Multi-threading commit hook leads to "Cannot lock .git/index" error

Author: reda-alaoui

core/src/main/java/com/cosium/code/format/git/GitStagedFiles.java

@@ -59,11 +59,16 @@ public static GitStagedFiles read(Log log, Repository repository, Predicate<Path
         Stream.concat(gitStatus.getChanged().stream(), gitStatus.getAdded().stream())
             .filter(relativePath -> fileFilter.test(workTree.resolve(relativePath)))
             .collect(Collectors.toSet());
-    log.debug("Staged files: " + filePaths.toString());
+    log.debug("Staged files: " + filePaths);
     return new GitStagedFiles(log, repository, filePaths);
   }
 
   public void format(CodeFormatters formatters) throws IOException {
+    if (filePaths.isEmpty()) {
+      log.debug("No staged files to format");
+      return;
+    }
+
     Git git = new Git(repository);
 
     try (Index index = Index.lock(repository);

core/src/main/java/com/cosium/code/format/git/Index.java

@@ -1,6 +1,11 @@
 package com.cosium.code.format.git;
 
+import java.io.File;
 import java.io.IOException;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import org.eclipse.jgit.dircache.DirCache;
 import org.eclipse.jgit.dircache.DirCacheEditor;
 import org.eclipse.jgit.dircache.DirCacheIterator;
@@ -12,10 +17,23 @@
  */
 public class Index implements AutoCloseable {
 
+  private static final Map<File, Lock> GLOBAL_LOCK_BY_REPOSITORY_DIRECTORY =
+      new ConcurrentHashMap<>();
+
+  private final Lock globalLock;
   private final DirCache dirCache;
 
   private Index(Repository repository) throws IOException {
-    dirCache = repository.lockDirCache();
+    globalLock =
+        GLOBAL_LOCK_BY_REPOSITORY_DIRECTORY.computeIfAbsent(
+            repository.getDirectory(), repositoryDirectory -> new ReentrantLock());
+    globalLock.lock();
+    try {
+      dirCache = repository.lockDirCache();
+    } catch (RuntimeException e) {
+      globalLock.unlock();
+      throw e;
+    }
   }
 
   public static Index lock(Repository repository) throws IOException {
@@ -40,6 +58,10 @@ public AbstractTreeIterator treeIterator() {
 
   @Override
   public void close() {
-    dirCache.unlock();
+    try {
+      dirCache.unlock();
+    } finally {
+      globalLock.unlock();
+    }
   }
 }