From 2832aa8e43cb7cc56ecb2bc00b66db1a1fb07a26 Mon Sep 17 00:00:00 2001
From: Jonathan Nieder <jrn@google.com>
Date: Tue, 25 Mar 2014 17:47:41 -0700
Subject: [PATCH] Allow plugins to replace gerrit-provided hot-replaceable
 DynamicItem, too

While at it, clean up the code path for non hot-replaceable
DynamicItem (in particular adding a defensive check for null even
though it should never be triggered since a DynamicItem from gerrit
core cannot be unloaded).

Change-Id: I5f4074a3752e8d84fc349b502408bdd520927d5e
---
 .../extensions/registration/DynamicItem.java  | 27 +++++++++----------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/gerrit-extension-api/src/main/java/com/google/gerrit/extensions/registration/DynamicItem.java b/gerrit-extension-api/src/main/java/com/google/gerrit/extensions/registration/DynamicItem.java
index cfb7bd97f5..91bf7a6117 100644
--- a/gerrit-extension-api/src/main/java/com/google/gerrit/extensions/registration/DynamicItem.java
+++ b/gerrit-extension-api/src/main/java/com/google/gerrit/extensions/registration/DynamicItem.java
@@ -150,15 +150,9 @@ public class DynamicItem<T> {
   public RegistrationHandle set(Provider<T> impl, String pluginName) {
     final NamedProvider<T> item = new NamedProvider<T>(impl, pluginName);
     NamedProvider<T> old = null;
-    while (!ref.compareAndSet(null, item)) {
+    while (!ref.compareAndSet(old, item)) {
       old = ref.get();
-      if (old != null) {
-        if ("gerrit".equals(old.pluginName)) {
-          if (ref.compareAndSet(old, item)) {
-            break;
-          }
-          old = ref.get();
-        }
+      if (old != null && !"gerrit".equals(old.pluginName)) {
         throw new ProvisionException(String.format(
             "%s already provided by %s, ignoring plugin %s",
             key.getTypeLiteral(), old.pluginName, pluginName));
@@ -187,24 +181,27 @@ public class DynamicItem<T> {
   public ReloadableRegistrationHandle<T> set(Key<T> key, Provider<T> impl,
       String pluginName) {
     final NamedProvider<T> item = new NamedProvider<T>(impl, pluginName);
-    while (!ref.compareAndSet(null, item)) {
-      NamedProvider<T> old = ref.get();
-      if (old != null) {
+    NamedProvider<T> old = null;
+    while (!ref.compareAndSet(old, item)) {
+      old = ref.get();
+      if (old != null && !"gerrit".equals(old.pluginName)) {
         throw new ProvisionException(String.format(
             "%s already provided by %s, ignoring plugin %s",
             this.key.getTypeLiteral(), old.pluginName, pluginName));
       }
     }
-    return new ReloadableHandle(key, item);
+    return new ReloadableHandle(key, item, old);
   }
 
   private class ReloadableHandle implements ReloadableRegistrationHandle<T> {
     private final Key<T> key;
     private final NamedProvider<T> item;
+    private final NamedProvider<T> defaultItem;
 
-    ReloadableHandle(Key<T> key, NamedProvider<T> item) {
+    ReloadableHandle(Key<T> key, NamedProvider<T> item, NamedProvider<T> defaultItem) {
       this.key = key;
       this.item = item;
+      this.defaultItem = defaultItem;
     }
 
     @Override
@@ -214,14 +211,14 @@ public class DynamicItem<T> {
 
     @Override
     public void remove() {
-      ref.compareAndSet(item, null);
+      ref.compareAndSet(item, defaultItem);
     }
 
     @Override
     public ReloadableHandle replace(Key<T> newKey, Provider<T> newItem) {
       NamedProvider<T> n = new NamedProvider<T>(newItem, item.pluginName);
       if (ref.compareAndSet(item, n)) {
-        return new ReloadableHandle(newKey, n);
+        return new ReloadableHandle(newKey, n, defaultItem);
       }
       return null;
     }