fix optimizer bug in CPP-Package

Jenkinsfile

@@ -314,6 +314,7 @@ try {
           make('build_cuda', flag)
           pack_lib('gpu')
           stash includes: 'build/cpp-package/example/test_score', name: 'cpp_test_score'
+          stash includes: 'build/cpp-package/example/test_optimizer', name: 'cpp_test_optimizer'
         }
       }
     },
@@ -658,6 +659,7 @@ try {
           init_git()
           unpack_lib('gpu')
           unstash 'cpp_test_score'
+          unstash 'cpp_test_optimizer'
           timeout(time: max_time, unit: 'MINUTES') {
             sh "${docker_run} gpu --dockerbinary nvidia-docker cpp-package/tests/ci_test.sh"
           }

cpp-package/example/test_optimizer.cpp

@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+#include "mxnet-cpp/MxNetCpp.h"
+
+using namespace std;
+using namespace mxnet::cpp;
+
+int main(int argc, char** argv) {
+  // Confirm >1 optimizers can be created w/o error
+  Optimizer* opt = OptimizerRegistry::Find("sgd");
+  opt = OptimizerRegistry::Find("adam");
+  int ret = (opt == 0) ? 1 : 0;
+
+  MXNotifyShutdown();
+  return ret;
+}

cpp-package/include/mxnet-cpp/optimizer.hpp

@@ -125,13 +125,16 @@ inline float Optimizer::GetWD_(int index) {
 }
 
 inline Optimizer* OptimizerRegistry::Find(const std::string& name) {
-  MXNETCPP_REGISTER_OPTIMIZER(sgd, SGDOptimizer);
-  MXNETCPP_REGISTER_OPTIMIZER(ccsgd, SGDOptimizer);  // For backward compatibility
-  MXNETCPP_REGISTER_OPTIMIZER(rmsprop, RMSPropOptimizer);
-  MXNETCPP_REGISTER_OPTIMIZER(adam, AdamOptimizer);
-  MXNETCPP_REGISTER_OPTIMIZER(adagrad, AdaGradOptimizer);
-  MXNETCPP_REGISTER_OPTIMIZER(adadelta, AdaDeltaOptimizer);
-  MXNETCPP_REGISTER_OPTIMIZER(signum, SignumOptimizer);
+  if (cmap().empty()) {
+    // Optimizers should only be registered once
+    MXNETCPP_REGISTER_OPTIMIZER(sgd, SGDOptimizer);
+    MXNETCPP_REGISTER_OPTIMIZER(ccsgd, SGDOptimizer);  // For backward compatibility
+    MXNETCPP_REGISTER_OPTIMIZER(rmsprop, RMSPropOptimizer);
+    MXNETCPP_REGISTER_OPTIMIZER(adam, AdamOptimizer);
+    MXNETCPP_REGISTER_OPTIMIZER(adagrad, AdaGradOptimizer);
+    MXNETCPP_REGISTER_OPTIMIZER(adadelta, AdaDeltaOptimizer);
+    MXNETCPP_REGISTER_OPTIMIZER(signum, SignumOptimizer);
+  }
   auto it = cmap().find(name);
   if (it == cmap().end())
     return nullptr;

cpp-package/tests/ci_test.sh

@@ -22,6 +22,9 @@ export LD_LIBRARY_PATH=$(readlink -f ../../lib):$LD_LIBRARY_PATH
 echo $LD_LIBRARY_PATH
 ls -l ../../lib/
 
+cp ../../build/cpp-package/example/test_optimizer .
+./test_optimizer
+
 cp ../../build/cpp-package/example/test_score .
 ./get_mnist.sh
 ./test_score 0.93