src/net/disk_cache/simple/simple_backend_impl.cc

   1 // Copyright (c) 2013 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 "net/disk_cache/simple/simple_backend_impl.h"
   6
   7 #include <algorithm>
   8 #include <cstdlib>
   9 #include <functional>
  10
  11 #if defined(OS_POSIX)
  12 #include <sys/resource.h>
  13 #endif
  14
  15 #include "base/bind.h"
  16 #include "base/callback.h"
  17 #include "base/files/file_util.h"
  18 #include "base/location.h"
  19 #include "base/metrics/field_trial.h"
  20 #include "base/metrics/histogram.h"
  21 #include "base/metrics/sparse_histogram.h"
  22 #include "base/single_thread_task_runner.h"
  23 #include "base/sys_info.h"
  24 #include "base/task_runner_util.h"
  25 #include "base/thread_task_runner_handle.h"
  26 #include "base/threading/sequenced_worker_pool.h"
  27 #include "base/time/time.h"
  28 #include "net/base/net_errors.h"
  29 #include "net/disk_cache/cache_util.h"
  30 #include "net/disk_cache/simple/simple_entry_format.h"
  31 #include "net/disk_cache/simple/simple_entry_impl.h"
  32 #include "net/disk_cache/simple/simple_histogram_macros.h"
  33 #include "net/disk_cache/simple/simple_index.h"
  34 #include "net/disk_cache/simple/simple_index_file.h"
  35 #include "net/disk_cache/simple/simple_synchronous_entry.h"
  36 #include "net/disk_cache/simple/simple_util.h"
  37 #include "net/disk_cache/simple/simple_version_upgrade.h"
  38
  39 using base::Callback;
  40 using base::Closure;
  41 using base::FilePath;
  42 using base::SequencedWorkerPool;
  43 using base::Time;
  44 using base::DirectoryExists;
  45 using base::CreateDirectory;
  46
  47 namespace disk_cache {
  48
  49 namespace {
  50
  51 // Maximum number of concurrent worker pool threads, which also is the limit
  52 // on concurrent IO (as we use one thread per IO request).
  53 const int kDefaultMaxWorkerThreads = 50;
  54
  55 const char kThreadNamePrefix[] = "SimpleCache";
  56
  57 // Maximum fraction of the cache that one entry can consume.
  58 const int kMaxFileRatio = 8;
  59
  60 // A global sequenced worker pool to use for launching all tasks.
  61 SequencedWorkerPool* g_sequenced_worker_pool = NULL;
  62
  63 void MaybeCreateSequencedWorkerPool() {
  64   if (!g_sequenced_worker_pool) {
  65     int max_worker_threads = kDefaultMaxWorkerThreads;
  66
  67     const std::string thread_count_field_trial =
  68         base::FieldTrialList::FindFullName("SimpleCacheMaxThreads");
  69     if (!thread_count_field_trial.empty()) {
  70       max_worker_threads =
  71           std::max(1, std::atoi(thread_count_field_trial.c_str()));
  72     }
  73
  74     g_sequenced_worker_pool = new SequencedWorkerPool(max_worker_threads,
  75                                                       kThreadNamePrefix);
  76     g_sequenced_worker_pool->AddRef();  // Leak it.
  77   }
  78 }
  79
  80 bool g_fd_limit_histogram_has_been_populated = false;
  81
  82 void MaybeHistogramFdLimit(net::CacheType cache_type) {
  83   if (g_fd_limit_histogram_has_been_populated)
  84     return;
  85
  86   // Used in histograms; add new entries at end.
  87   enum FdLimitStatus {
  88     FD_LIMIT_STATUS_UNSUPPORTED = 0,
  89     FD_LIMIT_STATUS_FAILED      = 1,
  90     FD_LIMIT_STATUS_SUCCEEDED   = 2,
  91     FD_LIMIT_STATUS_MAX         = 3
  92   };
  93   FdLimitStatus fd_limit_status = FD_LIMIT_STATUS_UNSUPPORTED;
  94   int soft_fd_limit = 0;
  95   int hard_fd_limit = 0;
  96
  97 #if defined(OS_POSIX)
  98   struct rlimit nofile;
  99   if (!getrlimit(RLIMIT_NOFILE, &nofile)) {
 100     soft_fd_limit = nofile.rlim_cur;
 101     hard_fd_limit = nofile.rlim_max;
 102     fd_limit_status = FD_LIMIT_STATUS_SUCCEEDED;
 103   } else {
 104     fd_limit_status = FD_LIMIT_STATUS_FAILED;
 105   }
 106 #endif
 107
 108   SIMPLE_CACHE_UMA(ENUMERATION,
 109                    "FileDescriptorLimitStatus", cache_type,
 110                    fd_limit_status, FD_LIMIT_STATUS_MAX);
 111   if (fd_limit_status == FD_LIMIT_STATUS_SUCCEEDED) {
 112     SIMPLE_CACHE_UMA(SPARSE_SLOWLY,
 113                      "FileDescriptorLimitSoft", cache_type, soft_fd_limit);
 114     SIMPLE_CACHE_UMA(SPARSE_SLOWLY,
 115                      "FileDescriptorLimitHard", cache_type, hard_fd_limit);
 116   }
 117
 118   g_fd_limit_histogram_has_been_populated = true;
 119 }
 120
 121 // Detects if the files in the cache directory match the current disk cache
 122 // backend type and version. If the directory contains no cache, occupies it
 123 // with the fresh structure.
 124 bool FileStructureConsistent(const base::FilePath& path) {
 125   if (!base::PathExists(path) && !base::CreateDirectory(path)) {
 126     LOG(ERROR) << "Failed to create directory: " << path.LossyDisplayName();
 127     return false;
 128   }
 129   return disk_cache::UpgradeSimpleCacheOnDisk(path);
 130 }
 131
 132 // A context used by a BarrierCompletionCallback to track state.
 133 struct BarrierContext {
 134   BarrierContext(int expected)
 135       : expected(expected),
 136         count(0),
 137         had_error(false) {}
 138
 139   const int expected;
 140   int count;
 141   bool had_error;
 142 };
 143
 144 void BarrierCompletionCallbackImpl(
 145     BarrierContext* context,
 146     const net::CompletionCallback& final_callback,
 147     int result) {
 148   DCHECK_GT(context->expected, context->count);
 149   if (context->had_error)
 150     return;
 151   if (result != net::OK) {
 152     context->had_error = true;
 153     final_callback.Run(result);
 154     return;
 155   }
 156   ++context->count;
 157   if (context->count == context->expected)
 158     final_callback.Run(net::OK);
 159 }
 160
 161 // A barrier completion callback is a net::CompletionCallback that waits for
 162 // |count| successful results before invoking |final_callback|. In the case of
 163 // an error, the first error is passed to |final_callback| and all others
 164 // are ignored.
 165 net::CompletionCallback MakeBarrierCompletionCallback(
 166     int count,
 167     const net::CompletionCallback& final_callback) {
 168   BarrierContext* context = new BarrierContext(count);
 169   return base::Bind(&BarrierCompletionCallbackImpl,
 170                     base::Owned(context), final_callback);
 171 }
 172
 173 // A short bindable thunk that ensures a completion callback is always called
 174 // after running an operation asynchronously.
 175 void RunOperationAndCallback(
 176     const Callback<int(const net::CompletionCallback&)>& operation,
 177     const net::CompletionCallback& operation_callback) {
 178   const int operation_result = operation.Run(operation_callback);
 179   if (operation_result != net::ERR_IO_PENDING)
 180     operation_callback.Run(operation_result);
 181 }
 182
 183 void RecordIndexLoad(net::CacheType cache_type,
 184                      base::TimeTicks constructed_since,
 185                      int result) {
 186   const base::TimeDelta creation_to_index = base::TimeTicks::Now() -
 187                                             constructed_since;
 188   if (result == net::OK) {
 189     SIMPLE_CACHE_UMA(TIMES, "CreationToIndex", cache_type, creation_to_index);
 190   } else {
 191     SIMPLE_CACHE_UMA(TIMES,
 192                      "CreationToIndexFail", cache_type, creation_to_index);
 193   }
 194 }
 195
 196 }  // namespace
 197
 198 class SimpleBackendImpl::ActiveEntryProxy
 199     : public SimpleEntryImpl::ActiveEntryProxy {
 200  public:
 201   ~ActiveEntryProxy() override {
 202     if (backend_) {
 203       DCHECK_EQ(1U, backend_->active_entries_.count(entry_hash_));
 204       backend_->active_entries_.erase(entry_hash_);
 205     }
 206   }
 207
 208   static scoped_ptr<SimpleEntryImpl::ActiveEntryProxy> Create(
 209       int64 entry_hash,
 210       SimpleBackendImpl* backend) {
 211     scoped_ptr<SimpleEntryImpl::ActiveEntryProxy>
 212         proxy(new ActiveEntryProxy(entry_hash, backend));
 213     return proxy.Pass();
 214   }
 215
 216  private:
 217   ActiveEntryProxy(uint64 entry_hash,
 218                    SimpleBackendImpl* backend)
 219       : entry_hash_(entry_hash),
 220         backend_(backend->AsWeakPtr()) {}
 221
 222   uint64 entry_hash_;
 223   base::WeakPtr<SimpleBackendImpl> backend_;
 224 };
 225
 226 SimpleBackendImpl::SimpleBackendImpl(
 227     const FilePath& path,
 228     int max_bytes,
 229     net::CacheType cache_type,
 230     const scoped_refptr<base::SingleThreadTaskRunner>& cache_thread,
 231     net::NetLog* net_log)
 232     : path_(path),
 233       cache_type_(cache_type),
 234       cache_thread_(cache_thread),
 235       orig_max_size_(max_bytes),
 236       entry_operations_mode_(cache_type == net::DISK_CACHE ?
 237                                  SimpleEntryImpl::OPTIMISTIC_OPERATIONS :
 238                                  SimpleEntryImpl::NON_OPTIMISTIC_OPERATIONS),
 239       net_log_(net_log) {
 240   MaybeHistogramFdLimit(cache_type_);
 241 }
 242
 243 SimpleBackendImpl::~SimpleBackendImpl() {
 244   index_->WriteToDisk();
 245 }
 246
 247 int SimpleBackendImpl::Init(const CompletionCallback& completion_callback) {
 248   MaybeCreateSequencedWorkerPool();
 249
 250   worker_pool_ = g_sequenced_worker_pool->GetTaskRunnerWithShutdownBehavior(
 251       SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
 252
 253   index_.reset(new SimpleIndex(
 254       base::ThreadTaskRunnerHandle::Get(),
 255       this,
 256       cache_type_,
 257       make_scoped_ptr(new SimpleIndexFile(
 258           cache_thread_, worker_pool_.get(), cache_type_, path_))));
 259   index_->ExecuteWhenReady(
 260       base::Bind(&RecordIndexLoad, cache_type_, base::TimeTicks::Now()));
 261
 262   PostTaskAndReplyWithResult(
 263       cache_thread_.get(),
 264       FROM_HERE,
 265       base::Bind(
 266           &SimpleBackendImpl::InitCacheStructureOnDisk, path_, orig_max_size_),
 267       base::Bind(&SimpleBackendImpl::InitializeIndex,
 268                  AsWeakPtr(),
 269                  completion_callback));
 270   return net::ERR_IO_PENDING;
 271 }
 272
 273 bool SimpleBackendImpl::SetMaxSize(int max_bytes) {
 274   orig_max_size_ = max_bytes;
 275   return index_->SetMaxSize(max_bytes);
 276 }
 277
 278 int SimpleBackendImpl::GetMaxFileSize() const {
 279   return index_->max_size() / kMaxFileRatio;
 280 }
 281
 282 void SimpleBackendImpl::OnDoomStart(uint64 entry_hash) {
 283   DCHECK_EQ(0u, entries_pending_doom_.count(entry_hash));
 284   entries_pending_doom_.insert(
 285       std::make_pair(entry_hash, std::vector<Closure>()));
 286 }
 287
 288 void SimpleBackendImpl::OnDoomComplete(uint64 entry_hash) {
 289   DCHECK_EQ(1u, entries_pending_doom_.count(entry_hash));
 290   base::hash_map<uint64, std::vector<Closure> >::iterator it =
 291       entries_pending_doom_.find(entry_hash);
 292   std::vector<Closure> to_run_closures;
 293   to_run_closures.swap(it->second);
 294   entries_pending_doom_.erase(it);
 295
 296   std::for_each(to_run_closures.begin(), to_run_closures.end(),
 297                 std::mem_fun_ref(&Closure::Run));
 298 }
 299
 300 void SimpleBackendImpl::DoomEntries(std::vector<uint64>* entry_hashes,
 301                                     const net::CompletionCallback& callback) {
 302   scoped_ptr<std::vector<uint64> >
 303       mass_doom_entry_hashes(new std::vector<uint64>());
 304   mass_doom_entry_hashes->swap(*entry_hashes);
 305
 306   std::vector<uint64> to_doom_individually_hashes;
 307
 308   // For each of the entry hashes, there are two cases:
 309   // 1. The entry is either open or pending doom, and so it should be doomed
 310   //    individually to avoid flakes.
 311   // 2. The entry is not in use at all, so we can call
 312   //    SimpleSynchronousEntry::DoomEntrySet and delete the files en masse.
 313   for (int i = mass_doom_entry_hashes->size() - 1; i >= 0; --i) {
 314     const uint64 entry_hash = (*mass_doom_entry_hashes)[i];
 315     DCHECK(active_entries_.count(entry_hash) == 0 ||
 316            entries_pending_doom_.count(entry_hash) == 0);
 317     if (!active_entries_.count(entry_hash) &&
 318         !entries_pending_doom_.count(entry_hash)) {
 319       continue;
 320     }
 321
 322     to_doom_individually_hashes.push_back(entry_hash);
 323
 324     (*mass_doom_entry_hashes)[i] = mass_doom_entry_hashes->back();
 325     mass_doom_entry_hashes->resize(mass_doom_entry_hashes->size() - 1);
 326   }
 327
 328   net::CompletionCallback barrier_callback =
 329       MakeBarrierCompletionCallback(to_doom_individually_hashes.size() + 1,
 330                                     callback);
 331   for (std::vector<uint64>::const_iterator
 332            it = to_doom_individually_hashes.begin(),
 333            end = to_doom_individually_hashes.end(); it != end; ++it) {
 334     const int doom_result = DoomEntryFromHash(*it, barrier_callback);
 335     DCHECK_EQ(net::ERR_IO_PENDING, doom_result);
 336     index_->Remove(*it);
 337   }
 338
 339   for (std::vector<uint64>::const_iterator it = mass_doom_entry_hashes->begin(),
 340                                            end = mass_doom_entry_hashes->end();
 341        it != end; ++it) {
 342     index_->Remove(*it);
 343     OnDoomStart(*it);
 344   }
 345
 346   // Taking this pointer here avoids undefined behaviour from calling
 347   // base::Passed before mass_doom_entry_hashes.get().
 348   std::vector<uint64>* mass_doom_entry_hashes_ptr =
 349       mass_doom_entry_hashes.get();
 350   PostTaskAndReplyWithResult(worker_pool_.get(),
 351                              FROM_HERE,
 352                              base::Bind(&SimpleSynchronousEntry::DoomEntrySet,
 353                                         mass_doom_entry_hashes_ptr,
 354                                         path_),
 355                              base::Bind(&SimpleBackendImpl::DoomEntriesComplete,
 356                                         AsWeakPtr(),
 357                                         base::Passed(&mass_doom_entry_hashes),
 358                                         barrier_callback));
 359 }
 360
 361 net::CacheType SimpleBackendImpl::GetCacheType() const {
 362   return net::DISK_CACHE;
 363 }
 364
 365 int32 SimpleBackendImpl::GetEntryCount() const {
 366   // TODO(pasko): Use directory file count when index is not ready.
 367   return index_->GetEntryCount();
 368 }
 369
 370 int SimpleBackendImpl::OpenEntry(const std::string& key,
 371                                  Entry** entry,
 372                                  const CompletionCallback& callback) {
 373   const uint64 entry_hash = simple_util::GetEntryHashKey(key);
 374
 375   // TODO(gavinp): Factor out this (not quite completely) repetitive code
 376   // block from OpenEntry/CreateEntry/DoomEntry.
 377   base::hash_map<uint64, std::vector<Closure> >::iterator it =
 378       entries_pending_doom_.find(entry_hash);
 379   if (it != entries_pending_doom_.end()) {
 380     Callback<int(const net::CompletionCallback&)> operation =
 381         base::Bind(&SimpleBackendImpl::OpenEntry,
 382                    base::Unretained(this), key, entry);
 383     it->second.push_back(base::Bind(&RunOperationAndCallback,
 384                                     operation, callback));
 385     return net::ERR_IO_PENDING;
 386   }
 387   scoped_refptr<SimpleEntryImpl> simple_entry =
 388       CreateOrFindActiveEntry(entry_hash, key);
 389   CompletionCallback backend_callback =
 390       base::Bind(&SimpleBackendImpl::OnEntryOpenedFromKey,
 391                  AsWeakPtr(),
 392                  key,
 393                  entry,
 394                  simple_entry,
 395                  callback);
 396   return simple_entry->OpenEntry(entry, backend_callback);
 397 }
 398
 399 int SimpleBackendImpl::CreateEntry(const std::string& key,
 400                                    Entry** entry,
 401                                    const CompletionCallback& callback) {
 402   DCHECK_LT(0u, key.size());
 403   const uint64 entry_hash = simple_util::GetEntryHashKey(key);
 404
 405   base::hash_map<uint64, std::vector<Closure> >::iterator it =
 406       entries_pending_doom_.find(entry_hash);
 407   if (it != entries_pending_doom_.end()) {
 408     Callback<int(const net::CompletionCallback&)> operation =
 409         base::Bind(&SimpleBackendImpl::CreateEntry,
 410                    base::Unretained(this), key, entry);
 411     it->second.push_back(base::Bind(&RunOperationAndCallback,
 412                                     operation, callback));
 413     return net::ERR_IO_PENDING;
 414   }
 415   scoped_refptr<SimpleEntryImpl> simple_entry =
 416       CreateOrFindActiveEntry(entry_hash, key);
 417   return simple_entry->CreateEntry(entry, callback);
 418 }
 419
 420 int SimpleBackendImpl::DoomEntry(const std::string& key,
 421                                  const net::CompletionCallback& callback) {
 422   const uint64 entry_hash = simple_util::GetEntryHashKey(key);
 423
 424   base::hash_map<uint64, std::vector<Closure> >::iterator it =
 425       entries_pending_doom_.find(entry_hash);
 426   if (it != entries_pending_doom_.end()) {
 427     Callback<int(const net::CompletionCallback&)> operation =
 428         base::Bind(&SimpleBackendImpl::DoomEntry, base::Unretained(this), key);
 429     it->second.push_back(base::Bind(&RunOperationAndCallback,
 430                                     operation, callback));
 431     return net::ERR_IO_PENDING;
 432   }
 433   scoped_refptr<SimpleEntryImpl> simple_entry =
 434       CreateOrFindActiveEntry(entry_hash, key);
 435   return simple_entry->DoomEntry(callback);
 436 }
 437
 438 int SimpleBackendImpl::DoomAllEntries(const CompletionCallback& callback) {
 439   return DoomEntriesBetween(Time(), Time(), callback);
 440 }
 441
 442 void SimpleBackendImpl::IndexReadyForDoom(Time initial_time,
 443                                           Time end_time,
 444                                           const CompletionCallback& callback,
 445                                           int result) {
 446   if (result != net::OK) {
 447     callback.Run(result);
 448     return;
 449   }
 450   scoped_ptr<std::vector<uint64> > removed_key_hashes(
 451       index_->GetEntriesBetween(initial_time, end_time).release());
 452   DoomEntries(removed_key_hashes.get(), callback);
 453 }
 454
 455 int SimpleBackendImpl::DoomEntriesBetween(
 456     const Time initial_time,
 457     const Time end_time,
 458     const CompletionCallback& callback) {
 459   return index_->ExecuteWhenReady(
 460       base::Bind(&SimpleBackendImpl::IndexReadyForDoom, AsWeakPtr(),
 461                  initial_time, end_time, callback));
 462 }
 463
 464 int SimpleBackendImpl::DoomEntriesSince(
 465     const Time initial_time,
 466     const CompletionCallback& callback) {
 467   return DoomEntriesBetween(initial_time, Time(), callback);
 468 }
 469
 470 class SimpleBackendImpl::SimpleIterator final : public Iterator {
 471  public:
 472   explicit SimpleIterator(base::WeakPtr<SimpleBackendImpl> backend)
 473       : backend_(backend),
 474         weak_factory_(this) {
 475   }
 476
 477   // From Backend::Iterator:
 478   int OpenNextEntry(Entry** next_entry,
 479                     const CompletionCallback& callback) override {
 480     CompletionCallback open_next_entry_impl =
 481         base::Bind(&SimpleIterator::OpenNextEntryImpl,
 482                    weak_factory_.GetWeakPtr(), next_entry, callback);
 483     return backend_->index_->ExecuteWhenReady(open_next_entry_impl);
 484   }
 485
 486   void OpenNextEntryImpl(Entry** next_entry,
 487                          const CompletionCallback& callback,
 488                          int index_initialization_error_code) {
 489     if (!backend_) {
 490       callback.Run(net::ERR_FAILED);
 491       return;
 492     }
 493     if (index_initialization_error_code != net::OK) {
 494       callback.Run(index_initialization_error_code);
 495       return;
 496     }
 497     if (!hashes_to_enumerate_)
 498       hashes_to_enumerate_ = backend_->index()->GetAllHashes().Pass();
 499
 500     while (!hashes_to_enumerate_->empty()) {
 501       uint64 entry_hash = hashes_to_enumerate_->back();
 502       hashes_to_enumerate_->pop_back();
 503       if (backend_->index()->Has(entry_hash)) {
 504         *next_entry = NULL;
 505         CompletionCallback continue_iteration = base::Bind(
 506             &SimpleIterator::CheckIterationReturnValue,
 507             weak_factory_.GetWeakPtr(),
 508             next_entry,
 509             callback);
 510         int error_code_open = backend_->OpenEntryFromHash(entry_hash,
 511                                                           next_entry,
 512                                                           continue_iteration);
 513         if (error_code_open == net::ERR_IO_PENDING)
 514           return;
 515         if (error_code_open != net::ERR_FAILED) {
 516           callback.Run(error_code_open);
 517           return;
 518         }
 519       }
 520     }
 521     callback.Run(net::ERR_FAILED);
 522   }
 523
 524   void CheckIterationReturnValue(Entry** entry,
 525                                  const CompletionCallback& callback,
 526                                  int error_code) {
 527     if (error_code == net::ERR_FAILED) {
 528       OpenNextEntry(entry, callback);
 529       return;
 530     }
 531     callback.Run(error_code);
 532   }
 533
 534  private:
 535   base::WeakPtr<SimpleBackendImpl> backend_;
 536   scoped_ptr<std::vector<uint64> > hashes_to_enumerate_;
 537   base::WeakPtrFactory<SimpleIterator> weak_factory_;
 538 };
 539
 540 scoped_ptr<Backend::Iterator> SimpleBackendImpl::CreateIterator() {
 541   return scoped_ptr<Iterator>(new SimpleIterator(AsWeakPtr()));
 542 }
 543
 544 void SimpleBackendImpl::GetStats(
 545     std::vector<std::pair<std::string, std::string> >* stats) {
 546   std::pair<std::string, std::string> item;
 547   item.first = "Cache type";
 548   item.second = "Simple Cache";
 549   stats->push_back(item);
 550 }
 551
 552 void SimpleBackendImpl::OnExternalCacheHit(const std::string& key) {
 553   index_->UseIfExists(simple_util::GetEntryHashKey(key));
 554 }
 555
 556 void SimpleBackendImpl::InitializeIndex(const CompletionCallback& callback,
 557                                         const DiskStatResult& result) {
 558   if (result.net_error == net::OK) {
 559     index_->SetMaxSize(result.max_size);
 560     index_->Initialize(result.cache_dir_mtime);
 561   }
 562   callback.Run(result.net_error);
 563 }
 564
 565 SimpleBackendImpl::DiskStatResult SimpleBackendImpl::InitCacheStructureOnDisk(
 566     const base::FilePath& path,
 567     uint64 suggested_max_size) {
 568   DiskStatResult result;
 569   result.max_size = suggested_max_size;
 570   result.net_error = net::OK;
 571   if (!FileStructureConsistent(path)) {
 572     LOG(ERROR) << "Simple Cache Backend: wrong file structure on disk: "
 573                << path.LossyDisplayName();
 574     result.net_error = net::ERR_FAILED;
 575   } else {
 576     bool mtime_result =
 577         disk_cache::simple_util::GetMTime(path, &result.cache_dir_mtime);
 578     DCHECK(mtime_result);
 579     if (!result.max_size) {
 580       int64 available = base::SysInfo::AmountOfFreeDiskSpace(path);
 581       result.max_size = disk_cache::PreferredCacheSize(available);
 582     }
 583     DCHECK(result.max_size);
 584   }
 585   return result;
 586 }
 587
 588 scoped_refptr<SimpleEntryImpl> SimpleBackendImpl::CreateOrFindActiveEntry(
 589     const uint64 entry_hash,
 590     const std::string& key) {
 591   DCHECK_EQ(entry_hash, simple_util::GetEntryHashKey(key));
 592   std::pair<EntryMap::iterator, bool> insert_result =
 593       active_entries_.insert(EntryMap::value_type(entry_hash, NULL));
 594   EntryMap::iterator& it = insert_result.first;
 595   const bool did_insert = insert_result.second;
 596   if (did_insert) {
 597     SimpleEntryImpl* entry = it->second =
 598         new SimpleEntryImpl(cache_type_, path_, entry_hash,
 599                             entry_operations_mode_,this, net_log_);
 600     entry->SetKey(key);
 601     entry->SetActiveEntryProxy(ActiveEntryProxy::Create(entry_hash, this));
 602   }
 603   DCHECK(it->second);
 604   // It's possible, but unlikely, that we have an entry hash collision with a
 605   // currently active entry.
 606   if (key != it->second->key()) {
 607     it->second->Doom();
 608     DCHECK_EQ(0U, active_entries_.count(entry_hash));
 609     return CreateOrFindActiveEntry(entry_hash, key);
 610   }
 611   return make_scoped_refptr(it->second);
 612 }
 613
 614 int SimpleBackendImpl::OpenEntryFromHash(uint64 entry_hash,
 615                                          Entry** entry,
 616                                          const CompletionCallback& callback) {
 617   base::hash_map<uint64, std::vector<Closure> >::iterator it =
 618       entries_pending_doom_.find(entry_hash);
 619   if (it != entries_pending_doom_.end()) {
 620     Callback<int(const net::CompletionCallback&)> operation =
 621         base::Bind(&SimpleBackendImpl::OpenEntryFromHash,
 622                    base::Unretained(this), entry_hash, entry);
 623     it->second.push_back(base::Bind(&RunOperationAndCallback,
 624                                     operation, callback));
 625     return net::ERR_IO_PENDING;
 626   }
 627
 628   EntryMap::iterator has_active = active_entries_.find(entry_hash);
 629   if (has_active != active_entries_.end()) {
 630     return OpenEntry(has_active->second->key(), entry, callback);
 631   }
 632
 633   scoped_refptr<SimpleEntryImpl> simple_entry = new SimpleEntryImpl(
 634       cache_type_, path_, entry_hash, entry_operations_mode_, this, net_log_);
 635   CompletionCallback backend_callback =
 636       base::Bind(&SimpleBackendImpl::OnEntryOpenedFromHash,
 637                  AsWeakPtr(), entry_hash, entry, simple_entry, callback);
 638   return simple_entry->OpenEntry(entry, backend_callback);
 639 }
 640
 641 int SimpleBackendImpl::DoomEntryFromHash(uint64 entry_hash,
 642                                          const CompletionCallback& callback) {
 643   Entry** entry = new Entry*();
 644   scoped_ptr<Entry*> scoped_entry(entry);
 645
 646   base::hash_map<uint64, std::vector<Closure> >::iterator pending_it =
 647       entries_pending_doom_.find(entry_hash);
 648   if (pending_it != entries_pending_doom_.end()) {
 649     Callback<int(const net::CompletionCallback&)> operation =
 650         base::Bind(&SimpleBackendImpl::DoomEntryFromHash,
 651                    base::Unretained(this), entry_hash);
 652     pending_it->second.push_back(base::Bind(&RunOperationAndCallback,
 653                                     operation, callback));
 654     return net::ERR_IO_PENDING;
 655   }
 656
 657   EntryMap::iterator active_it = active_entries_.find(entry_hash);
 658   if (active_it != active_entries_.end())
 659     return active_it->second->DoomEntry(callback);
 660
 661   // There's no pending dooms, nor any open entry. We can make a trivial
 662   // call to DoomEntries() to delete this entry.
 663   std::vector<uint64> entry_hash_vector;
 664   entry_hash_vector.push_back(entry_hash);
 665   DoomEntries(&entry_hash_vector, callback);
 666   return net::ERR_IO_PENDING;
 667 }
 668
 669 void SimpleBackendImpl::OnEntryOpenedFromHash(
 670     uint64 hash,
 671     Entry** entry,
 672     const scoped_refptr<SimpleEntryImpl>& simple_entry,
 673     const CompletionCallback& callback,
 674     int error_code) {
 675   if (error_code != net::OK) {
 676     callback.Run(error_code);
 677     return;
 678   }
 679   DCHECK(*entry);
 680   std::pair<EntryMap::iterator, bool> insert_result =
 681       active_entries_.insert(EntryMap::value_type(hash, simple_entry.get()));
 682   EntryMap::iterator& it = insert_result.first;
 683   const bool did_insert = insert_result.second;
 684   if (did_insert) {
 685     // There was no active entry corresponding to this hash. We've already put
 686     // the entry opened from hash in the |active_entries_|. We now provide the
 687     // proxy object to the entry.
 688     it->second->SetActiveEntryProxy(ActiveEntryProxy::Create(hash, this));
 689     callback.Run(net::OK);
 690   } else {
 691     // The entry was made active while we waiting for the open from hash to
 692     // finish. The entry created from hash needs to be closed, and the one
 693     // in |active_entries_| can be returned to the caller.
 694     simple_entry->Close();
 695     it->second->OpenEntry(entry, callback);
 696   }
 697 }
 698
 699 void SimpleBackendImpl::OnEntryOpenedFromKey(
 700     const std::string key,
 701     Entry** entry,
 702     const scoped_refptr<SimpleEntryImpl>& simple_entry,
 703     const CompletionCallback& callback,
 704     int error_code) {
 705   int final_code = error_code;
 706   if (final_code == net::OK) {
 707     bool key_matches = key.compare(simple_entry->key()) == 0;
 708     if (!key_matches) {
 709       // TODO(clamy): Add a unit test to check this code path.
 710       DLOG(WARNING) << "Key mismatch on open.";
 711       simple_entry->Doom();
 712       simple_entry->Close();
 713       final_code = net::ERR_FAILED;
 714     } else {
 715       DCHECK_EQ(simple_entry->entry_hash(), simple_util::GetEntryHashKey(key));
 716     }
 717     SIMPLE_CACHE_UMA(BOOLEAN, "KeyMatchedOnOpen", cache_type_, key_matches);
 718   }
 719   callback.Run(final_code);
 720 }
 721
 722 void SimpleBackendImpl::DoomEntriesComplete(
 723     scoped_ptr<std::vector<uint64> > entry_hashes,
 724     const net::CompletionCallback& callback,
 725     int result) {
 726   std::for_each(
 727       entry_hashes->begin(), entry_hashes->end(),
 728       std::bind1st(std::mem_fun(&SimpleBackendImpl::OnDoomComplete),
 729                    this));
 730   callback.Run(result);
 731 }
 732
 733 void SimpleBackendImpl::FlushWorkerPoolForTesting() {
 734   if (g_sequenced_worker_pool)
 735     g_sequenced_worker_pool->FlushForTesting();
 736 }
 737
 738 }  // namespace disk_cache