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

base/android/library_loader/library_prefetcher.h

+// Copyright 2015 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.
+
+#ifndef BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_
+#define BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_
+
+#include <jni.h>
+
+#include <stdint.h>
+#include <string>
+
+#include "base/debug/proc_maps_linux.h"
+#include "base/gtest_prod_util.h"
+
+namespace base {
+namespace android {
+
+// Forks and waits for a process prefetching the native library. This is done in
+// a forked process for the following reasons:
+// - Isolating the main process from mistakes in the parsing. If the parsing
+//   returns an incorrect address, only the forked process will crash.
+// - Not inflating the memory used by the main process uselessly, which could
+//   increase its likelihood to be killed.
+// The forked process has background priority and, since it is not declared to
+// the Android runtime, can be killed at any time, which is not an issue here.
+class BASE_EXPORT NativeLibraryPrefetcher {
+ public:
+  // Finds the ranges matching the native library, forks a low priority
+  // process pre-fetching these ranges and wait()s for it.
+  // Returns true for success.
+  static bool ForkAndPrefetchNativeLibrary();
+
+ private:
+  using AddressRange = std::pair<uintptr_t, uintptr_t>;
+  // Returns true if the region matches native code or data.
+  static bool IsGoodToPrefetch(const base::debug::MappedMemoryRegion& region);
+  // Filters the regions to keep only libchrome ranges if possible.
+  static void FilterLibchromeRangesOnlyIfPossible(
+      const std::vector<base::debug::MappedMemoryRegion>& regions,
+      std::vector<AddressRange>* ranges);
+  // Finds the ranges matching the native library in /proc/self/maps.
+  // Returns true for success.
+  static bool FindRanges(std::vector<AddressRange>* ranges);
+
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestIsGoodToPrefetchNoRange);
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestIsGoodToPrefetchUnreadableRange);
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestIsGoodToPrefetchSkipSharedRange);
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestIsGoodToPrefetchLibchromeRange);
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestIsGoodToPrefetchBaseApkRange);
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestFilterLibchromeRangesOnlyIfPossibleNoLibchrome);
+  FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
+                           TestFilterLibchromeRangesOnlyIfPossibleHasLibchrome);
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(NativeLibraryPrefetcher);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_