[JGIT PATCH 10/13] Add compare-and-swap semantics to RefUpdate

From

Shawn O. Pearce <spearce@spearce.org>

Date

Dec 23, 2008, 00:27 UTC

Message-ID

<1229992043-1053-11-git-send-email-spearce@spearce.org>

In-Reply-To

<1229992043-1053-10-git-send-email-spearce@spearce.org>

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
 .../src/org/spearce/jgit/lib/RefUpdate.java        |   30 ++++++++++++++++++++
 1 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/RefUpdate.java b/org.spearce.jgit/src/org/spearce/jgit/lib/RefUpdate.java
index 235c2fd..0c9ce91 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/RefUpdate.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/RefUpdate.java
@@ -149,6 +149,9 @@
 	/** Old value of the ref, obtained after we lock it. */
 	private ObjectId oldValue;
 
+	/** If non-null, the value {@link #oldValue} must have to continue. */
+	private ObjectId expValue;
+
 	/** Result of the update operation. */
 	private Result result = Result.NOT_ATTEMPTED;
 
@@ -190,6 +193,27 @@ public void setNewObjectId(final AnyObjectId id) {
 	}
 
 	/**
+	 * @return the expected value of the ref after the lock is taken, but before
+	 *         update occurs. Null to avoid the compare and swap test. Use
+	 *         {@link ObjectId#zeroId()} to indicate expectation of a
+	 *         non-existant ref.
+	 */
+	public ObjectId getExpectedOldObjectId() {
+		return expValue;
+	}
+
+	/**
+	 * @param id
+	 *            the expected value of the ref after the lock is taken, but
+	 *            before update occurs. Null to avoid the compare and swap test.
+	 *            Use {@link ObjectId#zeroId()} to indicate expectation of a
+	 *            non-existant ref.
+	 */
+	public void setExpectedOldObjectId(final AnyObjectId id) {
+		expValue = id != null ? id.toObjectId() : null;
+	}
+
+	/**
 	 * Check if this update wants to forcefully change the ref.
 	 * 
 	 * @return true if this update should ignore merge tests.
@@ -370,6 +394,12 @@ private Result updateImpl(final RevWalk walk, final Store store)
 			return Result.LOCK_FAILURE;
 		try {
 			oldValue = db.idOf(getName());
+			if (expValue != null) {
+				final ObjectId o;
+				o = oldValue != null ? oldValue : ObjectId.zeroId();
+				if (!expValue.equals(o))
+					return Result.LOCK_FAILURE;
+			}
 			if (oldValue == null)
 				return store.store(lock, Result.NEW);
 

-- 
1.6.1.rc4.301.g5497a