MidxIterator: Add reset method

We need to iterate twice over the input collection while building the
midx. We are creating a new iterator per iteration. This works fine
until we add single-pack midx to the merge, because it requires the
ctx (DfsReader) to create the iterator.

Offer a reset method in the MidxIterator. Then we can reuse the
iterator the two iterations, we do not need ctx and building the
merger is easier.

Change-Id: Iddfcfb304763de2997afd7e8b45a11996a6a6964

Author: ifradeo

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/midx/MidxIteratorsTest.java

@@ -31,8 +31,7 @@ public void fromPackIndexIterator_basicIteration() {
 		PackIndex index1 = indexOf(object("000001", 500),
 				object("000003", 3000), object("000005", 1500));
 
-		MidxIterator it = MidxIterators.fromPackIndexIterator("index1",
-				index1.iterator());
+		MidxIterator it = MidxIterators.fromPackIndexIterator("index1", index1);
 		assertNextEntry(it, "000001", 0, 500);
 		assertNextEntry(it, "000003", 0, 3000);
 		assertNextEntry(it, "000005", 0, 1500);
@@ -44,8 +43,7 @@ public void fromPackIndexIterator_peek() {
 		PackIndex index1 = indexOf(object("000001", 500),
 				object("000003", 3000), object("000005", 1500));
 
-		MidxIterator it = MidxIterators.fromPackIndexIterator("index1",
-				index1.iterator());
+		MidxIterator it = MidxIterators.fromPackIndexIterator("index1", index1);
 		assertPeekEntry(it, "000001", 0, 500);
 		assertPeekEntry(it, "000001", 0, 500);
 		assertNextEntry(it, "000001", 0, 500);
@@ -60,20 +58,35 @@ public void fromPackIndexIterator_peek() {
 		assertFalse(it.hasNext());
 	}
 
+	@Test
+	public void fromPackIndexIterator_reset() {
+		PackIndex index1 = indexOf(object("000001", 500),
+				object("000003", 3000), object("000005", 1500));
+
+		MidxIterator it = MidxIterators.fromPackIndexIterator("index1", index1);
+		while (it.hasNext()) {
+			it.next();
+		}
+		it.reset();
+		assertNextEntry(it, "000001", 0, 500);
+		assertNextEntry(it, "000003", 0, 3000);
+
+		it.reset();
+		assertPeekEntry(it, "000001", 0, 500);
+	}
+
 	@Test
 	public void fromPackIndexIterator_getPackNames() {
 		PackIndex index1 = indexOf(object("000001", 500),
 				object("000003", 1500), object("000005", 3000));
-		MidxIterator it = MidxIterators.fromPackIndexIterator("index1",
-				index1.iterator());
+		MidxIterator it = MidxIterators.fromPackIndexIterator("index1", index1);
 		assertEquals(List.of("index1"), it.getPackNames());
 	}
 
 	@Test
 	public void fromPackIndexIterator_empty() {
-		PackIndex index1 = indexOf();
 		MidxIterator it = MidxIterators.fromPackIndexIterator("index1",
-				index1.iterator());
+				indexOf());
 		assertFalse(it.hasNext());
 	}
 
@@ -104,10 +117,8 @@ public void join_basicIteration_packIndexIterators() {
 				object("000003", 1500), object("000004", 3000));
 
 		List<MidxIterator> packIts = List.of(
-				MidxIterators.fromPackIndexIterator("index1",
-						idxOne.iterator()),
-				MidxIterators.fromPackIndexIterator("index2",
-						idxTwo.iterator()));
+				MidxIterators.fromPackIndexIterator("index1", idxOne),
+				MidxIterators.fromPackIndexIterator("index2", idxTwo));
 		MidxIterator it = MidxIterators.join(packIts);
 		assertNextEntry(it, "000001", 0, 500);
 		assertNextEntry(it, "000002", 1, 500);
@@ -165,6 +176,29 @@ public void join_peek() {
 		assertFalse(it.hasNext());
 	}
 
+	@Test
+	public void join_reset() {
+		FakeMidxIterator itOne = FakeMidxIterator.from("itOne", 2,
+				List.of(new IndexEntry("000001", 0, 500),
+						new IndexEntry("000003", 1, 1500)));
+
+		FakeMidxIterator itTwo = FakeMidxIterator.from("itTwo", 2,
+				List.of(new IndexEntry("000002", 0, 500),
+						new IndexEntry("000004", 1, 1500)));
+
+		MidxIterator it = MidxIterators.join(List.of(itOne, itTwo));
+		while (it.hasNext()) {
+			it.next();
+		}
+
+		it.reset();
+		assertNextEntry(it, "000001", 0, 500);
+		assertNextEntry(it, "000002", 2, 500);
+
+		it.reset();
+		assertPeekEntry(it, "000001", 0, 500);
+	}
+
 	@Test
 	public void join_getPackNames() {
 		FakeMidxIterator itOne = FakeMidxIterator.from("itOne", 2,
@@ -236,6 +270,49 @@ public void dedup_peek() {
 		assertFalse(it.hasNext());
 	}
 
+	@Test
+	public void dedup_reset() {
+		FakeMidxIterator itOne = FakeMidxIterator.from("itOne", 2,
+				List.of(new IndexEntry("000001", 0, 500),
+						new IndexEntry("000001", 1, 600),
+						new IndexEntry("000003", 0, 1500),
+						new IndexEntry("000003", 1, 1501),
+						new IndexEntry("000005", 0, 200),
+						new IndexEntry("000005", 1, 201)));
+
+		MidxIterator it = MidxIterators.dedup(itOne);
+		while (it.hasNext()) {
+			it.next();
+		}
+		it.reset();
+		assertNextEntry(it, "000001", 0, 500);
+		assertNextEntry(it, "000003", 0, 1500);
+
+		it.reset();
+		assertPeekEntry(it, "000001", 0, 500);
+	}
+
+	@Test
+	public void dedup_reset_sameElement() {
+		FakeMidxIterator itOne = FakeMidxIterator.from("itOne", 2,
+				List.of(new IndexEntry("000001", 0, 500),
+						new IndexEntry("000001", 1, 600),
+						new IndexEntry("000001", 2, 1500),
+						new IndexEntry("000001", 3, 1501),
+						new IndexEntry("000001", 4, 200),
+						new IndexEntry("000001", 5, 201)));
+
+		MidxIterator it = MidxIterators.dedup(itOne);
+		while (it.hasNext()) {
+			it.next();
+		}
+		it.reset();
+		assertNextEntry(it, "000001", 0, 500);
+
+		it.reset();
+		assertPeekEntry(it, "000001", 0, 500);
+	}
+
 	@Test
 	public void dedup_getPackNames() {
 		FakeMidxIterator itOne = FakeMidxIterator.from("itOne", 4,
@@ -322,6 +399,10 @@ public MultiPackIndex.MutableEntry next() {
 			return entries.get(position++).asMutableEntry();
 		}
 
+		@Override
+		public void reset() {
+			position = 0;
+		}
 	}
 
 	record IndexEntry(String shortOid, int packId, int offset) {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/midx/MidxIterators.java

@@ -29,14 +29,14 @@ public final class MidxIterators {
 	 *
 	 * @param packName
 	 *            pack name this iterator is going over
-	 * @param idxIt
-	 *            iterator over a PackIndex
+	 * @param idx
+	 *            a PackIndex
 	 * @return a midx iterator that returns the objects of the pack index in the
 	 *         original iterator order
 	 */
 	public static MidxIterator fromPackIndexIterator(String packName,
-			Iterator<PackIndex.MutableEntry> idxIt) {
-		return new MidxIteratorOverPackIndex(packName, idxIt);
+			PackIndex idx) {
+		return new MidxIteratorOverPackIndex(packName, idx);
 	}
 
 	/**
@@ -80,17 +80,19 @@ private static class MidxIteratorOverPackIndex implements MidxIterator {
 
 		private final List<String> packNames;
 
-		private final Iterator<PackIndex.MutableEntry> idxIt;
+		private final PackIndex idx;
+
+		private Iterator<PackIndex.MutableEntry> idxIt;
 
 		private boolean peeked;
 
-		private final MutableEntry entry;
+		private final MutableEntry entry = new MutableEntry();
 
 		MidxIteratorOverPackIndex(String packName,
-				Iterator<PackIndex.MutableEntry> idxIt) {
+				PackIndex idx) {
 			this.packNames = List.of(packName);
-			this.idxIt = idxIt;
-			this.entry = new MutableEntry();
+			this.idx = idx;
+			this.idxIt = idx.iterator();
 		}
 
 		@Override
@@ -132,6 +134,13 @@ private void readNext() {
 			idx.copyOidTo(entry.oid);
 			entry.packOffset.setValues(0, idx.getOffset());
 		}
+
+		@Override
+		public void reset() {
+			this.idxIt = idx.iterator();
+			this.entry.clear();
+			peeked = false;
+		}
 	}
 
 	private static class JoinMidxIterator implements MidxIterator {
@@ -205,6 +214,12 @@ private int best() {
 
 			return winnerPos;
 		}
+
+		@Override
+		public void reset() {
+			indexIterators.stream().forEach(MidxIterator::reset);
+			local.clear();
+		}
 	}
 
 	private static class DedupMidxIterator implements MidxIterator {
@@ -264,5 +279,12 @@ private void readNext() {
 				}
 			}
 		}
+
+		@Override
+		public void reset() {
+			lastOid.clear();
+			src.reset();
+			readNext();
+		}
 	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/midx/MultiPackIndex.java

@@ -162,6 +162,11 @@ interface MidxIterator extends Iterator<MutableEntry> {
 		 * @return pack names
 		 */
 		List<String> getPackNames();
+
+		/**
+		 * Restart the iteration from the beginning
+		 */
+		void reset();
 	}
 
 	/**
@@ -278,6 +283,11 @@ public long getOffset() {
 			return packOffset.getOffset();
 		}
 
+		public void clear() {
+			oid.clear();
+			packOffset.setValues(0, 0);
+		}
+
 		@Override
 		public String toString() {
 			return String.format("%s,%s", oid.name(), packOffset);

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/midx/MultiPackIndexV1.java

@@ -392,6 +392,11 @@ public MutableEntry peek() {
 		public List<String> getPackNames() {
 			return Arrays.asList(midx.getPackNames());
 		}
+
+		@Override
+		public void reset() {
+			position = 0;
+		}
 	}
 
 	private static class ReverseIndex {

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/midx/PackIndexMerger.java

@@ -158,7 +158,7 @@ int getPackCount() {
 	MidxIterator bySha1Iterator() {
 		List<MidxIterator> list = packs.entrySet().stream()
 				.map(e -> MidxIterators.fromPackIndexIterator(e.getKey(),
-						e.getValue().iterator()))
+						e.getValue()))
 				.toList();
 		return MidxIterators.dedup(MidxIterators.join(list));
 	}