DfsBlockCache: refactor stats implementations.

The stats interface has an implementation in the interface itself and another inside the PackExtBlockCache class. This asymmetry gets on the way to implement stats-per-table later.

Make DfsBlockCacheStats (the stats of a single table) a top-level class and create an aggregator class to combine multiple stats. This makes the stats classes mirror the table classes structure (singles tables + composite).

This change is part of a refactor to support providing detailed stats
breakdowns for cache implementations using multiple table instances
while keeping the existing "aggregated" view of cache stats.

Change-Id: I79c11e4ea24afe4b449efdbb47bc81eed363ffd3

4 files changed, 332 insertions, 286 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/AggregatedBlockCacheStats.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/AggregatedBlockCacheStats.java
new file mode 100644
index 0000000000..743f4606c4
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/AggregatedBlockCacheStats.java
@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2024, Google LLC and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.storage.dfs;
+
+import static org.eclipse.jgit.internal.storage.dfs.DfsBlockCacheTable.BlockCacheStats;
+
+import java.util.List;
+
+import org.eclipse.jgit.internal.storage.pack.PackExt;
+
+/**
+ * Aggregates values for all given {@link BlockCacheStats}.
+ */
+class AggregatedBlockCacheStats implements BlockCacheStats {
+	private final String name;
+
+	private final List<BlockCacheStats> blockCacheStats;
+
+	static BlockCacheStats fromStatsList(String name,
+			List<BlockCacheStats> blockCacheStats) {
+		if (blockCacheStats.size() == 1) {
+			return blockCacheStats.get(0);
+		}
+		return new AggregatedBlockCacheStats(name, blockCacheStats);
+	}
+
+	private AggregatedBlockCacheStats(String name,
+			List<BlockCacheStats> blockCacheStats) {
+		this.name = name;
+		this.blockCacheStats = blockCacheStats;
+	}
+
+	@Override
+	public String getName() {
+		return name;
+	}
+
+	@Override
+	public long[] getCurrentSize() {
+		long[] sums = emptyPackStats();
+		for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
+			sums = add(sums, blockCacheStatsEntry.getCurrentSize());
+		}
+		return sums;
+	}
+
+	@Override
+	public long[] getHitCount() {
+		long[] sums = emptyPackStats();
+		for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
+			sums = add(sums, blockCacheStatsEntry.getHitCount());
+		}
+		return sums;
+	}
+
+	@Override
+	public long[] getMissCount() {
+		long[] sums = emptyPackStats();
+		for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
+			sums = add(sums, blockCacheStatsEntry.getMissCount());
+		}
+		return sums;
+	}
+
+	@Override
+	public long[] getTotalRequestCount() {
+		long[] sums = emptyPackStats();
+		for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
+			sums = add(sums, blockCacheStatsEntry.getTotalRequestCount());
+		}
+		return sums;
+	}
+
+	@Override
+	public long[] getHitRatio() {
+		long[] hit = getHitCount();
+		long[] miss = getMissCount();
+		long[] ratio = new long[Math.max(hit.length, miss.length)];
+		for (int i = 0; i < ratio.length; i++) {
+			if (i >= hit.length) {
+				ratio[i] = 0;
+			} else if (i >= miss.length) {
+				ratio[i] = 100;
+			} else {
+				long total = hit[i] + miss[i];
+				ratio[i] = total == 0 ? 0 : hit[i] * 100 / total;
+			}
+		}
+		return ratio;
+	}
+
+	@Override
+	public long[] getEvictions() {
+		long[] sums = emptyPackStats();
+		for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
+			sums = add(sums, blockCacheStatsEntry.getEvictions());
+		}
+		return sums;
+	}
+
+	private static long[] emptyPackStats() {
+		return new long[PackExt.values().length];
+	}
+
+	private static long[] add(long[] first, long[] second) {
+		long[] sums = new long[Integer.max(first.length, second.length)];
+		int i;
+		for (i = 0; i < Integer.min(first.length, second.length); i++) {
+			sums[i] = first[i] + second[i];
+		}
+		for (int j = i; j < first.length; j++) {
+			sums[j] = first[i];
+		}
+		for (int j = i; j < second.length; j++) {
+			sums[j] = second[i];
+		}
+		return sums;
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheStats.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheStats.java
new file mode 100644
index 0000000000..518db8c82d
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheStats.java
@@ -0,0 +1,197 @@
+/*
+ * Copyright (c) 2024, Google LLC and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.internal.storage.dfs;
+
+import static org.eclipse.jgit.internal.storage.dfs.DfsBlockCacheTable.BlockCacheStats;
+
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.eclipse.jgit.internal.storage.pack.PackExt;
+
+/**
+ * Keeps track of stats for a Block Cache table.
+ */
+class DfsBlockCacheStats implements BlockCacheStats {
+	private final String name;
+
+	/**
+	 * Number of times a block was found in the cache, per pack file extension.
+	 */
+	private final AtomicReference<AtomicLong[]> statHit;
+
+	/**
+	 * Number of times a block was not found, and had to be loaded, per pack
+	 * file extension.
+	 */
+	private final AtomicReference<AtomicLong[]> statMiss;
+
+	/**
+	 * Number of blocks evicted due to cache being full, per pack file
+	 * extension.
+	 */
+	private final AtomicReference<AtomicLong[]> statEvict;
+
+	/**
+	 * Number of bytes currently loaded in the cache, per pack file extension.
+	 */
+	private final AtomicReference<AtomicLong[]> liveBytes;
+
+	DfsBlockCacheStats() {
+		this("");
+	}
+
+	DfsBlockCacheStats(String name) {
+		this.name = name;
+		statHit = new AtomicReference<>(newCounters());
+		statMiss = new AtomicReference<>(newCounters());
+		statEvict = new AtomicReference<>(newCounters());
+		liveBytes = new AtomicReference<>(newCounters());
+	}
+
+	@Override
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Increment the {@code statHit} count.
+	 *
+	 * @param key
+	 *            key identifying which liveBytes entry to update.
+	 */
+	void incrementHit(DfsStreamKey key) {
+		getStat(statHit, key).incrementAndGet();
+	}
+
+	/**
+	 * Increment the {@code statMiss} count.
+	 *
+	 * @param key
+	 *            key identifying which liveBytes entry to update.
+	 */
+	void incrementMiss(DfsStreamKey key) {
+		getStat(statMiss, key).incrementAndGet();
+	}
+
+	/**
+	 * Increment the {@code statEvict} count.
+	 *
+	 * @param key
+	 *            key identifying which liveBytes entry to update.
+	 */
+	void incrementEvict(DfsStreamKey key) {
+		getStat(statEvict, key).incrementAndGet();
+	}
+
+	/**
+	 * Add {@code size} to the {@code liveBytes} count.
+	 *
+	 * @param key
+	 *            key identifying which liveBytes entry to update.
+	 * @param size
+	 *            amount to increment the count by.
+	 */
+	void addToLiveBytes(DfsStreamKey key, long size) {
+		getStat(liveBytes, key).addAndGet(size);
+	}
+
+	@Override
+	public long[] getCurrentSize() {
+		return getStatVals(liveBytes);
+	}
+
+	@Override
+	public long[] getHitCount() {
+		return getStatVals(statHit);
+	}
+
+	@Override
+	public long[] getMissCount() {
+		return getStatVals(statMiss);
+	}
+
+	@Override
+	public long[] getTotalRequestCount() {
+		AtomicLong[] hit = statHit.get();
+		AtomicLong[] miss = statMiss.get();
+		long[] cnt = new long[Math.max(hit.length, miss.length)];
+		for (int i = 0; i < hit.length; i++) {
+			cnt[i] += hit[i].get();
+		}
+		for (int i = 0; i < miss.length; i++) {
+			cnt[i] += miss[i].get();
+		}
+		return cnt;
+	}
+
+	@Override
+	public long[] getHitRatio() {
+		AtomicLong[] hit = statHit.get();
+		AtomicLong[] miss = statMiss.get();
+		long[] ratio = new long[Math.max(hit.length, miss.length)];
+		for (int i = 0; i < ratio.length; i++) {
+			if (i >= hit.length) {
+				ratio[i] = 0;
+			} else if (i >= miss.length) {
+				ratio[i] = 100;
+			} else {
+				long hitVal = hit[i].get();
+				long missVal = miss[i].get();
+				long total = hitVal + missVal;
+				ratio[i] = total == 0 ? 0 : hitVal * 100 / total;
+			}
+		}
+		return ratio;
+	}
+
+	@Override
+	public long[] getEvictions() {
+		return getStatVals(statEvict);
+	}
+
+	private static AtomicLong[] newCounters() {
+		AtomicLong[] ret = new AtomicLong[PackExt.values().length];
+		for (int i = 0; i < ret.length; i++) {
+			ret[i] = new AtomicLong();
+		}
+		return ret;
+	}
+
+	private static long[] getStatVals(AtomicReference<AtomicLong[]> stat) {
+		AtomicLong[] stats = stat.get();
+		long[] cnt = new long[stats.length];
+		for (int i = 0; i < stats.length; i++) {
+			cnt[i] = stats[i].get();
+		}
+		return cnt;
+	}
+
+	private static AtomicLong getStat(AtomicReference<AtomicLong[]> stats,
+			DfsStreamKey key) {
+		int pos = key.packExtPos;
+		while (true) {
+			AtomicLong[] vals = stats.get();
+			if (pos < vals.length) {
+				return vals[pos];
+			}
+			AtomicLong[] expect = vals;
+			vals = new AtomicLong[Math.max(pos + 1, PackExt.values().length)];
+			System.arraycopy(expect, 0, vals, 0, expect.length);
+			for (int i = expect.length; i < vals.length; i++) {
+				vals[i] = new AtomicLong();
+			}
+			if (stats.compareAndSet(expect, vals)) {
+				return vals[pos];
+			}
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTable.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTable.java
index de5dc23963..43ba8c36ab 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTable.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCacheTable.java
@@ -11,10 +11,6 @@
 package org.eclipse.jgit.internal.storage.dfs;
 
 import java.io.IOException;
-import java.util.concurrent.atomic.AtomicLong;
-import java.util.concurrent.atomic.AtomicReference;
-
-import org.eclipse.jgit.internal.storage.pack.PackExt;
 
 /**
  * Block cache table.
@@ -148,6 +144,12 @@ public interface DfsBlockCacheTable {
 	 * Provides methods used with Block Cache statistics.
 	 */
 	interface BlockCacheStats {
+
+		/**
+		 * Get the name of the block cache generating this instance.
+		 *
+		 * @return this cache's name.
+		 */
 		String getName();
 
 		/**
@@ -199,186 +201,4 @@ public interface DfsBlockCacheTable {
 		 */
 		long[] getEvictions();
 	}
-
-	/**
-	 * Keeps track of stats for a Block Cache table.
-	 */
-	class DfsBlockCacheStats implements BlockCacheStats {
-		private final String name;
-
-		/**
-		 * Number of times a block was found in the cache, per pack file
-		 * extension.
-		 */
-		private final AtomicReference<AtomicLong[]> statHit;
-
-		/**
-		 * Number of times a block was not found, and had to be loaded, per pack
-		 * file extension.
-		 */
-		private final AtomicReference<AtomicLong[]> statMiss;
-
-		/**
-		 * Number of blocks evicted due to cache being full, per pack file
-		 * extension.
-		 */
-		private final AtomicReference<AtomicLong[]> statEvict;
-
-		/**
-		 * Number of bytes currently loaded in the cache, per pack file
-		 * extension.
-		 */
-		private final AtomicReference<AtomicLong[]> liveBytes;
-
-		DfsBlockCacheStats() {
-			this("");
-		}
-
-		DfsBlockCacheStats(String name) {
-			this.name = name;
-			statHit = new AtomicReference<>(newCounters());
-			statMiss = new AtomicReference<>(newCounters());
-			statEvict = new AtomicReference<>(newCounters());
-			liveBytes = new AtomicReference<>(newCounters());
-		}
-
-		@Override
-		public String getName() {
-			return name;
-		}
-
-		/**
-		 * Increment the {@code statHit} count.
-		 *
-		 * @param key
-		 *            key identifying which liveBytes entry to update.
-		 */
-		void incrementHit(DfsStreamKey key) {
-			getStat(statHit, key).incrementAndGet();
-		}
-
-		/**
-		 * Increment the {@code statMiss} count.
-		 *
-		 * @param key
-		 *            key identifying which liveBytes entry to update.
-		 */
-		void incrementMiss(DfsStreamKey key) {
-			getStat(statMiss, key).incrementAndGet();
-		}
-
-		/**
-		 * Increment the {@code statEvict} count.
-		 *
-		 * @param key
-		 *            key identifying which liveBytes entry to update.
-		 */
-		void incrementEvict(DfsStreamKey key) {
-			getStat(statEvict, key).incrementAndGet();
-		}
-
-		/**
-		 * Add {@code size} to the {@code liveBytes} count.
-		 *
-		 * @param key
-		 *            key identifying which liveBytes entry to update.
-		 * @param size
-		 *            amount to increment the count by.
-		 */
-		void addToLiveBytes(DfsStreamKey key, long size) {
-			getStat(liveBytes, key).addAndGet(size);
-		}
-
-		@Override
-		public long[] getCurrentSize() {
-			return getStatVals(liveBytes);
-		}
-
-		@Override
-		public long[] getHitCount() {
-			return getStatVals(statHit);
-		}
-
-		@Override
-		public long[] getMissCount() {
-			return getStatVals(statMiss);
-		}
-
-		@Override
-		public long[] getTotalRequestCount() {
-			AtomicLong[] hit = statHit.get();
-			AtomicLong[] miss = statMiss.get();
-			long[] cnt = new long[Math.max(hit.length, miss.length)];
-			for (int i = 0; i < hit.length; i++) {
-				cnt[i] += hit[i].get();
-			}
-			for (int i = 0; i < miss.length; i++) {
-				cnt[i] += miss[i].get();
-			}
-			return cnt;
-		}
-
-		@Override
-		public long[] getHitRatio() {
-			AtomicLong[] hit = statHit.get();
-			AtomicLong[] miss = statMiss.get();
-			long[] ratio = new long[Math.max(hit.length, miss.length)];
-			for (int i = 0; i < ratio.length; i++) {
-				if (i >= hit.length) {
-					ratio[i] = 0;
-				} else if (i >= miss.length) {
-					ratio[i] = 100;
-				} else {
-					long hitVal = hit[i].get();
-					long missVal = miss[i].get();
-					long total = hitVal + missVal;
-					ratio[i] = total == 0 ? 0 : hitVal * 100 / total;
-				}
-			}
-			return ratio;
-		}
-
-		@Override
-		public long[] getEvictions() {
-			return getStatVals(statEvict);
-		}
-
-		private static AtomicLong[] newCounters() {
-			AtomicLong[] ret = new AtomicLong[PackExt.values().length];
-			for (int i = 0; i < ret.length; i++) {
-				ret[i] = new AtomicLong();
-			}
-			return ret;
-		}
-
-		private static long[] getStatVals(AtomicReference<AtomicLong[]> stat) {
-			AtomicLong[] stats = stat.get();
-			long[] cnt = new long[stats.length];
-			for (int i = 0; i < stats.length; i++) {
-				cnt[i] = stats[i].get();
-			}
-			return cnt;
-		}
-
-		private static AtomicLong getStat(AtomicReference<AtomicLong[]> stats,
-				DfsStreamKey key) {
-			int pos = key.packExtPos;
-			while (true) {
-				AtomicLong[] vals = stats.get();
-				if (pos < vals.length) {
-					return vals[pos];
-				}
-				AtomicLong[] expect = vals;
-				vals = new AtomicLong[Math.max(pos + 1,
-						PackExt.values().length)];
-				System.arraycopy(expect, 0, vals, 0, expect.length);
-				for (int i = expect.length; i < vals.length; i++) {
-					vals[i] = new AtomicLong();
-				}
-				if (stats.compareAndSet(expect, vals)) {
-					return vals[pos];
-				}
-			}
-		}
-	}
-}
\ No newline at end of file
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTable.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTable.java
index 7f21b3f10a..e45643be84 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTable.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTable.java
@@ -189,7 +189,7 @@ class PackExtBlockCacheTable implements DfsBlockCacheTable {
 
 	@Override
 	public BlockCacheStats getBlockCacheStats() {
-		return new CacheStats(name,
+		return AggregatedBlockCacheStats.fromStatsList(name,
 				blockCacheTableList.stream()
 						.map(DfsBlockCacheTable::getBlockCacheStats)
 						.collect(Collectors.toList()));
@@ -213,102 +213,4 @@ class PackExtBlockCacheTable implements DfsBlockCacheTable {
 	private static PackExt getPackExt(DfsStreamKey key) {
 		return PackExt.values()[key.packExtPos];
 	}
-
-	private static class CacheStats implements BlockCacheStats {
-		private final String name;
-
-		private final List<BlockCacheStats> blockCacheStats;
-
-		private CacheStats(String name, List<BlockCacheStats> blockCacheStats) {
-			this.name = name;
-			this.blockCacheStats = blockCacheStats;
-		}
-
-		@Override
-		public String getName() {
-			return name;
-		}
-
-		@Override
-		public long[] getCurrentSize() {
-			long[] sums = emptyPackStats();
-			for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
-				sums = add(sums, blockCacheStatsEntry.getCurrentSize());
-			}
-			return sums;
-		}
-
-		@Override
-		public long[] getHitCount() {
-			long[] sums = emptyPackStats();
-			for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
-				sums = add(sums, blockCacheStatsEntry.getHitCount());
-			}
-			return sums;
-		}
-
-		@Override
-		public long[] getMissCount() {
-			long[] sums = emptyPackStats();
-			for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
-				sums = add(sums, blockCacheStatsEntry.getMissCount());
-			}
-			return sums;
-		}
-
-		@Override
-		public long[] getTotalRequestCount() {
-			long[] sums = emptyPackStats();
-			for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
-				sums = add(sums, blockCacheStatsEntry.getTotalRequestCount());
-			}
-			return sums;
-		}
-
-		@Override
-		public long[] getHitRatio() {
-			long[] hit = getHitCount();
-			long[] miss = getMissCount();
-			long[] ratio = new long[Math.max(hit.length, miss.length)];
-			for (int i = 0; i < ratio.length; i++) {
-				if (i >= hit.length) {
-					ratio[i] = 0;
-				} else if (i >= miss.length) {
-					ratio[i] = 100;
-				} else {
-					long total = hit[i] + miss[i];
-					ratio[i] = total == 0 ? 0 : hit[i] * 100 / total;
-				}
-			}
-			return ratio;
-		}
-
-		@Override
-		public long[] getEvictions() {
-			long[] sums = emptyPackStats();
-			for (BlockCacheStats blockCacheStatsEntry : blockCacheStats) {
-				sums = add(sums, blockCacheStatsEntry.getEvictions());
-			}
-			return sums;
-		}
-
-		private static long[] emptyPackStats() {
-			return new long[PackExt.values().length];
-		}
-
-		private static long[] add(long[] first, long[] second) {
-			long[] sums = new long[Integer.max(first.length, second.length)];
-			int i;
-			for (i = 0; i < Integer.min(first.length, second.length); i++) {
-				sums[i] = first[i] + second[i];
-			}
-			for (int j = i; j < first.length; j++) {
-				sums[j] = first[i];
-			}
-			for (int j = i; j < second.length; j++) {
-				sums[j] = second[i];
-			}
-			return sums;
-		}
-	}
 }