Avoid allocations when reading VST3 process data

On the plugin side. We still need to do a lot of optimizations
elsewhere.

src/common/serialization/vst3/event-list.cpp

@@ -174,19 +174,24 @@ Steinberg::Vst::Event YaEvent::get() const {
     return event;
 }
 
-YaEventList::YaEventList(){FUNKNOWN_CTOR}
-
-YaEventList::YaEventList(Steinberg::Vst::IEventList& event_list) {
+YaEventList::YaEventList() {
     FUNKNOWN_CTOR
+}
 
+void YaEventList::clear() {
+    events.clear();
+}
+
+void YaEventList::repopulate(Steinberg::Vst::IEventList& event_list) {
+    // Copy over all events. Everything gets converted to `YaEvent`s. We sadly
+    // can't construct these in place because we don't know the event type yet.
+    events.clear();
     events.reserve(event_list.getEventCount());
-
-    // Copy over all events. Everything gets converted to `YaEvent`s.
-    Steinberg::Vst::Event event;
     for (int i = 0; i < event_list.getEventCount(); i++) {
         // We're skipping the `kResultOk` assertions here
+        Steinberg::Vst::Event event;
         event_list.getEvent(i, event);
-        events.push_back(event);
+        events.emplace_back(event);
     }
 }
 

src/common/serialization/vst3/event-list.h

@@ -213,15 +213,23 @@ struct YaEvent {
 class YaEventList : public Steinberg::Vst::IEventList {
    public:
     /**
-     * Default constructor with an empty event list. The plugin can use this to
-     * output data.
+     * We only provide a default constructor here, because we need to fill the
+     * existing object with new events every processing cycle to avoid
+     * reallocating a new object every time.
      */
     YaEventList();
 
     /**
-     * Read data from an existing `IEventList` object.
+     * Remove all events. Used when a null pointer gets passed to the input
+     * events field, and so the plugin can output its own events if the host
+     * supports this.
      */
-    YaEventList(Steinberg::Vst::IEventList& event_list);
+    void clear();
+
+    /**
+     * Read data from an `IEventList` object into this existing object.
+     */
+    void repopulate(Steinberg::Vst::IEventList& event_list);
 
     ~YaEventList();
 

src/common/serialization/vst3/param-value-queue.cpp

@@ -16,19 +16,22 @@
 
 #include "param-value-queue.h"
 
-YaParamValueQueue::YaParamValueQueue(){FUNKNOWN_CTOR}
-
-YaParamValueQueue::YaParamValueQueue(Steinberg::Vst::ParamID parameter_id)
-    : parameter_id(parameter_id){FUNKNOWN_CTOR}
-
-      // clang-format /really/ doesn't like these macros
-      YaParamValueQueue::YaParamValueQueue(Steinberg::Vst::IParamValueQueue &
-                                           original_queue)
-    : parameter_id(original_queue.getParameterId()),
-      queue(original_queue.getPointCount()) {
+YaParamValueQueue::YaParamValueQueue() {
     FUNKNOWN_CTOR
+}
+
+void YaParamValueQueue::clear_for_parameter(
+    Steinberg::Vst::ParamID parameter_id) {
+    this->parameter_id = parameter_id;
+    queue.clear();
+}
+
+void YaParamValueQueue::repopulate(
+    Steinberg::Vst::IParamValueQueue& original_queue) {
+    parameter_id = original_queue.getParameterId();
 
     // Copy over all points to our vector
+    queue.resize(original_queue.getPointCount());
     for (int i = 0; i < original_queue.getPointCount(); i++) {
         // We're skipping the assertions here and just assume that the function
         // returns `kResultOk`

src/common/serialization/vst3/param-value-queue.h

@@ -32,20 +32,22 @@
 class YaParamValueQueue : public Steinberg::Vst::IParamValueQueue {
    public:
     /**
-     * Default constructor with an empty queue.
+     * We only provide a default constructor here, because we need to fill the
+     * existing object with new data every processing cycle to avoid
+     * reallocating a new object every time.
      */
     YaParamValueQueue();
 
     /**
-     * Create an empty queue for a specific parameter. Used in
-     * `YaParameterChanges::addParameterData`.
+     * Clear this queue in place so that it can be used to write parameter data
+     * to. Used in `YaParameterChanges::addParameterData`.
      */
-    YaParamValueQueue(Steinberg::Vst::ParamID parameter_id);
+    void clear_for_parameter(Steinberg::Vst::ParamID parameter_id);
 
     /**
-     * Read data from an existing `IParamValueQueue` object.
+     * Read data from an `IParamValueQueue` object into this existing object.
      */
-    YaParamValueQueue(Steinberg::Vst::IParamValueQueue& original_queue);
+    void repopulate(Steinberg::Vst::IParamValueQueue& original_queue);
 
     ~YaParamValueQueue();
 

src/common/serialization/vst3/parameter-changes.cpp

@@ -16,17 +16,20 @@
 
 #include "parameter-changes.h"
 
-YaParameterChanges::YaParameterChanges(){FUNKNOWN_CTOR}
-
-YaParameterChanges::YaParameterChanges(
-    Steinberg::Vst::IParameterChanges& original_queues) {
+YaParameterChanges::YaParameterChanges() {
     FUNKNOWN_CTOR
+}
 
-    // Copy over all parameter changne queues. Everything gets converted to
-    // `YaParamValueQueue`s.
-    queues.reserve(original_queues.getParameterCount());
+void YaParameterChanges::clear() {
+    queues.clear();
+}
+
+void YaParameterChanges::repopulate(
+    Steinberg::Vst::IParameterChanges& original_queues) {
+    // Copy over all parameter changne queues
+    queues.resize(original_queues.getParameterCount());
     for (int i = 0; i < original_queues.getParameterCount(); i++) {
-        queues.push_back(*original_queues.getParameterData(i));
+        queues[i].repopulate(*original_queues.getParameterData(i));
     }
 }
 
@@ -75,7 +78,11 @@ Steinberg::Vst::IParamValueQueue* PLUGIN_API
 YaParameterChanges::addParameterData(const Steinberg::Vst::ParamID& id,
                                      int32& index /*out*/) {
     index = static_cast<int32>(queues.size());
-    queues.push_back(YaParamValueQueue(id));
+
+    // Tiny hack, resizing avoids calling the constructor the second time we
+    // resize the vector to the same size
+    queues.resize(queues.size() + 1);
+    queues[index].clear_for_parameter(id);
 
     return &queues[index];
 }

src/common/serialization/vst3/parameter-changes.h

@@ -31,15 +31,23 @@
 class YaParameterChanges : public Steinberg::Vst::IParameterChanges {
    public:
     /**
-     * Default constructor with an empty parameter changes list. The plugin can
-     * use this to output data.
+     * We only provide a default constructor here, because we need to fill the
+     * existing object with new data every processing cycle to avoid
+     * reallocating a new object every time.
      */
     YaParameterChanges();
 
     /**
-     * Read data from an existing `IParameterChanges` object.
+     * Remove all parameter changes. Used when a null pointer gets passed to the
+     * input parameters field, and so the plugin can output its own parameter
+     * changes.
      */
-    YaParameterChanges(Steinberg::Vst::IParameterChanges& original_queues);
+    void clear();
+
+    /**
+     * Read data from an `IParameterChanges` object into this existing object.
+     */
+    void repopulate(Steinberg::Vst::IParameterChanges& original_queues);
 
     ~YaParameterChanges();
 

src/common/serialization/vst3/process-data.cpp

@@ -31,33 +31,44 @@ YaAudioBusBuffers::YaAudioBusBuffers(int32 sample_size,
                         num_channels,
                         std::vector<float>(num_samples, 0.0)))) {}
 
-YaAudioBusBuffers::YaAudioBusBuffers(
+void YaAudioBusBuffers::repopulate(
     int32 sample_size,
     int32 num_samples,
-    const Steinberg::Vst::AudioBusBuffers& data)
-    : silence_flags(data.silenceFlags) {
+    const Steinberg::Vst::AudioBusBuffers& data) {
+    silence_flags = data.silenceFlags;
+
     switch (sample_size) {
         case Steinberg::Vst::kSample64: {
-            std::vector<std::vector<double>> vector_buffers(data.numChannels);
+            if (!std::holds_alternative<std::vector<std::vector<double>>>(
+                    buffers)) {
+                buffers.emplace<std::vector<std::vector<double>>>();
+            }
+
+            std::vector<std::vector<double>>& vector_buffers =
+                std::get<std::vector<std::vector<double>>>(buffers);
+            vector_buffers.resize(data.numChannels);
             for (int channel = 0; channel < data.numChannels; channel++) {
                 vector_buffers[channel].assign(
                     &data.channelBuffers64[channel][0],
                     &data.channelBuffers64[channel][num_samples]);
             }
-
-            buffers = std::move(vector_buffers);
         } break;
         case Steinberg::Vst::kSample32:
         // I don't think they'll add any other sample sizes any time soon
         default: {
-            std::vector<std::vector<float>> vector_buffers(data.numChannels);
+            if (!std::holds_alternative<std::vector<std::vector<float>>>(
+                    buffers)) {
+                buffers.emplace<std::vector<std::vector<float>>>();
+            }
+
+            std::vector<std::vector<float>>& vector_buffers =
+                std::get<std::vector<std::vector<float>>>(buffers);
+            vector_buffers.resize(data.numChannels);
             for (int channel = 0; channel < data.numChannels; channel++) {
                 vector_buffers[channel].assign(
                     &data.channelBuffers32[channel][0],
                     &data.channelBuffers32[channel][num_samples]);
             }
-
-            buffers = std::move(vector_buffers);
         } break;
     }
 }
@@ -140,39 +151,62 @@ void YaProcessDataResponse::write_back_outputs(
 
 YaProcessData::YaProcessData() {}
 
-YaProcessData::YaProcessData(const Steinberg::Vst::ProcessData& process_data)
-    : process_mode(process_data.processMode),
-      symbolic_sample_size(process_data.symbolicSampleSize),
-      num_samples(process_data.numSamples),
-      outputs_num_channels(process_data.numOutputs),
-      // Even though `ProcessData::inputParamterChanges` is mandatory, the VST3
-      // validator will pass a null pointer here
-      input_parameter_changes(
-          process_data.inputParameterChanges
-              ? YaParameterChanges(*process_data.inputParameterChanges)
-              : YaParameterChanges()),
-      output_parameter_changes_supported(process_data.outputParameterChanges),
-      input_events(process_data.inputEvents ? std::make_optional<YaEventList>(
-                                                  *process_data.inputEvents)
-                                            : std::nullopt),
-      output_events_supported(process_data.outputEvents),
-      process_context(process_data.processContext
-                          ? std::make_optional<Steinberg::Vst::ProcessContext>(
-                                *process_data.processContext)
-                          : std::nullopt) {
+void YaProcessData::repopulate(
+    const Steinberg::Vst::ProcessData& process_data) {
+    // In this function and in every function we call, we should be careful to
+    // not use `push_back`/`emplace_back` anywhere. Resizing vectors and
+    // modifying them in place performs much better because that avoids
+    // destroying and creating objects most of the time.
+    process_mode = process_data.processMode;
+    symbolic_sample_size = process_data.symbolicSampleSize;
+    num_samples = process_data.numSamples;
+
+    // We'll make sure to not do any allocations here after the first processing
+    // cycle
+    inputs.resize(process_data.numInputs);
     for (int i = 0; i < process_data.numInputs; i++) {
-        inputs.emplace_back(symbolic_sample_size, num_samples,
-                            process_data.inputs[i]);
+        inputs[i].repopulate(symbolic_sample_size, num_samples,
+                             process_data.inputs[i]);
     }
 
-    // Fetch the number of channels for each output so we can recreate these
-    // buffers in the Wine plugin host
+    // We only store how many channels ouch output has so we can recreate the
+    // objects on the Wine side
+    outputs_num_channels.resize(process_data.numOutputs);
     for (int i = 0; i < process_data.numOutputs; i++) {
         outputs_num_channels[i] = process_data.outputs[i].numChannels;
     }
+
+    // Even though `ProcessData::inputParamterChanges` is mandatory, the VST3
+    // validator will pass a null pointer here
+    if (process_data.inputParameterChanges) {
+        input_parameter_changes.repopulate(*process_data.inputParameterChanges);
+    } else {
+        input_parameter_changes.clear();
+    }
+
+    output_parameter_changes_supported = process_data.outputParameterChanges;
+
+    if (process_data.inputEvents) {
+        if (!input_events) {
+            input_events.emplace();
+        }
+        input_events->repopulate(*process_data.inputEvents);
+    } else {
+        input_events.reset();
+    }
+
+    output_events_supported = process_data.outputEvents;
+
+    if (process_data.processContext) {
+        process_context.emplace(*process_data.processContext);
+    } else {
+        process_context.reset();
+    }
 }
 
 Steinberg::Vst::ProcessData& YaProcessData::get() {
+    // TODO: Also optimize this to make use of the reused objects
+
     // We'll have to transform out `YaAudioBusBuffers` objects into an array of
     // `AudioBusBuffers` object so the plugin can deal with them. These objects
     // contain pointers to those original objects and thus don't store any
@@ -193,6 +227,13 @@ Steinberg::Vst::ProcessData& YaProcessData::get() {
         outputs_audio_bus_buffers.push_back(buffers.get());
     }
 
+    if (output_parameter_changes) {
+        output_parameter_changes->clear();
+    }
+    if (output_events) {
+        output_events->clear();
+    }
+
     reconstructed_process_data.processMode = process_mode;
     reconstructed_process_data.symbolicSampleSize = symbolic_sample_size;
     reconstructed_process_data.numSamples = num_samples;

src/common/serialization/vst3/process-data.h

@@ -39,14 +39,18 @@
 class YaAudioBusBuffers {
    public:
     /**
-     * A default constructor does not make any sense here since the actual data
-     * is a union, but we need a default constructor for bitsery.
+     * We only provide a default constructor here, because we need to fill the
+     * existing object with new audio data every processing cycle to avoid
+     * reallocating a new object every time.
      */
     YaAudioBusBuffers();
 
     /**
      * Create a new, zero initialize audio bus buffers object. Used to
      * reconstruct the output buffers during `YaProcessData::get()`.
+     *
+     * TODO: Replace with a function similar to `repopulate` that just reassigns
+     *       the existing buffers for the outputs created on the Wine side.
      */
     YaAudioBusBuffers(int32 sample_size,
                       size_t num_samples,
@@ -54,15 +58,15 @@ class YaAudioBusBuffers {
 
     /**
      * Copy data from a host provided `AudioBusBuffers` object during a process
-     * call. Constructed as part of `YaProcessData`. Since `AudioBusBuffers`
+     * call. Used in `YaProcessData::repopulate()`. Since `AudioBusBuffers`
      * contains an untagged union for storing single and double precision
      * floating point values, the original `ProcessData`'s `symbolicSampleSize`
      * field determines which variant of that union to use. Similarly the
      * `ProcessData`' `numSamples` field determines the extent of these arrays.
      */
-    YaAudioBusBuffers(int32 sample_size,
-                      int32 num_samples,
-                      const Steinberg::Vst::AudioBusBuffers& data);
+    void repopulate(int32 sample_size,
+                    int32 num_samples,
+                    const Steinberg::Vst::AudioBusBuffers& data);
 
     /**
      * Reconstruct the original `AudioBusBuffers` object passed to the
@@ -170,14 +174,21 @@ struct YaProcessDataResponse {
  */
 class YaProcessData {
    public:
+    /**
+     * Initialize the process data. We only provide a default constructor here,
+     * because we need to fill the existing object with new data every
+     * processing cycle to avoid reallocating a new object every time.
+     */
     YaProcessData();
 
     /**
      * Copy data from a host provided `ProcessData` object during a process
      * call. This struct can then be serialized, and `YaProcessData::get()` can
-     * then be used again to recreate the original `ProcessData` object.
+     * then be used again to recreate the original `ProcessData` object. This
+     * will avoid allocating unless it's absolutely necessary (e.g. when we
+     * receive more parameter changes than we've received in previous calls).
      */
-    YaProcessData(const Steinberg::Vst::ProcessData& process_data);
+    void repopulate(const Steinberg::Vst::ProcessData& process_data);
 
     /**
      * Reconstruct the original `ProcessData` object passed to the constructor

src/plugin/bridges/vst3-impls/plugin-proxy.cpp

@@ -186,10 +186,8 @@ Vst3PluginProxyImpl::process(Steinberg::Vst::ProcessData& data) {
         last_audio_thread_priority_synchronization = now;
     }
 
-    // TODO: Document
-    // TODO: Actually repopulate `process_data` with new data, right now this
-    //       assignment just destroys the old object and creates a new object.
-    process_data = data;
+    // We reuse this existing object to avoid allocations
+    process_data.repopulate(data);
 
     ProcessResponse response =
         bridge.send_audio_processor_message(YaAudioProcessor::Process{