dnn: configure plugin path for InferenceEngine

modules/dnn/src/op_inf_engine.cpp

@@ -409,6 +409,14 @@ void InfEngineBackendNet::initPlugin(InferenceEngine::ICNNNetwork& net)
                 enginePtr = dispatcher.getSuitablePlugin(targetDevice);
             sharedPlugins[targetDevice] = enginePtr;
 
+            std::vector<std::string> candidates;
+
+            std::string param_pluginPath = utils::getConfigurationParameterString("OPENCV_DNN_IE_EXTRA_PLUGIN_PATH", "");
+            if (!param_pluginPath.empty())
+            {
+                candidates.push_back(param_pluginPath);
+            }
+
             if (targetDevice == InferenceEngine::TargetDevice::eCPU ||
                 targetDevice == InferenceEngine::TargetDevice::eFPGA)
             {
@@ -422,24 +430,36 @@ void InfEngineBackendNet::initPlugin(InferenceEngine::ICNNNetwork& net)
                 {
                     if (!haveFeature[i])
                         continue;
-    #ifdef _WIN32
-                    std::string libName = "cpu_extension" + suffixes[i] + ".dll";
-    #elif defined(__APPLE__)
-                    std::string libName = "libcpu_extension" + suffixes[i] + ".dylib";
-    #else
-                    std::string libName = "libcpu_extension" + suffixes[i] + ".so";
-    #endif  // _WIN32
-                    try
-                    {
-                        InferenceEngine::IExtensionPtr extension =
-                            InferenceEngine::make_so_pointer<InferenceEngine::IExtension>(libName);
-                        enginePtr->AddExtension(extension, 0);
-                        break;
-                    }
-                    catch(...) {}
+#ifdef _WIN32
+                    candidates.push_back("cpu_extension" + suffixes[i] + ".dll");
+#elif defined(__APPLE__)
+                    candidates.push_back("libcpu_extension" + suffixes[i] + ".so");  // built as loadable module
+                    candidates.push_back("libcpu_extension" + suffixes[i] + ".dylib");  // built as shared library
+#else
+                    candidates.push_back("libcpu_extension" + suffixes[i] + ".so");
+#endif  // _WIN32
                 }
-                // Some of networks can work without a library of extra layers.
             }
+            bool found = false;
+            for (size_t i = 0; i != candidates.size(); ++i)
+            {
+                const std::string& libName = candidates[i];
+                try
+                {
+                    InferenceEngine::IExtensionPtr extension =
+                        InferenceEngine::make_so_pointer<InferenceEngine::IExtension>(libName);
+                    enginePtr->AddExtension(extension, 0);
+                    CV_LOG_INFO(NULL, "DNN-IE: Loaded extension plugin: " << libName);
+                    found = true;
+                    break;
+                }
+                catch(...) {}
+            }
+            if (!found && !candidates.empty())
+            {
+                CV_LOG_WARNING(NULL, "DNN-IE: Can't load extension plugin (extra layers for some networks). Specify path via OPENCV_DNN_IE_EXTRA_PLUGIN_PATH parameter");
+            }
+            // Some of networks can work without a library of extra layers.
         }
         plugin = InferenceEngine::InferencePlugin(enginePtr);