storage/mozStorageService.cpp
author Gregory Szorc <gps@mozilla.com>
Fri, 27 Oct 2017 14:55:31 -0700
changeset 442301 5e5ee518a4b9d43e72c879e9d124aa432fb06e1a
parent 441721 3feb5338f65c83d2af52fb8a53f866155e88dc15
child 444237 b98366a27c05e617771746cd10f1f685a1b82dff
permissions -rw-r--r--
Bug 1412431 - Remove support for MOZ_PREFLIGHT and MOZ_POSTFLIGHT; r=nalexander These variables are unused in the repo. The %_ALL variation is used for sccache, however. The last use of these variables was removed when support for MacOS universal builds was removed. Someone somewhere may be relying on this functionality. But I don't think it is worth continuing to support in client.mk. If someone really needs it, we can reintroduce support for the feature elsewhere, like in mach or via mozconfig support somehow. MozReview-Commit-ID: 4KznCmK3JTN

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: sw=2 ts=2 et lcs=trail\:.,tab\:>~ :
 * 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 "mozilla/Attributes.h"
#include "mozilla/DebugOnly.h"

#include "mozStorageService.h"
#include "mozStorageConnection.h"
#include "nsAutoPtr.h"
#include "nsCollationCID.h"
#include "nsEmbedCID.h"
#include "nsThreadUtils.h"
#include "mozStoragePrivateHelpers.h"
#include "nsIXPConnect.h"
#include "nsIObserverService.h"
#include "nsIPropertyBag2.h"
#include "mozilla/Services.h"
#include "mozilla/Preferences.h"
#include "mozilla/LateWriteChecks.h"
#include "mozIStorageCompletionCallback.h"
#include "mozIStoragePendingStatement.h"

#include "sqlite3.h"
#include "mozilla/AutoSQLiteLifetime.h"

#ifdef MOZ_CRASHREPORTER
#include "nsExceptionHandler.h"
#endif

#ifdef XP_WIN
// "windows.h" was included and it can #define lots of things we care about...
#undef CompareString
#endif

#include "nsIPromptService.h"

////////////////////////////////////////////////////////////////////////////////
//// Defines

#define PREF_TS_SYNCHRONOUS "toolkit.storage.synchronous"
#define PREF_TS_SYNCHRONOUS_DEFAULT 1

#define PREF_TS_PAGESIZE "toolkit.storage.pageSize"

// This value must be kept in sync with the value of SQLITE_DEFAULT_PAGE_SIZE in
// db/sqlite3/src/Makefile.in.
#define PREF_TS_PAGESIZE_DEFAULT 32768

namespace mozilla {
namespace storage {

////////////////////////////////////////////////////////////////////////////////
//// Memory Reporting

#ifdef MOZ_DMD
static mozilla::Atomic<size_t> gSqliteMemoryUsed;
#endif

static int64_t
StorageSQLiteDistinguishedAmount()
{
  return ::sqlite3_memory_used();
}

/**
 * Passes a single SQLite memory statistic to a memory reporter callback.
 *
 * @param aHandleReport
 *        The callback.
 * @param aData
 *        The data for the callback.
 * @param aConn
 *        The SQLite connection.
 * @param aPathHead
 *        Head of the path for the memory report.
 * @param aKind
 *        The memory report statistic kind, one of "stmt", "cache" or
 *        "schema".
 * @param aDesc
 *        The memory report description.
 * @param aOption
 *        The SQLite constant for getting the measurement.
 * @param aTotal
 *        The accumulator for the measurement.
 */
static void
ReportConn(nsIHandleReportCallback *aHandleReport,
           nsISupports *aData,
           Connection *aConn,
           const nsACString &aPathHead,
           const nsACString &aKind,
           const nsACString &aDesc,
           int32_t aOption,
           size_t *aTotal)
{
  nsCString path(aPathHead);
  path.Append(aKind);
  path.AppendLiteral("-used");

  int32_t val = aConn->getSqliteRuntimeStatus(aOption);
  aHandleReport->Callback(EmptyCString(), path,
                          nsIMemoryReporter::KIND_HEAP,
                          nsIMemoryReporter::UNITS_BYTES,
                          int64_t(val), aDesc, aData);
  *aTotal += val;
}

// Warning: To get a Connection's measurements requires holding its lock.
// There may be a delay getting the lock if another thread is accessing the
// Connection.  This isn't very nice if CollectReports is called from the main
// thread!  But at the time of writing this function is only called when
// about:memory is loaded (not, for example, when telemetry pings occur) and
// any delays in that case aren't so bad.
NS_IMETHODIMP
Service::CollectReports(nsIHandleReportCallback *aHandleReport,
                        nsISupports *aData, bool aAnonymize)
{
  size_t totalConnSize = 0;
  {
    nsTArray<RefPtr<Connection> > connections;
    getConnections(connections);

    for (uint32_t i = 0; i < connections.Length(); i++) {
      RefPtr<Connection> &conn = connections[i];

      // Someone may have closed the Connection, in which case we skip it.
      // Note that we have consumers of the synchronous API that are off the
      // main-thread, like the DOM Cache and IndexedDB, and as such we must be
      // sure that we have a connection.
      MutexAutoLock lockedAsyncScope(conn->sharedAsyncExecutionMutex);
      if (!conn->connectionReady()) {
          continue;
      }

      nsCString pathHead("explicit/storage/sqlite/");
      // This filename isn't privacy-sensitive, and so is never anonymized.
      pathHead.Append(conn->getFilename());
      pathHead.Append('/');

      SQLiteMutexAutoLock lockedScope(conn->sharedDBMutex);

      NS_NAMED_LITERAL_CSTRING(stmtDesc,
        "Memory (approximate) used by all prepared statements used by "
        "connections to this database.");
      ReportConn(aHandleReport, aData, conn, pathHead,
                 NS_LITERAL_CSTRING("stmt"), stmtDesc,
                 SQLITE_DBSTATUS_STMT_USED, &totalConnSize);

      NS_NAMED_LITERAL_CSTRING(cacheDesc,
        "Memory (approximate) used by all pager caches used by connections "
        "to this database.");
      ReportConn(aHandleReport, aData, conn, pathHead,
                 NS_LITERAL_CSTRING("cache"), cacheDesc,
                 SQLITE_DBSTATUS_CACHE_USED_SHARED, &totalConnSize);

      NS_NAMED_LITERAL_CSTRING(schemaDesc,
        "Memory (approximate) used to store the schema for all databases "
        "associated with connections to this database.");
      ReportConn(aHandleReport, aData, conn, pathHead,
                 NS_LITERAL_CSTRING("schema"), schemaDesc,
                 SQLITE_DBSTATUS_SCHEMA_USED, &totalConnSize);
    }

#ifdef MOZ_DMD
    if (::sqlite3_memory_used() != int64_t(gSqliteMemoryUsed)) {
      NS_WARNING("memory consumption reported by SQLite doesn't match "
                 "our measurements");
    }
#endif
  }

  int64_t other = ::sqlite3_memory_used() - totalConnSize;

  MOZ_COLLECT_REPORT(
    "explicit/storage/sqlite/other", KIND_HEAP, UNITS_BYTES, other,
    "All unclassified sqlite memory.");

  return NS_OK;
}

////////////////////////////////////////////////////////////////////////////////
//// Service

NS_IMPL_ISUPPORTS(
  Service,
  mozIStorageService,
  nsIObserver,
  nsIMemoryReporter
)

Service *Service::gService = nullptr;

already_AddRefed<Service>
Service::getSingleton()
{
  if (gService) {
    return do_AddRef(gService);
  }

  // Ensure that we are using the same version of SQLite that we compiled with
  // or newer.  Our configure check ensures we are using a new enough version
  // at compile time.
  if (SQLITE_VERSION_NUMBER > ::sqlite3_libversion_number()) {
    nsCOMPtr<nsIPromptService> ps(do_GetService(NS_PROMPTSERVICE_CONTRACTID));
    if (ps) {
      nsAutoString title, message;
      title.AppendLiteral("SQLite Version Error");
      message.AppendLiteral("The application has been updated, but the SQLite "
                            "library wasn't updated properly and the application "
                            "cannot run. Please try to launch the application again. "
                            "If that should still fail, please try reinstalling "
                            "it, or visit https://support.mozilla.org/.");
      (void)ps->Alert(nullptr, title.get(), message.get());
    }
    MOZ_CRASH("SQLite Version Error");
  }

  // The first reference to the storage service must be obtained on the
  // main thread.
  NS_ENSURE_TRUE(NS_IsMainThread(), nullptr);
  RefPtr<Service> service = new Service();
  gService = service.get();
  if (NS_FAILED(service->initialize())) {
    gService = nullptr;
    return nullptr;
  }

  return service.forget();
}

nsIXPConnect *Service::sXPConnect = nullptr;

// static
already_AddRefed<nsIXPConnect>
Service::getXPConnect()
{
  NS_PRECONDITION(NS_IsMainThread(),
                  "Must only get XPConnect on the main thread!");
  NS_PRECONDITION(gService,
                  "Can not get XPConnect without an instance of our service!");

  // If we've been shutdown, sXPConnect will be null.  To prevent leaks, we do
  // not cache the service after this point.
  nsCOMPtr<nsIXPConnect> xpc(sXPConnect);
  if (!xpc)
    xpc = do_GetService(nsIXPConnect::GetCID());
  NS_ASSERTION(xpc, "Could not get XPConnect!");
  return xpc.forget();
}

int32_t Service::sSynchronousPref;

// static
int32_t
Service::getSynchronousPref()
{
  return sSynchronousPref;
}

int32_t Service::sDefaultPageSize = PREF_TS_PAGESIZE_DEFAULT;

Service::Service()
: mMutex("Service::mMutex")
, mSqliteVFS(nullptr)
, mRegistrationMutex("Service::mRegistrationMutex")
, mConnections()
{
}

Service::~Service()
{
  mozilla::UnregisterWeakMemoryReporter(this);
  mozilla::UnregisterStorageSQLiteDistinguishedAmount();

  int rc = sqlite3_vfs_unregister(mSqliteVFS);
  if (rc != SQLITE_OK)
    NS_WARNING("Failed to unregister sqlite vfs wrapper.");

  shutdown(); // To release sXPConnect.

  gService = nullptr;
  delete mSqliteVFS;
  mSqliteVFS = nullptr;
}

void
Service::registerConnection(Connection *aConnection)
{
  mRegistrationMutex.AssertNotCurrentThreadOwns();
  MutexAutoLock mutex(mRegistrationMutex);
  (void)mConnections.AppendElement(aConnection);
}

void
Service::unregisterConnection(Connection *aConnection)
{
  // If this is the last Connection it might be the only thing keeping Service
  // alive.  So ensure that Service is destroyed only after the Connection is
  // cleanly unregistered and destroyed.
  RefPtr<Service> kungFuDeathGrip(this);
  RefPtr<Connection> forgettingRef;
  {
    mRegistrationMutex.AssertNotCurrentThreadOwns();
    MutexAutoLock mutex(mRegistrationMutex);

    for (uint32_t i = 0 ; i < mConnections.Length(); ++i) {
      if (mConnections[i] == aConnection) {
        // Because dropping the final reference can potentially result in
        // spinning a nested event loop if the connection was not properly
        // shutdown, we want to do that outside this loop so that we can finish
        // mutating the array and drop our mutex.
        forgettingRef = mConnections[i].forget();
        mConnections.RemoveElementAt(i);
        break;
      }
    }
  }

  MOZ_ASSERT(forgettingRef,
             "Attempt to unregister unknown storage connection!");

  // Ensure the connection is released on its opening thread.  We explicitly use
  // aAlwaysDispatch=false because at the time of writing this, LocalStorage's
  // StorageDBThread uses a hand-rolled PRThread implementation that cannot
  // handle us dispatching events at it during shutdown.  However, it is
  // arguably also desirable for callers to not be aware of our connection
  // tracking mechanism.  And by synchronously dropping the reference (when
  // on the correct thread), this avoids surprises for the caller and weird
  // shutdown edge cases.
  nsCOMPtr<nsIThread> thread = forgettingRef->threadOpenedOn;
  NS_ProxyRelease(
    "storage::Service::mConnections", thread, forgettingRef.forget(), false);
}

void
Service::getConnections(/* inout */ nsTArray<RefPtr<Connection> >& aConnections)
{
  mRegistrationMutex.AssertNotCurrentThreadOwns();
  MutexAutoLock mutex(mRegistrationMutex);
  aConnections.Clear();
  aConnections.AppendElements(mConnections);
}

void
Service::minimizeMemory()
{
  nsTArray<RefPtr<Connection> > connections;
  getConnections(connections);

  for (uint32_t i = 0; i < connections.Length(); i++) {
    RefPtr<Connection> conn = connections[i];
    // For non-main-thread owning/opening threads, we may be racing against them
    // closing their connection or their thread.  That's okay, see below.
    if (!conn->connectionReady())
      continue;

    NS_NAMED_LITERAL_CSTRING(shrinkPragma, "PRAGMA shrink_memory");
    nsCOMPtr<mozIStorageConnection> syncConn = do_QueryInterface(
      NS_ISUPPORTS_CAST(mozIStorageAsyncConnection*, conn));
    bool onOpenedThread = false;

    if (!syncConn) {
      // This is a mozIStorageAsyncConnection, it can only be used on the main
      // thread, so we can do a straight API call.
      nsCOMPtr<mozIStoragePendingStatement> ps;
      DebugOnly<nsresult> rv =
        conn->ExecuteSimpleSQLAsync(shrinkPragma, nullptr, getter_AddRefs(ps));
      MOZ_ASSERT(NS_SUCCEEDED(rv), "Should have purged sqlite caches");
    } else if (NS_SUCCEEDED(conn->threadOpenedOn->IsOnCurrentThread(&onOpenedThread)) &&
               onOpenedThread) {
      if (conn->isAsyncExecutionThreadAvailable()) {
        nsCOMPtr<mozIStoragePendingStatement> ps;
        DebugOnly<nsresult> rv =
          conn->ExecuteSimpleSQLAsync(shrinkPragma, nullptr, getter_AddRefs(ps));
        MOZ_ASSERT(NS_SUCCEEDED(rv), "Should have purged sqlite caches");
      } else {
        conn->ExecuteSimpleSQL(shrinkPragma);
      }
    } else {
      // We are on the wrong thread, the query should be executed on the
      // opener thread, so we must dispatch to it.
      // It's possible the connection is already closed or will be closed by the
      // time our runnable runs.  ExecuteSimpleSQL will safely return with a
      // failure in that case.  If the thread is shutting down or shut down, the
      // dispatch will fail and that's okay.
      nsCOMPtr<nsIRunnable> event =
        NewRunnableMethod<const nsCString>(
          "Connection::ExecuteSimpleSQL",
          conn, &Connection::ExecuteSimpleSQL, shrinkPragma);
      Unused << conn->threadOpenedOn->Dispatch(event, NS_DISPATCH_NORMAL);
    }
  }
}

void
Service::shutdown()
{
  NS_IF_RELEASE(sXPConnect);
}

sqlite3_vfs *ConstructTelemetryVFS();
const char *GetVFSName();

static const char* sObserverTopics[] = {
  "memory-pressure",
  "xpcom-shutdown",
  "xpcom-shutdown-threads"
};

nsresult
Service::initialize()
{
  MOZ_ASSERT(NS_IsMainThread(), "Must be initialized on the main thread");

  int rc = AutoSQLiteLifetime::getInitResult();
  if (rc != SQLITE_OK)
    return convertResultCode(rc);

  mSqliteVFS = ConstructTelemetryVFS();
  if (mSqliteVFS) {
    rc = sqlite3_vfs_register(mSqliteVFS, 0);
    if (rc != SQLITE_OK)
      return convertResultCode(rc);
  } else {
    NS_WARNING("Failed to register telemetry VFS");
  }

  // Register for xpcom-shutdown so we can cleanup after ourselves.  The
  // observer service can only be used on the main thread.
  nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
  NS_ENSURE_TRUE(os, NS_ERROR_FAILURE);

  for (size_t i = 0; i < ArrayLength(sObserverTopics); ++i) {
    nsresult rv = os->AddObserver(this, sObserverTopics[i], false);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }
  }

  // We cache XPConnect for our language helpers.  XPConnect can only be
  // used on the main thread.
  (void)CallGetService(nsIXPConnect::GetCID(), &sXPConnect);

  // We need to obtain the toolkit.storage.synchronous preferences on the main
  // thread because the preference service can only be accessed there.  This
  // is cached in the service for all future Open[Unshared]Database calls.
  sSynchronousPref =
    Preferences::GetInt(PREF_TS_SYNCHRONOUS, PREF_TS_SYNCHRONOUS_DEFAULT);

  // We need to obtain the toolkit.storage.pageSize preferences on the main
  // thread because the preference service can only be accessed there.  This
  // is cached in the service for all future Open[Unshared]Database calls.
  sDefaultPageSize =
      Preferences::GetInt(PREF_TS_PAGESIZE, PREF_TS_PAGESIZE_DEFAULT);

  mozilla::RegisterWeakMemoryReporter(this);
  mozilla::RegisterStorageSQLiteDistinguishedAmount(StorageSQLiteDistinguishedAmount);

  return NS_OK;
}

int
Service::localeCompareStrings(const nsAString &aStr1,
                              const nsAString &aStr2,
                              int32_t aComparisonStrength)
{
  // The implementation of nsICollation.CompareString() is platform-dependent.
  // On Linux it's not thread-safe.  It may not be on Windows and OS X either,
  // but it's more difficult to tell.  We therefore synchronize this method.
  MutexAutoLock mutex(mMutex);

  nsICollation *coll = getLocaleCollation();
  if (!coll) {
    NS_ERROR("Storage service has no collation");
    return 0;
  }

  int32_t res;
  nsresult rv = coll->CompareString(aComparisonStrength, aStr1, aStr2, &res);
  if (NS_FAILED(rv)) {
    NS_ERROR("Collation compare string failed");
    return 0;
  }

  return res;
}

nsICollation *
Service::getLocaleCollation()
{
  mMutex.AssertCurrentThreadOwns();

  if (mLocaleCollation)
    return mLocaleCollation;

  nsCOMPtr<nsICollationFactory> collFact =
    do_CreateInstance(NS_COLLATIONFACTORY_CONTRACTID);
  if (!collFact) {
    NS_WARNING("Could not create collation factory");
    return nullptr;
  }

  nsresult rv = collFact->CreateCollation(getter_AddRefs(mLocaleCollation));
  if (NS_FAILED(rv)) {
    NS_WARNING("Could not create collation");
    return nullptr;
  }

  return mLocaleCollation;
}

////////////////////////////////////////////////////////////////////////////////
//// mozIStorageService


NS_IMETHODIMP
Service::OpenSpecialDatabase(const char *aStorageKey,
                             mozIStorageConnection **_connection)
{
  nsresult rv;

  nsCOMPtr<nsIFile> storageFile;
  if (::strcmp(aStorageKey, "memory") == 0) {
    // just fall through with nullptr storageFile, this will cause the storage
    // connection to use a memory DB.
  }
  else {
    return NS_ERROR_INVALID_ARG;
  }

  RefPtr<Connection> msc = new Connection(this, SQLITE_OPEN_READWRITE, false);

  rv = storageFile ? msc->initialize(storageFile) : msc->initialize();
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;

}

namespace {

class AsyncInitDatabase final : public Runnable
{
public:
  AsyncInitDatabase(Connection* aConnection,
                    nsIFile* aStorageFile,
                    int32_t aGrowthIncrement,
                    mozIStorageCompletionCallback* aCallback)
    : Runnable("storage::AsyncInitDatabase")
    , mConnection(aConnection)
    , mStorageFile(aStorageFile)
    , mGrowthIncrement(aGrowthIncrement)
    , mCallback(aCallback)
  {
    MOZ_ASSERT(NS_IsMainThread());
  }

  NS_IMETHOD Run() override
  {
    MOZ_ASSERT(!NS_IsMainThread());
    nsresult rv = mConnection->initializeOnAsyncThread(mStorageFile);
    if (NS_FAILED(rv)) {
      return DispatchResult(rv, nullptr);
    }

    if (mGrowthIncrement >= 0) {
      // Ignore errors. In the future, we might wish to log them.
      (void)mConnection->SetGrowthIncrement(mGrowthIncrement, EmptyCString());
    }

    return DispatchResult(NS_OK, NS_ISUPPORTS_CAST(mozIStorageAsyncConnection*,
                          mConnection));
  }

private:
  nsresult DispatchResult(nsresult aStatus, nsISupports* aValue) {
    RefPtr<CallbackComplete> event =
      new CallbackComplete(aStatus,
                           aValue,
                           mCallback.forget());
    return NS_DispatchToMainThread(event);
  }

  ~AsyncInitDatabase()
  {
    NS_ReleaseOnMainThreadSystemGroup(
      "AsyncInitDatabase::mStorageFile", mStorageFile.forget());
    NS_ReleaseOnMainThreadSystemGroup(
      "AsyncInitDatabase::mConnection", mConnection.forget());

    // Generally, the callback will be released by CallbackComplete.
    // However, if for some reason Run() is not executed, we still
    // need to ensure that it is released here.
    NS_ReleaseOnMainThreadSystemGroup(
      "AsyncInitDatabase::mCallback", mCallback.forget());
  }

  RefPtr<Connection> mConnection;
  nsCOMPtr<nsIFile> mStorageFile;
  int32_t mGrowthIncrement;
  RefPtr<mozIStorageCompletionCallback> mCallback;
};

} // namespace

NS_IMETHODIMP
Service::OpenAsyncDatabase(nsIVariant *aDatabaseStore,
                           nsIPropertyBag2 *aOptions,
                           mozIStorageCompletionCallback *aCallback)
{
  if (!NS_IsMainThread()) {
    return NS_ERROR_NOT_SAME_THREAD;
  }
  NS_ENSURE_ARG(aDatabaseStore);
  NS_ENSURE_ARG(aCallback);

  nsresult rv;
  bool shared = false;
  bool readOnly = false;
  bool ignoreLockingMode = false;
  int32_t growthIncrement = -1;

#define FAIL_IF_SET_BUT_INVALID(rv)\
  if (NS_FAILED(rv) && rv != NS_ERROR_NOT_AVAILABLE) { \
    return NS_ERROR_INVALID_ARG; \
  }

  // Deal with options first:
  if (aOptions) {
    rv = aOptions->GetPropertyAsBool(NS_LITERAL_STRING("readOnly"), &readOnly);
    FAIL_IF_SET_BUT_INVALID(rv);

    rv = aOptions->GetPropertyAsBool(NS_LITERAL_STRING("ignoreLockingMode"),
                                     &ignoreLockingMode);
    FAIL_IF_SET_BUT_INVALID(rv);
    // Specifying ignoreLockingMode will force use of the readOnly flag:
    if (ignoreLockingMode) {
      readOnly = true;
    }

    rv = aOptions->GetPropertyAsBool(NS_LITERAL_STRING("shared"), &shared);
    FAIL_IF_SET_BUT_INVALID(rv);

    // NB: we re-set to -1 if we don't have a storage file later on.
    rv = aOptions->GetPropertyAsInt32(NS_LITERAL_STRING("growthIncrement"),
                                      &growthIncrement);
    FAIL_IF_SET_BUT_INVALID(rv);
  }
  int flags = readOnly ? SQLITE_OPEN_READONLY : SQLITE_OPEN_READWRITE;

  nsCOMPtr<nsIFile> storageFile;
  nsCOMPtr<nsISupports> dbStore;
  rv = aDatabaseStore->GetAsISupports(getter_AddRefs(dbStore));
  if (NS_SUCCEEDED(rv)) {
    // Generally, aDatabaseStore holds the database nsIFile.
    storageFile = do_QueryInterface(dbStore, &rv);
    if (NS_FAILED(rv)) {
      return NS_ERROR_INVALID_ARG;
    }

    rv = storageFile->Clone(getter_AddRefs(storageFile));
    MOZ_ASSERT(NS_SUCCEEDED(rv));

    if (!readOnly) {
      // Ensure that SQLITE_OPEN_CREATE is passed in for compatibility reasons.
      flags |= SQLITE_OPEN_CREATE;
    }

    // Apply the shared-cache option.
    flags |= shared ? SQLITE_OPEN_SHAREDCACHE : SQLITE_OPEN_PRIVATECACHE;
  } else {
    // Sometimes, however, it's a special database name.
    nsAutoCString keyString;
    rv = aDatabaseStore->GetAsACString(keyString);
    if (NS_FAILED(rv) || !keyString.EqualsLiteral("memory")) {
      return NS_ERROR_INVALID_ARG;
    }

    // Just fall through with nullptr storageFile, this will cause the storage
    // connection to use a memory DB.
  }

  if (!storageFile && growthIncrement >= 0) {
    return NS_ERROR_INVALID_ARG;
  }

  // Create connection on this thread, but initialize it on its helper thread.
  RefPtr<Connection> msc = new Connection(this, flags, true,
                                          ignoreLockingMode);
  nsCOMPtr<nsIEventTarget> target = msc->getAsyncExecutionTarget();
  MOZ_ASSERT(target, "Cannot initialize a connection that has been closed already");

  RefPtr<AsyncInitDatabase> asyncInit =
    new AsyncInitDatabase(msc,
                          storageFile,
                          growthIncrement,
                          aCallback);
  return target->Dispatch(asyncInit, nsIEventTarget::DISPATCH_NORMAL);
}

NS_IMETHODIMP
Service::OpenDatabase(nsIFile *aDatabaseFile,
                      mozIStorageConnection **_connection)
{
  NS_ENSURE_ARG(aDatabaseFile);

  // Always ensure that SQLITE_OPEN_CREATE is passed in for compatibility
  // reasons.
  int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_SHAREDCACHE |
              SQLITE_OPEN_CREATE;
  RefPtr<Connection> msc = new Connection(this, flags, false);

  nsresult rv = msc->initialize(aDatabaseFile);
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

NS_IMETHODIMP
Service::OpenUnsharedDatabase(nsIFile *aDatabaseFile,
                              mozIStorageConnection **_connection)
{
  NS_ENSURE_ARG(aDatabaseFile);

  // Always ensure that SQLITE_OPEN_CREATE is passed in for compatibility
  // reasons.
  int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_PRIVATECACHE |
              SQLITE_OPEN_CREATE;
  RefPtr<Connection> msc = new Connection(this, flags, false);

  nsresult rv = msc->initialize(aDatabaseFile);
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

NS_IMETHODIMP
Service::OpenDatabaseWithFileURL(nsIFileURL *aFileURL,
                                 mozIStorageConnection **_connection)
{
  NS_ENSURE_ARG(aFileURL);

  // Always ensure that SQLITE_OPEN_CREATE is passed in for compatibility
  // reasons.
  int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_SHAREDCACHE |
              SQLITE_OPEN_CREATE | SQLITE_OPEN_URI;
  RefPtr<Connection> msc = new Connection(this, flags, false);

  nsresult rv = msc->initialize(aFileURL);
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

NS_IMETHODIMP
Service::BackupDatabaseFile(nsIFile *aDBFile,
                            const nsAString &aBackupFileName,
                            nsIFile *aBackupParentDirectory,
                            nsIFile **backup)
{
  nsresult rv;
  nsCOMPtr<nsIFile> parentDir = aBackupParentDirectory;
  if (!parentDir) {
    // This argument is optional, and defaults to the same parent directory
    // as the current file.
    rv = aDBFile->GetParent(getter_AddRefs(parentDir));
    NS_ENSURE_SUCCESS(rv, rv);
  }

  nsCOMPtr<nsIFile> backupDB;
  rv = parentDir->Clone(getter_AddRefs(backupDB));
  NS_ENSURE_SUCCESS(rv, rv);

  rv = backupDB->Append(aBackupFileName);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = backupDB->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
  NS_ENSURE_SUCCESS(rv, rv);

  nsAutoString fileName;
  rv = backupDB->GetLeafName(fileName);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = backupDB->Remove(false);
  NS_ENSURE_SUCCESS(rv, rv);

  backupDB.forget(backup);

  return aDBFile->CopyTo(parentDir, fileName);
}

////////////////////////////////////////////////////////////////////////////////
//// nsIObserver

NS_IMETHODIMP
Service::Observe(nsISupports *, const char *aTopic, const char16_t *)
{
  if (strcmp(aTopic, "memory-pressure") == 0) {
    minimizeMemory();
  } else if (strcmp(aTopic, "xpcom-shutdown") == 0) {
    shutdown();
  } else if (strcmp(aTopic, "xpcom-shutdown-threads") == 0) {
    // The Service is kept alive by our strong observer references and
    // references held by Connection instances.  Since we're about to remove the
    // former and then wait for the latter ones to go away, it behooves us to
    // hold a strong reference to ourselves so our calls to getConnections() do
    // not happen on a deleted object.
    RefPtr<Service> kungFuDeathGrip = this;

    nsCOMPtr<nsIObserverService> os =
      mozilla::services::GetObserverService();

    for (size_t i = 0; i < ArrayLength(sObserverTopics); ++i) {
      (void)os->RemoveObserver(this, sObserverTopics[i]);
    }

    SpinEventLoopUntil([&]() -> bool {
      // We must wait until all the closing connections are closed.
      nsTArray<RefPtr<Connection>> connections;
      getConnections(connections);
      for (auto& conn : connections) {
        if (conn->isClosing()) {
          return false;
        }
      }
      return true;
    });

    if (gShutdownChecks == SCM_CRASH) {
      nsTArray<RefPtr<Connection> > connections;
      getConnections(connections);
      for (uint32_t i = 0, n = connections.Length(); i < n; i++) {
        if (!connections[i]->isClosed()) {
#ifdef MOZ_CRASHREPORTER
          // getFilename is only the leaf name for the database file,
          // so it shouldn't contain privacy-sensitive information.
          CrashReporter::AnnotateCrashReport(
            NS_LITERAL_CSTRING("StorageConnectionNotClosed"),
            connections[i]->getFilename());
#endif
#ifdef DEBUG
          printf_stderr("Storage connection not closed: %s",
                        connections[i]->getFilename().get());
#endif
          MOZ_CRASH();
        }
      }
    }
  }

  return NS_OK;
}

} // namespace storage
} // namespace mozilla