Frameworks/base: Optimize LoadedApk

Preallocate storage lists and avoid TextUtils and its string
builder for a common code path.

Optimize list join helper to not have a check in the loop.

Bug: 28801010
Change-Id: Iafc582031f973d718252b34bcda6405a77425628

2 files changed, 17 insertions, 9 deletions

diff --git a/core/java/android/app/LoadedApk.java b/core/java/android/app/LoadedApk.java
index 3f870005abfe..10566342325f 100644
--- a/core/java/android/app/LoadedApk.java
+++ b/core/java/android/app/LoadedApk.java
@@ -458,8 +458,14 @@ public final class LoadedApk {
             }
         }
 
-        final List<String> zipPaths = new ArrayList<>();
-        final List<String> libPaths = new ArrayList<>();
+        // Lists for the elements of zip/code and native libraries.
+        //
+        // Both lists are usually not empty. We expect on average one APK for the zip component,
+        // but shared libraries and splits are not uncommon. We expect at least three elements
+        // for native libraries (app-based, system, vendor). As such, give both some breathing
+        // space and initialize to a small value (instead of incurring growth code).
+        final List<String> zipPaths = new ArrayList<>(10);
+        final List<String> libPaths = new ArrayList<>(10);
         makePaths(mActivityThread, mApplicationInfo, zipPaths, libPaths);
 
         final boolean isBundledApp = mApplicationInfo.isSystemApp()
@@ -495,8 +501,11 @@ public final class LoadedApk {
         /*
          * With all the combination done (if necessary, actually create the java class
          * loader and set up JIT profiling support if necessary.
+         *
+         * In many cases this is a single APK, so try to avoid the StringBuilder in TextUtils.
          */
-        final String zip = TextUtils.join(File.pathSeparator, zipPaths);
+        final String zip = (zipPaths.size() == 1) ? zipPaths.get(0) :
+                TextUtils.join(File.pathSeparator, zipPaths);
 
         if (ActivityThread.localLOGV)
             Slog.v(ActivityThread.TAG, "Class path: " + zip +
diff --git a/core/java/android/text/TextUtils.java b/core/java/android/text/TextUtils.java
index 71b53f1f42ae..1c13962c7dfd 100644
--- a/core/java/android/text/TextUtils.java
+++ b/core/java/android/text/TextUtils.java
@@ -309,14 +309,13 @@ public class TextUtils {
      */
     public static String join(CharSequence delimiter, Iterable tokens) {
         StringBuilder sb = new StringBuilder();
-        boolean firstTime = true;
-        for (Object token: tokens) {
-            if (firstTime) {
-                firstTime = false;
-            } else {
+        Iterator<?> it = tokens.iterator();
+        if (it.hasNext()) {
+            sb.append(it.next());
+            while (it.hasNext()) {
                 sb.append(delimiter);
+                sb.append(it.next());
             }
-            sb.append(token);
         }
         return sb.toString();
     }