DPL: add api to easily load and act on a plugin

Framework/Core/CMakeLists.txt

@@ -83,6 +83,7 @@ o2_add_library(Framework
                        src/O2ControlLabels.cxx
                        src/OutputSpec.cxx
                        src/PropertyTreeHelpers.cxx
+                       src/Plugins.cxx
                        src/RCombinedDS.cxx
                        src/ReadoutAdapter.cxx
                        src/ResourcesMonitoringHelper.cxx

Framework/Core/include/Framework/Plugins.h

@@ -13,6 +13,9 @@
 
 #include "Framework/AlgorithmSpec.h"
 #include <cstring>
+#include <string>
+#include <functional>
+#include <uv.h>
 
 namespace o2::framework
 {
@@ -40,6 +43,14 @@ struct DPLPluginHandle {
   DPLPluginHandle* previous;
 };
 
+// Struct to hold live plugin information which the plugin itself cannot
+// know and that is owned by the framework.
+struct PluginInfo {
+  uv_lib_t* dso = nullptr;
+  std::string name;
+  DPLPluginHandle* instance = nullptr;
+};
+
 #define DEFINE_DPL_PLUGIN(NAME, KIND)                                                                    \
   extern "C" {                                                                                           \
   DPLPluginHandle* dpl_plugin_callback(DPLPluginHandle* previous)                                        \
@@ -75,7 +86,12 @@ struct PluginManager {
     }
     return nullptr;
   }
+  /// Load a DSO called @a dso and insert its handle in @a infos
+  /// On successfull completion @a onSuccess is called passing
+  /// the DPLPluginHandle provided by the library.
+  static void load(std::vector<PluginInfo>& infos, const char* dso, std::function<void(DPLPluginHandle*)>& onSuccess);
 };
+
 } // namespace o2::framework
 
 #endif // O2_FRAMEWORK_PLUGINS_H_

Framework/Core/src/Plugins.cxx

@@ -0,0 +1,55 @@
+// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+#include "Framework/Plugins.h"
+#include "Framework/Logger.h"
+#include <uv.h>
+#include <functional>
+#include <vector>
+
+namespace o2::framework
+{
+
+void PluginManager::load(std::vector<PluginInfo>& libs, const char* dso, std::function<void(DPLPluginHandle*)>& onSuccess)
+{
+  auto plugin = std::find_if(libs.begin(), libs.end(), [dso](PluginInfo& info) { return info.name == dso; });
+  if (plugin != libs.end()) {
+    return onSuccess(plugin->instance);
+  }
+  uv_lib_t* supportLib = (uv_lib_t*)malloc(sizeof(uv_lib_t));
+  int result = 0;
+#ifdef __APPLE__
+  char const* extension = "dylib";
+#else
+  char const* extension = "so";
+#endif
+  std::string filename = fmt::format("lib{}.{}", dso, extension);
+  result = uv_dlopen(filename.c_str(), supportLib);
+  if (result == -1) {
+    LOG(FATAL) << uv_dlerror(supportLib);
+    return;
+  }
+  void* callback = nullptr;
+  DPLPluginHandle* (*dpl_plugin_callback)(DPLPluginHandle*);
+
+  result = uv_dlsym(supportLib, "dpl_plugin_callback", (void**)&dpl_plugin_callback);
+  if (result == -1) {
+    LOG(FATAL) << uv_dlerror(supportLib);
+    return;
+  }
+  if (dpl_plugin_callback == nullptr) {
+    LOGP(FATAL, "Could not find the {} plugin.", dso);
+    return;
+  }
+  DPLPluginHandle* pluginInstance = dpl_plugin_callback(nullptr);
+  libs.push_back({supportLib, dso});
+  onSuccess(pluginInstance);
+}
+} // namespace o2::framework

Framework/Core/src/runDataProcessing.cxx

@@ -2143,6 +2143,8 @@ int doMain(int argc, char** argv, o2::framework::WorkflowSpec const& workflow,
 {
   O2_SIGNPOST_INIT();
   std::vector<std::string> currentArgs;
+  std::vector<PluginInfo> plugins;
+
   for (size_t ai = 1; ai < argc; ++ai) {
     currentArgs.push_back(argv[ai]);
   }