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 <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 {
+
+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.
+  class FileLineIterator {

[pasko, 2015/03/25 12:57:58]

To my taste this iterator adds unnecessary clutter converting ~5 lines of
implementation code into ~35 lines. Can you please put file opening and reading
logic directly into ProcMapsIterator::FindRanges?

[Benoit L, 2015/03/26 15:45:03]

Done.

+   public:
+    explicit FileLineIterator(const base::FilePath& path);
+    virtual ~FileLineIterator();
+    // Returns false on EOF or error.
+    virtual bool NextLine(std::string* line);
+
+   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/$PID/maps file.
+  class ProcMapsIterator {
+   public:
+    struct Mapping {
+      uint64_t start;
+      uint64_t end;
+      std::string flags;
+      uint64_t offset;
+      std::string device;
+      int64_t inode;
+      std::string filename;
+    };
+
+    explicit ProcMapsIterator(FileLineIterator* line_iterator);
+    bool Next(Mapping* mapping);
+
+    // Finds the ranges matching the native library in a /proc/$PID/maps file.
+    static std::vector<std::pair<uint64_t, uint64_t>> FindRanges(
+        FileLineIterator* file_line_iterator);
+
+   private:
+    FileLineIterator* line_iterator_;
+
+    DISALLOW_COPY_AND_ASSIGN(ProcMapsIterator);
+  };
+
+  NativeLibraryPrefetcher() {}
+  DISALLOW_COPY_AND_ASSIGN(NativeLibraryPrefetcher);
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_LIBRARY_LOADER_LIBRARY_PREFETCHER_H_