptr);
+    state_.num_entries = ring_buffer_buffer_.size / sizeof(ring_buffer_[0]);
+    state_.token = 10000;  // All token checks in the tests should pass.
+  }
+
   virtual void SetGetOffset(int32 get_offset) {
     state_.get_offset = get_offset;
   }
 
+  // Get's the Id of the next transfer buffer that will be returned
+  // by CreateTransferBuffer. This is useful for testing expected ids.
+  int32 GetNextFreeTransferBufferId() {
+    for (size_t ii = 0; ii < arraysize(transfer_buffers_); ++ii) {
+      if (!transfer_buffers_[ii].get()) {
+        return kTransferBufferBaseId + ii;
+      }
+    }
+    return -1;
+  }
+
   virtual int32 CreateTransferBuffer(size_t size, int32 id_request) {
-    transfer_buffer_.reset(new int8[size]);
-    transfer_buffer_buffer_.ptr = transfer_buffer_.get();
-    transfer_buffer_buffer_.size = size;
-    return kTransferBufferId;
+    int32 id = GetNextFreeTransferBufferId();
+    if (id >= 0) {
+      int32 ndx = id - kTransferBufferBaseId;
+      transfer_buffers_[ndx].reset(new int8[size]);
+      transfer_buffer_buffers_[ndx].ptr = transfer_buffers_[ndx].get();
+      transfer_buffer_buffers_[ndx].size = size;
+    }
+    return id;
   }
 
-  virtual void DestroyTransferBuffer(int32 /* id */) {
-    GPU_NOTREACHED();
+  void DestroyTransferBufferHelper(int32 id) {
+    GPU_DCHECK_GE(id, kTransferBufferBaseId);
+    GPU_DCHECK_LT(id, kTransferBufferBaseId + kMaxTransferBuffers);
+    id -= kTransferBufferBaseId;
+    transfer_buffers_[id].reset();
+    transfer_buffer_buffers_[id] = Buffer();
   }
 
   virtual Buffer GetTransferBuffer(int32 id) {
-    GPU_DCHECK_EQ(id, kTransferBufferId);
-    return transfer_buffer_buffer_;
+    GPU_DCHECK_GE(id, kTransferBufferBaseId);
+    GPU_DCHECK_LT(id, kTransferBufferBaseId + kMaxTransferBuffers);
+    return transfer_buffer_buffers_[id - kTransferBufferBaseId];
   }
 
   virtual int32 RegisterTransferBuffer(base::SharedMemory* shared_memory,
@@ -107,39 +132,41 @@ class GLES2MockCommandBufferHelper : public CommandBuffer {
   virtual void OnFlush(void* transfer_buffer) = 0;
 
  private:
-  scoped_array<int8> transfer_buffer_;
-  Buffer transfer_buffer_buffer_;
-  scoped_array<CommandBufferEntry> ring_buffer_;
+  scoped_array<int8> transfer_buffers_[kMaxTransferBuffers];
+  Buffer transfer_buffer_buffers_[kMaxTransferBuffers];
+  CommandBufferEntry* ring_buffer_;
   Buffer ring_buffer_buffer_;
   State state_;
 };
 
 class MockGLES2CommandBuffer : public GLES2MockCommandBufferHelper {
  public:
+  MockGLES2CommandBuffer() {
+    DelegateToFake();
+  }
+
   virtual ~MockGLES2CommandBuffer() {
   }
 
   // This is so we can use all the gmock functions when Flush is called.
   MOCK_METHOD1(OnFlush, void(void* result));
   MOCK_METHOD1(DestroyTransferBuffer, void(int32 id));
+
+  void DelegateToFake() {
+    ON_CALL(*this, DestroyTransferBuffer(_))
+        .WillByDefault(Invoke(
+            this, &GLES2MockCommandBufferHelper::DestroyTransferBufferHelper));
+  }
 };
 
 // GCC requires these declarations, but MSVC requires they not be present
 #ifndef _MSC_VER
-const int32 GLES2MockCommandBufferHelper::kTransferBufferId;
+const int32 GLES2MockCommandBufferHelper::kTransferBufferBaseId;
+const int32 GLES2MockCommandBufferHelper::kMaxTransferBuffers;
 #endif
 
 namespace gles2 {
 
-using testing::_;
-using testing::DoAll;
-using testing::InSequence;
-using testing::Invoke;
-using testing::Mock;
-using testing::Sequence;
-using testing::Truly;
-using testing::Return;
-
 ACTION_P(SetMemory, obj) {
   memcpy(arg0, &obj, sizeof(obj));
 }
@@ -194,8 +221,6 @@ class GLES2CommandBufferTestBase : public testing::Test {
   static const int32 kCommandBufferSizeBytes =
       kNumCommandEntries * sizeof(CommandBufferEntry);
   static const size_t kTransferBufferSize = 256;
-  static const int32 kTransferBufferId =
-      GLES2MockCommandBufferHelper::kTransferBufferId;
   static const uint8 kInitialValue = 0xBD;
 
   GLES2CommandBufferTestBase()
@@ -203,7 +228,8 @@ class GLES2CommandBufferTestBase : public testing::Test {
         token_(0),
         offset_(0),
         initial_offset_(0),
-        alignment_(0) {
+        alignment_(0),
+        transfer_buffer_id_(-1) {
   }
 
   void SetupCommandBuffer(unsigned int offset, unsigned alignment) {
@@ -212,11 +238,11 @@ class GLES2CommandBufferTestBase : public testing::Test {
     alignment_ = alignment;
 
     command_buffer_.reset(new MockGLES2CommandBuffer());
-    command_buffer_->Initialize(kCommandBufferSizeBytes);
+    command_buffer_->Initialize();
 
-    EXPECT_EQ(kTransferBufferId,
-              command_buffer_->CreateTransferBuffer(kTransferBufferSize, -1));
-    transfer_buffer_ = command_buffer_->GetTransferBuffer(kTransferBufferId);
+    transfer_buffer_id_ =
+        command_buffer_->CreateTransferBuffer(kTransferBufferSize, -1);
+    transfer_buffer_ = command_buffer_->GetTransferBuffer(transfer_buffer_id_);
     ClearTransferBuffer();
 
     helper_.reset(new GLES2CmdHelper(command_buffer_.get()));
@@ -232,7 +258,7 @@ class GLES2CommandBufferTestBase : public testing::Test {
   }
 
   void ClearCommands() {
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
+    Buffer ring_buffer = helper_->get_ring_buffer();
     memset(ring_buffer.ptr, kInitialValue, ring_buffer.size);
   }
 
@@ -253,6 +279,10 @@ class GLES2CommandBufferTestBase : public testing::Test {
     return ++token_;
   }
 
+  int32 GetNextFreeTransferBufferId() {
+    return command_buffer_->GetNextFreeTransferBufferId();
+  }
+
   uint32 AllocateTransferBuffer(size_t size) {
     if (offset_ + size > kTransferBufferSize) {
       offset_ = initial_offset_;
@@ -280,6 +310,7 @@ class GLES2CommandBufferTestBase : public testing::Test {
   uint32 offset_;
   uint32 initial_offset_;
   uint32 alignment_;
+  int32 transfer_buffer_id_;
 };
 
 // GCC requires these declarations, but MSVC requires they not be present
@@ -287,7 +318,6 @@ class GLES2CommandBufferTestBase : public testing::Test {
 const int32 GLES2CommandBufferTestBase::kNumCommandEntries;
 const int32 GLES2CommandBufferTestBase::kCommandBufferSizeBytes;
 const size_t GLES2CommandBufferTestBase::kTransferBufferSize;
-const int32 GLES2CommandBufferTestBase::kTransferBufferId;
 const uint8 GLES2CommandBufferTestBase::kInitialValue;
 #endif
 
@@ -303,9 +333,12 @@ class TransferBufferTest : public GLES2CommandBufferTestBase {
         GLES2Implementation::kStartingOffset,
         GLES2Implementation::kAlignment);
 
+    transfer_buffer_id_ =
+        command_buffer_->CreateTransferBuffer(kTransferBufferSize, -1);
+
     transfer_buffer_.reset(new TransferBuffer(
         helper_.get(),
-        kTransferBufferId,
+        transfer_buffer_id_,
         GetTransferAddressFromOffset(0, 0),
         kTransferBufferSize,
         kStartingOffset,
@@ -327,7 +360,7 @@ const unsigned int TransferBufferTest::kAlignment;
 
 TEST_F(TransferBufferTest, Basic) {
   EXPECT_TRUE(transfer_buffer_->HaveBuffer());
-  EXPECT_EQ(kTransferBufferId, transfer_buffer_->GetShmId());
+  EXPECT_EQ(transfer_buffer_id_, transfer_buffer_->GetShmId());
 }
 
 TEST_F(TransferBufferTest, Free) {
@@ -341,7 +374,7 @@ TEST_F(TransferBufferTest, Free) {
   // See it's freed.
   EXPECT_FALSE(transfer_buffer_->HaveBuffer());
   // See that it gets reallocated.
-  EXPECT_EQ(kTransferBufferId, transfer_buffer_->GetShmId());
+  EXPECT_EQ(transfer_buffer_id_, transfer_buffer_->GetShmId());
   EXPECT_TRUE(transfer_buffer_->HaveBuffer());
 
   // Free buffer.
@@ -473,7 +506,7 @@ class GLES2ImplementationTest : public GLES2CommandBufferTestBase {
           helper_.get(),
           kTransferBufferSize,
           transfer_buffer_.ptr,
-          kTransferBufferId,
+          transfer_buffer_id_,
           shared_resources,
           bind_generates_resource));
     }
@@ -482,7 +515,7 @@ class GLES2ImplementationTest : public GLES2CommandBufferTestBase {
         .Times(1)
         .RetiresOnSaturation();
     helper_->CommandBufferHelper::Finish();
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
+    Buffer ring_buffer = helper_->get_ring_buffer();
     commands_ = static_cast<CommandBufferEntry*>(ring_buffer.ptr) +
                 command_buffer_->GetState().put_offset;
     ClearCommands();
@@ -525,16 +558,16 @@ TEST_F(GLES2ImplementationTest, ShaderSource) {
   Cmds expected;
   expected.set_bucket_size.Init(kBucketId, kSourceSize);
   expected.set_bucket_data1.Init(
-      kBucketId, 0, kString1Size, kTransferBufferId,
+      kBucketId, 0, kString1Size, transfer_buffer_id_,
       AllocateTransferBuffer(kPaddedString1Size));
   expected.set_token1.Init(GetNextToken());
   expected.set_bucket_data2.Init(
-      kBucketId, kString1Size, kString2Size, kTransferBufferId,
+      kBucketId, kString1Size, kString2Size, transfer_buffer_id_,
       AllocateTransferBuffer(kPaddedString2Size));
   expected.set_token2.Init(GetNextToken());
   expected.set_bucket_data3.Init(
       kBucketId, kString1Size + kString2Size,
-      kString3Size, kTransferBufferId,
+      kString3Size, transfer_buffer_id_,
       AllocateTransferBuffer(kPaddedString3Size));
   expected.set_token3.Init(GetNextToken());
   expected.shader_source_bucket.Init(kShaderId, kBucketId);
@@ -564,9 +597,9 @@ TEST_F(GLES2ImplementationTest, GetShaderSource) {
   Cmds expected;
   expected.set_bucket_size1.Init(kBucketId, 0);
   expected.get_shader_source.Init(kShaderId, kBucketId);
-  expected.get_bucket_size.Init(kBucketId, kTransferBufferId, 0);
+  expected.get_bucket_size.Init(kBucketId, transfer_buffer_id_, 0);
   expected.get_bucket_data.Init(
-      kBucketId, 0, sizeof(kString), kTransferBufferId, offset);
+      kBucketId, 0, sizeof(kString), transfer_buffer_id_, offset);
   expected.set_token1.Init(GetNextToken());
   expected.set_bucket_size2.Init(kBucketId, 0);
   char buf[sizeof(kString) + 1];
@@ -628,13 +661,13 @@ TEST_F(GLES2ImplementationTest, DrawArraysClientSideBuffers) {
   expected.bind_to_emu.Init(GL_ARRAY_BUFFER, kEmuBufferId);
   expected.set_size.Init(GL_ARRAY_BUFFER, kTotalSize, 0, 0, GL_DYNAMIC_DRAW);
   expected.copy_data1.Init(
-      GL_ARRAY_BUFFER, kEmuOffset1, kSize1, kTransferBufferId,
+      GL_ARRAY_BUFFER, kEmuOffset1, kSize1, transfer_buffer_id_,
       AllocateTransferBuffer(kSize1));
   expected.set_token1.Init(GetNextToken());
   expected.set_pointer1.Init(kAttribIndex1, kNumComponents1,
                              GL_FLOAT, GL_FALSE, 0, kEmuOffset1);
   expected.copy_data2.Init(
-      GL_ARRAY_BUFFER, kEmuOffset2, kSize2, kTransferBufferId,
+      GL_ARRAY_BUFFER, kEmuOffset2, kSize2, transfer_buffer_id_,
       AllocateTransferBuffer(kSize2));
   expected.set_token2.Init(GetNextToken());
   expected.set_pointer2.Init(kAttribIndex2, kNumComponents2,
@@ -704,19 +737,19 @@ TEST_F(GLES2ImplementationTest, DrawElementsClientSideBuffers) {
   expected.set_index_size.Init(
       GL_ELEMENT_ARRAY_BUFFER, kIndexSize, 0, 0, GL_DYNAMIC_DRAW);
   expected.copy_data0.Init(
-      GL_ELEMENT_ARRAY_BUFFER, 0, kIndexSize, kTransferBufferId,
+      GL_ELEMENT_ARRAY_BUFFER, 0, kIndexSize, transfer_buffer_id_,
       AllocateTransferBuffer(kIndexSize));
   expected.set_token0.Init(GetNextToken());
   expected.bind_to_emu.Init(GL_ARRAY_BUFFER, kEmuBufferId);
   expected.set_size.Init(GL_ARRAY_BUFFER, kTotalSize, 0, 0, GL_DYNAMIC_DRAW);
   expected.copy_data1.Init(
-      GL_ARRAY_BUFFER, kEmuOffset1, kSize1, kTransferBufferId,
+      GL_ARRAY_BUFFER, kEmuOffset1, kSize1, transfer_buffer_id_,
       AllocateTransferBuffer(kSize1));
   expected.set_token1.Init(GetNextToken());
   expected.set_pointer1.Init(kAttribIndex1, kNumComponents1,
                              GL_FLOAT, GL_FALSE, 0, kEmuOffset1);
   expected.copy_data2.Init(
-      GL_ARRAY_BUFFER, kEmuOffset2, kSize2, kTransferBufferId,
+      GL_ARRAY_BUFFER, kEmuOffset2, kSize2, transfer_buffer_id_,
       AllocateTransferBuffer(kSize2));
   expected.set_token2.Init(GetNextToken());
   expected.set_pointer2.Init(kAttribIndex2, kNumComponents2,
@@ -780,17 +813,17 @@ TEST_F(GLES2ImplementationTest,
   expected.enable2.Init(kAttribIndex2);
   expected.bind_to_index.Init(GL_ELEMENT_ARRAY_BUFFER, kClientIndexBufferId);
   expected.get_max.Init(kClientIndexBufferId, kCount, GL_UNSIGNED_SHORT,
-                        kIndexOffset, kTransferBufferId, 0);
+                        kIndexOffset, transfer_buffer_id_, 0);
   expected.bind_to_emu.Init(GL_ARRAY_BUFFER, kEmuBufferId);
   expected.set_size.Init(GL_ARRAY_BUFFER, kTotalSize, 0, 0, GL_DYNAMIC_DRAW);
   expected.copy_data1.Init(
-      GL_ARRAY_BUFFER, kEmuOffset1, kSize1, kTransferBufferId,
+      GL_ARRAY_BUFFER, kEmuOffset1, kSize1, transfer_buffer_id_,
       AllocateTransferBuffer(kSize1));
   expected.set_token1.Init(GetNextToken());
   expected.set_pointer1.Init(kAttribIndex1, kNumComponents1,
                              GL_FLOAT, GL_FALSE, 0, kEmuOffset1);
   expected.copy_data2.Init(
-      GL_ARRAY_BUFFER, kEmuOffset2, kSize2, kTransferBufferId,
+      GL_ARRAY_BUFFER, kEmuOffset2, kSize2, transfer_buffer_id_,
       AllocateTransferBuffer(kSize2));
   expected.set_token2.Init(GetNextToken());
   expected.set_pointer2.Init(kAttribIndex2, kNumComponents2,
@@ -837,7 +870,7 @@ TEST_F(GLES2ImplementationTest, GetVertexBufferPointerv) {
   expected.set_pointer.Init(kAttribIndex2, kNumComponents2, GL_FLOAT, GL_FALSE,
                             kStride2, kOffset2);
   expected.get_pointer.Init(kAttribIndex2, GL_VERTEX_ATTRIB_ARRAY_POINTER,
-                            kTransferBufferId, 0);
+                            transfer_buffer_id_, 0);
 
   // One call to flush to way for GetVertexAttribPointerv
   EXPECT_CALL(*command_buffer_, OnFlush(_))
@@ -894,10 +927,10 @@ TEST_F(GLES2ImplementationTest, GetVertexAttrib) {
                             kStride2, kOffset2);
   expected.get1.Init(kAttribIndex2,
                      GL_VERTEX_ATTRIB_ARRAY_BUFFER_BINDING,
-                     kTransferBufferId, 0);
+                     transfer_buffer_id_, 0);
   expected.get2.Init(kAttribIndex1,
                      GL_CURRENT_VERTEX_ATTRIB,
-                     kTransferBufferId, 0);
+                     transfer_buffer_id_, 0);
 
   FourFloats current_attrib(1.2f, 3.4f, 5.6f, 7.8f);
 
@@ -960,7 +993,7 @@ TEST_F(GLES2ImplementationTest, ReservedIds) {
     GetError get;
   };
   Cmds expected;
-  expected.get.Init(kTransferBufferId, 0);
+  expected.get.Init(transfer_buffer_id_, 0);
 
   // One call to flush to wait for GetError
   EXPECT_CALL(*command_buffer_, OnFlush(_))
@@ -998,15 +1031,15 @@ TEST_F(GLES2ImplementationTest, ReadPixels2Reads) {
   Cmds expected;
   expected.read1.Init(
       0, 0, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId,
+      transfer_buffer_id_,
       AllocateTransferBuffer(kWidth * kHeight / 2 * kBytesPerPixel),
-      kTransferBufferId, 0);
+      transfer_buffer_id_, 0);
   expected.set_token1.Init(GetNextToken());
   expected.read2.Init(
       0, kHeight / 2, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId,
+      transfer_buffer_id_,
       AllocateTransferBuffer(kWidth * kHeight / 2 * kBytesPerPixel),
-      kTransferBufferId, 0);
+      transfer_buffer_id_, 0);
   expected.set_token2.Init(GetNextToken());
   scoped_array<int8> buffer(new int8[kWidth * kHeight * kBytesPerPixel]);
 
@@ -1033,9 +1066,9 @@ TEST_F(GLES2ImplementationTest, ReadPixelsBadFormatType) {
   Cmds expected;
   expected.read.Init(
       0, 0, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId,
+      transfer_buffer_id_,
       AllocateTransferBuffer(kWidth * kHeight * kBytesPerPixel),
-      kTransferBufferId, 0);
+      transfer_buffer_id_, 0);
   expected.set_token.Init(GetNextToken());
   scoped_array<int8> buffer(new int8[kWidth * kHeight * kBytesPerPixel]);
 
@@ -1058,7 +1091,7 @@ TEST_F(GLES2ImplementationTest, FreeUnusedSharedMemory) {
   uint32 offset = 0;
   Cmds expected;
   expected.buf.Init(
-    kTarget, kOffset, kSize, kTransferBufferId, offset);
+    kTarget, kOffset, kSize, transfer_buffer_id_, offset);
   expected.set_token.Init(GetNextToken());
 
   void* mem = gl_->MapBufferSubDataCHROMIUM(
@@ -1083,7 +1116,7 @@ TEST_F(GLES2ImplementationTest, MapUnmapBufferSubDataCHROMIUM) {
   uint32 offset = 0;
   Cmds expected;
   expected.buf.Init(
-    kTarget, kOffset, kSize, kTransferBufferId, offset);
+      kTarget, kOffset, kSize, GetNextFreeTransferBufferId(), offset);
   expected.set_token.Init(GetNextToken());
 
   void* mem = gl_->MapBufferSubDataCHROMIUM(
@@ -1138,7 +1171,7 @@ TEST_F(GLES2ImplementationTest, MapUnmapTexSubImage2DCHROMIUM) {
   Cmds expected;
   expected.tex.Init(
       GL_TEXTURE_2D, kLevel, kXOffset, kYOffset, kWidth, kHeight, kFormat,
-      kType, kTransferBufferId, offset, GL_FALSE);
+      kType, GetNextFreeTransferBufferId(), offset, GL_FALSE);
   expected.set_token.Init(GetNextToken());
 
   void* mem = gl_->MapTexSubImage2DCHROMIUM(
@@ -1273,8 +1306,8 @@ TEST_F(GLES2ImplementationTest, GetMultipleIntegervCHROMIUMValidArgs) {
   const uint32 kResultsOffset = AllocateTransferBuffer(kResultsSize);
   Cmds expected;
   expected.get_multiple.Init(
-      kTransferBufferId, kPnamesOffset, kNumPnames,
-      kTransferBufferId, kResultsOffset, kResultsSize);
+      transfer_buffer_id_, kPnamesOffset, kNumPnames,
+      transfer_buffer_id_, kResultsOffset, kResultsSize);
   expected.set_token.Init(GetNextToken());
 
   const GLint kSentinel = 0x12345678;
@@ -1383,9 +1416,9 @@ TEST_F(GLES2ImplementationTest, GetProgramInfoCHROMIUMGoodArgs) {
   Cmds expected;
   expected.set_bucket_size1.Init(kBucketId, 0);
   expected.get_program_info.Init(kProgramId, kBucketId);
-  expected.get_bucket_size.Init(kBucketId, kTransferBufferId, 0);
+  expected.get_bucket_size.Init(kBucketId, transfer_buffer_id_, 0);
   expected.get_bucket_data.Init(
-      kBucketId, 0, sizeof(kString), kTransferBufferId, offset);
+      kBucketId, 0, sizeof(kString), transfer_buffer_id_, offset);
   expected.set_token1.Init(GetNextToken());
   expected.set_bucket_size2.Init(kBucketId, 0);
   gl_->GetProgramInfoCHROMIUM(kProgramId, sizeof(buf), &size, &buf);
@@ -1424,9 +1457,9 @@ TEST_F(GLES2ImplementationTest, GetProgramInfoCHROMIUMBadArgs) {
   Cmds expected;
   expected.set_bucket_size1.Init(kBucketId, 0);
   expected.get_program_info.Init(kProgramId, kBucketId);
-  expected.get_bucket_size.Init(kBucketId, kTransferBufferId, 0);
+  expected.get_bucket_size.Init(kBucketId, transfer_buffer_id_, 0);
   expected.get_bucket_data.Init(
-      kBucketId, 0, sizeof(kString), kTransferBufferId, offset);
+      kBucketId, 0, sizeof(kString), transfer_buffer_id_, offset);
   expected.set_token1.Init(GetNextToken());
   expected.set_bucket_size2.Init(kBucketId, 0);
   gl_->GetProgramInfoCHROMIUM(kProgramId, 6, &size, &buf);
@@ -1602,7 +1635,7 @@ TEST_F(GLES2ImplementationTest, TexImage2D) {
   Cmds expected;
   expected.tex_image_2d.Init(
       kTarget, kLevel, kFormat, kWidth, kHeight, kBorder, kFormat, kType,
-      kTransferBufferId, offset);
+      transfer_buffer_id_, offset);
   expected.set_token.Init(GetNextToken());
   gl_->TexImage2D(
       kTarget, kLevel, kFormat, kWidth, kHeight, kBorder, kFormat, kType,
@@ -1617,7 +1650,7 @@ TEST_F(GLES2ImplementationTest, TexImage2D) {
   Cmds2 expected2;
   expected2.tex_image_2d.Init(
       kTarget, kLevel, kFormat, kWidth, kHeight, kBorder, kFormat, kType,
-      kTransferBufferId, offset2);
+      transfer_buffer_id_, offset2);
   expected2.set_token.Init(GetNextToken());
   const void* commands2 = GetPut();
   gl_->PixelStorei(GL_UNPACK_FLIP_Y_CHROMIUM, GL_TRUE);
@@ -1674,11 +1707,11 @@ TEST_F(GLES2ImplementationTest, TexImage2D2Writes) {
       0, 0);
   expected.tex_sub_image_2d1.Init(
       kTarget, kLevel, 0, 0, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId, offset1, true);
+      transfer_buffer_id_, offset1, true);
   expected.set_token1.Init(GetNextToken());
   expected.tex_sub_image_2d2.Init(
       kTarget, kLevel, 0, kHeight / 2, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId, offset2, true);
+      transfer_buffer_id_, offset2, true);
   expected.set_token2.Init(GetNextToken());
 
   // TODO(gman): Make it possible to run this test
@@ -1707,11 +1740,11 @@ TEST_F(GLES2ImplementationTest, TexImage2D2Writes) {
       0, 0);
   expected.tex_sub_image_2d1.Init(
       kTarget, kLevel, 0, kHeight / 2, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId, offset3, true);
+      transfer_buffer_id_, offset3, true);
   expected.set_token1.Init(GetNextToken());
   expected.tex_sub_image_2d2.Init(
       kTarget, kLevel, 0, 0, kWidth, kHeight / 2, kFormat, kType,
-      kTransferBufferId, offset4, true);
+      transfer_buffer_id_, offset4, true);
   expected.set_token2.Init(GetNextToken());
 
   // TODO(gman): Make it possible to run this test
@@ -1777,19 +1810,19 @@ TEST_F(GLES2ImplementationTest, TexImage2DSubRows) {
       0, 0);
   expected.tex_sub_image_2d1.Init(
       kTarget, kLevel, 0, 0, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset1, true);
+      transfer_buffer_id_, offset1, true);
   expected.set_token1.Init(GetNextToken());
   expected.tex_sub_image_2d2.Init(
       kTarget, kLevel, kWidth / 2, 0, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset2, true);
+      transfer_buffer_id_, offset2, true);
   expected.set_token2.Init(GetNextToken());
   expected.tex_sub_image_2d3.Init(
       kTarget, kLevel, 0, 1, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset3, true);
+      transfer_buffer_id_, offset3, true);
   expected.set_token3.Init(GetNextToken());
   expected.tex_sub_image_2d4.Init(
       kTarget, kLevel, kWidth / 2, 1, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset4, true);
+      transfer_buffer_id_, offset4, true);
   expected.set_token4.Init(GetNextToken());
 
   // TODO(gman): Make it possible to run this test
@@ -1828,19 +1861,19 @@ TEST_F(GLES2ImplementationTest, TexImage2DSubRows) {
       0, 0);
   expected.tex_sub_image_2d1.Init(
       kTarget, kLevel, 0, 1, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset1, true);
+      transfer_buffer_id_, offset1, true);
   expected.set_token1.Init(GetNextToken());
   expected.tex_sub_image_2d2.Init(
       kTarget, kLevel, kWidth / 2, 1, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset2, true);
+      transfer_buffer_id_, offset2, true);
   expected.set_token2.Init(GetNextToken());
   expected.tex_sub_image_2d3.Init(
       kTarget, kLevel, 0, 0, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset3, true);
+      transfer_buffer_id_, offset3, true);
   expected.set_token3.Init(GetNextToken());
   expected.tex_sub_image_2d4.Init(
       kTarget, kLevel, kWidth / 2, 0, kWidth / 2, 1, kFormat, kType,
-      kTransferBufferId, offset4, true);
+      transfer_buffer_id_, offset4, true);
   expected.set_token4.Init(GetNextToken());
 
   // TODO(gman): Make it possible to run this test
@@ -1908,10 +1941,10 @@ TEST_F(GLES2ImplementationTest, TexSubImage2DFlipY) {
       kType, 0, NULL);
   expected.tex_sub_image_2d1.Init(kTarget, kLevel, kSubImageXOffset,
       kSubImageYOffset + 2, kSubImageWidth, 2, kFormat, kType,
-      kTransferBufferId, offset1, false);
+      transfer_buffer_id_, offset1, false);
   expected.set_token1.Init(GetNextToken());
   expected.tex_sub_image_2d2.Init(kTarget, kLevel, kSubImageXOffset,
-      kSubImageYOffset, kSubImageWidth , 2, kFormat, kType, kTransferBufferId,
+      kSubImageYOffset, kSubImageWidth , 2, kFormat, kType, transfer_buffer_id_,
       offset2, false);
   expected.set_token2.Init(GetNextToken());
 
@@ -2020,7 +2053,7 @@ TEST_F(GLES2ImplementationTest, CreateStreamTextureCHROMIUM) {
   };
 
   Cmds expected;
-  expected.create_stream.Init(kTextureId, kTransferBufferId, kResultOffset);
+  expected.create_stream.Init(kTextureId, transfer_buffer_id_, kResultOffset);
 
   EXPECT_CALL(*command_buffer_, OnFlush(_))
       .WillOnce(SetMemoryAtOffset(kResultOffset, kResult))
diff --git a/gpu/command_buffer/client/mapped_memory_unittest.cc b/gpu/command_buffer/client/mapped_memory_unittest.cc
index 81b6655..c18ec9f 100644
--- a/gpu/command_buffer/client/mapped_memory_unittest.cc
+++ b/gpu/command_buffer/client/mapped_memory_unittest.cc
@@ -42,15 +42,9 @@ class MappedMemoryTestBase : public testing::Test {
                               Return(error::kNoError)));
 
     command_buffer_.reset(new CommandBufferService);
-    command_buffer_->Initialize(kBufferSize);
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
+    command_buffer_->Initialize();
 
-    parser_ = new CommandParser(ring_buffer.ptr,
-                                ring_buffer.size,
-                                0,
-                                ring_buffer.size,
-                                0,
-                                api_mock_.get());
+    parser_ = new CommandParser(api_mock_.get());
 
     gpu_scheduler_.reset(new GpuScheduler(
         command_buffer_.get(), NULL, parser_));
@@ -61,6 +55,12 @@ class MappedMemoryTestBase : public testing::Test {
 
     helper_.reset(new CommandBufferHelper(command_buffer_.get()));
     helper_->Initialize(kBufferSize);
+
+    // Note: parser->SetBuffer would normally be called through
+    // helper_->Initialize but currently it needs a GpuCommandBufferStub as the
+    // CommandBuffer instead of the CommandBufferService for that to happen.
+    Buffer ring_buffer = helper_->get_ring_buffer();
+    parser_->SetBuffer(ring_buffer.ptr, ring_buffer.size, 0, ring_buffer.size);
   }
 
   int32 GetToken() {
diff --git a/gpu/command_buffer/client/ring_buffer_test.cc b/gpu/command_buffer/client/ring_buffer_test.cc
index eb5a0cb..8b8e46e 100644
--- a/gpu/command_buffer/client/ring_buffer_test.cc
+++ b/gpu/command_buffer/client/ring_buffer_test.cc
@@ -65,15 +65,9 @@ class BaseRingBufferTest : public testing::Test {
                               Return(error::kNoError)));
 
     command_buffer_.reset(new CommandBufferService);
-    command_buffer_->Initialize(kBufferSize);
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
+    command_buffer_->Initialize();
 
-    parser_ = new CommandParser(ring_buffer.ptr,
-                                ring_buffer.size,
-                                0,
-                                ring_buffer.size,
-                                0,
-                                api_mock_.get());
+    parser_ = new CommandParser(api_mock_.get());
 
     gpu_scheduler_.reset(new GpuScheduler(
         command_buffer_.get(), NULL, parser_));
@@ -88,6 +82,12 @@ class BaseRingBufferTest : public testing::Test {
 
     helper_.reset(new CommandBufferHelper(command_buffer_.get()));
     helper_->Initialize(kBufferSize);
+
+    // Note: parser->SetBuffer would normally be called through
+    // helper_->Initialize but currently it needs a GpuCommandBufferStub as the
+    // CommandBuffer instead of the CommandBufferService for that to happen.
+    Buffer ring_buffer = helper_->get_ring_buffer();
+    parser_->SetBuffer(ring_buffer.ptr, ring_buffer.size, 0, ring_buffer.size);
   }
 
   int32 GetToken() {
diff --git a/gpu/command_buffer/common/command_buffer.h b/gpu/command_buffer/common/command_buffer.h
index 76124c8..e44df7f 100644
--- a/gpu/command_buffer/common/command_buffer.h
+++ b/gpu/command_buffer/common/command_buffer.h
@@ -67,13 +67,7 @@ class CommandBuffer {
   }
 
   // Initialize the command buffer with the given size.
-  virtual bool Initialize(int32 size) = 0;
-
-  // Initialize the command buffer using the given preallocated buffer.
-  virtual bool Initialize(base::SharedMemory* buffer, int32 size) = 0;
-
-  // Gets the ring buffer for the command buffer.
-  virtual Buffer GetRingBuffer() = 0;
+  virtual bool Initialize() = 0;
 
   // Returns the current status.
   virtual State GetState() = 0;
@@ -92,6 +86,10 @@ class CommandBuffer {
   // have been executed.
   virtual State FlushSync(int32 put_offset, int32 last_known_get) = 0;
 
+  // Sets the buffer commands are read from.
+  // Also resets the get and put offsets to 0.
+  virtual void SetGetBuffer(int32 transfer_buffer_id) = 0;
+
   // Sets the current get offset. This can be called from any thread.
   virtual void SetGetOffset(int32 get_offset) = 0;
 
diff --git a/gpu/command_buffer/common/command_buffer_mock.cc b/gpu/command_buffer/common/command_buffer_mock.cc
index d92c2c3..6ed2eee 100644
--- a/gpu/command_buffer/common/command_buffer_mock.cc
+++ b/gpu/command_buffer/common/command_buffer_mock.cc
@@ -7,8 +7,6 @@
 namespace gpu {
 
 MockCommandBuffer::MockCommandBuffer() {
-  ON_CALL(*this, GetRingBuffer())
-      .WillByDefault(testing::Return(Buffer()));
   ON_CALL(*this, GetTransferBuffer(testing::_))
       .WillByDefault(testing::Return(Buffer()));
 }
diff --git a/gpu/command_buffer/common/command_buffer_mock.h b/gpu/command_buffer/common/command_buffer_mock.h
index 321c40d..0379340 100644
--- a/gpu/command_buffer/common/command_buffer_mock.h
+++ b/gpu/command_buffer/common/command_buffer_mock.h
@@ -21,13 +21,12 @@ class MockCommandBuffer : public CommandBuffer {
   MockCommandBuffer();
   virtual ~MockCommandBuffer();
 
-  MOCK_METHOD1(Initialize, bool(int32 size));
-  MOCK_METHOD2(Initialize, bool(base::SharedMemory* buffer, int32 size));
-  MOCK_METHOD0(GetRingBuffer, Buffer());
+  MOCK_METHOD0(Initialize, bool());
   MOCK_METHOD0(GetState, State());
   MOCK_METHOD0(GetLastState, State());
   MOCK_METHOD1(Flush, void(int32 put_offset));
   MOCK_METHOD2(FlushSync, State(int32 put_offset, int32 last_known_get));
+  MOCK_METHOD1(SetGetBuffer, void(int32 transfer_buffer_id));
   MOCK_METHOD1(SetGetOffset, void(int32 get_offset));
   MOCK_METHOD2(CreateTransferBuffer, int32(size_t size, int32 id_request));
   MOCK_METHOD1(DestroyTransferBuffer, void(int32 handle));
diff --git a/gpu/command_buffer/service/cmd_buffer_engine.h b/gpu/command_buffer/service/cmd_buffer_engine.h
index 59e99ab..6aefe82 100644
--- a/gpu/command_buffer/service/cmd_buffer_engine.h
+++ b/gpu/command_buffer/service/cmd_buffer_engine.h
@@ -29,6 +29,9 @@ class CommandBufferEngine {
   // Sets the token value.
   virtual void set_token(int32 token) = 0;
 
+  // Sets the shared memory buffer used for commands.
+  virtual bool SetGetBuffer(int32 transfer_buffer_id) = 0;
+
   // Sets the "get" pointer. Return false if offset is out of range.
   virtual bool SetGetOffset(int32 offset) = 0;
 
diff --git a/gpu/command_buffer/service/cmd_parser.cc b/gpu/command_buffer/service/cmd_parser.cc
index fba06e6..b5383af 100644
--- a/gpu/command_buffer/service/cmd_parser.cc
+++ b/gpu/command_buffer/service/cmd_parser.cc
@@ -10,23 +10,29 @@
 
 namespace gpu {
 
-CommandParser::CommandParser(void *shm_address,
-                             size_t shm_size,
-                             ptrdiff_t offset,
-                             size_t size,
-                             CommandBufferOffset start_get,
-                             AsyncAPIInterface *handler)
-    : get_(start_get),
-      put_(start_get),
+CommandParser::CommandParser(AsyncAPIInterface* handler)
+    : get_(0),
+      put_(0),
+      buffer_(NULL),
+      entry_count_(0),
       handler_(handler) {
+}
+
+void CommandParser::SetBuffer(
+    void* shm_address,
+    size_t shm_size,
+    ptrdiff_t offset,
+    size_t size) {
   // check proper alignments.
   DCHECK_EQ(0, (reinterpret_cast<intptr_t>(shm_address)) % 4);
   DCHECK_EQ(0, offset % 4);
   DCHECK_EQ(0u, size % 4);
   // check that the command buffer fits into the memory buffer.
   DCHECK_GE(shm_size, offset + size);
-  char * buffer_begin = static_cast<char *>(shm_address) + offset;
-  buffer_ = reinterpret_cast<CommandBufferEntry *>(buffer_begin);
+  get_ = 0;
+  put_ = 0;
+  char* buffer_begin = static_cast<char*>(shm_address) + offset;
+  buffer_ = reinterpret_cast<CommandBufferEntry*>(buffer_begin);
   entry_count_ = size / 4;
 }
 
diff --git a/gpu/command_buffer/service/cmd_parser.h b/gpu/command_buffer/service/cmd_parser.h
index fe3eb12..567b7f6 100644
--- a/gpu/command_buffer/service/cmd_parser.h
+++ b/gpu/command_buffer/service/cmd_parser.h
@@ -18,12 +18,14 @@ class AsyncAPIInterface;
 // buffer, to implement some asynchronous RPC mechanism.
 class CommandParser {
  public:
-  CommandParser(void *shm_address,
-                size_t shm_size,
-                ptrdiff_t offset,
-                size_t size,
-                CommandBufferOffset start_get,
-                AsyncAPIInterface *handler);
+  explicit CommandParser(AsyncAPIInterface* handler);
+
+  // Sets the buffer to read commands from.
+  void SetBuffer(
+      void* shm_address,
+      size_t shm_size,
+      ptrdiff_t offset,
+      size_t size);
 
   // Gets the "get" pointer. The get pointer is an index into the command
   // buffer considered as an array of CommandBufferEntry.
@@ -63,9 +65,9 @@ class CommandParser {
  private:
   CommandBufferOffset get_;
   CommandBufferOffset put_;
-  CommandBufferEntry *buffer_;
+  CommandBufferEntry* buffer_;
   int32 entry_count_;
-  AsyncAPIInterface *handler_;
+  AsyncAPIInterface* handler_;
 };
 
 // This class defines the interface for an asynchronous API handler, that
diff --git a/gpu/command_buffer/service/cmd_parser_test.cc b/gpu/command_buffer/service/cmd_parser_test.cc
index 857ca8e..b86b0af 100644
--- a/gpu/command_buffer/service/cmd_parser_test.cc
+++ b/gpu/command_buffer/service/cmd_parser_test.cc
@@ -48,12 +48,10 @@ class CommandParserTest : public testing::Test {
     size_t command_buffer_size = entry_count *
                                  sizeof(CommandBufferEntry);  // NOLINT
     DCHECK_LE(command_buffer_size, shm_size);
-    return new CommandParser(buffer(),
-                             shm_size,
-                             0,
-                             command_buffer_size,
-                             0,
-                             api_mock());
+    CommandParser* parser = new CommandParser(api_mock());
+
+    parser->SetBuffer(buffer(), shm_size, 0, command_buffer_size);
+    return parser;
   }
 
   unsigned int buffer_entry_count() { return 20; }
@@ -288,4 +286,34 @@ TEST_F(CommandParserTest, TestError) {
   Mock::VerifyAndClearExpectations(api_mock());
 }
 
+TEST_F(CommandParserTest, SetBuffer) {
+  scoped_ptr<CommandParser> parser(MakeParser(3));
+  CommandBufferOffset put = parser->put();
+  CommandHeader header;
+
+  // add a single command, no args
+  header.size = 2;
+  header.command = 123;
+  buffer()[put++].value_header = header;
+  buffer()[put++].value_int32 = 456;
+
+  CommandBufferEntry param_array[1];
+  param_array[0].value_int32 = 456;
+
+  parser->set_put(put);
+  AddDoCommandExpect(error::kNoError, 123, 1, param_array);
+  EXPECT_EQ(error::kNoError, parser->ProcessAllCommands());
+  // We should have advanced 2 entries
+  EXPECT_EQ(2, parser->get());
+  Mock::VerifyAndClearExpectations(api_mock());
+
+  scoped_array<CommandBufferEntry> buffer2(new CommandBufferEntry[2]);
+  parser->SetBuffer(
+      buffer2.get(), sizeof(CommandBufferEntry) * 2, 0,
+      sizeof(CommandBufferEntry) * 2);
+  // The put and get should have reset to 0.
+  EXPECT_EQ(0, parser->get());
+  EXPECT_EQ(0, parser->put());
+}
+
 }  // namespace gpu
diff --git a/gpu/command_buffer/service/command_buffer_service.cc b/gpu/command_buffer/service/command_buffer_service.cc
index d126883..4047d1c 100644
--- a/gpu/command_buffer/service/command_buffer_service.cc
+++ b/gpu/command_buffer/service/command_buffer_service.cc
@@ -14,7 +14,8 @@ using ::base::SharedMemory;
 namespace gpu {
 
 CommandBufferService::CommandBufferService()
-    : num_entries_(0),
+    : ring_buffer_id_(-1),
+      num_entries_(0),
       get_offset_(0),
       put_offset_(0),
       token_(0),
@@ -25,71 +26,16 @@ CommandBufferService::CommandBufferService()
 }
 
 CommandBufferService::~CommandBufferService() {
-  delete ring_buffer_.shared_memory;
-
   for (size_t i = 0; i < registered_objects_.size(); ++i) {
     if (registered_objects_[i].shared_memory)
       delete registered_objects_[i].shared_memory;
   }
 }
 
-bool CommandBufferService::Initialize(int32 size) {
-  // Fail if already initialized.
-  if (ring_buffer_.shared_memory) {
-    LOG(ERROR) << "Failed because already initialized.";
-    return false;
-  }
-
-  if (size <= 0 || size > kMaxCommandBufferSize) {
-    LOG(ERROR) << "Failed because command buffer size was invalid.";
-    return false;
-  }
-
-  num_entries_ = size / sizeof(CommandBufferEntry);
-
-  SharedMemory shared_memory;
-  if (!shared_memory.CreateAnonymous(size)) {
-    LOG(ERROR) << "Failed to create shared memory for command buffer.";
-    return true;
-  }
-
-  return Initialize(&shared_memory, size);
-}
-
-bool CommandBufferService::Initialize(base::SharedMemory* buffer, int32 size) {
-  // Fail if already initialized.
-  if (ring_buffer_.shared_memory) {
-    LOG(ERROR) << "Failed because already initialized.";
-    return false;
-  }
-
-  base::SharedMemoryHandle shared_memory_handle;
-  if (!buffer->ShareToProcess(base::GetCurrentProcessHandle(),
-                              &shared_memory_handle)) {
-    LOG(ERROR) << "Failed to duplicate command buffer shared memory handle.";
-    return false;
-  }
-
-  ring_buffer_.shared_memory = new base::SharedMemory(shared_memory_handle,
-                                                      false);
-  if (!ring_buffer_.shared_memory->Map(size)) {
-    LOG(ERROR) << "Failed because ring buffer could not be created or mapped ";
-    delete ring_buffer_.shared_memory;
-    ring_buffer_.shared_memory = NULL;
-    return false;
-  }
-
-  ring_buffer_.ptr = ring_buffer_.shared_memory->memory();
-  ring_buffer_.size = size;
-  num_entries_ = size / sizeof(CommandBufferEntry);
-
+bool CommandBufferService::Initialize() {
   return true;
 }
 
-Buffer CommandBufferService::GetRingBuffer() {
-  return ring_buffer_;
-}
-
 CommandBufferService::State CommandBufferService::GetState() {
   State state;
   state.num_entries = num_entries_;
@@ -134,6 +80,20 @@ void CommandBufferService::Flush(int32 put_offset) {
     put_offset_change_callback_.Run();
 }
 
+void CommandBufferService::SetGetBuffer(int32 transfer_buffer_id) {
+  DCHECK_EQ(-1, ring_buffer_id_);
+  DCHECK_EQ(put_offset_, get_offset_);  // Only if it's empty.
+  ring_buffer_ = GetTransferBuffer(transfer_buffer_id);
+  DCHECK(ring_buffer_.ptr);
+  ring_buffer_id_ = transfer_buffer_id;
+  num_entries_ = ring_buffer_.size / sizeof(CommandBufferEntry);
+  put_offset_ = 0;
+  SetGetOffset(0);
+  if (!get_buffer_change_callback_.is_null()) {
+    get_buffer_change_callback_.Run(ring_buffer_id_);
+  }
+}
+
 void CommandBufferService::SetGetOffset(int32 get_offset) {
   DCHECK(get_offset >= 0 && get_offset < num_entries_);
   get_offset_ = get_offset;
@@ -223,6 +183,14 @@ void CommandBufferService::DestroyTransferBuffer(int32 handle) {
   registered_objects_[handle] = Buffer();
   unused_registered_object_elements_.insert(handle);
 
+  if (handle == ring_buffer_id_) {
+    ring_buffer_id_ = -1;
+    ring_buffer_ = Buffer();
+    num_entries_ = 0;
+    get_offset_ = 0;
+    put_offset_ = 0;
+  }
+
   // Remove all null objects from the end of the vector. This allows the vector
   // to shrink when, for example, all objects are unregistered. Note that this
   // loop never removes element zero, which is always NULL.
@@ -266,6 +234,11 @@ void CommandBufferService::SetPutOffsetChangeCallback(
   put_offset_change_callback_ = callback;
 }
 
+void CommandBufferService::SetGetBufferChangeCallback(
+    const GetBufferChangedCallback& callback) {
+  get_buffer_change_callback_ = callback;
+}
+
 void CommandBufferService::SetParseErrorCallback(
     const base::Closure& callback) {
   parse_error_callback_ = callback;
diff --git a/gpu/command_buffer/service/command_buffer_service.h b/gpu/command_buffer/service/command_buffer_service.h
index b48bd90..d7ea6fc 100644
--- a/gpu/command_buffer/service/command_buffer_service.h
+++ b/gpu/command_buffer/service/command_buffer_service.h
@@ -21,17 +21,17 @@ namespace gpu {
 // API to manage the put and get pointers.
 class CommandBufferService : public CommandBuffer {
  public:
+  typedef base::Callback<bool(int32)> GetBufferChangedCallback;
   CommandBufferService();
   virtual ~CommandBufferService();
 
   // CommandBuffer implementation:
-  virtual bool Initialize(int32 size) OVERRIDE;
-  virtual bool Initialize(base::SharedMemory* buffer, int32 size) OVERRIDE;
-  virtual Buffer GetRingBuffer() OVERRIDE;
+  virtual bool Initialize() OVERRIDE;
   virtual State GetState() OVERRIDE;
   virtual State GetLastState() OVERRIDE;
   virtual void Flush(int32 put_offset) OVERRIDE;
   virtual State FlushSync(int32 put_offset, int32 last_known_get) OVERRIDE;
+  virtual void SetGetBuffer(int32 transfer_buffer_id) OVERRIDE;
   virtual void SetGetOffset(int32 get_offset) OVERRIDE;
   virtual int32 CreateTransferBuffer(size_t size, int32 id_request) OVERRIDE;
   virtual int32 RegisterTransferBuffer(base::SharedMemory* shared_memory,
@@ -52,14 +52,19 @@ class CommandBufferService : public CommandBuffer {
   // attempting to write more to the command buffer. Takes ownership of
   // callback.
   virtual void SetPutOffsetChangeCallback(const base::Closure& callback);
+  // Sets a callback that is called whenever the get buffer is changed.
+  virtual void SetGetBufferChangeCallback(
+      const GetBufferChangedCallback& callback);
   virtual void SetParseErrorCallback(const base::Closure& callback);
 
  private:
+  int32 ring_buffer_id_;
   Buffer ring_buffer_;
   int32 num_entries_;
   int32 get_offset_;
   int32 put_offset_;
   base::Closure put_offset_change_callback_;
+  GetBufferChangedCallback get_buffer_change_callback_;
   base::Closure parse_error_callback_;
   std::vector<Buffer> registered_objects_;
   std::set<int32> unused_registered_object_elements_;
diff --git a/gpu/command_buffer/service/common_decoder_unittest.cc b/gpu/command_buffer/service/common_decoder_unittest.cc
index a240948..571ffa0 100644
--- a/gpu/command_buffer/service/common_decoder_unittest.cc
+++ b/gpu/command_buffer/service/common_decoder_unittest.cc
@@ -116,6 +116,12 @@ class MockCommandBufferEngine : public CommandBufferEngine {
   }
 
   // Overridden from CommandBufferEngine.
+  virtual bool SetGetBuffer(int32 transfer_buffer_id) {
+    NOTREACHED();
+    return false;
+  }
+
+  // Overridden from CommandBufferEngine.
   virtual bool SetGetOffset(int32 offset) {
     if (static_cast<size_t>(offset) < kBufferSize) {
       get_offset_ = offset;
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_unittest_base.h b/gpu/command_buffer/service/gles2_cmd_decoder_unittest_base.h
index 92abfc0..a57df77 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_unittest_base.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_unittest_base.h
@@ -431,6 +431,11 @@ class GLES2DecoderTestBase : public testing::Test {
       DCHECK(false);
     }
 
+    virtual bool SetGetBuffer(int32 /* transfer_buffer_id */) OVERRIDE {
+      DCHECK(false);
+      return false;
+    }
+
     // Overridden from CommandBufferEngine.
     virtual bool SetGetOffset(int32 offset) OVERRIDE {
       DCHECK(false);
diff --git a/gpu/command_buffer/service/gpu_scheduler.cc b/gpu/command_buffer/service/gpu_scheduler.cc
index f37c1a0..610f401 100644
--- a/gpu/command_buffer/service/gpu_scheduler.cc
+++ b/gpu/command_buffer/service/gpu_scheduler.cc
@@ -29,21 +29,6 @@ GpuScheduler::GpuScheduler(CommandBuffer* command_buffer,
       decoder_(decoder),
       parser_(parser),
       unscheduled_count_(0) {
-  // Map the ring buffer and create the parser.
-  if (!parser) {
-    Buffer ring_buffer = command_buffer_->GetRingBuffer();
-    if (ring_buffer.ptr) {
-      parser_.reset(new CommandParser(ring_buffer.ptr,
-                                      ring_buffer.size,
-                                      0,
-                                      ring_buffer.size,
-                                      0,
-                                      decoder_));
-    } else {
-      parser_.reset(new CommandParser(NULL, 0, 0, 0, 0,
-                                      decoder_));
-    }
-  }
 }
 
 GpuScheduler::~GpuScheduler() {
@@ -150,6 +135,26 @@ void GpuScheduler::set_token(int32 token) {
   command_buffer_->SetToken(token);
 }
 
+bool GpuScheduler::SetGetBuffer(int32 transfer_buffer_id) {
+  Buffer ring_buffer = command_buffer_->GetTransferBuffer(transfer_buffer_id);
+  if (!ring_buffer.ptr) {
+    return false;
+  }
+
+  if (!parser_.get()) {
+    parser_.reset(new CommandParser(decoder_));
+  }
+
+  parser_->SetBuffer(
+      ring_buffer.ptr,
+      ring_buffer.size,
+      0,
+      ring_buffer.size);
+
+  SetGetOffset(0);
+  return true;
+}
+
 bool GpuScheduler::SetGetOffset(int32 offset) {
   if (parser_->set_get(offset)) {
     command_buffer_->SetGetOffset(static_cast<int32>(parser_->get()));
diff --git a/gpu/command_buffer/service/gpu_scheduler.h b/gpu/command_buffer/service/gpu_scheduler.h
index 5256e49..9b7d9cd 100644
--- a/gpu/command_buffer/service/gpu_scheduler.h
+++ b/gpu/command_buffer/service/gpu_scheduler.h
@@ -51,6 +51,7 @@ class GpuScheduler
   // Implementation of CommandBufferEngine.
   virtual Buffer GetSharedMemoryBuffer(int32 shm_id) OVERRIDE;
   virtual void set_token(int32 token) OVERRIDE;
+  virtual bool SetGetBuffer(int32 transfer_buffer_id) OVERRIDE;
   virtual bool SetGetOffset(int32 offset) OVERRIDE;
   virtual int32 GetGetOffset() OVERRIDE;
 
diff --git a/gpu/command_buffer/service/gpu_scheduler_unittest.cc b/gpu/command_buffer/service/gpu_scheduler_unittest.cc
index 2d230ec..cf881e6 100644
--- a/gpu/command_buffer/service/gpu_scheduler_unittest.cc
+++ b/gpu/command_buffer/service/gpu_scheduler_unittest.cc
@@ -30,6 +30,8 @@ const size_t kRingBufferEntries = kRingBufferSize / sizeof(CommandBufferEntry);
 
 class GpuSchedulerTest : public testing::Test {
  protected:
+  static const int32 kTransferBufferId = 123;
+
   virtual void SetUp() {
     shared_memory_.reset(new ::base::SharedMemory);
     shared_memory_->CreateAndMapAnonymous(kRingBufferSize);
@@ -39,28 +41,20 @@ class GpuSchedulerTest : public testing::Test {
     memset(buffer_, 0, kRingBufferSize);
 
     command_buffer_.reset(new MockCommandBuffer);
-    ON_CALL(*command_buffer_.get(), GetRingBuffer())
-      .WillByDefault(Return(shared_memory_buffer_));
 
     CommandBuffer::State default_state;
     default_state.num_entries = kRingBufferEntries;
     ON_CALL(*command_buffer_.get(), GetState())
       .WillByDefault(Return(default_state));
 
-    async_api_.reset(new StrictMock<AsyncAPIMock>);
-
     decoder_.reset(new gles2::MockGLES2Decoder());
-
-    parser_ = new CommandParser(buffer_,
-                                kRingBufferEntries,
-                                0,
-                                kRingBufferEntries,
-                                0,
-                                async_api_.get());
-
     scheduler_.reset(new gpu::GpuScheduler(command_buffer_.get(),
                                            decoder_.get(),
-                                           parser_));
+                                           NULL));
+    EXPECT_CALL(*command_buffer_, GetTransferBuffer(kTransferBufferId))
+       .WillOnce(Return(shared_memory_buffer_));
+    EXPECT_CALL(*command_buffer_, SetGetOffset(0));
+    EXPECT_TRUE(scheduler_->SetGetBuffer(kTransferBufferId));
   }
 
   virtual void TearDown() {
@@ -82,8 +76,6 @@ class GpuSchedulerTest : public testing::Test {
   Buffer shared_memory_buffer_;
   int32* buffer_;
   scoped_ptr<gles2::MockGLES2Decoder> decoder_;
-  CommandParser* parser_;
-  scoped_ptr<AsyncAPIMock> async_api_;
   scoped_ptr<GpuScheduler> scheduler_;
 };
 
@@ -100,6 +92,24 @@ TEST_F(GpuSchedulerTest, SchedulerDoesNothingIfRingBufferIsEmpty) {
   scheduler_->PutChanged();
 }
 
+TEST_F(GpuSchedulerTest, GetSetBuffer) {
+  CommandBuffer::State state;
+
+  // Set the get offset to something not 0.
+  EXPECT_CALL(*command_buffer_, SetGetOffset(2));
+  scheduler_->SetGetOffset(2);
+  EXPECT_EQ(2, scheduler_->GetGetOffset());
+
+  // Set the buffer.
+  EXPECT_CALL(*command_buffer_, GetTransferBuffer(kTransferBufferId))
+     .WillOnce(Return(shared_memory_buffer_));
+  EXPECT_CALL(*command_buffer_, SetGetOffset(0));
+  EXPECT_TRUE(scheduler_->SetGetBuffer(kTransferBufferId));
+
+  // Check the get offset was reset.
+  EXPECT_EQ(0, scheduler_->GetGetOffset());
+}
+
 TEST_F(GpuSchedulerTest, ProcessesOneCommand) {
   CommandHeader* header = reinterpret_cast<CommandHeader*>(&buffer_[0]);
   header[0].command = 7;
@@ -113,7 +123,7 @@ TEST_F(GpuSchedulerTest, ProcessesOneCommand) {
     .WillRepeatedly(Return(state));
   EXPECT_CALL(*command_buffer_, SetGetOffset(2));
 
-  EXPECT_CALL(*async_api_, DoCommand(7, 1, &buffer_[0]))
+  EXPECT_CALL(*decoder_, DoCommand(7, 1, &buffer_[0]))
     .WillOnce(Return(error::kNoError));
 
   EXPECT_CALL(*command_buffer_, SetParseError(_))
@@ -136,11 +146,11 @@ TEST_F(GpuSchedulerTest, ProcessesTwoCommands) {
   EXPECT_CALL(*command_buffer_, GetState())
     .WillRepeatedly(Return(state));
 
-  EXPECT_CALL(*async_api_, DoCommand(7, 1, &buffer_[0]))
+  EXPECT_CALL(*decoder_, DoCommand(7, 1, &buffer_[0]))
     .WillOnce(Return(error::kNoError));
   EXPECT_CALL(*command_buffer_, SetGetOffset(2));
 
-  EXPECT_CALL(*async_api_, DoCommand(8, 0, &buffer_[2]))
+  EXPECT_CALL(*decoder_, DoCommand(8, 0, &buffer_[2]))
     .WillOnce(Return(error::kNoError));
   EXPECT_CALL(*command_buffer_, SetGetOffset(3));
 
@@ -158,11 +168,12 @@ TEST_F(GpuSchedulerTest, SetsErrorCodeOnCommandBuffer) {
   EXPECT_CALL(*command_buffer_, GetState())
     .WillRepeatedly(Return(state));
 
-  EXPECT_CALL(*async_api_, DoCommand(7, 0, &buffer_[0]))
+  EXPECT_CALL(*decoder_, DoCommand(7, 0, &buffer_[0]))
     .WillOnce(Return(
         error::kUnknownCommand));
   EXPECT_CALL(*command_buffer_, SetGetOffset(1));
 
+  EXPECT_CALL(*command_buffer_, SetContextLostReason(_));
   EXPECT_CALL(*decoder_, GetContextLostReason())
     .WillOnce(Return(error::kUnknown));
   EXPECT_CALL(*command_buffer_,
diff --git a/gpu/demos/framework/window.cc b/gpu/demos/framework/window.cc
index 526f9da..48ed58c 100644
--- a/gpu/demos/framework/window.cc
+++ b/gpu/demos/framework/window.cc
@@ -54,7 +54,7 @@ void Window::OnPaint() {
 
 bool Window::CreateRenderContext(gfx::PluginWindowHandle hwnd) {
   command_buffer_.reset(new CommandBufferService);
-  if (!command_buffer_->Initialize(kCommandBufferSize)) {
+  if (!command_buffer_->Initialize()) {
     return false;
   }
 
diff --git a/gpu/gles2_conform_support/egl/display.cc b/gpu/gles2_conform_support/egl/display.cc
index 18c9727..928d5fd 100644
--- a/gpu/gles2_conform_support/egl/display.cc
+++ b/gpu/gles2_conform_support/egl/display.cc
@@ -32,7 +32,7 @@ Display::~Display() {
 bool Display::Initialize() {
   scoped_ptr<gpu::CommandBufferService> command_buffer(
       new gpu::CommandBufferService);
-  if (!command_buffer->Initialize(kCommandBufferSize))
+  if (!command_buffer->Initialize())
     return false;
 
   int32 transfer_buffer_id =