perf(modules): Pre-load modules on a background thread (#4348)

* perf(modules): Pre-load modules on a background thread

* Changelog

* Use a simple Thread instead of executor service

Author: romtsn

CHANGELOG.md

@@ -18,6 +18,7 @@
 ### Improvements
 
 - Make user interaction tracing faster and do fewer allocations ([#4347](https://github.com/getsentry/sentry-java/pull/4347))
+- Pre-load modules on a background thread upon SDK init ([#4348](https://github.com/getsentry/sentry-java/pull/4348))
 
 ## 8.8.0
 

sentry-android-core/src/main/java/io/sentry/android/core/internal/modules/AssetsModulesLoader.java

@@ -21,6 +21,10 @@ public final class AssetsModulesLoader extends ModulesLoader {
   public AssetsModulesLoader(final @NotNull Context context, final @NotNull ILogger logger) {
     super(logger);
     this.context = ContextUtils.getApplicationContext(context);
+
+    // pre-load modules on a bg thread to avoid doing so on the main thread in case of a crash/error
+    //noinspection Convert2MethodRef
+    new Thread(() -> getOrLoadModules()).start();
   }
 
   @Override

sentry/src/main/java/io/sentry/internal/modules/ModulesLoader.java

@@ -1,7 +1,9 @@
 package io.sentry.internal.modules;
 
 import io.sentry.ILogger;
+import io.sentry.ISentryLifecycleToken;
 import io.sentry.SentryLevel;
+import io.sentry.util.AutoClosableReentrantLock;
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
@@ -21,18 +23,23 @@ public abstract class ModulesLoader implements IModulesLoader {
 
   public static final String EXTERNAL_MODULES_FILENAME = "sentry-external-modules.txt";
   protected final @NotNull ILogger logger;
-  private @Nullable Map<String, String> cachedModules = null;
+
+  private final @NotNull AutoClosableReentrantLock modulesLock = new AutoClosableReentrantLock();
+  private volatile @Nullable Map<String, String> cachedModules = null;
 
   public ModulesLoader(final @NotNull ILogger logger) {
     this.logger = logger;
   }
 
   @Override
   public @Nullable Map<String, String> getOrLoadModules() {
-    if (cachedModules != null) {
-      return cachedModules;
+    if (cachedModules == null) {
+      try (final @NotNull ISentryLifecycleToken ignored = modulesLock.acquire()) {
+        if (cachedModules == null) {
+          cachedModules = loadModules();
+        }
+      }
     }
-    cachedModules = loadModules();
     return cachedModules;
   }