DirectApkSoSource: optimize ZipEntry lookup

Summary:
DirectApkSoSource.loadLibrary() has quadratic behavior: for every library it
loads (either directly or as a dependency), it iterates over ZipFile entries
to find a match.

This patch replaces the linear search with ZipFile#getEntry. This results in
an ~8x startup improvement in a large app that loads ~1k shared libraries.

This can be optimized further if needed, by potentially trading some memory
(reusing open ZipFile objects) or doing more work up front (computing all
the dependencies on startup) for faster lookups.

Reviewed By: simpleton

Differential Revision: D54651944

fbshipit-source-id: 5d0fc8fb31decfc3bd246a7c02a342c25a5f9427

java/com/facebook/soloader/DirectApkSoSource.java

@@ -174,8 +174,8 @@ protected void prepare(int flags) throws IOException {
   }
 
   private void prepare() throws IOException {
-    String subDir = null;
     for (String directApkLdPath : mDirectApkLdPaths) {
+      String subDir = null;
       if (!TextUtils.isEmpty(directApkLdPath)) {
         final int i = directApkLdPath.indexOf('!');
         if (i >= 0 && i + 2 < directApkLdPath.length()) {
@@ -203,14 +203,18 @@ private void prepare() throws IOException {
   }
 
   private void buildLibDepsCache(String directApkLdPath, String soName) throws IOException {
-    try (ZipFile mZipFile = new ZipFile(getApkPathFromLdPath(directApkLdPath))) {
-      Enumeration<? extends ZipEntry> entries = mZipFile.entries();
-      while (entries.hasMoreElements()) {
-        ZipEntry entry = entries.nextElement();
-        if (entry != null && entry.getName().endsWith("/" + soName)) {
-          buildLibDepsCacheImpl(directApkLdPath, mZipFile, entry, soName);
-        }
+    final String apkPath = getApkPathFromLdPath(directApkLdPath);
+
+    try (ZipFile mZipFile = new ZipFile(apkPath)) {
+      final String path = getLibraryPathInApk(directApkLdPath, soName);
+      final ZipEntry entry = mZipFile.getEntry(path);
+
+      if (entry == null) {
+        LogUtil.e(SoLoader.TAG, path + " not found in " + apkPath);
+        return;
       }
+
+      buildLibDepsCacheImpl(directApkLdPath, mZipFile, entry, soName);
     }
   }
 
@@ -273,6 +277,11 @@ private static String getApkPathFromLdPath(String ldPath) {
     return ldPath.substring(0, ldPath.indexOf('!'));
   }
 
+  private static String getLibraryPathInApk(String directApkLdPath, String soName) {
+    final int index = directApkLdPath.indexOf('!');
+    return directApkLdPath.substring(index + 2) + File.separator + soName;
+  }
+
   @Override
   public SoSource recover(Context context) {
     DirectApkSoSource recovered = new DirectApkSoSource(context);