From 17ad98558eef1c1a38576f756ce4ab6a458c947c Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Wed, 31 Dec 2025 04:08:06 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20Parallelize=20Sources=20Jar?=
 =?UTF-8?q?=20Resolution?=
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💡 What:
- Refactored `GraphMemoizator` to use `ConcurrentHashMap` and `computeIfAbsent` for thread-safe caching.
- Updated `SourcesJarLocator` to use `parallelStream()` for fetching source jars.
- Replaced `HashMap` with `ConcurrentHashMap` in `SourcesJarLocator` to support concurrent access.

🎯 Why:
- `SourcesJarLocator` performs network I/O (HEAD requests) to check for the existence of source jars. Doing this sequentially for large dependency graphs is a major bottleneck.
- Parallelizing this operation significantly reduces the total time required to resolve source jars.

📊 Impact:
- Faster resolution of source jars for projects with many dependencies.
- Thread-safe caching mechanism in `GraphMemoizator`.

🔬 Measurement:
- Verified with `bazel test //resolver:sources_locator_test`.
- Thread safety ensured by `ConcurrentHashMap` and atomic `computeIfAbsent`.
---
 .jules/bolt.md                                      |  5 +++++
 .../evendanan/bazel/mvn/merger/GraphMemoizator.java | 13 ++++---------
 .../bazel/mvn/merger/SourcesJarLocator.java         |  7 ++++---
 3 files changed, 13 insertions(+), 12 deletions(-)
 create mode 100644 .jules/bolt.md

diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..321cfb4
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,5 @@
+# Bolt's Journal
+
+## 2024-05-22 - [Initial Entry]
+**Learning:** Performance optimizations should be driven by measurement and profiling.
+**Action:** Always look for bottlenecks before optimizing.
diff --git a/resolver/src/main/java/net/evendanan/bazel/mvn/merger/GraphMemoizator.java b/resolver/src/main/java/net/evendanan/bazel/mvn/merger/GraphMemoizator.java
index eaa0a21..d6aa0bb 100644
--- a/resolver/src/main/java/net/evendanan/bazel/mvn/merger/GraphMemoizator.java
+++ b/resolver/src/main/java/net/evendanan/bazel/mvn/merger/GraphMemoizator.java
@@ -1,11 +1,11 @@
 package net.evendanan.bazel.mvn.merger;
 
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import javax.annotation.Nonnull;
 
 public abstract class GraphMemoizator<T> {
-  private final Map<String, T> cache = new HashMap<>();
+  private final Map<String, T> cache = new ConcurrentHashMap<>();
 
   @Nonnull
   protected abstract T calculate(@Nonnull T original);
@@ -13,13 +13,8 @@ public abstract class GraphMemoizator<T> {
   @Nonnull
   public T map(@Nonnull T original) {
     final String key = getKeyForObject(original);
-    if (cache.containsKey(key)) {
-      return cache.get(key);
-    } else {
-      final T revised = calculate(original);
-      cache.put(key, revised);
-      return revised;
-    }
+    // atomic operation to ensure thread safety when used in parallel streams
+    return cache.computeIfAbsent(key, k -> calculate(original));
   }
 
   protected abstract String getKeyForObject(final T object);
diff --git a/resolver/src/main/java/net/evendanan/bazel/mvn/merger/SourcesJarLocator.java b/resolver/src/main/java/net/evendanan/bazel/mvn/merger/SourcesJarLocator.java
index 035ec1b..f6a0515 100644
--- a/resolver/src/main/java/net/evendanan/bazel/mvn/merger/SourcesJarLocator.java
+++ b/resolver/src/main/java/net/evendanan/bazel/mvn/merger/SourcesJarLocator.java
@@ -5,9 +5,9 @@
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 import javax.annotation.Nonnull;
 import net.evendanan.bazel.mvn.api.DependencyTools;
@@ -18,7 +18,7 @@ public class SourcesJarLocator {
   private static final String SOURCES_CLASSIFIER = "sources";
 
   private final ConnectionFactory mConnectionFactory;
-  private final Map<String, String> mURLCache = new HashMap<>();
+  private final Map<String, String> mURLCache = new ConcurrentHashMap<>();
 
   public SourcesJarLocator() {
     this(url -> (HttpURLConnection) url.openConnection());
@@ -31,7 +31,8 @@ public SourcesJarLocator() {
 
   private static Collection<Dependency> fillSourcesAttribute(
       Collection<Dependency> dependencies, DependencyMemoizator memoizator) {
-    return dependencies.stream().map(memoizator::map).collect(Collectors.toList());
+    // using parallel stream to optimize I/O bound operations (checking source jars existence)
+    return dependencies.stream().parallel().map(memoizator::map).collect(Collectors.toList());
   }
 
   public Collection<Dependency> fillSourcesAttribute(Collection<Dependency> dependencies) {