From 08b79a30f6a48425cd2bc558f17e4e3d306dfe8b Mon Sep 17 00:00:00 2001
From: Chris Lu <chrislusf@users.noreply.github.com>
Date: Thu, 19 Mar 2026 16:08:24 -0700
Subject: [PATCH] Fix lock table shared wait condition (#8707)

* Fix lock table shared wait condition (#8696)

* Refactor lock table waiter check

* Add exclusive lock wait helper test
---
 weed/util/lock_table.go      | 16 +++++++++++--
 weed/util/lock_table_test.go | 44 ++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/weed/util/lock_table.go b/weed/util/lock_table.go
index a932ae5b1..8f65aac06 100644
--- a/weed/util/lock_table.go
+++ b/weed/util/lock_table.go
@@ -52,6 +52,18 @@ func (lt *LockTable[T]) NewActiveLock(intention string, lockType LockType) *Acti
 	return l
 }
 
+func isNotFirstWaiter(lock *ActiveLock, entry *LockEntry) bool {
+	return len(entry.waiters) > 0 && lock.ID != entry.waiters[0].ID
+}
+
+func shouldWaitForExclusiveLock(lock *ActiveLock, entry *LockEntry) bool {
+	return !lock.isDeleted && (isNotFirstWaiter(lock, entry) || entry.activeExclusiveLockOwnerCount > 0 || entry.activeSharedLockOwnerCount > 0)
+}
+
+func shouldWaitForSharedLock(lock *ActiveLock, entry *LockEntry) bool {
+	return !lock.isDeleted && (isNotFirstWaiter(lock, entry) || entry.activeExclusiveLockOwnerCount > 0)
+}
+
 func (lt *LockTable[T]) AcquireLock(intention string, key T, lockType LockType) (lock *ActiveLock) {
 	lt.mu.Lock()
 	// Get or create the lock entry for the key
@@ -81,11 +93,11 @@ func (lt *LockTable[T]) AcquireLock(intention string, key T, lockType LockType)
 		}
 		entry.waiters = append(entry.waiters, lock)
 		if lockType == ExclusiveLock {
-			for !lock.isDeleted && ((len(entry.waiters) > 0 && lock.ID != entry.waiters[0].ID) || entry.activeExclusiveLockOwnerCount > 0 || entry.activeSharedLockOwnerCount > 0) {
+			for shouldWaitForExclusiveLock(lock, entry) {
 				entry.cond.Wait()
 			}
 		} else {
-			for !lock.isDeleted && (len(entry.waiters) > 0 && lock.ID != entry.waiters[0].ID) || entry.activeExclusiveLockOwnerCount > 0 {
+			for shouldWaitForSharedLock(lock, entry) {
 				entry.cond.Wait()
 			}
 		}
diff --git a/weed/util/lock_table_test.go b/weed/util/lock_table_test.go
index 001fa0bdf..eb5152d0b 100644
--- a/weed/util/lock_table_test.go
+++ b/weed/util/lock_table_test.go
@@ -40,3 +40,47 @@ func TestOrderedLock(t *testing.T) {
 
 	wg.Wait()
 }
+
+func TestShouldWaitForSharedLock(t *testing.T) {
+	lock := &ActiveLock{ID: 2, lockType: SharedLock}
+	entry := &LockEntry{
+		waiters: []*ActiveLock{{ID: 1}, lock},
+	}
+
+	if !shouldWaitForSharedLock(lock, entry) {
+		t.Fatal("shared lock should wait behind earlier waiters")
+	}
+
+	entry.waiters = []*ActiveLock{lock}
+	entry.activeExclusiveLockOwnerCount = 1
+	if !shouldWaitForSharedLock(lock, entry) {
+		t.Fatal("shared lock should wait while an exclusive owner is active")
+	}
+
+	lock.isDeleted = true
+	if shouldWaitForSharedLock(lock, entry) {
+		t.Fatal("deleted shared lock should stop waiting even if an exclusive owner is active")
+	}
+}
+
+func TestShouldWaitForExclusiveLock(t *testing.T) {
+	lock := &ActiveLock{ID: 2, lockType: ExclusiveLock}
+	entry := &LockEntry{
+		waiters: []*ActiveLock{{ID: 1}, lock},
+	}
+
+	if !shouldWaitForExclusiveLock(lock, entry) {
+		t.Fatal("exclusive lock should wait behind earlier waiters")
+	}
+
+	entry.waiters = []*ActiveLock{lock}
+	entry.activeSharedLockOwnerCount = 1
+	if !shouldWaitForExclusiveLock(lock, entry) {
+		t.Fatal("exclusive lock should wait while shared owners are active")
+	}
+
+	lock.isDeleted = true
+	if shouldWaitForExclusiveLock(lock, entry) {
+		t.Fatal("deleted exclusive lock should stop waiting even if shared owners are active")
+	}
+}