Add helper classes to for managing shared buffers.

mojo/services/media/common/cpp/mapped_shared_buffer.cc

Index: mojo/services/media/common/cpp/mapped_shared_buffer.cc
diff --git a/mojo/services/media/common/cpp/mapped_shared_buffer.cc b/mojo/services/media/common/cpp/mapped_shared_buffer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..db2de1de164c039abb96366d5b9f61b75159674d
--- /dev/null
+++ b/mojo/services/media/common/cpp/mapped_shared_buffer.cc
@@ -0,0 +1,101 @@
+// Copyright 2015 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.
+
+#include <cassert>

[johngro, 2015/12/05 00:45:55]

same comment as in the previous file, MOJO_DCHECK instead of assert

[dalesat, 2015/12/07 18:30:20]

Done.

+
+#include "mojo/services/media/common/cpp/mapped_shared_buffer.h"
+
+namespace mojo {
+namespace media {
+
+MappedSharedBuffer::MappedSharedBuffer() {}
+
+MappedSharedBuffer::~MappedSharedBuffer() {}
+
+void MappedSharedBuffer::InitNew(uint64_t size) {
+  assert(size > 0);
+
+  buffer_.reset(new SharedBuffer(size));
+  handle_.reset();
+
+  InitInternal(buffer_->handle, size);
+}
+
+void MappedSharedBuffer::InitFromHandle(
+    ScopedSharedBufferHandle handle,
+    uint64_t size) {
+  assert(handle.is_valid());
+  assert(size > 0);
+
+  buffer_.reset();
+  handle_ = handle.Pass();
+
+  InitInternal(handle_, size);
+}
+
+void MappedSharedBuffer::InitInternal(
+    ScopedSharedBufferHandle& handle,
+    uint64_t size) {
+  assert(handle.is_valid());
+  assert(size > 0);
+
+  size_ = size;
+  buffer_ptr_.reset();
+
+  void* ptr;
+  auto result = MapBuffer(
+      handle.get(),
+      0, // offset
+      size,
+      &ptr,
+      MOJO_MAP_BUFFER_FLAG_NONE);
+  assert(result == MOJO_RESULT_OK);
+  assert(ptr);
+
+  buffer_ptr_.reset(reinterpret_cast<uint8_t*>(ptr));
+
+  OnInit();
+}
+
+bool MappedSharedBuffer::initialized() {
+  return buffer_ptr_ != nullptr;
+}
+
+uint64_t MappedSharedBuffer::size() {
+  return size_;
+}
+
+ScopedSharedBufferHandle MappedSharedBuffer::GetDuplicateHandle() {
+  assert(initialized());
+  ScopedSharedBufferHandle handle;
+  // TODO: We should create a read-only duplicate of the handle.

[johngro, 2015/12/05 00:45:55]

TODO(dalesat)

[dalesat, 2015/12/07 18:30:20]

Removed. Also added a check so this works when InitFromHandle is used.

+  DuplicateBuffer(buffer_->handle.get(), nullptr, &handle);
+  return handle.Pass();
+}
+
+void* MappedSharedBuffer::PtrFromOffset(uint64_t offset) {
+  assert(buffer_ptr_);
+
+  if (offset == FifoAllocator::kNullOffset) {
+    return nullptr;
+  }
+
+  assert(offset < size_);
+  return buffer_ptr_.get() + offset;
+}
+
+uint64_t MappedSharedBuffer::OffsetFromPtr(void *ptr) {
+  assert(buffer_ptr_);
+  if (ptr == nullptr) {
+    return FifoAllocator::kNullOffset;
+  }
+  uint64_t offset = reinterpret_cast<uint8_t*>(ptr) - buffer_ptr_.get();
+  assert(offset < size_);
+  return offset;
+}
+
+void MappedSharedBuffer::OnInit() {}
+
+} // namespace media
+} // namespace mojo