fix(latency): threadpool renders + RENDER_LOCK + client pre-render cache

app/core/render_engine.py

@@ -11,6 +11,7 @@ from app.core.vst_engine import (
     HAS_PEDALBOARD,
     HAS_PYFLUIDSYNTH,
     apply_preset_to_plugin,
+    RENDER_LOCK,
 )
 
 logger = logging.getLogger(__name__)
@@ -451,30 +452,31 @@ class PythonRenderEngine:
         return session_buffer
 
     def render_project(self, project_json: dict, output_filepath: str):
-        bpm = project_json["metadata"]["bpm"]
-        time_sig_num = project_json["metadata"].get("time_signature_numerator", 4)
-        main_session = project_json["main_session"]
-        section_store = project_json.get("section_store", {})
+        with RENDER_LOCK:
+            bpm = project_json["metadata"]["bpm"]
+            time_sig_num = project_json["metadata"].get("time_signature_numerator", 4)
+            main_session = project_json["main_session"]
+            section_store = project_json.get("section_store", {})
 
-        # Compute total project samples
-        total_bars = main_session.get("length_bars", 16.0)
-        total_samples = self.bars_to_samples(total_bars, bpm, time_sig_num)
-        
-        # Render main session
-        master_buffer = self.render_session_container(
-            session=main_session,
-            section_store=section_store,
-            bpm=bpm,
-            time_sig_num=time_sig_num,
-            total_samples=total_samples,
-            _cache={},
-        )
+            # Compute total project samples
+            total_bars = main_session.get("length_bars", 16.0)
+            total_samples = self.bars_to_samples(total_bars, bpm, time_sig_num)
 
-        # Normalization to prevent clipping
-        max_peak = np.max(np.abs(master_buffer))
-        if max_peak > 1.0:
-            master_buffer /= max_peak
+            # Render main session
+            master_buffer = self.render_session_container(
+                session=main_session,
+                section_store=section_store,
+                bpm=bpm,
+                time_sig_num=time_sig_num,
+                total_samples=total_samples,
+                _cache={},
+            )
 
-        # Write final output file
-        sf.write(output_filepath, master_buffer.T, self.sample_rate)
-        return output_filepath
+            # Normalization to prevent clipping
+            max_peak = np.max(np.abs(master_buffer))
+            if max_peak > 1.0:
+                master_buffer /= max_peak
+
+            # Write final output file
+            sf.write(output_filepath, master_buffer.T, self.sample_rate)
+            return output_filepath