Test quick trick to always load custom libjack on jack apps start

source/backend/plugin/CarlaPluginDSSI.cpp

@@ -162,7 +162,7 @@ public:
             {
                 std::snprintf(winIdStr, STR_MAX, P_UINTPTR, winId);
                 ldPreloadValue = (CarlaString(kEngine->getOptions().binaryDir)
-                               + CARLA_OS_SEP_STR "libcarla_interposer-x11.so");
+                               + "/libcarla_interposer-x11.so");
             }
             else
             {

source/backend/plugin/CarlaPluginJack.cpp

@@ -119,14 +119,22 @@ protected:
             CarlaString libjackdir(options.binaryDir);
             libjackdir += "/jack";
 
+            CarlaString ldpreload;
+
+            if (options.frontendWinId != 0)
+            {
+                ldpreload = (CarlaString(options.binaryDir)
+                          + "/libcarla_interposer-x11.so");
+            }
+
             const ScopedEngineEnvironmentLocker _seel(kEngine);
 
-            const ScopedEnvVar sev1("LD_PRELOAD", nullptr);
             const ScopedEnvVar sev2("LD_LIBRARY_PATH", libjackdir.buffer());
+            const ScopedEnvVar sev1("LD_PRELOAD", ldpreload.isNotEmpty() ? ldpreload.buffer() : nullptr);
 
             carla_setenv("CARLA_FRONTEND_WIN_ID", strBuf);
-            carla_setenv("CARLA_SHM_IDS", fShmIds.buffer());
             carla_setenv("CARLA_LIBJACK_SETUP", fNumPorts.buffer());
+            carla_setenv("CARLA_SHM_IDS", fShmIds.buffer());
 
             started = fProcess->start(arguments);
         }

source/interposer/interposer-x11.cpp

@@ -63,6 +63,15 @@ int XMapWindow(Display* display, Window w)
         if (++sMapWindowCounter != 1)
             break;
 
+        static bool libjackopen = false;
+
+        if (! libjackopen && std::getenv("CARLA_LIBJACK_SETUP") != nullptr)
+        {
+            libjackopen = true;
+            dlopen("libjack.so.0", RTLD_NOW|RTLD_LOCAL);
+            carla_stdout("------------------------------- libjack opened");
+        }
+
         if (const char* const winIdStr = std::getenv("CARLA_ENGINE_OPTION_FRONTEND_WIN_ID"))
         {
             CARLA_SAFE_ASSERT_BREAK(winIdStr[0] != '\0');