PackBitmapIndexV1: support parallel loading of reverse index

Speed up bitmap creation by loading reverse index in parallel
to reading bitmap from storage. Latency changes from
(time_to_read_bitmap + time_to_load_reverse_index) to
max(time_to_read_bitmap, time_to_load_reverse_index).

Add new option to DfsReaderOptions to control parallel reverse index
loading. Static cached thread pool is added to PackBitmapIndexV1 for
reverse index loading, and when not in use consumes minimal resources.

Signed-off-by: Alina Djamankulova <adjama@google.com>
Change-Id: Ia37a1d739631d053e8bddb925ac8b0b81d22379e

1 files changed, 25 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTest.java
index 4f1314057f..070d666ee5 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTest.java
@@ -290,6 +290,31 @@ public class DfsBlockCacheTest {
 		assertEquals(1, cache.getMissCount()[0]);
 	}
 
+	@SuppressWarnings("resource")
+	@Test
+	public void highConcurrencyParallelReads_oneRepoParallelReverseIndex()
+			throws Exception {
+		InMemoryRepository r1 = createRepoWithBitmap("test");
+		resetCache();
+
+		DfsReader reader = (DfsReader) r1.newObjectReader();
+		reader.getOptions().setLoadRevIndexInParallel(true);
+		for (DfsPackFile pack : r1.getObjectDatabase().getPacks()) {
+			// Only load non-garbage pack with bitmap.
+			if (pack.isGarbage()) {
+				continue;
+			}
+			asyncRun(() -> pack.getBitmapIndex(reader));
+			asyncRun(() -> pack.getPackIndex(reader));
+			asyncRun(() -> pack.getBitmapIndex(reader));
+		}
+		waitForExecutorPoolTermination();
+
+		assertEquals(1, cache.getMissCount()[PackExt.BITMAP_INDEX.ordinal()]);
+		assertEquals(1, cache.getMissCount()[PackExt.INDEX.ordinal()]);
+		assertEquals(1, cache.getMissCount()[0]);
+	}
+
 	private void resetCache() {
 		resetCache(32);
 	}