Do not fake a SymbolicRef as an ObjectIdRef
When doing a detaching operation, JGit fakes a SymbolicRef as an ObjectIdRef. This is because RefUpdate#updateImpl dereferences the SymbolicRef when updating it. For example, assume that HEAD is pointing to refs/heads/master. If I try to make a detached HEAD pointing to a commit c0ffee, RefUpdate dereferences HEAD as refs/heads/master first and changes refs/heads/master to c0ffee. The detach argument of RefDatabase#newUpdate avoids this dereference by faking HEAD as ObjectIdRef. This faking is problematic for the linking operation of DfsRefDatabase. It does a compare-and-swap operation on every reference change because of its distributed systems nature. If a SymbolicRef is faked as an ObjectRef, it thinks that there is a racing change in the reference and rejects the update. Because of this, DFS based repositories cannot change the link target of symbolic refs. This has not been a problem for file-based repositories because they have a file-lock based semantics instead of the CAS based one. The reference implementation, InMemoryRepository, is not affected because it only compares ObjectIds. When [1] introduced this faking code, there was no way for RefUpdate to distinguish the detaching operation. When [2] fixed the detaching operation, it introduced a detachingSymbolicRef flag. This commit uses this flag to control whether it needs to dereference the symbolic refs by calling Ref#getLeaf. The same flag is used in the reflog update operation. This commit does not affect any operation that succeeds currently. In some DFS repository implementations, this fixes a ref linking operation, which is currently failing. [1]:01b5392cdb
[2]:3a86868c08
Change-Id: I118f85f0414dbfad02250944e28d74dddd59469b Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>
This commit is contained in:
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@ -217,10 +217,6 @@ public RefUpdate newUpdate(String refName, boolean detach)
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else
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detachingSymbolicRef = detach && ref.isSymbolic();
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if (detachingSymbolicRef) {
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ref = new ObjectIdRef.Unpeeled(NEW, refName, ref.getObjectId());
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}
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DfsRefUpdate update = new DfsRefUpdate(this, ref);
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if (detachingSymbolicRef)
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update.setDetachingSymbolicRef();
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@ -545,8 +545,6 @@ public RefDirectoryUpdate newUpdate(String name, boolean detach)
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ref = new ObjectIdRef.Unpeeled(NEW, name, null);
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else {
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detachingSymbolicRef = detach && ref.isSymbolic();
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if (detachingSymbolicRef)
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ref = new ObjectIdRef.Unpeeled(LOOSE, name, ref.getObjectId());
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}
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RefDirectoryUpdate refDirUpdate = new RefDirectoryUpdate(this, ref);
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if (detachingSymbolicRef)
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@ -579,7 +577,7 @@ private void putLooseRef(LooseRef ref) {
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}
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void delete(RefDirectoryUpdate update) throws IOException {
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Ref dst = update.getRef().getLeaf();
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Ref dst = update.getRef();
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String name = dst.getName();
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// Write the packed-refs file using an atomic update. We might
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@ -56,6 +56,7 @@
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class RefDirectoryUpdate extends RefUpdate {
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private final RefDirectory database;
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private boolean shouldDeref;
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private LockFile lock;
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RefDirectoryUpdate(final RefDirectory r, final Ref ref) {
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@ -75,6 +76,7 @@ protected Repository getRepository() {
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@Override
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protected boolean tryLock(boolean deref) throws IOException {
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shouldDeref = deref;
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Ref dst = getRef();
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if (deref)
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dst = dst.getLeaf();
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@ -117,7 +119,7 @@ protected Result doUpdate(final Result status) throws IOException {
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msg = strResult;
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}
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}
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database.log(this, msg, true);
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database.log(this, msg, shouldDeref);
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}
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if (!lock.commit())
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return Result.LOCK_FAILURE;
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@ -140,7 +142,7 @@ private String toResultString(final Result status) {
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@Override
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protected Result doDelete(final Result status) throws IOException {
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if (getRef().getLeaf().getStorage() != Ref.Storage.NEW)
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if (getRef().getStorage() != Ref.Storage.NEW)
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database.delete(this);
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return status;
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}
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@ -551,7 +551,9 @@ public Result delete() throws IOException {
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* @throws IOException
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*/
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public Result delete(final RevWalk walk) throws IOException {
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final String myName = getRef().getLeaf().getName();
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final String myName = detachingSymbolicRef
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? getRef().getName()
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: getRef().getLeaf().getName();
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if (myName.startsWith(Constants.R_HEADS) && !getRepository().isBare()) {
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// Don't allow the currently checked out branch to be deleted.
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Ref head = getRefDatabase().getRef(Constants.HEAD);
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@ -628,7 +630,10 @@ private Result updateImpl(final RevWalk walk, final Store store)
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if (oldValue == null && checkConflicting && getRefDatabase().isNameConflicting(getName()))
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return Result.LOCK_FAILURE;
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try {
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if (!tryLock(true))
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// If we're detaching a symbolic reference, we should update the reference
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// itself. Otherwise, we will update the leaf reference, which should be
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// an ObjectIdRef.
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if (!tryLock(!detachingSymbolicRef))
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return Result.LOCK_FAILURE;
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if (expValue != null) {
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final ObjectId o;
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