[Linux] Do not try to call readdir() on a null DIR* in base::ProcessIterator.

base/process/process_iterator_linux.cc

 // Copyright (c) 2013 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/process/process_iterator.h"
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/process/internal_linux.h"
 #include "base/strings/string_split.h"
@@ skipping 41 matching lines @@
   *proc_cmd_line_args = SplitString(cmd_line, delimiters, KEEP_WHITESPACE,
                                     SPLIT_WANT_NONEMPTY);
   return true;
 }
 
 }  // namespace
 
 ProcessIterator::ProcessIterator(const ProcessFilter* filter)
     : filter_(filter) {
   procfs_dir_ = opendir(internal::kProcDir);
+  if (!procfs_dir_) {

[Nico, 2016/01/27 18:54:34]

Can you add a comment when this can happen? From the bug, sounds like this can
happen on Android -- and it kind of sounds like it might happen there
consistently. Is it useful to LOG(ERROR) about this on android when this happens
if it's going to happen every time there?

What do we use ProcessIterator for on Android? I thought it's mostly for task
manager and about:memory etc, which don't exist there.

[Robert Sesek, 2016/01/27 18:58:42]

Added a comment. This *shouldn't* happen every time, it seems like the SELinux
policies may not be sorted out right.
Given what nnk@ wrote on the bug, it seems like collecting memory stats this way
isn't going to work anyways. I'll file a bug with the person who wrote
memory_details_android.cc.

[Robert Sesek, 2016/01/27 19:11:11]

Filed https://code.google.com/p/chromium/issues/detail?id=581778

+    PLOG(ERROR) << "opendir " << internal::kProcDir;
+  }
 }
 
 ProcessIterator::~ProcessIterator() {
   if (procfs_dir_) {
     closedir(procfs_dir_);
-    procfs_dir_ = NULL;
+    procfs_dir_ = nullptr;
   }
 }
 
 bool ProcessIterator::CheckForNextProcess() {
   // TODO(port): skip processes owned by different UID
 
+  if (!procfs_dir_) {
+    DLOG(ERROR) << "Skipping CheckForNextProcess(), no procfs_dir_";
+    return false;
+  }
+
   pid_t pid = kNullProcessId;
   std::vector<std::string> cmd_line_args;
   std::string stats_data;
   std::vector<std::string> proc_stats;
 
   // Arbitrarily guess that there will never be more than 200 non-process
   // files in /proc.  Hardy has 53 and Lucid has 61.
   int skipped = 0;
   const int kSkipLimit = 200;
   while (skipped < kSkipLimit) {
@@ skipping 46 matching lines @@
   return true;
 }
 
 bool NamedProcessIterator::IncludeEntry() {
   if (executable_name_ != entry().exe_file())
     return false;
   return ProcessIterator::IncludeEntry();
 }
 
 }  // namespace base