G4.3 idle-skip + no fixed-tick render: idle CPU ~0, latency 9.8ms

20260815-tasks-g4.md

@@ -128,4 +128,12 @@ G4.1 → G4.2 → G4.3.
 - Build Release PASS (daw_vst_bridge.exe + plugin_host.exe). Deploy shutil.copy2 (kill proc giu file truoc).
 - Verify (probe_g43.py, bridge standalone env `SF_SANDBOX_VST3=1` + state file rong): LOAD Nexus ch0+ch1 -> 2 plugin_host [con song song]; heartbeat ca 2 OK; note-on ch0 C4 + ch1 E4 -> main audio peak 0.71835 (tong 2 channel); writeSlot flip 64 blocks/s = latency 15.6ms < 20ms (khong yeu cau 172/s thuc - Nexus render ~10ms/block that, CPU-bound); kill child0 -> child1 van phat 0.36972, bridge song + heartbeat + child0 respawn - PASS.
 - Regression: G1.5 stress 3 iter PASS (writeIndex delta 286); G2.5 stress 2 iter PASS (kill bridge -> respawn -> preset exact + LOAD-skip OK). App deploy (install/sonicforge-daw.exe) dang chay, bridge pid moi.
-- ponytail: child render lien tuc ke ca im lang (CPU cao khi idle) - toi uu idle-skip khi can.
+- FIX idle-skip (G4.3.1): plugin_host_main.cpp them `activeNotes` dem (note-on ++, note-off --, clamp >= 0)
+  + `idle` flag. Khi khong con note dang giu va peak block < 0.0005f -> idle = true,
+  loop Sleep(15) bo qua render (van PeekMessage + parent-alive check). Bo `Sleep(1)`
+  hot loop -> `Sleep(0)` yield. KET QUA: writeSlot flip 0 blocks/s khi im lang (truoc day
+  render lien tuc ~100/s, CPU cao); khi dang giu note flip 101.6 blocks/s = latency 9.8ms
+  (truoc 64/s = 15.6ms) - ca 2 loi G4.3 xac nhan da het.
+- Verify lai: probe_g43.py PASS (2 children song song, peak 0.67273, kill child0 -> child1
+  0.36972, isolation OK); dbg_rate.py idle 0 flips/3s; G1.5 3 iter PASS (delta 287);
+  G2.5 2 iter PASS. Deploy install/plugin_host.exe moi. App dang chay pid 21396.

native_bridge/src/plugin_host_main.cpp

@@ -98,6 +98,8 @@ int main(int argc, char* argv[]) {
         }
     }).detach();
 
+    int activeNotes = 0;
+    bool idle = false;
     for (;;) {
         MSG msg;
         while (PeekMessageW(&msg, nullptr, 0, 0, PM_REMOVE)) {
@@ -105,14 +107,15 @@ int main(int argc, char* argv[]) {
             DispatchMessageW(&msg);
         }
         uint32_t n = ipc->base.midiQueueCount > 64 ? 64 : ipc->base.midiQueueCount;
+        bool midiActivity = n > 0;
         for (uint32_t i = 0; i < n; ++i) {
             const SharedAudioBufferIPC::MidiEventIPC& e = ipc->base.midiQueue[i];
             switch (e.command) {
                 case 0x9:
-                    if (e.velocity > 0) inst.noteOn(e.channel, e.pitch, e.velocity / 127.0f, 0);
-                    else inst.noteOff(e.channel, e.pitch, 0);
+                    if (e.velocity > 0) { inst.noteOn(e.channel, e.pitch, e.velocity / 127.0f, 0); ++activeNotes; }
+                    else { inst.noteOff(e.channel, e.pitch, 0); if (activeNotes > 0) --activeNotes; }
                     break;
-                case 0x8: inst.noteOff(e.channel, e.pitch, 0); break;
+                case 0x8: inst.noteOff(e.channel, e.pitch, 0); if (activeNotes > 0) --activeNotes; break;
                 case 0xB: inst.controlChange(e.channel, e.pitch, e.data2); break;
                 case 0xC: inst.programChange(e.channel, e.data2); break;
                 case 0xE: inst.pitchBend(e.channel, e.data2 | (uint32_t(e.data3) << 7)); break;
@@ -120,6 +123,15 @@ int main(int argc, char* argv[]) {
             }
         }
         ipc->base.midiQueueCount = 0;
+        if (midiActivity) idle = false;
+        if (parentPid && !parent_alive(parentPid)) {
+            printf("[plugin_host] parent gone - exiting\n");
+            break;
+        }
+        if (idle) {
+            Sleep(15);
+            continue;
+        }
         // G4.3 double buffer: render into the slot we are NOT publishing, then
         // publish. The bridge keeps the last published block, so a slow child
         // never tears audio (it just repeats the previous block).
@@ -127,11 +139,19 @@ int main(int argc, char* argv[]) {
         inst.processAudioBlock(ipc->audioLeft[slot], ipc->audioRight[slot], block);
         ipc->writeSlot = slot;
         ipc->base.bridgeWriteIndex++;
-        if (parentPid && !parent_alive(parentPid)) {
-            printf("[plugin_host] parent gone - exiting\n");
-            break;
+        if (activeNotes == 0) {
+            float peak = 0.0f;
+            for (uint32_t i = 0; i < block; ++i) {
+                float l = ipc->audioLeft[slot][i];
+                if (l < 0.0f) l = -l;
+                float r = ipc->audioRight[slot][i];
+                if (r < 0.0f) r = -r;
+                if (l > peak) peak = l;
+                if (r > peak) peak = r;
+            }
+            if (peak < 0.0005f) idle = true;
         }
-        Sleep(1);
+        Sleep(0);
     }
     inst.closeGUI();
 #ifdef _WIN32