Reduce allocations associated with src/cpp/util/byte_buffer.cc.

1 files changed, 19 insertions, 6 deletions

diff --git a/src/cpp/util/byte_buffer.cc b/src/cpp/util/byte_buffer.cc
index c2cd20ee07..4c4772a92b 100644
--- a/src/cpp/util/byte_buffer.cc
+++ b/src/cpp/util/byte_buffer.cc
@@ -37,12 +37,19 @@
 namespace grpc {
 
 ByteBuffer::ByteBuffer(const Slice* slices, size_t nslices) {
-  // TODO(yangg) maybe expose some core API to simplify this
-  std::vector<gpr_slice> c_slices(nslices);
-  for (size_t i = 0; i < nslices; i++) {
-    c_slices[i] = slices[i].slice_;
-  }
-  buffer_ = grpc_raw_byte_buffer_create(c_slices.data(), nslices);
+  // The following assertions check that the representation of a grpc::Slice is
+  // identical to that of a gpr_slice:  it has a gpr_slice field, and nothing
+  // else.
+  static_assert(std::is_same<decltype(slices[0].slice_), gpr_slice>::value,
+                "Slice must have same representation as gpr_slice");
+  static_assert(sizeof(Slice) == sizeof(gpr_slice),
+                "Slice must have same representation as gpr_slice");
+  // The const_cast is legal if grpc_raw_byte_buffer_create() does no more
+  // than its advertised side effect of increasing the reference count of the
+  // slices it processes, and such an increase does not affect the semantics
+  // seen by the caller of this constructor.
+  buffer_ = grpc_raw_byte_buffer_create(
+      reinterpret_cast<gpr_slice*>(const_cast<Slice*>(slices)), nslices);
 }
 
 ByteBuffer::~ByteBuffer() {
@@ -95,4 +102,10 @@ ByteBuffer& ByteBuffer::operator=(const ByteBuffer& buf) {
   return *this;
 }
 
+void ByteBuffer::Swap(ByteBuffer* other) {
+  grpc_byte_buffer* tmp = other->buffer_;
+  other->buffer_ = this->buffer_;
+  this->buffer_ = tmp;
+}
+
 }  // namespace grpc