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hold evalLock during mlx_save_safetensors etc #379

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Merged
davidkoski merged 1 commit into from
Apr 1, 2026
Merged

hold evalLock during mlx_save_safetensors etc #379

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14 changes: 11 additions & 3 deletions Source/MLX/IO.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,9 @@ public func save(array: MLXArray, url: URL, stream: StreamOrDevice = .default) t
switch url.pathExtension {
case "npy":
_ = try withError {
mlx_save(path.cString(using: .utf8), array.ctx)
_ = evalLock.withLock {
mlx_save(path.cString(using: .utf8), array.ctx)
}
}

default:
Expand Down Expand Up @@ -72,7 +74,9 @@ public func save(
switch url.pathExtension {
case "safetensors":
_ = try withError {
mlx_save_safetensors(path.cString(using: .utf8), mlx_arrays, mlx_metadata)
_ = evalLock.withLock {
mlx_save_safetensors(path.cString(using: .utf8), mlx_arrays, mlx_metadata)

@davidkoski davidkoski Mar 27, 2026

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internally these functions prepare contiguous arrays and use eval to realize them. eval is not thread safe so the entire thing has to be run under the evalLock.

See #378 for the use case.

}
}

default:
Expand Down Expand Up @@ -283,7 +287,11 @@ public func saveToData(
let writer = new_mlx_io_writer_dataIO()
defer { mlx_io_writer_free(writer) }

mlx_save_safetensors_writer(writer, mlx_arrays, mlx_metadata)
_ = evalLock.withLock {
_ = evalLock.withLock {
mlx_save_safetensors_writer(writer, mlx_arrays, mlx_metadata)
}
}

return getData(writer)
}
Expand Down
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