From 5adad1a8adc6bcd46fffa2adb2411782a32b7623 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <me@lukaswirth.dev>
Date: Sun, 28 Dec 2025 11:43:08 +0100
Subject: [PATCH] perf: Reduce channel lock contention for drop-threads

---
 src/tools/rust-analyzer/crates/span/src/map.rs  | 17 ++++++++++++++++-
 .../rust-analyzer/crates/syntax/src/lib.rs      | 13 ++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/tools/rust-analyzer/crates/span/src/map.rs b/src/tools/rust-analyzer/crates/span/src/map.rs
index 7faf6f1b1a68..f5c083a9f650 100644
--- a/src/tools/rust-analyzer/crates/span/src/map.rs
+++ b/src/tools/rust-analyzer/crates/span/src/map.rs
@@ -163,7 +163,22 @@ unsafe impl Send for SendPtr {}
                 let (sender, receiver) = std::sync::mpsc::channel::<(SendPtr, fn(SendPtr))>();
                 std::thread::Builder::new()
                     .name("SpanMapDropper".to_owned())
-                    .spawn(move || receiver.iter().for_each(|(b, drop)| drop(b)))
+                    .spawn(move || {
+                        loop {
+                            // block on a receive
+                            if let Ok((b, drop)) = receiver.recv() {
+                                drop(b);
+                            }
+                            // then drain the entire channel
+                            while let Ok((b, drop)) = receiver.try_recv() {
+                                drop(b);
+                            }
+                            // 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
             })
diff --git a/src/tools/rust-analyzer/crates/syntax/src/lib.rs b/src/tools/rust-analyzer/crates/syntax/src/lib.rs
index 9e3083066c94..d36019514016 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/lib.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/lib.rs
@@ -218,7 +218,18 @@ fn drop(&mut self) {
                 let (sender, receiver) = std::sync::mpsc::channel::<GreenNode>();
                 std::thread::Builder::new()
                     .name("ParseNodeDropper".to_owned())
-                    .spawn(move || receiver.iter().for_each(drop))
+                    .spawn(move || {
+                        loop {
+                            // block on a receive
+                            _ = receiver.recv();
+                            // then drain the entire channel
+                            while let Ok(_) = receiver.try_recv() {}
+                            // 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
             })