Prefetch the native library from native code by parsing /proc/pid/maps.

base/android/java/src/org/chromium/base/library_loader/LibraryLoader.java

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.base.library_loader;
 
 import android.content.Context;
 import android.content.pm.ApplicationInfo;
 import android.os.AsyncTask;
 import android.os.SystemClock;
@@ skipping 232 matching lines @@
      *
      * This is done this way, as testing shows that fadvise(FADV_WILLNEED) is
      * detrimental to the startup time.
      *
      * @param context the application context.
      */
     public void asyncPrefetchLibrariesToMemory(final Context context) {
         new AsyncTask<Void, Void, Void>() {
             @Override
             protected Void doInBackground(Void... params) {
-                // Note: AsyncTasks are executed in a low priority background
-                // thread, which is the desired behavior here since we don't
-                // want to interfere with the rest of the initialization.
-                for (String library : NativeLibraries.LIBRARIES) {
-                    if (Linker.isChromiumLinkerLibrary(library)) {
-                        continue;
+                TraceEvent.begin("LibraryLoader.asyncPrefetchLibrariesToMemory");
+                // First, try to fork a new process to do the prefetch. If it
+                // fails, fall back to doing it by mapping the library.
+                boolean ok = nativeForkAndPrefetchNativeLibrary();
+                if (!ok) {
+                    Log.w(TAG, "Forking a process to prefetch the native library failed.");
+                    // AsyncTasks are executed in a low priority background
+                    // thread, which is the desired behavior to avoid
+                    // interfering with the rest of the initialization.
+                    for (String library : NativeLibraries.LIBRARIES) {
+                        if (Linker.isChromiumLinkerLibrary(library)) {
+                            continue;
+                        }
+                        prefetchLibraryToMemory(context, library);
                     }
-                    prefetchLibraryToMemory(context, library);
                 }
+                TraceEvent.end("LibraryLoader.asyncPrefetchLibrariesToMemory");
                 return null;
             }
         }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }
 
     // Invoke System.loadLibrary(...), triggering JNI_OnLoad in native code
     private void loadAlreadyLocked(
             Context context, boolean shouldDeleteFallbackLibraries)
             throws ProcessInitException {
         try {
@@ skipping 294 matching lines @@
     // Method called to register (for later recording) statistics about the Chromium linker
     // operation for a renderer process. Indicates whether the linker attempted relro sharing,
     // and if it did, whether the library failed to load at a fixed address.
     private native void nativeRegisterChromiumAndroidLinkerRendererHistogram(
             boolean requestedSharedRelro,
             boolean loadAtFixedAddressFailed);
 
     // Get the version of the native library. This is needed so that we can check we
     // have the right version before initializing the (rest of the) JNI.
     private native String nativeGetVersionNumber();
+
+    // Finds the ranges corresponding to the native library pages, forks a new
+    // process to prefetch these pages and waits for it. The new process then
+    // terminates. This is blocking.
+    private static native boolean nativeForkAndPrefetchNativeLibrary();
 }