Go: Provide a mechanism to configure the Session.

A Session is configured using the ConfigProto protocol buffer.
For now, continuing with attempts to keep the 'tensorflow' go package
free of any protocol buffer dependencies, SessionOptions uses a serialized
representation of this message. This choice might make sense to revisit.
Change: 148750535

tensorflow/go/saved_model.go

@@ -45,7 +45,11 @@ type SavedModel struct {
 // https://www.tensorflow.org/code/tensorflow/python/saved_model/
 func LoadSavedModel(exportDir string, tags []string, options *SessionOptions) (*SavedModel, error) {
 	status := newStatus()
-	cOpt := options.c()
+	cOpt, doneOpt, err := options.c()
+	defer doneOpt()
+	if err != nil {
+		return nil, err
+	}
 	cExportDir := C.CString(exportDir)
 	cTags := make([]*C.char, len(tags))
 	for i := range tags {
@@ -58,7 +62,6 @@ func LoadSavedModel(exportDir string, tags []string, options *SessionOptions) (*
 		C.free(unsafe.Pointer(cTags[i]))
 	}
 	C.free(unsafe.Pointer(cExportDir))
-	C.TF_DeleteSessionOptions(cOpt)
 
 	if err := status.Err(); err != nil {
 		return nil, err

tensorflow/go/session.go

@@ -20,6 +20,7 @@ import "C"
 
 import (
 	"errors"
+	"fmt"
 	"runtime"
 	"sync"
 	"unsafe"
@@ -47,9 +48,12 @@ type Session struct {
 // options may be nil to use the default options.
 func NewSession(graph *Graph, options *SessionOptions) (*Session, error) {
 	status := newStatus()
-	cOpt := options.c()
+	cOpt, doneOpt, err := options.c()
+	defer doneOpt()
+	if err != nil {
+		return nil, err
+	}
 	cSess := C.TF_NewSession(graph.c, cOpt, status.c)
-	C.TF_DeleteSessionOptions(cOpt)
 	if err := status.Err(); err != nil {
 		return nil, err
 	}
@@ -243,19 +247,42 @@ type SessionOptions struct {
 	// If the session disconnects from the remote process during its
 	// lifetime, session calls may fail immediately.
 	Target string
+
+	// Config is a binary-serialized representation of the
+	// tensorflow.ConfigProto protocol message
+	// (https://www.tensorflow.org/code/tensorflow/core/protobuf/config.proto).
+	Config []byte
 }
 
 // c converts the SessionOptions to the C API's TF_SessionOptions. Callers must
-// deallocate by calling C.TF_DeleteSessionOptions().
-func (o *SessionOptions) c() *C.TF_SessionOptions {
+// deallocate by calling the returned done() closure.
+func (o *SessionOptions) c() (ret *C.TF_SessionOptions, done func(), err error) {
 	opt := C.TF_NewSessionOptions()
 	if o == nil {
-		return opt
+		return opt, func() { C.TF_DeleteSessionOptions(opt) }, nil
 	}
 	t := C.CString(o.Target)
 	C.TF_SetTarget(opt, t)
 	C.free(unsafe.Pointer(t))
-	return opt
+
+	var cConfig unsafe.Pointer
+	if sz := len(o.Config); sz > 0 {
+		status := newStatus()
+		// Copying into C-memory is the simplest thing to do in terms
+		// of memory safety and cgo rules ("C code may not keep a copy
+		// of a Go pointer after the call returns" from
+		// https://golang.org/cmd/cgo/#hdr-Passing_pointers).
+		cConfig = C.CBytes(o.Config)
+		C.TF_SetConfig(opt, cConfig, C.size_t(sz), status.c)
+		if err := status.Err(); err != nil {
+			C.TF_DeleteSessionOptions(opt)
+			return nil, func() {}, fmt.Errorf("invalid SessionOptions.Config: %v", err)
+		}
+	}
+	return opt, func() {
+		C.TF_DeleteSessionOptions(opt)
+		C.free(cConfig)
+	}, nil
 }
 
 // cRunArgs translates the arguments to Session.Run and PartialRun.Run into

tensorflow/go/session_test.go

@@ -246,3 +246,38 @@ func ExamplePartialRun() {
 	fmt.Println(v1, v2)
 	// Output: 3 10
 }
+
+func TestSessionConfig(t *testing.T) {
+	// Exercise SessionOptions.
+	// Arguably, a better API would be for SessionOptions.Config to be the
+	// type generated by the protocol buffer compiler. But for now, the
+	// tensorflow package continues to be independent of protocol buffers
+	// and this test exercises the option since the implementation has a
+	// nuanced conversion to C types.
+	//
+	// Till then, the []byte form of Config here was generated using a toy
+	// tensorflow Python program:
+	/*
+	 import tensorflow
+	 c = tensorflow.ConfigProto()
+	 c.intra_op_parallelism_threads = 1
+	 print c.SerializeToString()
+	*/
+	graph := NewGraph()
+	c, err := Const(graph, "Const", int32(14))
+	if err != nil {
+		t.Fatal(err)
+	}
+	opts := SessionOptions{Config: []byte("(\x01")}
+	s, err := NewSession(graph, &opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+	output, err := s.Run(nil, []Output{c}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if output[0].Value().(int32) != 14 {
+		t.Fatalf("Got %v, want -1", output[0].Value())
+	}
+}