idea for doing synchronous evals but _not_ holding evalLock

Source/MLX/MLXArray.swift

@@ -554,9 +554,7 @@ public final class MLXArray {
     /// MLX is lazy and arrays are not fully realized until they are evaluated.  This method is typically
     /// not needed as all reads ensure the contents are evaluated.
     public func eval() {
-        _ = withEvalLock {
-            mlx_array_eval(ctx)
-        }
+        MLX.eval(self)
     }
 
     /// Replace the contents with a reference to a new array (INTERNAL).

Source/MLX/Transforms+Eval.swift

@@ -115,13 +115,31 @@ func withEvalLock<R>(_ body: () throws -> R) rethrows -> R {
     return try body()
 }
 
+/// Is the array's data computed?
+///
+/// This is the observable difference between ``eval(_:)-(MLXArray...)`` and
+/// ``asyncEval(_:)-(Collection<MLXArray>)``, and the only direct way to check
+/// that `eval` is still synchronous now that it schedules with
+/// `mlx_async_eval` and waits with `mlx_eval`.
+///
+/// Internal: exists for the tests (`EvalTests`), which cannot reach `Cmlx`
+/// directly.  Call this only on the thread that owns `array`.
+func isEvaluated(_ array: MLXArray) -> Bool {
+    var available = false
+    _mlx_array_is_available(&available, array.ctx)
+    return available
+}
+
 /// Evaluate one or more `MLXArray`
 ///
 /// ### See Also
 /// - <doc:lazy-evaluation>
 public func eval(_ arrays: MLXArray...) {
     let vector_array = new_mlx_vector_array(arrays)
-    _ = withEvalLock {
+    let result = withEvalLock {
+        mlx_async_eval(vector_array)
+    }
+    if result == 0 {
         mlx_eval(vector_array)
     }
     mlx_vector_array_free(vector_array)
@@ -133,7 +151,10 @@ public func eval(_ arrays: MLXArray...) {
 /// - <doc:lazy-evaluation>
 public func eval(_ arrays: some Collection<MLXArray>) {
     let vector_array = new_mlx_vector_array(arrays)
-    _ = withEvalLock {
+    let result = withEvalLock {
+        mlx_async_eval(vector_array)
+    }
+    if result == 0 {
         mlx_eval(vector_array)
     }
     mlx_vector_array_free(vector_array)