From 3f1e172c6f8adf9db2d782e043032c0848b63d45 Mon Sep 17 00:00:00 2001
From: Tamo <tamo@meilisearch.com>
Date: Tue, 5 Aug 2025 16:47:35 +0200
Subject: [PATCH] fix race condition: take the rtxn before entering the thread
 so we're sure we won't try to retrieve deleted tasks

---
 crates/index-scheduler/src/lib.rs           | 65 ++++++++++++---------
 crates/index-scheduler/src/scheduler/mod.rs | 11 +---
 2 files changed, 40 insertions(+), 36 deletions(-)

diff --git a/crates/index-scheduler/src/lib.rs b/crates/index-scheduler/src/lib.rs
index d04b8f9e2..419e6f21e 100644
--- a/crates/index-scheduler/src/lib.rs
+++ b/crates/index-scheduler/src/lib.rs
@@ -784,7 +784,7 @@ impl IndexScheduler {
     }
 
     /// Once the tasks changes have been committed we must send all the tasks that were updated to our webhooks
-    fn notify_webhooks(&self, webhooks: Webhooks, updated: &RoaringBitmap) -> Result<()> {
+    fn notify_webhooks(&self, updated: RoaringBitmap) {
         struct TaskReader<'a, 'b> {
             rtxn: &'a RoTxn<'a>,
             index_scheduler: &'a IndexScheduler,
@@ -829,33 +829,46 @@ impl IndexScheduler {
             }
         }
 
-        let rtxn = self.env.read_txn()?;
-
-        for (uuid, Webhook { url, headers }) in webhooks.webhooks.iter() {
-            let task_reader = TaskReader {
-                rtxn: &rtxn,
-                index_scheduler: self,
-                tasks: &mut updated.into_iter(),
-                buffer: Vec::with_capacity(page_size::get()),
-                written: 0,
-            };
-
-            let reader = GzEncoder::new(BufReader::new(task_reader), Compression::default());
-
-            let mut request = ureq::post(url)
-                .timeout(Duration::from_secs(30))
-                .set("Content-Encoding", "gzip")
-                .set("Content-Type", "application/x-ndjson");
-            for (header_name, header_value) in headers.iter() {
-                request = request.set(header_name, header_value);
-            }
-
-            if let Err(e) = request.send(reader) {
-                tracing::error!("While sending data to the webhook {uuid}: {e}");
-            }
+        let webhooks = self.webhooks();
+        if webhooks.webhooks.is_empty() {
+            return;
         }
+        let this = self.private_clone();
+        // We must take the RoTxn before entering the thread::spawn otherwise another batch may be
+        // processed before we had the time to take our txn.
+        let rtxn = match self.env.clone().static_read_txn() {
+            Ok(rtxn) => rtxn,
+            Err(e) => {
+                tracing::error!("Couldn't get an rtxn to notify the webhook: {e}");
+                return;
+            }
+        };
 
-        Ok(())
+        std::thread::spawn(move || {
+            for (uuid, Webhook { url, headers }) in webhooks.webhooks.iter() {
+                let task_reader = TaskReader {
+                    rtxn: &rtxn,
+                    index_scheduler: &this,
+                    tasks: &mut updated.iter(),
+                    buffer: Vec::with_capacity(page_size::get()),
+                    written: 0,
+                };
+
+                let reader = GzEncoder::new(BufReader::new(task_reader), Compression::default());
+
+                let mut request = ureq::post(url)
+                    .timeout(Duration::from_secs(30))
+                    .set("Content-Encoding", "gzip")
+                    .set("Content-Type", "application/x-ndjson");
+                for (header_name, header_value) in headers.iter() {
+                    request = request.set(header_name, header_value);
+                }
+
+                if let Err(e) = request.send(reader) {
+                    tracing::error!("While sending data to the webhook {uuid}: {e}");
+                }
+            }
+        });
     }
 
     pub fn index_stats(&self, index_uid: &str) -> Result<IndexStats> {
diff --git a/crates/index-scheduler/src/scheduler/mod.rs b/crates/index-scheduler/src/scheduler/mod.rs
index bbfc4e058..b2bb90c0b 100644
--- a/crates/index-scheduler/src/scheduler/mod.rs
+++ b/crates/index-scheduler/src/scheduler/mod.rs
@@ -446,16 +446,7 @@ impl IndexScheduler {
             Ok(())
         })?;
 
-        // We shouldn't crash the tick function if we can't send data to the webhooks
-        let webhooks = self.webhooks();
-        if !webhooks.webhooks.is_empty() {
-            let cloned_index_scheduler = self.private_clone();
-            std::thread::spawn(move || {
-                if let Err(e) = cloned_index_scheduler.notify_webhooks(webhooks, &ids) {
-                    tracing::error!("Failure to notify webhooks: {e}");
-                }
-            });
-        }
+        self.notify_webhooks(ids);
 
         #[cfg(test)]
         self.breakpoint(crate::test_utils::Breakpoint::AfterProcessing);