[WebGPU] Implement async tensor api and event api (ggml-org#22099)

* Only run webgpu CI on my fork

* Implement set_tensor_async

* Implement synchronize api

* Implement event creation and deletion API

* Cleanup

* Cleanup

* Comment out jobs for local CI run

* Add webgpu only workflow

* Delete .github/workflows/build-webgpu.yml

* Cleanup

* Cleanup

* Update API with function handlers

* Run clang-format

* Replace one-shot buffer with a direct queue.WriteBuffer using the buffer context

Author: nikhilJain17

ggml/src/ggml-webgpu/ggml-webgpu.cpp

@@ -2832,22 +2832,107 @@ static ggml_status ggml_backend_webgpu_graph_compute(ggml_backend_t backend, str
     return GGML_STATUS_SUCCESS;
 }
 
+struct ggml_backend_webgpu_event_context {
+    webgpu_global_context global_ctx;
+    wgpu::Future          future;
+    bool                  recorded = false;
+};
+
+static ggml_backend_event_t ggml_backend_webgpu_device_event_new(ggml_backend_dev_t device) {
+    ggml_backend_webgpu_device_context * dev_ctx = (ggml_backend_webgpu_device_context *) device->context;
+
+    auto * event_ctx      = new ggml_backend_webgpu_event_context();
+    event_ctx->global_ctx = dev_ctx->webgpu_global_ctx;
+
+    auto * event   = new ggml_backend_event;
+    event->device  = device;
+    event->context = event_ctx;
+    return event;
+}
+
+static void ggml_backend_webgpu_device_event_free(ggml_backend_dev_t dev, ggml_backend_event_t event) {
+    GGML_UNUSED(dev);
+    delete static_cast<ggml_backend_webgpu_event_context *>(event->context);
+    delete event;
+}
+
+static void ggml_backend_webgpu_device_event_synchronize(ggml_backend_dev_t dev, ggml_backend_event_t event) {
+    GGML_UNUSED(dev);
+    ggml_backend_webgpu_event_context * event_ctx = (ggml_backend_webgpu_event_context *) event->context;
+    if (!event_ctx->recorded) {
+        return;
+    }
+    wgpu::WaitStatus status =
+        event_ctx->global_ctx->instance.WaitAny(event_ctx->future, WEBGPU_RUNTIME_WAIT_TIMEOUT_NS);
+    if (status == wgpu::WaitStatus::TimedOut) {
+        GGML_ABORT("ggml_webgpu: event_synchronize timed out after %u ms\n", WEBGPU_RUNTIME_WAIT_TIMEOUT_MS);
+    }
+    event_ctx->recorded = false;
+}
+
+static void ggml_backend_webgpu_event_record(ggml_backend_t backend, ggml_backend_event_t event) {
+    ggml_backend_webgpu_context *       backend_ctx = (ggml_backend_webgpu_context *) backend->context;
+    ggml_backend_webgpu_event_context * event_ctx   = (ggml_backend_webgpu_event_context *) event->context;
+
+    event_ctx->future = backend_ctx->webgpu_ctx->global_ctx->queue.OnSubmittedWorkDone(
+        wgpu::CallbackMode::AllowSpontaneous, [](wgpu::QueueWorkDoneStatus, wgpu::StringView) {});
+    event_ctx->recorded = true;
+}
+
+static void ggml_backend_webgpu_event_wait(ggml_backend_t backend, ggml_backend_event_t event) {
+    GGML_UNUSED(backend);
+    ggml_backend_webgpu_device_event_synchronize(nullptr, event);
+}
+
+static void ggml_backend_webgpu_set_tensor_async(ggml_backend_t backend,
+                                                 ggml_tensor *  tensor,
+                                                 const void *   data,
+                                                 size_t         offset,
+                                                 size_t         size) {
+    GGML_UNUSED(backend);
+    auto * buf_ctx      = (ggml_backend_webgpu_buffer_context *) tensor->buffer->context;
+    size_t total_offset = webgpu_tensor_offset(tensor) + tensor->view_offs + offset;
+
+    // Write aligned portion
+    buf_ctx->global_ctx->queue.WriteBuffer(buf_ctx->buffer, total_offset, data, (size / 4) * 4);
+
+    if (size % 4 != 0) {
+        // If size is not a multiple of 4, we need to memset the remaining bytes
+        size_t remaining_size = size % 4;
+
+        // pack the remaining bytes into a uint32_t
+        uint32_t val32 = 0;
+
+        for (size_t i = 0; i < remaining_size; i++) {
+            ((uint8_t *) &val32)[i] = ((const uint8_t *) data)[size - remaining_size + i];
+        }
+        // memset the remaining bytes
+        ggml_backend_webgpu_buffer_memset(buf_ctx->global_ctx, buf_ctx->buffer, val32,
+                                          total_offset + (size - remaining_size), remaining_size);
+    }
+}
+
+static void ggml_backend_webgpu_synchronize(ggml_backend_t backend) {
+    ggml_backend_webgpu_context * backend_ctx = (ggml_backend_webgpu_context *) backend->context;
+    ggml_backend_webgpu_wait_queue(backend_ctx->webgpu_ctx->global_ctx);
+}
+
 static ggml_backend_i ggml_backend_webgpu_i = {
     /* .get_name                = */ ggml_backend_webgpu_name,
     /* .free                    = */ ggml_backend_webgpu_free,
-    /* .set_tensor_async        = */ NULL,
+    /* .set_tensor_async        = */ ggml_backend_webgpu_set_tensor_async,
     /* .get_tensor_async        = */ NULL,
     /* .get_tensor_2d_async     = */ NULL,
     /* .set_tensor_2d_async     = */ NULL,
     /* .cpy_tensor_async        = */ NULL,
-    /* .synchronize             = */ NULL,
+    /* .synchronize             = */ ggml_backend_webgpu_synchronize,
     /* .graph_plan_create       = */ NULL,
     /* .graph_plan_free         = */ NULL,
     /* .graph_plan_update       = */ NULL,
     /* .graph_plan_compute      = */ NULL,
     /* .graph_compute           = */ ggml_backend_webgpu_graph_compute,
-    /* .event_record            = */ NULL,
-    /* .event_wait              = */ NULL,
+    /* .event_record            = */ ggml_backend_webgpu_event_record,
+    /* .event_wait              = */ ggml_backend_webgpu_event_wait,
     /* .graph_optimize          = */ NULL,
 };
 
@@ -3810,9 +3895,9 @@ static struct ggml_backend_device_i ggml_backend_webgpu_device_i = {
     /* .supports_op          = */ ggml_backend_webgpu_device_supports_op,
     /* .supports_buft        = */ ggml_backend_webgpu_device_supports_buft,
     /* .offload_op           = */ NULL,
-    /* .event_new            = */ NULL,
-    /* .event_free           = */ NULL,
-    /* .event_synchronize    = */ NULL,
+    /* .event_new            = */ ggml_backend_webgpu_device_event_new,
+    /* .event_free           = */ ggml_backend_webgpu_device_event_free,
+    /* .event_synchronize    = */ ggml_backend_webgpu_device_event_synchronize,
 };
 
 /* End GGML Backend Device Interface */