From e3a454a9004fc6ad5cd02bcac09b222d62212226 Mon Sep 17 00:00:00 2001
From: Chris Povirk <cpovirk@google.com>
Date: Wed, 5 Aug 2026 13:04:32 -0400
Subject: [PATCH] Annotate `Lock` and `ReentrantLock`.

(prompted by https://github.com/google/xplat/commit/7ab1a2c5b64d57086a7d5050de3f517b4ffb8283)
---
 .../share/classes/java/util/concurrent/locks/Lock.java       | 2 ++
 .../classes/java/util/concurrent/locks/ReentrantLock.java    | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/java.base/share/classes/java/util/concurrent/locks/Lock.java b/src/java.base/share/classes/java/util/concurrent/locks/Lock.java
index bd6ce2eb6f9..ec5758a3256 100644
--- a/src/java.base/share/classes/java/util/concurrent/locks/Lock.java
+++ b/src/java.base/share/classes/java/util/concurrent/locks/Lock.java
@@ -36,6 +36,7 @@
 package java.util.concurrent.locks;
 
 import java.util.concurrent.TimeUnit;
+import org.jspecify.annotations.NullMarked;
 
 /**
  * {@code Lock} implementations provide more extensive locking
@@ -166,6 +167,7 @@
  * @since 1.5
  * @author Doug Lea
  */
+@NullMarked
 public interface Lock {
 
     /**
diff --git a/src/java.base/share/classes/java/util/concurrent/locks/ReentrantLock.java b/src/java.base/share/classes/java/util/concurrent/locks/ReentrantLock.java
index d0ad4cae428..5c15ac5b984 100644
--- a/src/java.base/share/classes/java/util/concurrent/locks/ReentrantLock.java
+++ b/src/java.base/share/classes/java/util/concurrent/locks/ReentrantLock.java
@@ -38,6 +38,8 @@
 import java.util.Collection;
 import java.util.concurrent.TimeUnit;
 import jdk.internal.vm.annotation.ReservedStackAccess;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A reentrant mutual exclusion {@link Lock} with the same basic
@@ -106,6 +108,7 @@
  * @since 1.5
  * @author Doug Lea
  */
+@NullMarked
 public class ReentrantLock implements Lock, java.io.Serializable {
     private static final long serialVersionUID = 7373984872572414699L;
     /** @serial Synchronizer providing all implementation mechanics */
@@ -650,7 +653,7 @@ public final boolean isFair() {
      *
      * @return the owner, or {@code null} if not owned
      */
-    protected Thread getOwner() {
+    protected @Nullable Thread getOwner() {
         return sync.getOwner();
     }