base/files/important_file_writer.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/files/important_file_writer.h"
   6
   7 #include <stdio.h>
   8
   9 #include <string>
  10
  11 #include "base/bind.h"
  12 #include "base/critical_closure.h"
  13 #include "base/debug/alias.h"
  14 #include "base/files/file.h"
  15 #include "base/files/file_path.h"
  16 #include "base/files/file_util.h"
  17 #include "base/logging.h"
  18 #include "base/metrics/histogram.h"
  19 #include "base/strings/string_number_conversions.h"
  20 #include "base/strings/string_util.h"
  21 #include "base/task_runner.h"
  22 #include "base/task_runner_util.h"
  23 #include "base/threading/thread.h"
  24 #include "base/time/time.h"
  25
  26 namespace base {
  27
  28 namespace {
  29
  30 const int kDefaultCommitIntervalMs = 10000;
  31
  32 // This enum is used to define the buckets for an enumerated UMA histogram.
  33 // Hence,
  34 //   (a) existing enumerated constants should never be deleted or reordered, and
  35 //   (b) new constants should only be appended at the end of the enumeration.
  36 enum TempFileFailure {
  37   FAILED_CREATING,
  38   FAILED_OPENING,
  39   FAILED_CLOSING,  // Unused.
  40   FAILED_WRITING,
  41   FAILED_RENAMING,
  42   FAILED_FLUSHING,
  43   TEMP_FILE_FAILURE_MAX
  44 };
  45
  46 void LogFailure(const FilePath& path, TempFileFailure failure_code,
  47                 const std::string& message) {
  48   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
  49                             TEMP_FILE_FAILURE_MAX);
  50   DPLOG(WARNING) << "temp file failure: " << path.value().c_str()
  51                  << " : " << message;
  52 }
  53
  54 }  // namespace
  55
  56 // static
  57 bool ImportantFileWriter::WriteFileAtomically(const FilePath& path,
  58                                               const std::string& data) {
  59 #if defined(OS_CHROMEOS)
  60   // On Chrome OS, chrome gets killed when it cannot finish shutdown quickly,
  61   // and this function seems to be one of the slowest shutdown steps.
  62   // Include some info to the report for investigation. crbug.com/418627
  63   // TODO(hashimoto): Remove this.
  64   struct {
  65     size_t data_size;
  66     char path[128];
  67   } file_info;
  68   file_info.data_size = data.size();
  69   base::strlcpy(file_info.path, path.value().c_str(),
  70                 arraysize(file_info.path));
  71   base::debug::Alias(&file_info);
  72 #endif
  73   // Write the data to a temp file then rename to avoid data loss if we crash
  74   // while writing the file. Ensure that the temp file is on the same volume
  75   // as target file, so it can be moved in one step, and that the temp file
  76   // is securely created.
  77   FilePath tmp_file_path;
  78   if (!base::CreateTemporaryFileInDir(path.DirName(), &tmp_file_path)) {
  79     LogFailure(path, FAILED_CREATING, "could not create temporary file");
  80     return false;
  81   }
  82
  83   File tmp_file(tmp_file_path, File::FLAG_OPEN | File::FLAG_WRITE);
  84   if (!tmp_file.IsValid()) {
  85     LogFailure(path, FAILED_OPENING, "could not open temporary file");
  86     return false;
  87   }
  88
  89   // If this happens in the wild something really bad is going on.
  90   CHECK_LE(data.length(), static_cast<size_t>(kint32max));
  91   int bytes_written = tmp_file.Write(0, data.data(),
  92                                      static_cast<int>(data.length()));
  93   bool flush_success = tmp_file.Flush();
  94   tmp_file.Close();
  95
  96   if (bytes_written < static_cast<int>(data.length())) {
  97     LogFailure(path, FAILED_WRITING, "error writing, bytes_written=" +
  98                IntToString(bytes_written));
  99     base::DeleteFile(tmp_file_path, false);
 100     return false;
 101   }
 102
 103   if (!flush_success) {
 104     LogFailure(path, FAILED_FLUSHING, "error flushing");
 105     base::DeleteFile(tmp_file_path, false);
 106     return false;
 107   }
 108
 109   if (!base::ReplaceFile(tmp_file_path, path, NULL)) {
 110     LogFailure(path, FAILED_RENAMING, "could not rename temporary file");
 111     base::DeleteFile(tmp_file_path, false);
 112     return false;
 113   }
 114
 115   return true;
 116 }
 117
 118 ImportantFileWriter::ImportantFileWriter(
 119     const FilePath& path,
 120     const scoped_refptr<base::SequencedTaskRunner>& task_runner)
 121     : path_(path),
 122       task_runner_(task_runner),
 123       serializer_(NULL),
 124       commit_interval_(TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)),
 125       weak_factory_(this) {
 126   DCHECK(CalledOnValidThread());
 127   DCHECK(task_runner_.get());
 128 }
 129
 130 ImportantFileWriter::~ImportantFileWriter() {
 131   // We're usually a member variable of some other object, which also tends
 132   // to be our serializer. It may not be safe to call back to the parent object
 133   // being destructed.
 134   DCHECK(!HasPendingWrite());
 135 }
 136
 137 bool ImportantFileWriter::HasPendingWrite() const {
 138   DCHECK(CalledOnValidThread());
 139   return timer_.IsRunning();
 140 }
 141
 142 void ImportantFileWriter::WriteNow(const std::string& data) {
 143   DCHECK(CalledOnValidThread());
 144   if (data.length() > static_cast<size_t>(kint32max)) {
 145     NOTREACHED();
 146     return;
 147   }
 148
 149   if (HasPendingWrite())
 150     timer_.Stop();
 151
 152   if (!PostWriteTask(data)) {
 153     // Posting the task to background message loop is not expected
 154     // to fail, but if it does, avoid losing data and just hit the disk
 155     // on the current thread.
 156     NOTREACHED();
 157
 158     WriteFileAtomically(path_, data);
 159   }
 160 }
 161
 162 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
 163   DCHECK(CalledOnValidThread());
 164
 165   DCHECK(serializer);
 166   serializer_ = serializer;
 167
 168   if (!timer_.IsRunning()) {
 169     timer_.Start(FROM_HERE, commit_interval_, this,
 170                  &ImportantFileWriter::DoScheduledWrite);
 171   }
 172 }
 173
 174 void ImportantFileWriter::DoScheduledWrite() {
 175   DCHECK(serializer_);
 176   std::string data;
 177   if (serializer_->SerializeData(&data)) {
 178     WriteNow(data);
 179   } else {
 180     DLOG(WARNING) << "failed to serialize data to be saved in "
 181                   << path_.value().c_str();
 182   }
 183   serializer_ = NULL;
 184 }
 185
 186 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
 187     const base::Closure& on_next_successful_write) {
 188   DCHECK(on_next_successful_write_.is_null());
 189   on_next_successful_write_ = on_next_successful_write;
 190 }
 191
 192 bool ImportantFileWriter::PostWriteTask(const std::string& data) {
 193   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
 194   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
 195   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
 196   // suppressing all of those is unrealistic hence we avoid most of them by
 197   // using PostTask() in the typical scenario below.
 198   if (!on_next_successful_write_.is_null()) {
 199     return base::PostTaskAndReplyWithResult(
 200         task_runner_.get(),
 201         FROM_HERE,
 202         MakeCriticalClosure(
 203             Bind(&ImportantFileWriter::WriteFileAtomically, path_, data)),
 204         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
 205              weak_factory_.GetWeakPtr()));
 206   }
 207   return task_runner_->PostTask(
 208       FROM_HERE,
 209       MakeCriticalClosure(
 210           Bind(IgnoreResult(&ImportantFileWriter::WriteFileAtomically),
 211                path_, data)));
 212 }
 213
 214 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
 215   DCHECK(CalledOnValidThread());
 216   if (result && !on_next_successful_write_.is_null()) {
 217     on_next_successful_write_.Run();
 218     on_next_successful_write_.Reset();
 219   }
 220 }
 221
 222 }  // namespace base