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..8566d4d7d9a3b906c705962768e51ae2dc2020ba
--- /dev/null
+++ b/base/android/library_loader/library_prefetcher.h
@@ -0,0 +1,73 @@
+// 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_PREFETCHER_H_
+#define BASE_ANDROID_LIBRARY_PREFETCHER_H_

[pasko, 2015/03/24 17:10:36]

should be: BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_

[Benoit L, 2015/03/25 10:36:19]

Done.

+
+#include <jni.h>
+
+#include <stdio.h>
+#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 {
+
+// Reads a file line by line.
+// This class is visible for testing.
+class FileLineIterator {
+ public:
+  explicit FileLineIterator(const base::FilePath& path);
+  virtual ~FileLineIterator();
+  // Returns an empty string on EOF or error. Don't use on files containing
+  // empty lines.

[rmcilroy, 2015/03/24 15:18:26]

This seems slightly dangerous. Maybe just make NextLine return a bool for EOF
signaling and fill in a std::string* argument.

[Benoit L, 2015/03/25 10:36:19]

Done.

+  virtual std::string NextLine();
+
+ protected:
+  FileLineIterator() : file_(nullptr){};
+
+ private:
+  FILE* file_;
+  static const int kMaxLineLength = 4096;
+  char line_buffer_[kMaxLineLength];
+
+  DISALLOW_COPY_AND_ASSIGN(FileLineIterator);
+};
+
+// Iterates over a /proc/$PID/maps file.
+// This class is visible for testing.
+class ProcMapsIterator {
+ public:
+  explicit ProcMapsIterator(FileLineIterator* line_iterator);
+  bool Next(uint64_t* start,
+            uint64_t* end,
+            std::string* flags,
+            uint64_t* offset,
+            std::string* device,
+            int64_t* inode,
+            std::string* filename);
+
+ private:
+  FileLineIterator* line_iterator_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProcMapsIterator);
+};
+
+// Finds the ranges matching the native library in a /proc/$PID/maps file.
+// Visible for testing.
+std::vector<std::pair<uint64_t, uint64_t>> FindRanges(
+    FileLineIterator* file_line_iterator);
+
+// Finds the ranges matching the native library and forks a low priority
+// process pre-fetching these ranges.
+void ForkAndPrefetchNativeLibrary();

[rmcilroy, 2015/03/24 15:18:26]

Could we wrap ForkAndPrefetchNativeLibrary as a static function in a class, then
have ProcMapsIterator, FileLineIterator and FindRanges as private
classes/functions and make ProcMapsIteratorTest a friend to minimize the API
exposed for testing.

[Benoit L, 2015/03/25 10:36:19]

Yes, thank you for the suggestion. Only protected instead of private, because
testing.
Done.

+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_LIBRARY_PREFETCHER_H_