Fix usage and crashes under multi-client mode

source/backend/engine/CarlaEngine.cpp

@@ -1498,7 +1498,7 @@ void CarlaEngine::processRack(float* inBuf[2], float* outBuf[2], const uint32_t
     {
         CarlaPlugin* const plugin = kData->plugins[i].plugin;
 
-        if (plugin == nullptr || ! plugin->enabled())
+        if (plugin == nullptr || ! plugin->enabled() || ! plugin->tryLock())
             continue;
 
         if (processed)
@@ -1517,6 +1517,7 @@ void CarlaEngine::processRack(float* inBuf[2], float* outBuf[2], const uint32_t
         // process
         plugin->initBuffers();
         plugin->process(inBuf, outBuf, frames);
+        plugin->unlock();
 
 #if 0
         // if plugin has no audio inputs, add previous buffers

source/backend/engine/CarlaEngineJack.cpp

@@ -886,10 +886,11 @@ protected:
 #ifdef BUILD_BRIDGE
         CarlaPlugin* const plugin = getPluginUnchecked(0);
 
-        if (plugin && plugin->enabled())
+        if (plugin && plugin->enabled() && plugin->tryLock())
         {
             plugin->initBuffers();
             processPlugin(plugin, nframes);
+            plugin->unlock();
         }
 #else
         if (fOptions.processMode == PROCESS_MODE_SINGLE_CLIENT)
@@ -898,10 +899,11 @@ protected:
             {
                 CarlaPlugin* const plugin = getPluginUnchecked(i);
 
-                if (plugin && plugin->enabled())
+                if (plugin && plugin->enabled() && plugin->tryLock())
                 {
                     plugin->initBuffers();
                     processPlugin(plugin, nframes);
+                    plugin->unlock();
                 }
             }
         }
@@ -1616,13 +1618,14 @@ private:
     {
         CarlaPlugin* const plugin = (CarlaPlugin*)arg;
 
-        if (plugin != nullptr && plugin->enabled())
+        if (plugin != nullptr && plugin->enabled() && plugin->tryLock())
         {
             CarlaEngineJack* const engine = (CarlaEngineJack*)CarlaPluginGetEngine(plugin);
 
             plugin->initBuffers();
             engine->saveTransportInfo();
             engine->processPlugin(plugin, nframes);
+            plugin->unlock();
         }
 
         return 0;

source/backend/plugin/CarlaPlugin.cpp

@@ -95,6 +95,8 @@ CarlaPlugin::~CarlaPlugin()
 {
     carla_debug("CarlaPlugin::~CarlaPlugin()");
 
+    kData->mutex.lock();
+
     // Remove client and ports
     if (kData->client != nullptr)
     {
@@ -118,6 +120,7 @@ CarlaPlugin::~CarlaPlugin()
     kData->prog.clear();
     kData->midiprog.clear();
     kData->custom.clear();
+    kData->mutex.unlock();
 
     libClose();
 
@@ -1899,11 +1902,10 @@ CarlaPlugin::ScopedDisabler::ScopedDisabler(CarlaPlugin* const plugin)
     carla_debug("CarlaPlugin::ScopedDisabler(%p)", plugin);
     CARLA_ASSERT(plugin != nullptr);
 
+    plugin->kData->mutex.lock();
+
     if (plugin->fEnabled)
-    {
         plugin->fEnabled = false;
-        plugin->kData->engine->waitForProccessEnd(plugin->id());
-    }
 
     if (plugin->kData->client->isActive())
         plugin->kData->client->deactivate();
@@ -1915,6 +1917,7 @@ CarlaPlugin::ScopedDisabler::~ScopedDisabler()
 
     kPlugin->fEnabled = true;
     kPlugin->kData->client->activate();
+    kPlugin->kData->mutex.unlock();
 }
 
 // -------------------------------------------------------------------