explicitely drop the search permit

meilisearch/src/routes/indexes/facet_search.rs

@@ -81,7 +81,7 @@ pub async fn search(
     let index = index_scheduler.index(&index_uid)?;
     let features = index_scheduler.features();
     let search_kind = search_kind(&search_query, &index_scheduler, &index, features)?;
-    let _permit = search_queue.try_get_search_permit().await?;
+    let permit = search_queue.try_get_search_permit().await?;
     let search_result = tokio::task::spawn_blocking(move || {
         perform_facet_search(
             &index,
@@ -94,6 +94,7 @@ pub async fn search(
         )
     })
     .await?;
+    permit.drop().await;
 
     if let Ok(ref search_result) = search_result {
         aggregate.succeed(search_result);

meilisearch/src/routes/indexes/search.rs

@@ -233,11 +233,12 @@ pub async fn search_with_url_query(
 
     let search_kind = search_kind(&query, index_scheduler.get_ref(), &index, features)?;
     let retrieve_vector = RetrieveVectors::new(query.retrieve_vectors, features)?;
-    let _permit = search_queue.try_get_search_permit().await?;
+    let permit = search_queue.try_get_search_permit().await?;
     let search_result = tokio::task::spawn_blocking(move || {
         perform_search(&index, query, search_kind, retrieve_vector, index_scheduler.features())
     })
     .await?;
+    permit.drop().await;
     if let Ok(ref search_result) = search_result {
         aggregate.succeed(search_result);
     }
@@ -276,11 +277,12 @@ pub async fn search_with_post(
     let search_kind = search_kind(&query, index_scheduler.get_ref(), &index, features)?;
     let retrieve_vectors = RetrieveVectors::new(query.retrieve_vectors, features)?;
 
-    let _permit = search_queue.try_get_search_permit().await?;
+    let permit = search_queue.try_get_search_permit().await?;
     let search_result = tokio::task::spawn_blocking(move || {
         perform_search(&index, query, search_kind, retrieve_vectors, index_scheduler.features())
     })
     .await?;
+    permit.drop().await;
     if let Ok(ref search_result) = search_result {
         aggregate.succeed(search_result);
         if search_result.degraded {

meilisearch/src/routes/multi_search.rs

@@ -39,7 +39,7 @@ pub async fn multi_search_with_post(
 ) -> Result<HttpResponse, ResponseError> {
     // Since we don't want to process half of the search requests and then get a permit refused
     // we're going to get one permit for the whole duration of the multi-search request.
-    let _permit = search_queue.try_get_search_permit().await?;
+    let permit = search_queue.try_get_search_permit().await?;
 
     let federated_search = params.into_inner();
 
@@ -162,6 +162,7 @@ pub async fn multi_search_with_post(
             HttpResponse::Ok().json(SearchResults { results: search_results })
         }
     };
+    permit.drop().await;
 
     Ok(response)
 }

meilisearch/src/search_queue.rs

@@ -33,11 +33,20 @@ pub struct SearchQueue {
 
 /// You should only run search requests while holding this permit.
 /// Once it's dropped, a new search request will be able to process.
+/// You should always try to drop the permit yourself calling the `drop` async method on it.
 #[derive(Debug)]
 pub struct Permit {
     sender: mpsc::Sender<()>,
 }
 
+impl Permit {
+    /// Drop the permit giving back on permit to the search queue.
+    pub async fn drop(self) {
+        // if the channel is closed then the whole instance is down
+        let _ = self.sender.send(()).await;
+    }
+}
+
 impl Drop for Permit {
     fn drop(&mut self) {
         let sender = self.sender.clone();

meilisearch/tests/search/search_queue.rs

@@ -37,6 +37,25 @@ async fn search_queue_register() {
         .unwrap();
 }
 
+#[actix_rt::test]
+async fn search_queue_register_with_explicit_drop() {
+    let queue = SearchQueue::new(4, NonZeroUsize::new(2).unwrap());
+
+    // First, use all the cores
+    let permit1 = queue.try_get_search_permit().await.unwrap();
+    let _permit2 = queue.try_get_search_permit().await.unwrap();
+
+    // If we free one spot we should be able to register one new search
+    permit1.drop().await;
+
+    let permit3 = queue.try_get_search_permit().await.unwrap();
+
+    // And again
+    permit3.drop().await;
+
+    let _permit4 = queue.try_get_search_permit().await.unwrap();
+}
+
 #[actix_rt::test]
 async fn wait_till_cores_are_available() {
     let queue = Arc::new(SearchQueue::new(4, NonZeroUsize::new(1).unwrap()));