Submitting http://codereview.chromium.org/87039 on behalf of hamaji.

base/file_util_posix.cc

 // Copyright (c) 2006-2008 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.
 
 #include "base/file_util.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <fnmatch.h>
@@ skipping 43 matching lines @@
   *path = FilePath(full_path);
   return true;
 }
 
 int CountFilesCreatedAfter(const FilePath& path,
                            const base::Time& comparison_time) {
   int file_count = 0;
 
   DIR* dir = opendir(path.value().c_str());
   if (dir) {
+    struct dirent ent_buf;
     struct dirent* ent;
-    while ((ent = readdir(dir)) != NULL) {
+    while (readdir_r(dir, &ent_buf, &ent) == 0 && ent) {
       if ((strcmp(ent->d_name, ".") == 0) ||
           (strcmp(ent->d_name, "..") == 0))
         continue;
 
       struct stat64 st;
       int test = stat64(path.Append(ent->d_name).value().c_str(), &st);
       if (test != 0) {
         LOG(ERROR) << "stat64 failed: " << strerror(errno);
         continue;
       }
+      // Here, we use Time::TimeT(), which discards microseconds. This
+      // means that files which are newer than |comparison_time| may
+      // be considered older. If we don't discard microseconds, it
+      // introduces another issue. Suppose the following case:
+      //
+      // 1. Get |comparison_time| by Time::Now() and the value is 10.1 (secs).
+      // 2. Create a file and the current time is 10.3 (secs).
+      //
+      // As POSIX doesn't have microsecond precision for |st_ctime|,
+      // the creation time of the file created in the step 2 is 10 and
+      // the file is considered older than |comparison_time|. After
+      // all, we may have to accept either of the two issues: 1. files
+      // which are older than |comparison_time| are considered newer
+      // (current implementation) 2. files newer than
+      // |comparison_time| are considered older.
       if (st.st_ctime >= comparison_time.ToTimeT())
         ++file_count;
     }
     closedir(dir);
   }
   return file_count;
 }
 
 // TODO(erikkay): The Windows version of this accepts paths like "foo/bar/*"
 // which works both with and without the recursive flag.  I'm not sure we need
@@ skipping 528 matching lines @@
     munmap(data_, length_);
   if (file_ != -1)
     close(file_);
 
   data_ = NULL;
   length_ = 0;
   file_ = -1;
 }
 
 } // namespace file_util