pantShrey commented on code in PR #21882:
URL: https://github.com/apache/datafusion/pull/21882#discussion_r3473897803


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datafusion/execution/src/spill_file.rs:
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@@ -0,0 +1,54 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use bytes::Bytes;
+use datafusion_common::Result;
+use futures::Stream;
+use std::path::Path;
+use std::pin::Pin;
+use std::sync::Arc;
+
+/// Abstraction over a spill file backend.
+/// Implementations handle their own quota enforcement and blocking concerns.
+pub trait SpillFile: Send + Sync {
+    /// Returns the OS path if this is a local file, None otherwise.
+    fn path(&self) -> Option<&Path> {
+        None
+    }
+
+    /// Returns current size in bytes if cheaply available.
+    fn size(&self) -> Option<u64>;
+
+    /// Returns file contents as an async stream of byte chunks.
+    fn read_stream(&self) -> Result<Pin<Box<dyn Stream<Item = Result<Bytes>> + 
Send>>>;
+
+    /// Opens a writer for appending data to this file.
+    fn open_writer(&self) -> Result<Box<dyn SpillWriter>>;
+}
+
+/// Writer for spill file backends.
+pub trait SpillWriter: std::io::Write + Send {
+    /// Intended for close/sync/commit operations.    
+    fn finish(&mut self) -> Result<()>;
+}
+
+/// Factory for creating spill files.
+pub trait TempFileFactory:
+    Send + Sync + std::panic::UnwindSafe + std::panic::RefUnwindSafe

Review Comment:
   IIRC, it was a semver failure that forced me to add it. 
   
   Because `DiskManager` and `DiskManagerBuilder` now hold an `Arc<dyn 
TempFileFactory>`, they lost their auto-implemented `UnwindSafe` and 
`RefUnwindSafe` traits. This triggered a `cargo-semver-checks` failure because 
existing downstream code relies on `DiskManager` being unwind-safe:
   
   ```text
   Checking datafusion-execution v53.1.0 -> v53.1.0 (no change; assume patch)
   --- failure auto_trait_impl_removed: auto trait no longer implemented ---
   type DiskManagerBuilder is no longer UnwindSafe
   type DiskManagerBuilder is no longer RefUnwindSafe
   type DiskManager is no longer UnwindSafe
   ...
   ```
   
   I didn't have any other architectural reason for adding the bounds beyond 
satisfying the checker. Since this PR already requires an upgrade guide, would 
you prefer I remove these bounds and we just accept the semver break, or should 
I keep them and add a doc comment explaining why they are there?



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