Cache IAudioProcessor::canProcessSampleSize()

CHANGELOG.md

@@ -13,6 +13,11 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 - Added a timed cache for the `IPluginView::canResize()` VST3 function, so value
   will be remembered during an active resize. This makes resizing VST3 plugin
   editor windows more responsive.
+- Add a cache for VST3 function calls where the host asks the plugin whether it
+  can process 32-bit or 64-bit floating point audio. Some hosts will call this
+  function every processing cycle even though the value doesn't change. Caching
+  this can significantly reduce the overhead of bridging VST3 plugins under
+  those hosts.
 
 ## [3.2.0] - 2021-05-03
 

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

@@ -139,10 +139,37 @@ tresult PLUGIN_API Vst3PluginProxyImpl::getBusArrangement(
 
 tresult PLUGIN_API
 Vst3PluginProxyImpl::canProcessSampleSize(int32 symbolicSampleSize) {
-    return bridge.send_audio_processor_message(
-        YaAudioProcessor::CanProcessSampleSize{
-            .instance_id = instance_id(),
-            .symbolic_sample_size = symbolicSampleSize});
+    const auto request = YaAudioProcessor::CanProcessSampleSize{
+        .instance_id = instance_id(),
+        .symbolic_sample_size = symbolicSampleSize};
+
+    {
+        std::lock_guard lock(function_result_cache_mutex);
+        if (auto it = function_result_cache.can_process_sample_size.find(
+                symbolicSampleSize);
+            it != function_result_cache.can_process_sample_size.end()) {
+            const bool log_response = bridge.logger.log_request(true, request);
+            if (log_response) {
+                bridge.logger.log_response(
+                    true,
+                    YaAudioProcessor::CanProcessSampleSize::Response(
+                        it->second),
+                    true);
+            }
+
+            return *function_result_cache.parameter_count;
+        }
+    }
+
+    const tresult result = bridge.send_audio_processor_message(request);
+
+    {
+        std::lock_guard lock(function_result_cache_mutex);
+        function_result_cache.can_process_sample_size[symbolicSampleSize] =
+            result;
+    }
+
+    return result;
 }
 
 uint32 PLUGIN_API Vst3PluginProxyImpl::getLatencySamples() {

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

@@ -531,6 +531,11 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
      * @see function_result_cache
      */
     struct FunctionResultCache {
+        /**
+         * Memoizes `IAudioProcessor::canProcessSampleSize()`, since some hosts
+         * call this every processing cycle.
+         */
+        std::map<int32, tresult> can_process_sample_size;
         /**
          * Memoizes `IEditController::getParameterCount()`.
          */