Merge branch 'stable-3.1' into stable-3.2

* stable-3.1:
    Set PerThreadCache as readonly after creating a new patch-set
    Set PerThreadCache as readonly when formatting change e-mails
    Set PerThreadCache as readonly when formatting change JSON
    Set PerThreadCache as readonly after deleting a change
    Set PerThreadCache as readonly after abandoning a change
    Set PerThreadCache as readonly after merging a change
    Set PerThreadCache as readonly after posting review comments
    Introduce unloaders on PerThreadCache entries
[I] RepoRefCache: Hold a reference to the refDatabase with ref counting
    Remove use of RefCache in ChangeNotes
    Cache change /meta ref SHA1 for each change indexing task

Only the commit prefixed by [I] is included, all the others
are reverted in the merge because they are not needed to be merged
upstream from stable-3.2 onwards.

Since stable-3.2 we have more general solution to the problem
with modules/cached-refdb [1] which provides a pluggable cached refdatabase
without the need to fiddle with the thread-local caching.

[1] https://gerrit-review.googlesource.com/admin/repos/modules/cached-refdb,branches

Release-Notes: skip
Change-Id: Ibc0485dfb37e6d4c7c46e34959f9ab6513838ecb

4 files changed, 300 insertions, 1 deletions

diff --git a/java/com/google/gerrit/server/git/RefCache.java b/java/com/google/gerrit/server/git/RefCache.java
index 5a5cae9332..2dee427bf7 100644
--- a/java/com/google/gerrit/server/git/RefCache.java
+++ b/java/com/google/gerrit/server/git/RefCache.java
@@ -37,4 +37,7 @@ public interface RefCache {
    *     present with a value of {@link ObjectId#zeroId()}.
    */
   Optional<ObjectId> get(String refName) throws IOException;
+
+  /** Closes this cache, releasing the references to any underlying resources. */
+  void close();
 }
diff --git a/java/com/google/gerrit/server/git/RepoRefCache.java b/java/com/google/gerrit/server/git/RepoRefCache.java
index 6b2493a9f1..7a61e67982 100644
--- a/java/com/google/gerrit/server/git/RepoRefCache.java
+++ b/java/com/google/gerrit/server/git/RepoRefCache.java
@@ -28,8 +28,11 @@ import org.eclipse.jgit.lib.Repository;
 public class RepoRefCache implements RefCache {
   private final RefDatabase refdb;
   private final Map<String, Optional<ObjectId>> ids;
+  private final Repository repo;
 
   public RepoRefCache(Repository repo) {
+    repo.incrementOpen();
+    this.repo = repo;
     this.refdb = repo.getRefDatabase();
     this.ids = new HashMap<>();
   }
@@ -50,4 +53,9 @@ public class RepoRefCache implements RefCache {
   public Map<String, Optional<ObjectId>> getCachedRefs() {
     return Collections.unmodifiableMap(ids);
   }
+
+  @Override
+  public void close() {
+    repo.close();
+  }
 }
diff --git a/java/com/google/gerrit/server/update/ChainedReceiveCommands.java b/java/com/google/gerrit/server/update/ChainedReceiveCommands.java
index c223aec637..9a395759bf 100644
--- a/java/com/google/gerrit/server/update/ChainedReceiveCommands.java
+++ b/java/com/google/gerrit/server/update/ChainedReceiveCommands.java
@@ -39,13 +39,19 @@ import org.eclipse.jgit.transport.ReceiveCommand;
 public class ChainedReceiveCommands implements RefCache {
   private final Map<String, ReceiveCommand> commands = new LinkedHashMap<>();
   private final RepoRefCache refCache;
+  private final boolean closeRefCache;
 
   public ChainedReceiveCommands(Repository repo) {
-    this(new RepoRefCache(repo));
+    this(new RepoRefCache(repo), true);
   }
 
   public ChainedReceiveCommands(RepoRefCache refCache) {
+    this(refCache, false);
+  }
+
+  private ChainedReceiveCommands(RepoRefCache refCache, boolean closeRefCache) {
     this.refCache = requireNonNull(refCache);
+    this.closeRefCache = closeRefCache;
   }
 
   public RepoRefCache getRepoRefCache() {
@@ -122,4 +128,11 @@ public class ChainedReceiveCommands implements RefCache {
   public Map<String, ReceiveCommand> getCommands() {
     return Collections.unmodifiableMap(commands);
   }
+
+  @Override
+  public void close() {
+    if (closeRefCache) {
+      refCache.close();
+    }
+  }
 }
diff --git a/javatests/com/google/gerrit/server/git/RepoRefCacheTest.java b/javatests/com/google/gerrit/server/git/RepoRefCacheTest.java
new file mode 100644
index 0000000000..81d68147ea
--- /dev/null
+++ b/javatests/com/google/gerrit/server/git/RepoRefCacheTest.java
@@ -0,0 +1,275 @@
+// Copyright (C) 2022 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.git;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import org.eclipse.jgit.attributes.AttributesNodeProvider;
+import org.eclipse.jgit.internal.storage.dfs.DfsRepositoryDescription;
+import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
+import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository.Builder;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.lib.BatchRefUpdate;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectDatabase;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.RefDatabase;
+import org.eclipse.jgit.lib.RefRename;
+import org.eclipse.jgit.lib.RefUpdate;
+import org.eclipse.jgit.lib.ReflogReader;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.lib.StoredConfig;
+import org.eclipse.jgit.util.FS;
+import org.junit.Test;
+
+public class RepoRefCacheTest {
+  private static final String TEST_BRANCH = "main";
+
+  @Test
+  @SuppressWarnings("resource")
+  public void repositoryUseShouldBeTrackedByRepoRefCache() throws Exception {
+    RefCache cache;
+    TestRepositoryWithRefCounting repoWithRefCounting;
+
+    try (TestRepositoryWithRefCounting repo =
+        TestRepositoryWithRefCounting.createWithBranch(TEST_BRANCH)) {
+      assertThat(repo.refCounter()).isEqualTo(1);
+      repoWithRefCounting = repo;
+      cache = new RepoRefCache(repo);
+    }
+
+    assertThat(repoWithRefCounting.refCounter()).isEqualTo(1);
+    assertThat(cache.get(Constants.R_HEADS + TEST_BRANCH)).isNotNull();
+  }
+
+  private static class TestRepositoryWithRefCounting extends Repository {
+    private int refCounter;
+
+    static TestRepositoryWithRefCounting createWithBranch(String branchName) throws Exception {
+      Builder builder =
+          new InMemoryRepository.Builder()
+              .setRepositoryDescription(new DfsRepositoryDescription(""))
+              .setFS(FS.detect().setUserHome(null));
+      TestRepositoryWithRefCounting testRepo = new TestRepositoryWithRefCounting(builder);
+      new TestRepository<>(testRepo).branch(branchName).commit().message("").create();
+      return testRepo;
+    }
+
+    private final Repository repo;
+
+    private TestRepositoryWithRefCounting(InMemoryRepository.Builder builder) throws IOException {
+      super(builder);
+
+      repo = builder.build();
+      refCounter = 1;
+    }
+
+    public int refCounter() {
+      return refCounter;
+    }
+
+    @Override
+    public void incrementOpen() {
+      repo.incrementOpen();
+      refCounter++;
+    }
+
+    @Override
+    public void close() {
+      repo.close();
+      refCounter--;
+    }
+
+    @Override
+    public void create(boolean bare) throws IOException {}
+
+    @Override
+    public ObjectDatabase getObjectDatabase() {
+      checkIsOpen();
+      return repo.getObjectDatabase();
+    }
+
+    @Override
+    public RefDatabase getRefDatabase() {
+      RefDatabase refDatabase = repo.getRefDatabase();
+      return new RefDatabase() {
+
+        @Override
+        public int hashCode() {
+          return refDatabase.hashCode();
+        }
+
+        @Override
+        public void create() throws IOException {
+          refDatabase.create();
+        }
+
+        @Override
+        public void close() {
+          checkIsOpen();
+          refDatabase.close();
+        }
+
+        @Override
+        public boolean isNameConflicting(String name) throws IOException {
+          checkIsOpen();
+          return refDatabase.isNameConflicting(name);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+          return refDatabase.equals(obj);
+        }
+
+        @Override
+        public Collection<String> getConflictingNames(String name) throws IOException {
+          checkIsOpen();
+          return refDatabase.getConflictingNames(name);
+        }
+
+        @Override
+        public RefUpdate newUpdate(String name, boolean detach) throws IOException {
+          checkIsOpen();
+          return refDatabase.newUpdate(name, detach);
+        }
+
+        @Override
+        public RefRename newRename(String fromName, String toName) throws IOException {
+          checkIsOpen();
+          return refDatabase.newRename(fromName, toName);
+        }
+
+        @Override
+        public BatchRefUpdate newBatchUpdate() {
+          checkIsOpen();
+          return refDatabase.newBatchUpdate();
+        }
+
+        @Override
+        public boolean performsAtomicTransactions() {
+          checkIsOpen();
+          return refDatabase.performsAtomicTransactions();
+        }
+
+        @Override
+        public Ref exactRef(String name) throws IOException {
+          checkIsOpen();
+          return refDatabase.exactRef(name);
+        }
+
+        @Override
+        public String toString() {
+          return refDatabase.toString();
+        }
+
+        @Override
+        public Map<String, Ref> exactRef(String... refs) throws IOException {
+          checkIsOpen();
+          return refDatabase.exactRef(refs);
+        }
+
+        @Override
+        public Ref firstExactRef(String... refs) throws IOException {
+          checkIsOpen();
+          return refDatabase.firstExactRef(refs);
+        }
+
+        @Override
+        public List<Ref> getRefs() throws IOException {
+          checkIsOpen();
+          return refDatabase.getRefs();
+        }
+
+        @Override
+        public Map<String, Ref> getRefs(String prefix) throws IOException {
+          checkIsOpen();
+          return refDatabase.getRefs(prefix);
+        }
+
+        @Override
+        public List<Ref> getRefsByPrefix(String prefix) throws IOException {
+          checkIsOpen();
+          return refDatabase.getRefsByPrefix(prefix);
+        }
+
+        @Override
+        public boolean hasRefs() throws IOException {
+          checkIsOpen();
+          return refDatabase.hasRefs();
+        }
+
+        @Override
+        public List<Ref> getAdditionalRefs() throws IOException {
+          checkIsOpen();
+          return refDatabase.getAdditionalRefs();
+        }
+
+        @Override
+        public Ref peel(Ref ref) throws IOException {
+          checkIsOpen();
+          return refDatabase.peel(ref);
+        }
+
+        @Override
+        public void refresh() {
+          checkIsOpen();
+          refDatabase.refresh();
+        }
+      };
+    }
+
+    @Override
+    public StoredConfig getConfig() {
+      return repo.getConfig();
+    }
+
+    @Override
+    public AttributesNodeProvider createAttributesNodeProvider() {
+      checkIsOpen();
+      return repo.createAttributesNodeProvider();
+    }
+
+    @Override
+    public void scanForRepoChanges() throws IOException {
+      checkIsOpen();
+    }
+
+    @Override
+    public void notifyIndexChanged(boolean internal) {
+      checkIsOpen();
+    }
+
+    @Override
+    public ReflogReader getReflogReader(String refName) throws IOException {
+      checkIsOpen();
+      return repo.getReflogReader(refName);
+    }
+
+    private void checkIsOpen() {
+      if (refCounter <= 0) {
+        throw new IllegalStateException("Repository is not open (refCounter=" + refCounter + ")");
+      }
+    }
+
+    @Override
+    public String getIdentifier() {
+      return "foo";
+    }
+  }
+}