hold evalLock while computing tostring

.github/workflows/pull_request.yml

@@ -103,7 +103,6 @@ jobs:
         shell: sh
         run: |
           xcodebuild -version
-          xcrun --show-sdk-build-version
           swift --version
           rm -rf ~/Library/Developer/Xcode/DerivedData/*
           xcodebuild build-for-testing -scheme mlx-swift-Package -destination 'platform=macOS'

Source/MLX/Device.swift

@@ -173,8 +173,10 @@ public final class Device: @unchecked Sendable, Equatable {
 extension Device: CustomStringConvertible {
     public var description: String {
         var s = mlx_string_new()
-        mlx_device_tostring(&s, ctx)
         defer { mlx_string_free(s) }
+        _ = evalLock.withLock {
+            mlx_device_tostring(&s, ctx)
+        }
         return String(cString: mlx_string_data(s), encoding: .utf8)!
     }
 }

Source/MLX/MLXArray.swift

@@ -616,8 +616,10 @@ extension MLXArray: Updatable, Evaluatable {
 extension MLXArray: CustomStringConvertible {
     public var description: String {
         var s = mlx_string_new()
-        mlx_array_tostring(&s, ctx)
         defer { mlx_string_free(s) }
+        _ = evalLock.withLock {
+            mlx_array_tostring(&s, ctx)
+        }
         return String(cString: mlx_string_data(s), encoding: .utf8)!
     }
 }

Source/MLX/Stream.swift

@@ -161,8 +161,10 @@ public final class Stream: @unchecked Sendable, Equatable {
 extension Stream: CustomStringConvertible {
     public var description: String {
         var s = mlx_string_new()
-        mlx_stream_tostring(&s, ctx)
         defer { mlx_string_free(s) }
+        _ = evalLock.withLock {
+            mlx_stream_tostring(&s, ctx)
+        }
         return String(cString: mlx_string_data(s), encoding: .utf8)!
     }
 }