Fix the problem that Lucene lock is held by VM (#6570)

#### What type of PR is this?

/kind bug
/area core
/milestone 2.20.x

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

This PR add keyword synchronized for methods `addOrUpdateDocuments`, `deleteDocuments` and `deleteAll` to ensure the write lock of Lucene is obtained only by one IndexWriter at the same time.

#### Which issue(s) this PR fixes:

Fixes #6569 

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

```release-note
修复重启后无法搜索部分文档的问题
```

application/src/main/java/run/halo/app/search/lucene/LuceneSearchEngine.java

@@ -84,7 +84,7 @@ public class LuceneSearchEngine implements SearchEngine, InitializingBean, Dispo
 
     private Directory directory;
 
-    public LuceneSearchEngine(Path indexRootDir) throws IOException {
+    public LuceneSearchEngine(Path indexRootDir) {
         this.indexRootDir = indexRootDir;
     }
 
@@ -106,12 +106,14 @@ public void addOrUpdate(Iterable<HaloDocument> haloDocs) {
 
         var writerConfig = new IndexWriterConfig(this.analyzer)
             .setOpenMode(CREATE_OR_APPEND);
-        try (var indexWriter = new IndexWriter(this.directory, writerConfig)) {
-            indexWriter.updateDocuments(deleteQuery, docs);
-        } catch (IOException e) {
-            throw Exceptions.propagate(e);
-        } finally {
-            this.refreshSearcherManager();
+        synchronized (this) {
+            try (var indexWriter = new IndexWriter(this.directory, writerConfig)) {
+                indexWriter.updateDocuments(deleteQuery, docs);
+            } catch (IOException e) {
+                throw Exceptions.propagate(e);
+            } finally {
+                this.refreshSearcherManager();
+            }
         }
     }
 
@@ -122,25 +124,29 @@ public void deleteDocument(Iterable<String> haloDocIds) {
         var deleteQuery = new TermInSetQuery("id", terms);
         var writerConfig = new IndexWriterConfig(this.analyzer)
             .setOpenMode(CREATE_OR_APPEND);
-        try (var indexWriter = new IndexWriter(this.directory, writerConfig)) {
-            indexWriter.deleteDocuments(deleteQuery);
-        } catch (IOException e) {
-            throw Exceptions.propagate(e);
-        } finally {
-            this.refreshSearcherManager();
+        synchronized (this) {
+            try (var indexWriter = new IndexWriter(this.directory, writerConfig)) {
+                indexWriter.deleteDocuments(deleteQuery);
+            } catch (IOException e) {
+                throw Exceptions.propagate(e);
+            } finally {
+                this.refreshSearcherManager();
+            }
         }
     }
 
     @Override
     public void deleteAll() {
         var writerConfig = new IndexWriterConfig(this.analyzer)
             .setOpenMode(CREATE_OR_APPEND);
-        try (var indexWriter = new IndexWriter(this.directory, writerConfig)) {
-            indexWriter.deleteAll();
-        } catch (IOException e) {
-            throw Exceptions.propagate(e);
-        } finally {
-            this.refreshSearcherManager();
+        synchronized (this) {
+            try (var indexWriter = new IndexWriter(this.directory, writerConfig)) {
+                indexWriter.deleteAll();
+            } catch (IOException e) {
+                throw Exceptions.propagate(e);
+            } finally {
+                this.refreshSearcherManager();
+            }
         }
     }
 

application/src/test/java/run/halo/app/search/lucene/LuceneSearchEngineTest.java

@@ -3,12 +3,19 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.IOException;
 import java.nio.file.Path;
 import java.time.Instant;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.stream.IntStream;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.junit.jupiter.api.AfterEach;
@@ -76,6 +83,35 @@ void shouldDeleteAll() throws IOException {
         assertEquals(0, reader.getDocCount("id"));
     }
 
+    @Test
+    void shouldAddOrUpdateDocumentConcurrently()
+        throws ExecutionException, InterruptedException, TimeoutException {
+        runConcurrently(() -> {
+            var haloDoc = createFakeHaloDoc();
+            searchEngine.addOrUpdate(List.of(haloDoc));
+        });
+    }
+
+    @Test
+    void shouldDeleteDocumentConcurrently()
+        throws ExecutionException, InterruptedException, TimeoutException {
+        runConcurrently(() -> {
+            var haloDoc = createFakeHaloDoc();
+            searchEngine.addOrUpdate(List.of(haloDoc));
+            searchEngine.deleteDocument(List.of(haloDoc.getId()));
+        });
+    }
+
+    @Test
+    void shouldDeleteAllConcurrently()
+        throws ExecutionException, InterruptedException, TimeoutException {
+        runConcurrently(() -> {
+            var haloDoc = createFakeHaloDoc();
+            searchEngine.addOrUpdate(List.of(haloDoc));
+            searchEngine.deleteAll();
+        });
+    }
+
     @Test
     void shouldDestroy() throws Exception {
         var directory = this.searchEngine.getDirectory();
@@ -118,6 +154,17 @@ void shouldSearch() {
         assertEquals("<fake-tag>fake</fake-tag>-content", gotHaloDoc.getContent());
     }
 
+    void runConcurrently(Runnable runnable)
+        throws ExecutionException, InterruptedException, TimeoutException {
+        var executorService = Executors.newFixedThreadPool(10);
+        var futures = IntStream.of(0, 10)
+            .mapToObj(i -> CompletableFuture.runAsync(runnable, executorService))
+            .toArray(CompletableFuture[]::new);
+        CompletableFuture.allOf(futures).get(10, TimeUnit.SECONDS);
+        executorService.shutdownNow();
+        assertTrue(executorService.awaitTermination(10, TimeUnit.SECONDS));
+    }
+
     HaloDocument createFakeHaloDoc() {
         var haloDoc = new HaloDocument();
         haloDoc.setId("fake-id");