Delete all loose refs empty directories

Remove completely the empty directories under refs/<namespace>
including the first level partition of the changes, when they are
completely empty.

Bug: 536777
Change-Id: I88304d34cc42435919c2d1480258684d993dfdca
Signed-off-by: Luca Milanesio <luca.milanesio@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

3 files changed, 19 insertions, 11 deletions

diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
index 68bb68e426..16f184babc 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties
@@ -45,6 +45,7 @@ branchNameInvalid=Branch name {0} is not allowed
 buildingBitmaps=Building bitmaps
 cachedPacksPreventsIndexCreation=Using cached packs prevents index creation
 cachedPacksPreventsListingObjects=Using cached packs prevents listing objects
+cannotAccessLastModifiedForSafeDeletion=Unable to access lastModifiedTime of file {0}, skip deletion since we cannot safely avoid race condition
 cannotBeCombined=Cannot be combined.
 cannotBeRecursiveWhenTreesAreIncluded=TreeWalk shouldn't be recursive when tree objects are included.
 cannotChangeActionOnComment=Cannot change action on comment line in git-rebase-todo file, old action: {0}, new action: {1}.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
index 56a24482be..4b7459c15b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java
@@ -104,6 +104,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String buildingBitmaps;
 	/***/ public String cachedPacksPreventsIndexCreation;
 	/***/ public String cachedPacksPreventsListingObjects;
+	/***/ public String cannotAccessLastModifiedForSafeDeletion;
 	/***/ public String cannotBeCombined;
 	/***/ public String cannotBeRecursiveWhenTreesAreIncluded;
 	/***/ public String cannotChangeActionOnComment;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
index eb5c1db50e..d99a485249 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java
@@ -885,16 +885,31 @@ public class GC {
 
 	private void deleteEmptyRefsFolders() throws IOException {
 		Path refs = repo.getDirectory().toPath().resolve(Constants.R_REFS);
+		// Avoid deleting a folder that was created after the threshold so that concurrent
+		// operations trying to create a reference are not impacted
+		Instant threshold = Instant.now().minus(30, ChronoUnit.SECONDS);
 		try (Stream<Path> entries = Files.list(refs)) {
 			Iterator<Path> iterator = entries.iterator();
 			while (iterator.hasNext()) {
 				try (Stream<Path> s = Files.list(iterator.next())) {
-					s.forEach(this::deleteDir);
+					s.filter(path -> canBeSafelyDeleted(path, threshold)).forEach(this::deleteDir);
 				}
 			}
 		}
 	}
 
+	private boolean canBeSafelyDeleted(Path path, Instant threshold) {
+		try {
+			return Files.getLastModifiedTime(path).toInstant().isBefore(threshold);
+		}
+		catch (IOException e) {
+			LOG.warn(MessageFormat.format(
+					JGitText.get().cannotAccessLastModifiedForSafeDeletion,
+					path), e);
+			return false;
+		}
+	}
+
 	private void deleteDir(Path dir) {
 		try (Stream<Path> dirs = Files.walk(dir)) {
 			dirs.filter(this::isDirectory).sorted(Comparator.reverseOrder())
@@ -910,16 +925,7 @@ public class GC {
 
 	private void delete(Path d) {
 		try {
-			// Avoid deleting a folder that was just created so that concurrent
-			// operations trying to create a reference are not impacted
-			Instant threshold = Instant.now().minus(30, ChronoUnit.SECONDS);
-			Instant lastModified = Files.getLastModifiedTime(d).toInstant();
-			if (lastModified.isBefore(threshold)) {
-				// If the folder is not empty, the delete operation will fail
-				// silently. This is a cheaper alternative to filtering the
-				// stream in the calling method.
-				Files.delete(d);
-			}
+			Files.delete(d);
 		} catch (IOException e) {
 			LOG.error(MessageFormat.format(JGitText.get().cannotDeleteFile, d),
 					e);