From 3870a374afd0e7694e53449e08e5f693b4ff0cee Mon Sep 17 00:00:00 2001
From: Louis Dureuil <louis@meilisearch.com>
Date: Thu, 2 Oct 2025 16:56:25 +0200
Subject: [PATCH] Compression: implement cancellation and change env copy
 method

---
 crates/meilisearch-types/src/compression.rs | 104 ++++++++++++++++----
 1 file changed, 84 insertions(+), 20 deletions(-)

diff --git a/crates/meilisearch-types/src/compression.rs b/crates/meilisearch-types/src/compression.rs
index de2145428..414c873f3 100644
--- a/crates/meilisearch-types/src/compression.rs
+++ b/crates/meilisearch-types/src/compression.rs
@@ -1,8 +1,10 @@
 use std::fs::{create_dir_all, File};
-use std::io::{Read, Write};
-use std::os::fd::AsRawFd;
+use std::io::{PipeWriter, Read, Write};
+use std::mem::ManuallyDrop;
+use std::ops::DerefMut;
+use std::os::fd::{AsRawFd, FromRawFd};
 use std::path::{Path, PathBuf};
-use std::sync::mpsc::{Receiver, Sender};
+use std::sync::mpsc::{Receiver, RecvTimeoutError, Sender};
 use std::thread::JoinHandle;
 
 use flate2::read::GzDecoder;
@@ -32,8 +34,10 @@ pub fn from_tar_gz(src: impl AsRef<Path>, dest: impl AsRef<Path>) -> anyhow::Res
 }
 
 pub struct PipedArchiveBuilder {
-    send: Sender<CompressionMessage>,
-    join_handle: JoinHandle<anyhow::Result<File>>,
+    send_compression: Sender<CompressionMessage>,
+    send_cancellation: Sender<CancellationMessage>,
+    processing_thread: JoinHandle<anyhow::Result<File>>,
+    cancellation_thread: JoinHandle<()>,
 }
 
 enum CompressionMessage {
@@ -43,13 +47,29 @@ enum CompressionMessage {
 }
 
 impl PipedArchiveBuilder {
-    pub fn new(dest_dir: PathBuf, dest_filename: String, base_path: PathBuf) -> Self {
-        let (send, recv) = std::sync::mpsc::channel();
-        let join_handle = std::thread::Builder::new()
-            .name("piped-archive-builer".into())
-            .spawn(|| Self::run(dest_dir, dest_filename, recv, base_path))
+    pub fn new<F>(
+        dest_dir: PathBuf,
+        dest_filename: String,
+        base_path: PathBuf,
+        must_stop_processing: F,
+    ) -> Self
+    where
+        F: Fn() -> bool + Send + 'static,
+    {
+        let (send_compression, recv) = std::sync::mpsc::channel();
+        let processing_thread = std::thread::Builder::new()
+            .name("piped-archive-builder".into())
+            .spawn(|| Self::run_processing(dest_dir, dest_filename, recv, base_path))
             .unwrap();
-        Self { send, join_handle }
+
+        let (send_cancellation, recv) = std::sync::mpsc::channel();
+
+        let cancellation_thread = std::thread::Builder::new()
+            .name("piped-archive-builder-cancellation".into())
+            .spawn(|| Self::run_cancellation(must_stop_processing, recv))
+            .unwrap();
+
+        Self { send_compression, send_cancellation, processing_thread, cancellation_thread }
     }
 
     pub fn add_env_to_archive<T>(&mut self, env: &Env<T>) -> anyhow::Result<()> {
@@ -59,9 +79,22 @@ impl PipedArchiveBuilder {
         // as any concurrent change would corrupt the copy.
         let env_wtxn = env.write_txn()?;
 
-        self.send.send(CompressionMessage::Env { path, reader });
-        // SAFETY: the writer end of the pipe is available for write access
-        unsafe { env.copy_to_fd(writer.as_raw_fd(), milli::heed::CompactionOption::Disabled)? }
+        // SAFETY: only the cancellation thread has the actual responsibility of closing the pipe since
+        // the clone is `ManuallyDrop`.
+        let mut cloned_writer = unsafe {
+            let writer_raw_fd = writer.as_raw_fd();
+            ManuallyDrop::new(PipeWriter::from_raw_fd(writer_raw_fd))
+        };
+
+        self.send_cancellation.send(CancellationMessage::OpenedPipe { pipe: writer });
+
+        self.send_compression.send(CompressionMessage::Env { path, reader });
+
+        let mdb_path = env.path().join("data.mdb");
+        let mut file = std::fs::File::open(&mdb_path)?;
+        std::io::copy(&mut file, cloned_writer.deref_mut())?;
+
+        self.send_cancellation.send(CancellationMessage::ClosingPipe);
 
         // no change we might want to commit
         env_wtxn.abort();
@@ -69,23 +102,25 @@ impl PipedArchiveBuilder {
     }
 
     pub fn add_file_to_archive(&mut self, path: PathBuf) -> anyhow::Result<()> {
-        self.send.send(CompressionMessage::File { path });
+        self.send_compression.send(CompressionMessage::File { path });
         Ok(())
     }
 
     pub fn add_dir_to_archive(&mut self, path: PathBuf) -> anyhow::Result<()> {
-        self.send.send(CompressionMessage::Dir { path });
+        self.send_compression.send(CompressionMessage::Dir { path });
         Ok(())
     }
 
     pub fn finish(self) -> anyhow::Result<File> {
-        drop(self.send);
-        /// FIXME catch panic
-        let file = self.join_handle.join().unwrap()?;
+        drop(self.send_cancellation);
+        drop(self.send_compression);
+        /// FIXME catch panics
+        let file = self.processing_thread.join().unwrap()?;
+        self.cancellation_thread.join().unwrap();
         Ok(file)
     }
 
-    fn run(
+    fn run_processing(
         dest_dir: PathBuf,
         dest_filename: String,
         recv: Receiver<CompressionMessage>,
@@ -128,6 +163,30 @@ impl PipedArchiveBuilder {
         Ok(archive)
     }
 
+    fn run_cancellation<F>(must_stop_processing: F, recv: Receiver<CancellationMessage>)
+    where
+        F: Fn() -> bool + Send + 'static,
+    {
+        let mut current_pipe = None;
+        loop {
+            let next_message = match recv.recv_timeout(std::time::Duration::from_secs(60)) {
+                Ok(message) => message,
+                Err(RecvTimeoutError::Disconnected) => break,
+                Err(RecvTimeoutError::Timeout) => {
+                    if must_stop_processing() {
+                        break;
+                    }
+                    continue;
+                }
+            };
+            match next_message {
+                CancellationMessage::OpenedPipe { pipe } => current_pipe = Some(pipe),
+                CancellationMessage::ClosingPipe => current_pipe = None,
+            }
+        }
+        drop(current_pipe);
+    }
+
     fn add_to_archive(
         tar_encoder: &mut Builder<impl Write>,
         path: &Path,
@@ -144,6 +203,11 @@ impl PipedArchiveBuilder {
     }
 }
 
+enum CancellationMessage {
+    OpenedPipe { pipe: PipeWriter },
+    ClosingPipe,
+}
+
 struct PathInArchive(PathBuf);
 
 impl PathInArchive {