Make the GPU device more thread safe (#1478)

* gpu stream safety

* comment

* fix

python/tests/test_eval.py

@@ -122,6 +122,21 @@ class TestEval(mlx_tests.MLXTestCase):
             out = mx.vjp(fn, (x,), (y,))
             self.assertEqual(peak_mem, mx.metal.get_peak_memory())
 
+    def test_async_eval_with_multiple_streams(self):
+        x = mx.array([1.0])
+        y = mx.array([1.0])
+        a = mx.array([1.0])
+        b = mx.array([1.0])
+
+        d = mx.default_device()
+        s2 = mx.new_stream(d)
+
+        for _ in range(50):
+            for _ in range(20):
+                x = x + y
+            mx.async_eval(x)
+            mx.eval(a + b)
+
 
 if __name__ == "__main__":
     unittest.main()