Add Mutex back, since evidently it was causing issues.

Hopefully I can figure out a way to remove it again.

dfdx-core/src/tensor/webgpu/device.rs

@@ -1,6 +1,6 @@
 use wgpu::{
-    util::DownloadBuffer, Adapter, Backends, BufferDescriptor, BufferUsages, Device, Instance,
-    InstanceDescriptor, Maintain, Queue, RequestDeviceError, COPY_BUFFER_ALIGNMENT,
+    Adapter, BufferDescriptor, BufferUsages, Device, Instance, InstanceDescriptor, Maintain, Queue,
+    RequestDeviceError,
 };
 
 use crate::{
@@ -11,12 +11,7 @@ use crate::{
     },
 };
 
-use core::sync::atomic::AtomicPtr;
-use std::{
-    marker::PhantomData,
-    sync::{atomic::Ordering, Arc},
-    vec::Vec,
-};
+use std::{marker::PhantomData, sync::Arc, vec::Vec};
 
 use super::allocate::round_to_buffer_alignment;
 
@@ -45,7 +40,12 @@ impl Buffer {
     }
 
     pub(crate) fn copy_to_device<E: Unit>(&self, dev: &Device, queue: &Queue, slice: &[E]) {
-        let slice = unsafe { std::slice::from_raw_parts(slice.as_ptr() as *const u8, self.size()) };
+        let slice = unsafe {
+            std::slice::from_raw_parts(
+                slice.as_ptr() as *const u8,
+                slice.len() * std::mem::size_of::<E>(),
+            )
+        };
         queue.write_buffer(&self.data, 0, slice);
         queue.submit(std::iter::empty());
         dev.poll(Maintain::Wait);
@@ -80,13 +80,17 @@ impl Buffer {
             )
         };
         buf.copy_from_slice(slice);
+        drop(data);
+        buffer.unmap();
     }
 }
 
 #[derive(Clone, Debug)]
 pub struct Webgpu {
     pub(crate) cpu: Cpu,
+    #[allow(unused)]
     pub(crate) instance: Arc<Instance>,
+    #[allow(unused)]
     pub(crate) adapter: Arc<Adapter>,
     pub(crate) dev: Arc<Device>,
     pub(crate) queue: Arc<Queue>,
@@ -106,12 +110,15 @@ impl Default for Webgpu {
     }
 }
 
+static CONSTRUCTOR_MUTEX: std::sync::Mutex<()> = std::sync::Mutex::new(());
+
 impl Webgpu {
     pub fn seed_from_u64(seed: u64) -> Self {
         Self::try_build(seed).unwrap()
     }
 
     pub fn try_build(seed: u64) -> Result<Self, Error> {
+        let _lock = CONSTRUCTOR_MUTEX.lock().unwrap();
         let cpu = Cpu::seed_from_u64(seed);
         let instance = Arc::new(Instance::new(InstanceDescriptor::default()));
         let adapter = futures_lite::future::block_on(instance.request_adapter(&Default::default()))