Use CopyOnWriteArrayList on SchemeManager (#2612)

#### What type of PR is this?

/kind bug
/area core
/milestone 2.0

#### What this PR does / why we need it:

Use CopyOnWriteArrayList on SchemeManager to prevent concurrent modification when link plugin is installed.

#### How to test?

1. Install link plugin
2. Restart Halo
3. Delete any extensions
4. Check the result

#### Does this PR introduce a user-facing change?

```release-note
修复数据一直处于删除中的错误
```

src/main/java/run/halo/app/extension/DefaultSchemeManager.java

@@ -1,9 +1,9 @@
 package run.halo.app.extension;
 
 import java.util.Collections;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Optional;
+import java.util.concurrent.CopyOnWriteArrayList;
 import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import run.halo.app.extension.SchemeWatcherManager.SchemeRegistered;
@@ -18,7 +18,9 @@ public class DefaultSchemeManager implements SchemeManager {
 
     public DefaultSchemeManager(@Nullable SchemeWatcherManager watcherManager) {
         this.watcherManager = watcherManager;
-        schemes = new LinkedList<>();
+        // we have to use CopyOnWriteArrayList at here to prevent concurrent modification between
+        // registering and listing.
+        schemes = new CopyOnWriteArrayList<>();
     }
 
     @Override

src/main/java/run/halo/app/extension/DefaultSchemeWatcherManager.java

@@ -1,7 +1,8 @@
 package run.halo.app.extension;
 
-import java.util.LinkedList;
+import java.util.Collections;
 import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
 import org.springframework.lang.NonNull;
 import org.springframework.util.Assert;
 
@@ -10,7 +11,7 @@ public class DefaultSchemeWatcherManager implements SchemeWatcherManager {
     private final List<SchemeWatcher> watchers;
 
     public DefaultSchemeWatcherManager() {
-        watchers = new LinkedList<>();
+        watchers = new CopyOnWriteArrayList<>();
     }
 
     @Override
@@ -28,6 +29,6 @@ public class DefaultSchemeWatcherManager implements SchemeWatcherManager {
     @Override
     public List<SchemeWatcher> watchers() {
         // we have to copy the watchers entirely to prevent concurrent modification.
-        return List.copyOf(watchers);
+        return Collections.unmodifiableList(watchers);
     }
 }

src/main/java/run/halo/app/extension/controller/DefaultController.java

@@ -1,12 +1,15 @@
 package run.halo.app.extension.controller;
 
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+
 import java.time.Duration;
 import java.time.Instant;
 import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
 import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.lang3.concurrent.BasicThreadFactory;
 import org.springframework.util.StopWatch;
 import run.halo.app.extension.controller.RequestQueue.DelayedEntry;
 
@@ -68,7 +71,16 @@ public class DefaultController<R> implements Controller {
         Duration minDelay,
         Duration maxDelay) {
         this(name, reconciler, queue, synchronizer, nowSupplier, minDelay, maxDelay,
-            Executors.newSingleThreadExecutor());
+            newSingleThreadExecutor(threadFactory()));
+    }
+
+    private static ThreadFactory threadFactory() {
+        return new BasicThreadFactory.Builder()
+            .namingPattern("reconciler-thread-%d")
+            .daemon(false)
+            .uncaughtExceptionHandler((t, e) ->
+                log.error("Controller " + t.getName() + " encountered an error unexpectedly", e))
+            .build();
     }
 
     @Override

src/test/java/run/halo/app/extension/DefaultSchemeManagerTest.java

@@ -116,5 +116,20 @@ class DefaultSchemeManagerTest {
         schemeManager.unregister(schemeManager.get(FakeExtension.class));
         assertEquals(0, schemeManager.size());
     }
+
+    @Test
+    void shouldReturnCopyOnWriteList() {
+        schemeManager.register(FakeExtension.class);
+        var schemes = schemeManager.schemes();
+        schemes.forEach(scheme -> {
+            // make sure concurrent modification won't happen
+            schemeManager.register(FooExtension.class);
+        });
+    }
+
+    @GVK(group = "fake.halo.run", version = "v1alpha1", kind = "Foo",
+        plural = "foos", singular = "foo")
+    static class FooExtension extends AbstractExtension {
+    }
 }
 

src/test/java/run/halo/app/extension/DefaultSchemeWatcherManagerTest.java

@@ -49,15 +49,11 @@ class DefaultSchemeWatcherManagerTest {
 
     @Test
     void shouldReturnCopyOfWatchers() {
-        var watcher = mock(SchemeWatcher.class);
-        watcherManager.register(watcher);
-        assertEquals(List.of(watcher), watcherManager.watchers());
+        var firstWatcher = mock(SchemeWatcher.class);
+        var secondWatcher = mock(SchemeWatcher.class);
+        watcherManager.register(firstWatcher);
 
-        var watchersBeforeRegister = watcherManager.watchers();
-        watcherManager.unregister(watcher);
-
-        // watchers are not changed even if unregistered
-        assertEquals(List.of(watcher), watchersBeforeRegister);
-        assertEquals(Collections.emptyList(), watcherManager.watchers());
+        var watchers = watcherManager.watchers();
+        watchers.forEach(watcher -> watcherManager.register(secondWatcher));
     }
 }