From b322d0415a9b7ac7c29082d9a8b38561bce2ba15 Mon Sep 17 00:00:00 2001
From: Chayim Refael Friedman <chayimfr@gmail.com>
Date: Sun, 3 May 2026 17:11:07 +0300
Subject: [PATCH] Do not drop `ExpansionSpanMap` and `AstIdMap` asynchronously

They do not contain things that require looping when dropping, only `Vec`/`Arena`/`HashTable` of non-`Drop` types. Therefore sending to an external channel is likely to be slower than just dropping.
---
 crates/span/src/ast_id.rs | 42 ---------------------------------------
 crates/span/src/map.rs    | 33 ------------------------------
 2 files changed, 75 deletions(-)

diff --git a/crates/span/src/ast_id.rs b/crates/span/src/ast_id.rs
index f6500a9b4dbe..2193f70d47d0 100644
--- a/crates/span/src/ast_id.rs
+++ b/crates/span/src/ast_id.rs
@@ -810,48 +810,6 @@ impl AstIdMap {
     }
 }
 
-#[cfg(not(no_salsa_async_drops))]
-impl Drop for AstIdMap {
-    fn drop(&mut self) {
-        let arena = std::mem::take(&mut self.arena);
-        let ptr_map = std::mem::take(&mut self.ptr_map);
-        let id_map = std::mem::take(&mut self.id_map);
-        static AST_ID_MAP_DROP_THREAD: std::sync::OnceLock<
-            std::sync::mpsc::Sender<(
-                Arena<(SyntaxNodePtr, ErasedFileAstId)>,
-                hashbrown::HashTable<ArenaId>,
-                hashbrown::HashTable<ArenaId>,
-            )>,
-        > = std::sync::OnceLock::new();
-        AST_ID_MAP_DROP_THREAD
-            .get_or_init(|| {
-                let (sender, receiver) = std::sync::mpsc::channel::<(
-                    Arena<(SyntaxNodePtr, ErasedFileAstId)>,
-                    hashbrown::HashTable<ArenaId>,
-                    hashbrown::HashTable<ArenaId>,
-                )>();
-                std::thread::Builder::new()
-                    .name("AstIdMapDropper".to_owned())
-                    .spawn(move || {
-                        loop {
-                            // block on a receive
-                            _ = receiver.recv();
-                            // then drain the entire channel
-                            while receiver.try_recv().is_ok() {}
-                            // and sleep for a bit
-                            std::thread::sleep(std::time::Duration::from_millis(100));
-                        }
-                        // why do this over just a `receiver.iter().for_each(drop)`? To reduce contention on the channel lock.
-                        // otherwise this thread will constantly wake up and sleep again.
-                    })
-                    .unwrap();
-                sender
-            })
-            .send((arena, ptr_map, id_map))
-            .unwrap();
-    }
-}
-
 #[inline]
 fn hash_ptr(ptr: &SyntaxNodePtr) -> u64 {
     FxBuildHasher.hash_one(ptr)
diff --git a/crates/span/src/map.rs b/crates/span/src/map.rs
index dc7d471aa03a..5b92096ef87b 100644
--- a/crates/span/src/map.rs
+++ b/crates/span/src/map.rs
@@ -150,39 +150,6 @@ impl SpanMap {
     }
 }
 
-#[cfg(not(no_salsa_async_drops))]
-impl Drop for SpanMap {
-    fn drop(&mut self) {
-        let spans = std::mem::take(&mut self.spans);
-        static SPAN_MAP_DROP_THREAD: std::sync::OnceLock<
-            std::sync::mpsc::Sender<Vec<(TextSize, Span)>>,
-        > = std::sync::OnceLock::new();
-
-        SPAN_MAP_DROP_THREAD
-            .get_or_init(|| {
-                let (sender, receiver) = std::sync::mpsc::channel::<Vec<(TextSize, Span)>>();
-                std::thread::Builder::new()
-                    .name("SpanMapDropper".to_owned())
-                    .spawn(move || {
-                        loop {
-                            // block on a receive
-                            _ = receiver.recv();
-                            // then drain the entire channel
-                            while receiver.try_recv().is_ok() {}
-                            // and sleep for a bit
-                            std::thread::sleep(std::time::Duration::from_millis(100));
-                        }
-                        // why do this over just a `receiver.iter().for_each(drop)`? To reduce contention on the channel lock.
-                        // otherwise this thread will constantly wake up and sleep again.
-                    })
-                    .unwrap();
-                sender
-            })
-            .send(spans)
-            .unwrap();
-    }
-}
-
 #[derive(PartialEq, Eq, Hash, Debug)]
 pub struct RealSpanMap {
     file_id: EditionedFileId,