Several small changes to reduce the number of memory allocations along

Send/Recv paths:

o Allow SendOp and RecvOp implementations to directly use the string buffer
contained in a Rendezvous::ParsedKey object, rather than allocating their
own string object.  Saves two allocations per Send/Recv pair.

o Use std::move in a few places to avoid copying a std::function object.

o Eliminated unused ParsedName variable declaration in
DeviceNameUtils::ParseLocalName.
Change: 127630066

5 files changed, 28 insertions, 20 deletions

diff --git a/tensorflow/core/common_runtime/device.h b/tensorflow/core/common_runtime/device.h
index f70fd986ef..0057c3c609 100644
--- a/tensorflow/core/common_runtime/device.h
+++ b/tensorflow/core/common_runtime/device.h
@@ -85,7 +85,7 @@ class Device : public DeviceBase {
   // Asynchronous kernel's compute.
   virtual void ComputeAsync(AsyncOpKernel* op_kernel, OpKernelContext* context,
                             AsyncOpKernel::DoneCallback done) {
-    op_kernel->ComputeAsync(context, done);
+    op_kernel->ComputeAsync(context, std::move(done));
   }
 
   // Takes ownership of the references in tensors. If necessary, a
diff --git a/tensorflow/core/framework/rendezvous.cc b/tensorflow/core/framework/rendezvous.cc
index 715397e6d6..45a30319ab 100644
--- a/tensorflow/core/framework/rendezvous.cc
+++ b/tensorflow/core/framework/rendezvous.cc
@@ -81,8 +81,16 @@ static StringPiece ConsumeNextPart(StringPiece* s, char delim) {
 }
 
 /* static */
-Status Rendezvous::ParseKey(const string& key, ParsedKey* out) {
-  out->buf_ = key;  // Make a copy that our StringPieces can point at
+Status Rendezvous::ParseKey(StringPiece key, ParsedKey* out) {
+  if (key.data() == out->buf_.data()) {
+    // Caller used our buf_ string directly, so we don't need to copy.  (The
+    // SendOp and RecvOp implementations do this, for example).
+    DCHECK_EQ(key.size(), out->buf_.size());
+  } else {
+    // Make a copy that our StringPieces can point at a copy that will persist
+    // for the lifetime of the ParsedKey object.
+    out->buf_.assign(key.data(), key.size());
+  }
   StringPiece s(out->buf_);
   StringPiece parts[5];
   for (int i = 0; i < 5; i++) {
@@ -99,7 +107,7 @@ Status Rendezvous::ParseKey(const string& key, ParsedKey* out) {
     out->edge_name.set(parts[3].data(), parts[3].size());
     return Status::OK();
   }
-  return errors::InvalidArgument("Invalid rendezvous key: ", key);
+  return errors::InvalidArgument("Invalid  rendezvous key: ", key);
 }
 
 Rendezvous::~Rendezvous() {}
diff --git a/tensorflow/core/framework/rendezvous.h b/tensorflow/core/framework/rendezvous.h
index 17cae35155..ff13dc5f41 100644
--- a/tensorflow/core/framework/rendezvous.h
+++ b/tensorflow/core/framework/rendezvous.h
@@ -69,9 +69,11 @@ class Rendezvous : public core::RefCounted {
 
    private:
     friend class Rendezvous;
+    friend class SendOp;
+    friend class RecvOp;
     string buf_;
   };
-  static Status ParseKey(const string& key, ParsedKey* out);
+  static Status ParseKey(StringPiece key, ParsedKey* out);
 
   // The caller is a tensor producer and it sends a message (a tensor
   // "val" and a bool "is_dead") under the given "key".
diff --git a/tensorflow/core/kernels/sendrecv_ops.cc b/tensorflow/core/kernels/sendrecv_ops.cc
index 613aaecabb..06b6060607 100644
--- a/tensorflow/core/kernels/sendrecv_ops.cc
+++ b/tensorflow/core/kernels/sendrecv_ops.cc
@@ -58,12 +58,11 @@ void SendOp::Compute(OpKernelContext* ctx) {
   OP_REQUIRES(
       ctx, ctx->rendezvous() != nullptr,
       errors::Internal("Op kernel context needs to provide a rendezvous."));
-  string key;
-  GetRendezvousKey(key_prefix_, ctx->frame_iter(), &key);
-  VLOG(2) << "Send " << key;
-
   Rendezvous::ParsedKey parsed;
-  OP_REQUIRES_OK(ctx, Rendezvous::ParseKey(key, &parsed));
+  GetRendezvousKey(key_prefix_, ctx->frame_iter(), &parsed.buf_);
+  VLOG(2) << "Send " << parsed.buf_;
+
+  OP_REQUIRES_OK(ctx, Rendezvous::ParseKey(parsed.buf_, &parsed));
 
   // The device context may be passed between the Send/Recv
   // boundary, so that the device context used to produce the Tensor
@@ -102,21 +101,21 @@ void RecvOp::ComputeAsync(OpKernelContext* ctx, DoneCallback done) {
   OP_REQUIRES(
       ctx, ctx->rendezvous() != nullptr,
       errors::Internal("Op kernel context needs to provide a rendezvous."));
-  string key;
-  GetRendezvousKey(key_prefix_, ctx->frame_iter(), &key);
-  VLOG(2) << "Recv " << key;
-
   Rendezvous::ParsedKey parsed;
-  OP_REQUIRES_OK_ASYNC(ctx, Rendezvous::ParseKey(key, &parsed), done);
+  GetRendezvousKey(key_prefix_, ctx->frame_iter(), &parsed.buf_);
+  VLOG(2) << "Recv " << parsed.buf_;
+
+  OP_REQUIRES_OK_ASYNC(ctx, Rendezvous::ParseKey(parsed.buf_, &parsed), done);
 
   Rendezvous::Args args;
   args.device_context = ctx->op_device_context();
   args.alloc_attrs = ctx->output_alloc_attr(0);
+  DoneCallback done_cb = std::move(done);
   ctx->rendezvous()->RecvAsync(
       parsed, args,
-      [ctx, done](const Status& s, const Rendezvous::Args& send_args,
-                  const Rendezvous::Args& recv_args, const Tensor& val,
-                  bool is_dead) {
+      [ctx, done_cb](const Status& s, const Rendezvous::Args& send_args,
+                     const Rendezvous::Args& recv_args, const Tensor& val,
+                     bool is_dead) {
         ctx->SetStatus(s);
         if (s.ok()) {
           // 'ctx' allocates the output tensor of the expected type.  The
@@ -126,7 +125,7 @@ void RecvOp::ComputeAsync(OpKernelContext* ctx, DoneCallback done) {
           }
           *ctx->is_output_dead() = is_dead;
         }
-        done();
+        done_cb();
       });
 }
 
diff --git a/tensorflow/core/util/device_name_utils.cc b/tensorflow/core/util/device_name_utils.cc
index 5816dbd40c..c38b5758fa 100644
--- a/tensorflow/core/util/device_name_utils.cc
+++ b/tensorflow/core/util/device_name_utils.cc
@@ -336,7 +336,6 @@ string DeviceNameUtils::LocalName(StringPiece fullname) {
 
 /* static */
 bool DeviceNameUtils::ParseLocalName(StringPiece name, ParsedName* p) {
-  ParsedName x;
   if (!ConsumeDeviceType(&name, &p->type)) {
     return false;
   }