From 42bb0f47f1c58d5b00b904c6385099b346a1d23e Mon Sep 17 00:00:00 2001
From: sumeerbhola <sumeer@cockroachlabs.com>
Date: Mon, 16 Dec 2024 13:06:46 -0500
Subject: [PATCH] cache: tiny tweaks to readShard

- acquire a read lock instead of a write lock, when context is canceled.
- add another assertion.
---
 internal/cache/read_shard.go | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/internal/cache/read_shard.go b/internal/cache/read_shard.go
index 432edc1e4c..474433b1c8 100644
--- a/internal/cache/read_shard.go
+++ b/internal/cache/read_shard.go
@@ -251,8 +251,8 @@ func (e *readEntry) waitForReadPermissionOrHandle(
 		e.mu.Unlock()
 		select {
 		case <-ctx.Done():
-			e.mu.Lock()
-			errorDuration = unlockAndUnrefAndTryRemoveFromMap(false)
+			e.mu.RLock()
+			errorDuration = unlockAndUnrefAndTryRemoveFromMap(true)
 			return Handle{}, errorDuration, ctx.Err()
 		case _, ok := <-ch:
 			if !ok {
@@ -344,6 +344,9 @@ func (e *readEntry) setReadValue(v *Value) Handle {
 	e.mu.Lock()
 	// Acquire a ref for readEntry, since we are going to remember it in e.mu.v.
 	v.acquire()
+	if e.mu.v != nil {
+		panic("value already set")
+	}
 	e.mu.v = v
 	if !e.mu.isReading {
 		panic("isReading is false")