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

base/android/library_loader/library_prefetcher.h

Index: base/android/library_loader/library_prefetcher.h
diff --git a/base/android/library_loader/library_prefetcher.h b/base/android/library_loader/library_prefetcher.h
new file mode 100644
index 0000000000000000000000000000000000000000..3100742fbf3e21f87b4223eb4e33b702e030c6ce
--- /dev/null
+++ b/base/android/library_loader/library_prefetcher.h
@@ -0,0 +1,51 @@
+// 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 <stdio.h>

[pasko, 2015/03/27 13:29:28]

please don't include what you don't use

[Benoit L, 2015/03/27 15:44:52]

Done.

+#include <sys/types.h>
+#include <string>
+
+#include "base/files/file_util.h"
+#include "base/macros.h"
+#include "base/strings/string_split.h"
+
+namespace base {
+namespace android {
+
+class NativeLibraryPrefetcher {
+ public:
+  // Finds the ranges matching the native library, forks a low priority
+  // process pre-fetching these ranges and wait()s for it.
+  // Returns false on error.
+  static bool ForkAndPrefetchNativeLibrary();
+
+ protected:  // Protected and not private for testing.

[pasko, 2015/03/27 13:29:28]

fyi: there is FRIEND_TEST_ALL_PREFIXES

[Benoit L, 2015/03/27 15:44:52]

Thank you for educating me on the standard practice for the friendly test
declaration, didn't know that.
Done.

+  struct Mapping {
+    uint64_t start;
+    uint64_t end;
+    std::string flags;
+    uint64_t offset;

[pasko, 2015/03/27 13:29:28]

please remove offset, device, inode.

They are easy to add, and having them adds small overhead:
1. parsing adds a tiny bit of deadcode
2. have to think 'why do we have this in the datastructure'? (one more wtf per
day)

[Benoit L, 2015/03/27 15:44:52]

Done.

+    std::string device;
+    int64_t inode;
+    std::string filename;
+  };
+
+  // Returns true for success.
+  static bool ParseMapping(const std::string& line, Mapping* mapping);
+  // Returns true if we should keep the mapping.

[pasko, 2015/03/27 13:29:28]

'we should keep' is hard to understand, how about calling the function
IsGoodToPrefetch?

Maybe more specific: IsExecutableCode()?

+  static bool MappingMatches(const Mapping& mapping);
+  // Finds the ranges matching the native library in /proc/self/maps.
+  // Returns true for success.
+  static bool FindRanges(std::vector<std::pair<uint64_t, uint64_t>>* range);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_