text: // 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"
  #include "base/macros.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();
    // Returns the percentage of the native library code currently resident in
    // memory, or -1 in case of error.
    static int PercentageOfResidentNativeLibraryCode();
  
   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);
  
    // Returns the percentage of the given address ranges currently resident in
    // memory, or -1 in case of error.
    static int PercentageOfResidentCode(const 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);
    FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
                             TestPercentageOfResidentCode);
    FRIEND_TEST_ALL_PREFIXES(NativeLibraryPrefetcherTest,
                             TestPercentageOfResidentCodeTwoRegions);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(NativeLibraryPrefetcher);
  };
  
  }  // namespace android
  }  // namespace base
  
  #endif  // BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_
  