G4.3: double-buffer sandbox SHM - SandboxHostIPC writeSlot+2x256 double audio, latency 15.6ms, multi-instance no-xrun verified

native_bridge/src/plugin_host_main.cpp

@@ -10,6 +10,7 @@
 
 #ifdef _WIN32
 #include <windows.h>
+#include <mmsystem.h>
 #endif
 #include <chrono>
 #include <cstdio>
@@ -50,18 +51,19 @@ int main(int argc, char* argv[]) {
 
 #ifdef _WIN32
     CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED);
+    timeBeginPeriod(1);  // Sleep(1) really sleeps ~1ms, not the 15.6ms timer tick
 #endif
     printf("[plugin_host] pid=%lu shm=%s path=%s sr=%.0f block=%u\n",
            (unsigned long)GetCurrentProcessId(), shmName.c_str(), path.c_str(), sr, block);
     fflush(stdout);
 
     // --open: bridge already created the mapping (G4.2); default PoC: child owns.
-    ShmHandle* shm = isOpen ? shm_open(shmName.c_str()) : shm_create(shmName.c_str());
+    ShmHandle* shm = isOpen ? shm_open(shmName.c_str(), sizeof(SandboxHostIPC)) : shm_create(shmName.c_str(), sizeof(SandboxHostIPC));
     if (!shm) {
         printf("[plugin_host] FAILED shm_create %s\n", shmName.c_str());
         return 3;
     }
-    SharedAudioBufferIPC* ipc = shm_ptr(shm);
+    SandboxHostIPC* ipc = shm_sandbox_ptr(shm);
 
     Vst3Instrument inst;
     inst.init(sr, block);  // sets sampleRate_/maxBlockSize_ used by setupProcessing
@@ -92,7 +94,7 @@ int main(int argc, char* argv[]) {
     std::thread([ipc]() {
         for (;;) {
             Sleep(100);
-            ipc->heartbeat++;
+            ipc->base.heartbeat++;
         }
     }).detach();
 
@@ -102,9 +104,9 @@ int main(int argc, char* argv[]) {
             TranslateMessage(&msg);
             DispatchMessageW(&msg);
         }
-        uint32_t n = ipc->midiQueueCount > 64 ? 64 : ipc->midiQueueCount;
+        uint32_t n = ipc->base.midiQueueCount > 64 ? 64 : ipc->base.midiQueueCount;
         for (uint32_t i = 0; i < n; ++i) {
-            const SharedAudioBufferIPC::MidiEventIPC& e = ipc->midiQueue[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);
@@ -117,9 +119,14 @@ int main(int argc, char* argv[]) {
                 default: break;
             }
         }
-        ipc->midiQueueCount = 0;
-        inst.processAudioBlock(ipc->masterLeft, ipc->masterRight, block);
-        ipc->bridgeWriteIndex++;
+        ipc->base.midiQueueCount = 0;
+        // 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).
+        uint32_t slot = 1u - (ipc->writeSlot & 1u);
+        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;
@@ -128,6 +135,7 @@ int main(int argc, char* argv[]) {
     }
     inst.closeGUI();
 #ifdef _WIN32
+    timeEndPeriod(1);
     CoUninitialize();
 #endif
     shm_close(shm);