Proxy webgpu calls back to the main thread. NFC (emscripten-core#20124)

Until we have real multi-threaded webgpu support this is probable
the best we can do.

I tested these locally. I don't think we actually have WebGPU support
in our CI yet, but that is something else I'm working on.

Fixes: emscripten-core#19645

src/library.js

@@ -73,7 +73,7 @@ addToLibrary({
       assert(!implicit);
 #endif
 #if PTHREADS_DEBUG
-      dbg(`Pthread ${ptrToString(_pthread_self())} called exit(), posting exitOnMainThread.`);
+      dbg(`Pthread ${ptrToString(_pthread_self())} called exit(${status}), posting exitOnMainThread.`);
 #endif
       // When running in a pthread we propagate the exit back to the main thread
       // where it can decide if the whole process should be shut down or not.
@@ -83,7 +83,7 @@ addToLibrary({
       throw 'unwind';
     }
 #if PTHREADS_DEBUG
-    err(`main thread called exit: keepRuntimeAlive=${keepRuntimeAlive()} (counter=${runtimeKeepaliveCounter})`);
+    err(`main thread called exit(${status}): keepRuntimeAlive=${keepRuntimeAlive()} (counter=${runtimeKeepaliveCounter})`);
 #endif // PTHREADS_DEBUG
 #endif // PTHREADS
 

src/library_html5_webgpu.js

@@ -90,4 +90,10 @@ var LibraryHTML5WebGPU = {
 {{{ html5_gpu.makeImportExport('render_bundle_encoder', 'RenderBundleEncoder') }}}
 {{{ html5_gpu.makeImportExport('render_bundle', 'RenderBundle') }}}
 
+for (const key of Object.keys(LibraryHTML5WebGPU)) {
+  if (typeof LibraryHTML5WebGPU[key] === 'function' && !(key + '__proxy' in LibraryHTML5WebGPU)) {
+    LibraryHTML5WebGPU[key + '__proxy'] = 'sync';
+  }
+}
+
 addToLibrary(LibraryHTML5WebGPU);

src/library_webgpu.js

@@ -2198,7 +2198,7 @@ var LibraryWebGPU = {
 #endif
 
     var bundles = Array.from(HEAP32.subarray(bundlesPtr >> 2, (bundlesPtr >> 2) + count),
-      function(id) { return WebGPU.mgrRenderBundle.get(id); });
+      (id) => WebGPU.mgrRenderBundle.get(id));
     pass["executeBundles"](bundles);
   },
 
@@ -2586,23 +2586,22 @@ var LibraryWebGPU = {
     var device = WebGPU.mgrDevice.get(deviceId);
     var context = WebGPU.mgrSurface.get(surfaceId);
 
-
 #if ASSERTIONS
     assert({{{ gpu.PresentMode.Fifo }}} ===
       {{{ gpu.makeGetU32('descriptor', C_STRUCTS.WGPUSwapChainDescriptor.presentMode) }}});
 #endif
 
     var canvasSize = [
-        {{{ gpu.makeGetU32('descriptor', C_STRUCTS.WGPUSwapChainDescriptor.width) }}},
-        {{{ gpu.makeGetU32('descriptor', C_STRUCTS.WGPUSwapChainDescriptor.height) }}}
+      {{{ gpu.makeGetU32('descriptor', C_STRUCTS.WGPUSwapChainDescriptor.width) }}},
+      {{{ gpu.makeGetU32('descriptor', C_STRUCTS.WGPUSwapChainDescriptor.height) }}}
     ];
 
     if (canvasSize[0] !== 0) {
-        context["canvas"]["width"] = canvasSize[0];
+      context["canvas"]["width"] = canvasSize[0];
     }
 
     if (canvasSize[1] !== 0) {
-        context["canvas"]["height"] = canvasSize[1];
+      context["canvas"]["height"] = canvasSize[1];
     }
 
     var configuration = {
@@ -2645,7 +2644,12 @@ for (var value in LibraryWebGPU.$WebGPU.FeatureName) {
 }
 
 for (const key of Object.keys(LibraryWebGPU)) {
-  LibraryWebGPU[key + '__i53abi'] = true;
+  if (typeof LibraryWebGPU[key] === 'function') {
+    LibraryWebGPU[key + '__i53abi'] = true;
+    if (!(key + '__proxy' in LibraryWebGPU)) {
+      LibraryWebGPU[key + '__proxy'] = 'sync';
+    }
+  }
 }
 
 autoAddDeps(LibraryWebGPU, '$WebGPU');

test/test_browser.py

@@ -4664,9 +4664,18 @@ def test_webgl_simple_enable_extensions(self):
   def test_webgpu_basic_rendering(self, args):
     self.btest_exit('webgpu_basic_rendering.cpp', args=['-sUSE_WEBGPU'] + args)
 
+  @requires_graphics_hardware
+  @requires_threads
+  def test_webgpu_basic_rendering_pthreads(self):
+    self.btest_exit('webgpu_basic_rendering.cpp', args=['-sUSE_WEBGPU', '-pthread', '-sPROXY_TO_PTHREAD'])
+
   def test_webgpu_get_device(self):
     self.btest_exit('webgpu_get_device.cpp', args=['-sUSE_WEBGPU', '-sASSERTIONS', '--closure=1'])
 
+  @requires_threads
+  def test_webgpu_get_device_pthreads(self):
+    self.btest_exit('webgpu_get_device.cpp', args=['-sUSE_WEBGPU', '-pthread', '-sPROXY_TO_PTHREAD'])
+
   # Tests the feature that shell html page can preallocate the typed array and place it
   # to Module.buffer before loading the script page.
   # In this build mode, the -sINITIAL_MEMORY=xxx option will be ignored.

test/webgpu_basic_rendering.cpp

@@ -26,8 +26,16 @@ void GetDevice(void (*callback)(wgpu::Device)) {
         }
         if (status == WGPURequestAdapterStatus_Unavailable) {
             printf("WebGPU unavailable; exiting cleanly\n");
-            // exit(0) (rather than emscripten_force_exit(0)) ensures there is no dangling keepalive.
+            // exit(0) (rather than emscripten_force_exit(0)) ensures there is
+            // no dangling keepalive.
+#if _REENTRANT
+            // FIXME: In multi-threaded builds this callback runs on the main
+            // which seems to be causing the runtime to stay alive here and
+            // results in the 99 being returned.
+            emscripten_force_exit(0);
+#else
             exit(0);
+#endif
         }
         assert(status == WGPURequestAdapterStatus_Success);
 
@@ -410,6 +418,7 @@ int main() {
     // emscripten_set_main_loop, and that should keep it alive until
     // emscripten_cancel_main_loop.
     //
-    // This code is returned when the runtime exits unless something else sets it, like exit(0).
+    // This code is returned when the runtime exits unless something else sets
+    // it, like exit(0).
     return 99;
 }

test/webgpu_get_device.cpp

@@ -1,9 +1,16 @@
-#include <emscripten.h>
+#include <stdio.h>
+
+#include <emscripten/em_asm.h>
 #include <emscripten/html5_webgpu.h>
 
-int main() {
+__attribute__((constructor)) void init() {
   EM_ASM({
     Module['preinitializedWebGPUDevice'] = { this_is: 'a_dummy_object' };
   });
-  emscripten_webgpu_get_device();
+}
+
+int main() {
+  WGPUDevice d = emscripten_webgpu_get_device();
+  printf("emscripten_webgpu_get_device: %p\n", d);
+  return 0;
 }