palemoon27/dom/storage/DOMStorageDBThread.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "DOMStorageDBThread.h"
#include "DOMStorageCache.h"

#include "nsIEffectiveTLDService.h"
#include "nsDirectoryServiceUtils.h"
#include "nsAppDirectoryServiceDefs.h"
#include "nsThreadUtils.h"
#include "nsProxyRelease.h"
#include "mozStorageCID.h"
#include "mozStorageHelper.h"
#include "mozIStorageService.h"
#include "mozIStorageBindingParamsArray.h"
#include "mozIStorageBindingParams.h"
#include "mozIStorageValueArray.h"
#include "mozIStorageFunction.h"
#include "nsIObserverService.h"
#include "nsVariant.h"
#include "mozilla/IOInterposer.h"
#include "mozilla/Services.h"

// How long we collect write oprerations
// before they are flushed to the database
// In milliseconds.
#define FLUSHING_INTERVAL_MS 5000

// Write Ahead Log's maximum size is 512KB
#define MAX_WAL_SIZE_BYTES 512 * 1024

namespace mozilla {
namespace dom {

DOMStorageDBBridge::DOMStorageDBBridge()
{
}


DOMStorageDBThread::DOMStorageDBThread()
: mThread(nullptr)
, mThreadObserver(new ThreadObserver())
, mStopIOThread(false)
, mWALModeEnabled(false)
, mDBReady(false)
, mStatus(NS_OK)
, mWorkerStatements(mWorkerConnection)
, mReaderStatements(mReaderConnection)
, mDirtyEpoch(0)
, mFlushImmediately(false)
, mPriorityCounter(0)
{
}

nsresult
DOMStorageDBThread::Init()
{
  nsresult rv;

  // Need to determine location on the main thread, since
  // NS_GetSpecialDirectory access the atom table that can
  // be accessed only on the main thread.
  rv = NS_GetSpecialDirectory(NS_APP_USER_PROFILE_50_DIR,
                              getter_AddRefs(mDatabaseFile));
  NS_ENSURE_SUCCESS(rv, rv);

  rv = mDatabaseFile->Append(NS_LITERAL_STRING("webappsstore.sqlite"));
  NS_ENSURE_SUCCESS(rv, rv);

  // Ensure mozIStorageService init on the main thread first.
  nsCOMPtr<mozIStorageService> service =
    do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
  NS_ENSURE_SUCCESS(rv, rv);

  // Need to keep the lock to avoid setting mThread later then
  // the thread body executes.
  MonitorAutoLock monitor(mThreadObserver->GetMonitor());

  mThread = PR_CreateThread(PR_USER_THREAD, &DOMStorageDBThread::ThreadFunc, this,
                            PR_PRIORITY_LOW, PR_GLOBAL_THREAD, PR_JOINABLE_THREAD,
                            262144);
  if (!mThread) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  return NS_OK;
}

nsresult
DOMStorageDBThread::Shutdown()
{
  if (!mThread) {
    return NS_ERROR_NOT_INITIALIZED;
  }

  Telemetry::AutoTimer<Telemetry::LOCALDOMSTORAGE_SHUTDOWN_DATABASE_MS> timer;

  {
    MonitorAutoLock monitor(mThreadObserver->GetMonitor());

    // After we stop, no other operations can be accepted
    mFlushImmediately = true;
    mStopIOThread = true;
    monitor.Notify();
  }

  PR_JoinThread(mThread);
  mThread = nullptr;

  return mStatus;
}

void
DOMStorageDBThread::SyncPreload(DOMStorageCacheBridge* aCache, bool aForceSync)
{
  PROFILER_LABEL_FUNC(js::ProfileEntry::Category::STORAGE);
  if (!aForceSync && aCache->LoadedCount()) {
    // Preload already started for this cache, just wait for it to finish.
    // LoadWait will exit after LoadDone on the cache has been called.
    SetHigherPriority();
    aCache->LoadWait();
    SetDefaultPriority();
    return;
  }

  // Bypass sync load when an update is pending in the queue to write, we would
  // get incosistent data in the cache.  Also don't allow sync main-thread preload
  // when DB open and init is still pending on the background thread.
  if (mDBReady && mWALModeEnabled) {
    bool pendingTasks;
    {
      MonitorAutoLock monitor(mThreadObserver->GetMonitor());
      pendingTasks = mPendingTasks.IsScopeUpdatePending(aCache->Scope()) ||
                     mPendingTasks.IsScopeClearPending(aCache->Scope());
    }

    if (!pendingTasks) {
      // WAL is enabled, thus do the load synchronously on the main thread.
      DBOperation preload(DBOperation::opPreload, aCache);
      preload.PerformAndFinalize(this);
      return;
    }
  }

  // Need to go asynchronously since WAL is not allowed or scheduled updates
  // need to be flushed first.
  // Schedule preload for this cache as the first operation.
  nsresult rv = InsertDBOp(new DBOperation(DBOperation::opPreloadUrgent, aCache));

  // LoadWait exits after LoadDone of the cache has been called.
  if (NS_SUCCEEDED(rv)) {
    aCache->LoadWait();
  }
}

void
DOMStorageDBThread::AsyncFlush()
{
  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
  mFlushImmediately = true;
  monitor.Notify();
}

bool
DOMStorageDBThread::ShouldPreloadScope(const nsACString& aScope)
{
  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
  return mScopesHavingData.Contains(aScope);
}

void
DOMStorageDBThread::GetScopesHavingData(InfallibleTArray<nsCString>* aScopes)
{
  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
  for (auto iter = mScopesHavingData.Iter(); !iter.Done(); iter.Next()) {
    aScopes->AppendElement(iter.Get()->GetKey());
  }
}

nsresult
DOMStorageDBThread::InsertDBOp(DOMStorageDBThread::DBOperation* aOperation)
{
  MonitorAutoLock monitor(mThreadObserver->GetMonitor());

  // Sentinel to don't forget to delete the operation when we exit early.
  nsAutoPtr<DOMStorageDBThread::DBOperation> opScope(aOperation);

  if (NS_FAILED(mStatus)) {
    MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
    aOperation->Finalize(mStatus);
    return mStatus;
  }

  if (mStopIOThread) {
    // Thread use after shutdown demanded.
    MOZ_ASSERT(false);
    return NS_ERROR_NOT_INITIALIZED;
  }

  switch (aOperation->Type()) {
  case DBOperation::opPreload:
  case DBOperation::opPreloadUrgent:
    if (mPendingTasks.IsScopeUpdatePending(aOperation->Scope())) {
      // If there is a pending update operation for the scope first do the flush
      // before we preload the cache.  This may happen in an extremely rare case
      // when a child process throws away its cache before flush on the parent
      // has finished.  If we would preloaded the cache as a priority operation 
      // before the pending flush, we would have got an inconsistent cache content.
      mFlushImmediately = true;
    } else if (mPendingTasks.IsScopeClearPending(aOperation->Scope())) {
      // The scope is scheduled to be cleared, so just quickly load as empty.
      // We need to do this to prevent load of the DB data before the scope has
      // actually been cleared from the database.  Preloads are processed
      // immediately before update and clear operations on the database that
      // are flushed periodically in batches.
      MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
      aOperation->Finalize(NS_OK);
      return NS_OK;
    }
    // NO BREAK

  case DBOperation::opGetUsage:
    if (aOperation->Type() == DBOperation::opPreloadUrgent) {
      SetHigherPriority(); // Dropped back after urgent preload execution
      mPreloads.InsertElementAt(0, aOperation);
    } else {
      mPreloads.AppendElement(aOperation);
    }

    // DB operation adopted, don't delete it.
    opScope.forget();

    // Immediately start executing this.
    monitor.Notify();
    break;

  default:
    // Update operations are first collected, coalesced and then flushed
    // after a short time.
    mPendingTasks.Add(aOperation);

    // DB operation adopted, don't delete it.
    opScope.forget();

    ScheduleFlush();
    break;
  }

  return NS_OK;
}

void
DOMStorageDBThread::SetHigherPriority()
{
  ++mPriorityCounter;
  PR_SetThreadPriority(mThread, PR_PRIORITY_URGENT);
}

void
DOMStorageDBThread::SetDefaultPriority()
{
  if (--mPriorityCounter <= 0) {
    PR_SetThreadPriority(mThread, PR_PRIORITY_LOW);
  }
}

void
DOMStorageDBThread::ThreadFunc(void* aArg)
{
  PR_SetCurrentThreadName("localStorage DB");
  mozilla::IOInterposer::RegisterCurrentThread();

  DOMStorageDBThread* thread = static_cast<DOMStorageDBThread*>(aArg);
  thread->ThreadFunc();
  mozilla::IOInterposer::UnregisterCurrentThread();
}

void
DOMStorageDBThread::ThreadFunc()
{
  nsresult rv = InitDatabase();

  MonitorAutoLock lockMonitor(mThreadObserver->GetMonitor());

  if (NS_FAILED(rv)) {
    mStatus = rv;
    mStopIOThread = true;
    return;
  }

  // Create an nsIThread for the current PRThread, so we can observe runnables
  // dispatched to it.
  nsCOMPtr<nsIThread> thread = NS_GetCurrentThread();
  nsCOMPtr<nsIThreadInternal> threadInternal = do_QueryInterface(thread);
  MOZ_ASSERT(threadInternal); // Should always succeed.
  threadInternal->SetObserver(mThreadObserver);

  while (MOZ_LIKELY(!mStopIOThread || mPreloads.Length() ||
                    mPendingTasks.HasTasks() ||
                    mThreadObserver->HasPendingEvents())) {
    // Process xpcom events first.
    while (MOZ_UNLIKELY(mThreadObserver->HasPendingEvents())) {
      mThreadObserver->ClearPendingEvents();
      MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
      bool processedEvent;
      do {
        rv = thread->ProcessNextEvent(false, &processedEvent);
      } while (NS_SUCCEEDED(rv) && processedEvent);
    }

    if (MOZ_UNLIKELY(TimeUntilFlush() == 0)) {
      // Flush time is up or flush has been forced, do it now.
      UnscheduleFlush();
      if (mPendingTasks.Prepare()) {
        {
          MonitorAutoUnlock unlockMonitor(mThreadObserver->GetMonitor());
          rv = mPendingTasks.Execute(this);
        }

        if (!mPendingTasks.Finalize(rv)) {
          mStatus = rv;
          NS_WARNING("localStorage DB access broken");
        }
      }
      NotifyFlushCompletion();
    } else if (MOZ_LIKELY(mPreloads.Length())) {
      nsAutoPtr<DBOperation> op(mPreloads[0]);
      mPreloads.RemoveElementAt(0);
      {
        MonitorAutoUnlock unlockMonitor(mThreadObserver->GetMonitor());
        op->PerformAndFinalize(this);
      }

      if (op->Type() == DBOperation::opPreloadUrgent) {
        SetDefaultPriority(); // urgent preload unscheduled
      }
    } else if (MOZ_UNLIKELY(!mStopIOThread)) {
      lockMonitor.Wait(TimeUntilFlush());
    }
  } // thread loop

  mStatus = ShutdownDatabase();

  if (threadInternal) {
    threadInternal->SetObserver(nullptr);
  }
}


NS_IMPL_ISUPPORTS(DOMStorageDBThread::ThreadObserver, nsIThreadObserver)

NS_IMETHODIMP
DOMStorageDBThread::ThreadObserver::OnDispatchedEvent(nsIThreadInternal *thread)
{
  MonitorAutoLock lock(mMonitor);
  mHasPendingEvents = true;
  lock.Notify();
  return NS_OK;
}

NS_IMETHODIMP
DOMStorageDBThread::ThreadObserver::OnProcessNextEvent(nsIThreadInternal *thread,
                                       bool mayWait)
{
  return NS_OK;
}

NS_IMETHODIMP
DOMStorageDBThread::ThreadObserver::AfterProcessNextEvent(nsIThreadInternal *thread,
                                          bool eventWasProcessed)
{
  return NS_OK;
}


extern void
ReverseString(const nsCSubstring& aSource, nsCSubstring& aResult);

namespace {

class nsReverseStringSQLFunction final : public mozIStorageFunction
{
  ~nsReverseStringSQLFunction() {}

  NS_DECL_ISUPPORTS
  NS_DECL_MOZISTORAGEFUNCTION
};

NS_IMPL_ISUPPORTS(nsReverseStringSQLFunction, mozIStorageFunction)

NS_IMETHODIMP
nsReverseStringSQLFunction::OnFunctionCall(
    mozIStorageValueArray* aFunctionArguments, nsIVariant** aResult)
{
  nsresult rv;

  nsAutoCString stringToReverse;
  rv = aFunctionArguments->GetUTF8String(0, stringToReverse);
  NS_ENSURE_SUCCESS(rv, rv);

  nsAutoCString result;
  ReverseString(stringToReverse, result);

  RefPtr<nsVariant> outVar(new nsVariant());
  rv = outVar->SetAsAUTF8String(result);
  NS_ENSURE_SUCCESS(rv, rv);

  outVar.forget(aResult);
  return NS_OK;
}

} // namespace

nsresult
DOMStorageDBThread::OpenDatabaseConnection()
{
  nsresult rv;

  MOZ_ASSERT(!NS_IsMainThread());

  nsCOMPtr<mozIStorageService> service
      = do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<mozIStorageConnection> connection;
  rv = service->OpenUnsharedDatabase(mDatabaseFile, getter_AddRefs(mWorkerConnection));
  if (rv == NS_ERROR_FILE_CORRUPTED) {
    // delete the db and try opening again
    rv = mDatabaseFile->Remove(false);
    NS_ENSURE_SUCCESS(rv, rv);
    rv = service->OpenUnsharedDatabase(mDatabaseFile, getter_AddRefs(mWorkerConnection));
  }
  NS_ENSURE_SUCCESS(rv, rv);

  return NS_OK;
}

nsresult
DOMStorageDBThread::InitDatabase()
{
  Telemetry::AutoTimer<Telemetry::LOCALDOMSTORAGE_INIT_DATABASE_MS> timer;

  nsresult rv;

  // Here we are on the worker thread. This opens the worker connection.
  MOZ_ASSERT(!NS_IsMainThread());

  rv = OpenDatabaseConnection();
  NS_ENSURE_SUCCESS(rv, rv);

  rv = TryJournalMode();
  NS_ENSURE_SUCCESS(rv, rv);

  // Create a read-only clone
  (void)mWorkerConnection->Clone(true, getter_AddRefs(mReaderConnection));
  NS_ENSURE_TRUE(mReaderConnection, NS_ERROR_FAILURE);

  mozStorageTransaction transaction(mWorkerConnection, false);

  // Ensure Gecko 1.9.1 storage table
  rv = mWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
         "CREATE TABLE IF NOT EXISTS webappsstore2 ("
         "scope TEXT, "
         "key TEXT, "
         "value TEXT, "
         "secure INTEGER, "
         "owner TEXT)"));
  NS_ENSURE_SUCCESS(rv, rv);

  rv = mWorkerConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING(
        "CREATE UNIQUE INDEX IF NOT EXISTS scope_key_index"
        " ON webappsstore2(scope, key)"));
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<mozIStorageFunction> function1(new nsReverseStringSQLFunction());
  NS_ENSURE_TRUE(function1, NS_ERROR_OUT_OF_MEMORY);

  rv = mWorkerConnection->CreateFunction(NS_LITERAL_CSTRING("REVERSESTRING"), 1, function1);
  NS_ENSURE_SUCCESS(rv, rv);

  bool exists;

  // Check if there is storage of Gecko 1.9.0 and if so, upgrade that storage
  // to actual webappsstore2 table and drop the obsolete table. First process
  // this newer table upgrade to priority potential duplicates from older
  // storage table.
  rv = mWorkerConnection->TableExists(NS_LITERAL_CSTRING("webappsstore"),
                                &exists);
  NS_ENSURE_SUCCESS(rv, rv);

  if (exists) {
    rv = mWorkerConnection->ExecuteSimpleSQL(
      NS_LITERAL_CSTRING("INSERT OR IGNORE INTO "
                         "webappsstore2(scope, key, value, secure, owner) "
                         "SELECT REVERSESTRING(domain) || '.:', key, value, secure, owner "
                         "FROM webappsstore"));
    NS_ENSURE_SUCCESS(rv, rv);

    rv = mWorkerConnection->ExecuteSimpleSQL(
      NS_LITERAL_CSTRING("DROP TABLE webappsstore"));
    NS_ENSURE_SUCCESS(rv, rv);
  }

  // Check if there is storage of Gecko 1.8 and if so, upgrade that storage
  // to actual webappsstore2 table and drop the obsolete table. Potential
  // duplicates will be ignored.
  rv = mWorkerConnection->TableExists(NS_LITERAL_CSTRING("moz_webappsstore"),
                                &exists);
  NS_ENSURE_SUCCESS(rv, rv);

  if (exists) {
    rv = mWorkerConnection->ExecuteSimpleSQL(
      NS_LITERAL_CSTRING("INSERT OR IGNORE INTO "
                         "webappsstore2(scope, key, value, secure, owner) "
                         "SELECT REVERSESTRING(domain) || '.:', key, value, secure, domain "
                         "FROM moz_webappsstore"));
    NS_ENSURE_SUCCESS(rv, rv);

    rv = mWorkerConnection->ExecuteSimpleSQL(
      NS_LITERAL_CSTRING("DROP TABLE moz_webappsstore"));
    NS_ENSURE_SUCCESS(rv, rv);
  }

  rv = transaction.Commit();
  NS_ENSURE_SUCCESS(rv, rv);

  // Database open and all initiation operation are done.  Switching this flag
  // to true allow main thread to read directly from the database.
  // If we would allow this sooner, we would have opened a window where main thread
  // read might operate on a totaly broken and incosistent database.
  mDBReady = true;

  // List scopes having any stored data
  nsCOMPtr<mozIStorageStatement> stmt;
  rv = mWorkerConnection->CreateStatement(NS_LITERAL_CSTRING("SELECT DISTINCT scope FROM webappsstore2"),
                                    getter_AddRefs(stmt));
  NS_ENSURE_SUCCESS(rv, rv);
  mozStorageStatementScoper scope(stmt);

  while (NS_SUCCEEDED(rv = stmt->ExecuteStep(&exists)) && exists) {
    nsAutoCString foundScope;
    rv = stmt->GetUTF8String(0, foundScope);
    NS_ENSURE_SUCCESS(rv, rv);

    MonitorAutoLock monitor(mThreadObserver->GetMonitor());
    mScopesHavingData.PutEntry(foundScope);
  }

  return NS_OK;
}

nsresult
DOMStorageDBThread::SetJournalMode(bool aIsWal)
{
  nsresult rv;

  nsAutoCString stmtString(
    MOZ_STORAGE_UNIQUIFY_QUERY_STR "PRAGMA journal_mode = ");
  if (aIsWal) {
    stmtString.AppendLiteral("wal");
  } else {
    stmtString.AppendLiteral("truncate");
  }

  nsCOMPtr<mozIStorageStatement> stmt;
  rv = mWorkerConnection->CreateStatement(stmtString, getter_AddRefs(stmt));
  NS_ENSURE_SUCCESS(rv, rv);
  mozStorageStatementScoper scope(stmt);

  bool hasResult = false;
  rv = stmt->ExecuteStep(&hasResult);
  NS_ENSURE_SUCCESS(rv, rv);
  if (!hasResult) {
    return NS_ERROR_FAILURE;
  }

  nsAutoCString journalMode;
  rv = stmt->GetUTF8String(0, journalMode);
  NS_ENSURE_SUCCESS(rv, rv);
  if ((aIsWal && !journalMode.EqualsLiteral("wal")) ||
      (!aIsWal && !journalMode.EqualsLiteral("truncate"))) {
    return NS_ERROR_FAILURE;
  }

  return NS_OK;
}

nsresult
DOMStorageDBThread::TryJournalMode()
{
  nsresult rv;

  rv = SetJournalMode(true);
  if (NS_FAILED(rv)) {
    mWALModeEnabled = false;

    rv = SetJournalMode(false);
    NS_ENSURE_SUCCESS(rv, rv);
  } else {
    mWALModeEnabled = true;

    rv = ConfigureWALBehavior();
    NS_ENSURE_SUCCESS(rv, rv);
  }

  return NS_OK;
}

nsresult
DOMStorageDBThread::ConfigureWALBehavior()
{
  // Get the DB's page size
  nsCOMPtr<mozIStorageStatement> stmt;
  nsresult rv = mWorkerConnection->CreateStatement(NS_LITERAL_CSTRING(
    MOZ_STORAGE_UNIQUIFY_QUERY_STR "PRAGMA page_size"
  ), getter_AddRefs(stmt));
  NS_ENSURE_SUCCESS(rv, rv);

  bool hasResult = false;
  rv = stmt->ExecuteStep(&hasResult);
  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && hasResult, NS_ERROR_FAILURE);

  int32_t pageSize = 0;
  rv = stmt->GetInt32(0, &pageSize);
  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && pageSize > 0, NS_ERROR_UNEXPECTED);

  // Set the threshold for auto-checkpointing the WAL.
  // We don't want giant logs slowing down reads & shutdown.
  int32_t thresholdInPages = static_cast<int32_t>(MAX_WAL_SIZE_BYTES / pageSize);
  nsAutoCString thresholdPragma("PRAGMA wal_autocheckpoint = ");
  thresholdPragma.AppendInt(thresholdInPages);
  rv = mWorkerConnection->ExecuteSimpleSQL(thresholdPragma);
  NS_ENSURE_SUCCESS(rv, rv);

  // Set the maximum WAL log size to reduce footprint on mobile (large empty
  // WAL files will be truncated)
  nsAutoCString journalSizePragma("PRAGMA journal_size_limit = ");
  // bug 600307: mak recommends setting this to 3 times the auto-checkpoint threshold
  journalSizePragma.AppendInt(MAX_WAL_SIZE_BYTES * 3);
  rv = mWorkerConnection->ExecuteSimpleSQL(journalSizePragma);
  NS_ENSURE_SUCCESS(rv, rv);

  return NS_OK;
}

nsresult
DOMStorageDBThread::ShutdownDatabase()
{
  // Has to be called on the worker thread.
  MOZ_ASSERT(!NS_IsMainThread());

  nsresult rv = mStatus;

  mDBReady = false;

  // Finalize the cached statements.
  mReaderStatements.FinalizeStatements();
  mWorkerStatements.FinalizeStatements();

  if (mReaderConnection) {
    // No need to sync access to mReaderConnection since the main thread
    // is right now joining this thread, unable to execute any events.
    mReaderConnection->Close();
    mReaderConnection = nullptr;
  }

  if (mWorkerConnection) {
    rv = mWorkerConnection->Close();
    mWorkerConnection = nullptr;
  }

  return rv;
}

void
DOMStorageDBThread::ScheduleFlush()
{
  if (mDirtyEpoch) {
    return; // Already scheduled
  }

  mDirtyEpoch = PR_IntervalNow() | 1; // Must be non-zero to indicate we are scheduled

  // Wake the monitor from indefinite sleep...
  (mThreadObserver->GetMonitor()).Notify();
}

void
DOMStorageDBThread::UnscheduleFlush()
{
  // We are just about to do the flush, drop flags
  mFlushImmediately = false;
  mDirtyEpoch = 0;
}

PRIntervalTime
DOMStorageDBThread::TimeUntilFlush()
{
  if (mFlushImmediately) {
    return 0; // Do it now regardless the timeout.
  }

  static_assert(PR_INTERVAL_NO_TIMEOUT != 0,
      "PR_INTERVAL_NO_TIMEOUT must be non-zero");

  if (!mDirtyEpoch) {
    return PR_INTERVAL_NO_TIMEOUT; // No pending task...
  }

  static const PRIntervalTime kMaxAge = PR_MillisecondsToInterval(FLUSHING_INTERVAL_MS);

  PRIntervalTime now = PR_IntervalNow() | 1;
  PRIntervalTime age = now - mDirtyEpoch;
  if (age > kMaxAge) {
    return 0; // It is time.
  }

  return kMaxAge - age; // Time left, this is used to sleep the monitor
}

void
DOMStorageDBThread::NotifyFlushCompletion()
{
#ifdef DOM_STORAGE_TESTS
  if (!NS_IsMainThread()) {
    RefPtr<nsRunnableMethod<DOMStorageDBThread, void, false> > event =
      NS_NewNonOwningRunnableMethod(this, &DOMStorageDBThread::NotifyFlushCompletion);
    NS_DispatchToMainThread(event);
    return;
  }

  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
  if (obs) {
    obs->NotifyObservers(nullptr, "domstorage-test-flushed", nullptr);
  }
#endif
}

// DOMStorageDBThread::DBOperation

DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
                                             DOMStorageCacheBridge* aCache,
                                             const nsAString& aKey,
                                             const nsAString& aValue)
: mType(aType)
, mCache(aCache)
, mKey(aKey)
, mValue(aValue)
{
  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
}

DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
                                             DOMStorageUsageBridge* aUsage)
: mType(aType)
, mUsage(aUsage)
{
  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
}

DOMStorageDBThread::DBOperation::DBOperation(const OperationType aType,
                                             const nsACString& aScope)
: mType(aType)
, mCache(nullptr)
, mScope(aScope)
{
  MOZ_COUNT_CTOR(DOMStorageDBThread::DBOperation);
}

DOMStorageDBThread::DBOperation::~DBOperation()
{
  MOZ_COUNT_DTOR(DOMStorageDBThread::DBOperation);
}

const nsCString
DOMStorageDBThread::DBOperation::Scope()
{
  if (mCache) {
    return mCache->Scope();
  }

  return mScope;
}

const nsCString
DOMStorageDBThread::DBOperation::Target()
{
  switch (mType) {
    case opAddItem:
    case opUpdateItem:
    case opRemoveItem:
      return Scope() + NS_LITERAL_CSTRING("|") + NS_ConvertUTF16toUTF8(mKey);

    default:
      return Scope();
  }
}

void
DOMStorageDBThread::DBOperation::PerformAndFinalize(DOMStorageDBThread* aThread)
{
  Finalize(Perform(aThread));
}

nsresult
DOMStorageDBThread::DBOperation::Perform(DOMStorageDBThread* aThread)
{
  nsresult rv;

  switch (mType) {
  case opPreload:
  case opPreloadUrgent:
  {
    // Already loaded?
    if (mCache->Loaded()) {
      break;
    }

    StatementCache* statements;
    if (MOZ_UNLIKELY(NS_IsMainThread())) {
      statements = &aThread->mReaderStatements;
    } else {
      statements = &aThread->mWorkerStatements;
    }

    // OFFSET is an optimization when we have to do a sync load
    // and cache has already loaded some parts asynchronously.
    // It skips keys we have already loaded.
    nsCOMPtr<mozIStorageStatement> stmt = statements->GetCachedStatement(
        "SELECT key, value FROM webappsstore2 "
        "WHERE scope = :scope ORDER BY key "
        "LIMIT -1 OFFSET :offset");
    NS_ENSURE_STATE(stmt);
    mozStorageStatementScoper scope(stmt);

    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
                                    mCache->Scope());
    NS_ENSURE_SUCCESS(rv, rv);

    rv = stmt->BindInt32ByName(NS_LITERAL_CSTRING("offset"),
                               static_cast<int32_t>(mCache->LoadedCount()));
    NS_ENSURE_SUCCESS(rv, rv);

    bool exists;
    while (NS_SUCCEEDED(rv = stmt->ExecuteStep(&exists)) && exists) {
      nsAutoString key;
      rv = stmt->GetString(0, key);
      NS_ENSURE_SUCCESS(rv, rv);

      nsAutoString value;
      rv = stmt->GetString(1, value);
      NS_ENSURE_SUCCESS(rv, rv);

      if (!mCache->LoadItem(key, value)) {
        break;
      }
    }

    // The loop condition's call to ExecuteStep() may have terminated because
    // !NS_SUCCEEDED(), we need an early return to cover that case.  This also
    // covers success cases as well, but that's inductively safe.
    NS_ENSURE_SUCCESS(rv, rv);
    break;
  }

  case opGetUsage:
  {
    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
      "SELECT SUM(LENGTH(key) + LENGTH(value)) FROM webappsstore2"
      " WHERE scope LIKE :scope"
    );
    NS_ENSURE_STATE(stmt);

    mozStorageStatementScoper scope(stmt);

    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
                                    mUsage->Scope() + NS_LITERAL_CSTRING("%"));
    NS_ENSURE_SUCCESS(rv, rv);

    bool exists;
    rv = stmt->ExecuteStep(&exists);
    NS_ENSURE_SUCCESS(rv, rv);

    int64_t usage = 0;
    if (exists) {
      rv = stmt->GetInt64(0, &usage);
      NS_ENSURE_SUCCESS(rv, rv);
    }

    mUsage->LoadUsage(usage);
    break;
  }

  case opAddItem:
  case opUpdateItem:
  {
    MOZ_ASSERT(!NS_IsMainThread());

    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
      "INSERT OR REPLACE INTO webappsstore2 (scope, key, value) "
      "VALUES (:scope, :key, :value) "
    );
    NS_ENSURE_STATE(stmt);

    mozStorageStatementScoper scope(stmt);

    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
                                    mCache->Scope());
    NS_ENSURE_SUCCESS(rv, rv);
    rv = stmt->BindStringByName(NS_LITERAL_CSTRING("key"),
                                mKey);
    NS_ENSURE_SUCCESS(rv, rv);
    rv = stmt->BindStringByName(NS_LITERAL_CSTRING("value"),
                                mValue);
    NS_ENSURE_SUCCESS(rv, rv);

    rv = stmt->Execute();
    NS_ENSURE_SUCCESS(rv, rv);

    aThread->mScopesHavingData.PutEntry(Scope());
    break;
  }

  case opRemoveItem:
  {
    MOZ_ASSERT(!NS_IsMainThread());

    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
      "DELETE FROM webappsstore2 "
      "WHERE scope = :scope "
        "AND key = :key "
    );
    NS_ENSURE_STATE(stmt);
    mozStorageStatementScoper scope(stmt);

    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
                                    mCache->Scope());
    NS_ENSURE_SUCCESS(rv, rv);
    rv = stmt->BindStringByName(NS_LITERAL_CSTRING("key"),
                                mKey);
    NS_ENSURE_SUCCESS(rv, rv);

    rv = stmt->Execute();
    NS_ENSURE_SUCCESS(rv, rv);

    break;
  }

  case opClear:
  {
    MOZ_ASSERT(!NS_IsMainThread());

    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
      "DELETE FROM webappsstore2 "
      "WHERE scope = :scope"
    );
    NS_ENSURE_STATE(stmt);
    mozStorageStatementScoper scope(stmt);

    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
                                    mCache->Scope());
    NS_ENSURE_SUCCESS(rv, rv);

    rv = stmt->Execute();
    NS_ENSURE_SUCCESS(rv, rv);

    aThread->mScopesHavingData.RemoveEntry(Scope());
    break;
  }

  case opClearAll:
  {
    MOZ_ASSERT(!NS_IsMainThread());

    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
      "DELETE FROM webappsstore2"
    );
    NS_ENSURE_STATE(stmt);
    mozStorageStatementScoper scope(stmt);

    rv = stmt->Execute();
    NS_ENSURE_SUCCESS(rv, rv);

    aThread->mScopesHavingData.Clear();
    break;
  }

  case opClearMatchingScope:
  {
    MOZ_ASSERT(!NS_IsMainThread());

    nsCOMPtr<mozIStorageStatement> stmt = aThread->mWorkerStatements.GetCachedStatement(
      "DELETE FROM webappsstore2"
      " WHERE scope GLOB :scope"
    );
    NS_ENSURE_STATE(stmt);
    mozStorageStatementScoper scope(stmt);

    rv = stmt->BindUTF8StringByName(NS_LITERAL_CSTRING("scope"),
                                    mScope + NS_LITERAL_CSTRING("*"));
    NS_ENSURE_SUCCESS(rv, rv);

    rv = stmt->Execute();
    NS_ENSURE_SUCCESS(rv, rv);

    break;
  }

  default:
    NS_ERROR("Unknown task type");
    break;
  }

  return NS_OK;
}

void
DOMStorageDBThread::DBOperation::Finalize(nsresult aRv)
{
  switch (mType) {
  case opPreloadUrgent:
  case opPreload:
    if (NS_FAILED(aRv)) {
      // When we are here, something failed when loading from the database.
      // Notify that the storage is loaded to prevent deadlock of the main thread,
      // even though it is actually empty or incomplete.
      NS_WARNING("Failed to preload localStorage");
    }

    mCache->LoadDone(aRv);
    break;

  case opGetUsage:
    if (NS_FAILED(aRv)) {
      mUsage->LoadUsage(0);
    }

    break;

  default:
    if (NS_FAILED(aRv)) {
      NS_WARNING("localStorage update/clear operation failed,"
                 " data may not persist or clean up");
    }

    break;
  }
}

// DOMStorageDBThread::PendingOperations

DOMStorageDBThread::PendingOperations::PendingOperations()
: mFlushFailureCount(0)
{
}

bool
DOMStorageDBThread::PendingOperations::HasTasks()
{
  return !!mUpdates.Count() || !!mClears.Count();
}

namespace {

} // namespace

bool
DOMStorageDBThread::PendingOperations::CheckForCoalesceOpportunity(DBOperation* aNewOp,
                                                                   DBOperation::OperationType aPendingType,
                                                                   DBOperation::OperationType aNewType)
{
  if (aNewOp->Type() != aNewType) {
    return false;
  }

  DOMStorageDBThread::DBOperation* pendingTask;
  if (!mUpdates.Get(aNewOp->Target(), &pendingTask)) {
    return false;
  }

  if (pendingTask->Type() != aPendingType) {
    return false;
  }

  return true;
}

void
DOMStorageDBThread::PendingOperations::Add(DOMStorageDBThread::DBOperation* aOperation)
{
  // Optimize: when a key to remove has never been written to disk
  // just bypass this operation.  A kew is new when an operation scheduled
  // to write it to the database is of type opAddItem.
  if (CheckForCoalesceOpportunity(aOperation, DBOperation::opAddItem, DBOperation::opRemoveItem)) {
    mUpdates.Remove(aOperation->Target());
    delete aOperation;
    return;
  }

  // Optimize: when changing a key that is new and has never been
  // written to disk, keep type of the operation to store it at opAddItem.
  // This allows optimization to just forget adding a new key when
  // it is removed from the storage before flush.
  if (CheckForCoalesceOpportunity(aOperation, DBOperation::opAddItem, DBOperation::opUpdateItem)) {
    aOperation->mType = DBOperation::opAddItem;
  }

  // Optimize: to prevent lose of remove operation on a key when doing
  // remove/set/remove on a previously existing key we have to change
  // opAddItem to opUpdateItem on the new operation when there is opRemoveItem
  // pending for the key.
  if (CheckForCoalesceOpportunity(aOperation, DBOperation::opRemoveItem, DBOperation::opAddItem)) {
    aOperation->mType = DBOperation::opUpdateItem;
  }

  switch (aOperation->Type())
  {
  // Operations on single keys

  case DBOperation::opAddItem:
  case DBOperation::opUpdateItem:
  case DBOperation::opRemoveItem:
    // Override any existing operation for the target (=scope+key).
    mUpdates.Put(aOperation->Target(), aOperation);
    break;

  // Clear operations

  case DBOperation::opClear:
  case DBOperation::opClearMatchingScope:
    // Drop all update (insert/remove) operations for equivavelent or matching scope.
    // We do this as an optimization as well as a must based on the logic,
    // if we would not delete the update tasks, changes would have been stored
    // to the database after clear operations have been executed.
    for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
      nsAutoPtr<DBOperation>& pendingTask = iter.Data();

      if (aOperation->Type() == DBOperation::opClear &&
          pendingTask->Scope() != aOperation->Scope()) {
        continue;
      }

      if (aOperation->Type() == DBOperation::opClearMatchingScope &&
          !StringBeginsWith(pendingTask->Scope(), aOperation->Scope())) {
        continue;
      }

      iter.Remove();
    }

    mClears.Put(aOperation->Target(), aOperation);
    break;

  case DBOperation::opClearAll:
    // Drop simply everything, this is a super-operation.
    mUpdates.Clear();
    mClears.Clear();
    mClears.Put(aOperation->Target(), aOperation);
    break;

  default:
    MOZ_ASSERT(false);
    break;
  }
}

bool
DOMStorageDBThread::PendingOperations::Prepare()
{
  // Called under the lock

  // First collect clear operations and then updates, we can
  // do this since whenever a clear operation for a scope is
  // scheduled, we drop all updates matching that scope. So,
  // all scope-related update operations we have here now were
  // scheduled after the clear operations.
  for (auto iter = mClears.Iter(); !iter.Done(); iter.Next()) {
    mExecList.AppendElement(iter.Data().forget());
  }
  mClears.Clear();

  for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
    mExecList.AppendElement(iter.Data().forget());
  }
  mUpdates.Clear();

  return !!mExecList.Length();
}

nsresult
DOMStorageDBThread::PendingOperations::Execute(DOMStorageDBThread* aThread)
{
  // Called outside the lock

  mozStorageTransaction transaction(aThread->mWorkerConnection, false);

  nsresult rv;

  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
    DOMStorageDBThread::DBOperation* task = mExecList[i];
    rv = task->Perform(aThread);
    if (NS_FAILED(rv)) {
      return rv;
    }
  }

  rv = transaction.Commit();
  if (NS_FAILED(rv)) {
    return rv;
  }

  return NS_OK;
}

bool
DOMStorageDBThread::PendingOperations::Finalize(nsresult aRv)
{
  // Called under the lock

  // The list is kept on a failure to retry it
  if (NS_FAILED(aRv)) {
    // XXX Followup: we may try to reopen the database and flush these
    // pending tasks, however testing showed that even though I/O is actually
    // broken some amount of operations is left in sqlite+system buffers and
    // seems like successfully flushed to disk.
    // Tested by removing a flash card and disconnecting from network while
    // using a network drive on Windows system.
    NS_WARNING("Flush operation on localStorage database failed");

    ++mFlushFailureCount;

    return mFlushFailureCount >= 5;
  }

  mFlushFailureCount = 0;
  mExecList.Clear();
  return true;
}

namespace {

bool
FindPendingClearForScope(const nsACString& aScope,
                         DOMStorageDBThread::DBOperation* aPendingOperation)
{
  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClearAll) {
    return true;
  }

  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClear &&
      aScope == aPendingOperation->Scope()) {
    return true;
  }

  if (aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opClearMatchingScope &&
      StringBeginsWith(aScope, aPendingOperation->Scope())) {
    return true;
  }

  return false;
}

} // namespace

bool
DOMStorageDBThread::PendingOperations::IsScopeClearPending(const nsACString& aScope)
{
  // Called under the lock

  for (auto iter = mClears.Iter(); !iter.Done(); iter.Next()) {
    if (FindPendingClearForScope(aScope, iter.UserData())) {
      return true;
    }
  }

  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
    if (FindPendingClearForScope(aScope, mExecList[i])) {
      return true;
    }
  }

  return false;
}

namespace {

bool
FindPendingUpdateForScope(const nsACString& aScope,
                          DOMStorageDBThread::DBOperation* aPendingOperation)
{
  if ((aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opAddItem ||
       aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opUpdateItem ||
       aPendingOperation->Type() == DOMStorageDBThread::DBOperation::opRemoveItem) &&
       aScope == aPendingOperation->Scope()) {
    return true;
  }

  return false;
}

} // namespace

bool
DOMStorageDBThread::PendingOperations::IsScopeUpdatePending(const nsACString& aScope)
{
  // Called under the lock

  for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
    if (FindPendingUpdateForScope(aScope, iter.UserData())) {
      return true;
    }
  }

  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
    if (FindPendingUpdateForScope(aScope, mExecList[i])) {
      return true;
    }
  }

  return false;
}

} // namespace dom
} // namespace mozilla