Add option to use RTLD_NODELETE when loading a library

loader/include/gz/plugin/Loader.hh

@@ -133,6 +133,18 @@ namespace gz
       public: std::unordered_set<std::string> LoadLib(
                   const std::string &_pathToLibrary);
 
+
+      /// \brief Load a library at the given path
+      ///
+      /// \param[in] _pathToLibrary
+      ///   The path to a library
+      /// \param[in] _noDelete
+      ///   If true, RTLD_NODELETE will be used when loading the library.
+      ///
+      /// \returns The set of plugins that have been loaded from the library
+      public: std::unordered_set<std::string> LoadLib(
+                  const std::string &_pathToLibrary, bool _noDelete);
+
       /// \brief Instantiates a plugin for the given plugin name
       ///
       /// \param[in] _pluginNameOrAlias

loader/src/Loader.cc

@@ -46,7 +46,7 @@ namespace gz
       /// \return If a library exists at the given path, get a point to its dl
       /// handle. If the library does not exist, get a nullptr.
       public: std::shared_ptr<void> LoadLib(
-        const std::string &_pathToLibrary);
+        const std::string &_pathToLibrary, bool _noDelete);
 
       /// \brief Using a dl handle produced by LoadLib, extract the
       /// Info from the loaded library.
@@ -139,12 +139,18 @@ namespace gz
     /////////////////////////////////////////////////
     std::unordered_set<std::string> Loader::LoadLib(
         const std::string &_pathToLibrary)
+    {
+      return this->LoadLib(_pathToLibrary, false);
+    }
+    /////////////////////////////////////////////////
+    std::unordered_set<std::string> Loader::LoadLib(
+        const std::string &_pathToLibrary, bool _noDelete)
     {
       std::unordered_set<std::string> newPlugins;
 
       // Attempt to load the library at this path
       const std::shared_ptr<void> &dlHandle =
-          this->dataPtr->LoadLib(_pathToLibrary);
+          this->dataPtr->LoadLib(_pathToLibrary, _noDelete);
 
       // Quit early and return an empty set of plugin names if we did not
       // actually get a valid dlHandle.
@@ -420,7 +426,7 @@ namespace gz
 
     /////////////////////////////////////////////////
     std::shared_ptr<void> Loader::Implementation::LoadLib(
-        const std::string &_full_path)
+        const std::string &_full_path, bool _noDelete)
     {
       std::shared_ptr<void> dlHandlePtr;
 
@@ -431,7 +437,14 @@ namespace gz
 
       // NOTE: We open using RTLD_LOCAL instead of RTLD_GLOBAL to prevent the
       // symbols of different libraries from writing over each other.
-      void *dlHandle = dlopen(_full_path.c_str(), RTLD_LAZY | RTLD_LOCAL);
+#ifdef _WIN32
+      // RTLD_NODELETE is not defined in dlfcn-32.
+      (void) _noDelete;
+      int dlopenMode = RTLD_LAZY | RTLD_LOCAL;
+#else
+      int dlopenMode = RTLD_LAZY | RTLD_LOCAL | (_noDelete ? RTLD_NODELETE : 0);
+#endif
+      void *dlHandle = dlopen(_full_path.c_str(), dlopenMode);
 
       const char *loadError = dlerror();
       if (nullptr == dlHandle || nullptr != loadError)

test/integration/CMakeLists.txt

@@ -20,7 +20,8 @@ foreach(test ${test_targets})
       GzBadPluginSize
       GzDummyPlugins
       GzFactoryPlugins
-      GzTemplatedPlugins)
+      GzTemplatedPlugins
+      GzInstanceCounter)
 
     target_compile_definitions(${test} PRIVATE
       "${plugin_target}_LIB=\"$<TARGET_FILE:${plugin_target}>\"")
@@ -33,6 +34,8 @@ foreach(test
     INTEGRATION_EnablePluginFromThis_TEST
     INTEGRATION_factory
     INTEGRATION_plugin
+    INTEGRATION_plugin_unload_with_nodelete
+    INTEGRATION_plugin_unload_without_nodelete
     INTEGRATION_WeakPluginPtr)
 
   if(TARGET ${test})

test/integration/plugin_unload.hh

@@ -0,0 +1,63 @@
+
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * Licensed 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.
+ *
+ */
+
+#ifndef GZ_PLUGIN_TEST_INTEGRATION_PLUGIN_UNLOAD_HH
+#define GZ_PLUGIN_TEST_INTEGRATION_PLUGIN_UNLOAD_HH
+
+#include <gtest/gtest.h>
+
+#include <iostream>
+#include <string>
+#include <unordered_set>
+
+#include "../plugins/InstanceCounter.hh"
+#include "gz/plugin/Loader.hh"
+#include "gz/plugin/PluginPtr.hh"
+#include "gz/plugin/SpecializedPluginPtr.hh"
+
+/////////////////////////////////////////////////
+/// \brief Load the InstanceCounter plugin
+/// \param[in] _nodelete True if RTLD_NODELETE should be used when loading the
+gz::plugin::PluginPtr LoadInstanceCounter(bool _nodelete)
+{
+  gz::plugin::Loader pl;
+
+  std::unordered_set<std::string> pluginNames =
+      pl.LoadLib(GzInstanceCounter_LIB, _nodelete);
+
+  return pl.Instantiate("test::util::InstanceCounter");
+}
+
+/////////////////////////////////////////////////
+/// \brief Load plugin, Instantiate the InstanceCounter, check the number of
+/// instances, and finally unload the plugin. Note, the plugin is unloaded when
+/// `instanceCounterPlugin` goes out of scope.
+/// \param[in] _nodelete True if RTLD_NODELETE should be used when loading the
+/// library.
+/// \param[in] _numExpectedInstances Expected number of instances of the plugin.
+void LoadAndTestInstanceCounter(bool _nodelete, int _numExpectedInstances)
+{
+  gz::plugin::PluginPtr instanceCounterPlugin = LoadInstanceCounter(_nodelete);
+  test::util::InstanceCounterBase *instanceCounter =
+      instanceCounterPlugin->QueryInterface<test::util::InstanceCounterBase>();
+  ASSERT_NE(nullptr, instanceCounter);
+
+  EXPECT_EQ(_numExpectedInstances, instanceCounter->Instances());
+}
+
+#endif

test/integration/plugin_unload_with_nodelete.cc

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * Licensed 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 <gz/utils/ExtraTestMacros.hh>
+
+#include "plugin_unload.hh"
+
+/////////////////////////////////////////////////
+TEST(PluginsWithNoDelete,
+     GZ_UTILS_TEST_ENABLED_ONLY_ON_LINUX(AreNotDeletedOnUnload))
+{
+  LoadAndTestInstanceCounter(true, 1);
+  // Since the plugin is not deleted on unload, the second time we load the
+  // plugin, the instance count is incremenetd.
+  LoadAndTestInstanceCounter(true, 2);
+}

test/integration/plugin_unload_without_nodelete.cc

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * Licensed 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 <gz/utils/ExtraTestMacros.hh>
+
+#include "plugin_unload.hh"
+
+/////////////////////////////////////////////////
+TEST(PluginsWithoutNoDelete,
+     GZ_UTILS_TEST_ENABLED_ONLY_ON_LINUX(AreDeletedOnUnload))
+{
+  LoadAndTestInstanceCounter(false, 1);
+  // Unlike the test in *with* nodelete, the number of instances will remain 1
+  // after loading the plugin a second time.
+  LoadAndTestInstanceCounter(false, 1);
+}

test/plugins/CMakeLists.txt

@@ -10,6 +10,8 @@ add_library(GzDummyPlugins SHARED
   DummyPlugins.cc
   DummyPluginsOtherTranslationUnit.cc)
 
+add_library(GzInstanceCounter SHARED InstanceCounter.cc)
+
 add_library(GzDummyStaticPlugin       STATIC DummyStaticPlugin.cc)
 
 # Create a variable for the name of the header which will contain the dummy plugin path.
@@ -23,6 +25,7 @@ foreach(plugin_target
     GzDummyPlugins
     GzFactoryPlugins
     GzTemplatedPlugins
+    GzInstanceCounter
     GzDummyStaticPlugin)
 
   target_link_libraries(${plugin_target} PRIVATE

test/plugins/InstanceCounter.cc

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * Licensed 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 <gz/plugin/Register.hh>
+
+#include "InstanceCounter.hh"
+
+namespace test
+{
+namespace util
+{
+
+namespace {
+
+/////////////////////////////////////////////////
+int numInstancesImpl() {
+  // Use a static variable that never gets deleted as a way to demonstrate
+  // that plugins with RTLD_NODELETE are not deleted when unloaded.
+  static int *instances = new int(0);
+  ++(*instances);
+  return *instances;
+}
+}
+
+/// \brief A class that counts the number of times a plugin has been 
+/// instantiated.
+class InstanceCounter : public InstanceCounterBase
+{
+  public: InstanceCounter() : instances(numInstancesImpl())
+  {
+  }
+
+  public: ~InstanceCounter() override = default;
+
+  public: int Instances() override
+  {
+    return this->instances;
+  }
+
+  private: int instances;
+};
+
+GZ_ADD_PLUGIN(InstanceCounter, InstanceCounterBase)
+}  // namespace util
+}  // namespace test

test/plugins/InstanceCounter.hh

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * Licensed 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.
+ *
+ */
+
+#ifndef GZ_PLUGIN_TEST_PLUGINS_INSTANCECOUNTER_HH_
+#define GZ_PLUGIN_TEST_PLUGINS_INSTANCECOUNTER_HH_
+
+namespace test
+{
+namespace util
+{
+/// \brief Get the instance count of this plugin, that's the number of times
+/// this plugin has been instantiated in this process.
+class InstanceCounterBase
+{
+  public: virtual ~InstanceCounterBase() = default;
+
+  public: virtual int Instances() = 0;
+};
+
+}  // namespace util
+}  // namespace test
+#endif