Quelle mozStorageHelper.h Sprache: C

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

#ifndef MOZSTORAGEHELPER_H
#define MOZSTORAGEHELPER_H

#include "nsCOMPtr.h"
#include "nsString.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/ScopeExit.h"

#include "mozilla/storage/SQLiteMutex.h"
#include "mozIStorageConnection.h"
#include "mozIStorageStatement.h"
#include "mozIStoragePendingStatement.h"
#include "mozilla/DebugOnly.h"
#include "nsCOMPtr.h"
#include "nsError.h"

/**
* This class wraps a transaction inside a given C++ scope, guaranteeing that
* the transaction will be completed even if you have an exception or
* return early.
*
* A common use is to create an instance with aCommitOnComplete = false
* (rollback), then call Commit() on this object manually when your function
* completes successfully.
*
* @note nested transactions are not supported by Sqlite, only nested
* savepoints, so if a transaction is already in progress, this object creates
* a nested savepoint to the existing transaction which is considered as
* anonymous savepoint itself. However, aType and aAsyncCommit are ignored
* in the case of nested savepoints.
*
* @param aConnection
*        The connection to create the transaction on.
* @param aCommitOnComplete
*        Controls whether the transaction is committed or rolled back when
*        this object goes out of scope.
* @param aType [optional]
*        The transaction type, as defined in mozIStorageConnection. Uses the
*        default transaction behavior for the connection if unspecified.
* @param aAsyncCommit [optional]
*        Whether commit should be executed asynchronously on the helper thread.
*        This is a special option introduced as an interim solution to reduce
*        main-thread fsyncs in Places.  Can only be used on main-thread.
*
*        WARNING: YOU SHOULD _NOT_ WRITE NEW MAIN-THREAD CODE USING THIS!
*
*        Notice that async commit might cause synchronous statements to fail
*        with SQLITE_BUSY.  A possible mitigation strategy is to use
*        PRAGMA busy_timeout, but notice that might cause main-thread jank.
*        Finally, if the database is using WAL journaling mode, other
*        connections won't see the changes done in async committed transactions
*        until commit is complete.
*
*        For all of the above reasons, this should only be used as an interim
*        solution and avoided completely if possible.
*/
class mozStorageTransaction {
  using SQLiteMutexAutoLock = mozilla::storage::SQLiteMutexAutoLock;

public:
  mozStorageTransaction(
      mozIStorageConnection* aConnection, bool aCommitOnComplete,
      int32_t aType = mozIStorageConnection::TRANSACTION_DEFAULT,
      bool aAsyncCommit = false)
      : mConnection(aConnection),
        mType(aType),
        mNestingLevel(0),
        mHasTransaction(false),
        mCommitOnComplete(aCommitOnComplete),
        mCompleted(false),
        mAsyncCommit(aAsyncCommit) {}

  ~mozStorageTransaction() {
    if (mConnection && mHasTransaction && !mCompleted) {
      if (mCommitOnComplete) {
        mozilla::DebugOnly<nsresult> rv = Commit();
        NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
                             "A transaction didn't commit correctly");
      } else {
        mozilla::DebugOnly<nsresult> rv = Rollback();
        NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
                             "A transaction didn't rollback correctly");
      }
    }
  }

  /**
   * Starts the transaction.
   */
  nsresult Start() {
    // XXX We should probably get rid of mHasTransaction and use mConnection
    // for checking if a transaction has been started. However, we need to
    // first stop supporting null mConnection and also move aConnection from
    // the constructor to Start.
    MOZ_DIAGNOSTIC_ASSERT(!mHasTransaction);

    // XXX We should probably stop supporting null mConnection.

    // XXX We should probably get rid of mCompleted and allow to start the
    // transaction again if it was already committed or rolled back.
    if (!mConnection || mCompleted) {
      return NS_OK;
    }

    SQLiteMutexAutoLock lock(mConnection->GetSharedDBMutex());

    // We nee to speculatively set the nesting level to be able to decide
    // if this is a top level transaction and to be able to generate the
    // savepoint name.
    TransactionStarted(lock);

    // If there's a failure we need to revert the speculatively set nesting
    // level on the connection.
    auto autoFinishTransaction =
        mozilla::MakeScopeExit([&] { TransactionFinished(lock); });

    nsAutoCString query;

    if (TopLevelTransaction(lock)) {
      query.Assign("BEGIN");
      int32_t type = mType;
      if (type == mozIStorageConnection::TRANSACTION_DEFAULT) {
        MOZ_ALWAYS_SUCCEEDS(mConnection->GetDefaultTransactionType(&type));
      }
      switch (type) {
        case mozIStorageConnection::TRANSACTION_IMMEDIATE:
          query.AppendLiteral(" IMMEDIATE");
          break;
        case mozIStorageConnection::TRANSACTION_EXCLUSIVE:
          query.AppendLiteral(" EXCLUSIVE");
          break;
        case mozIStorageConnection::TRANSACTION_DEFERRED:
          query.AppendLiteral(" DEFERRED");
          break;
        default:
          MOZ_ASSERT(false, "Unknown transaction type");
      }
    } else {
      query.Assign("SAVEPOINT sp"_ns + IntToCString(mNestingLevel));
    }

    nsresult rv = mConnection->ExecuteSimpleSQL(query);
    NS_ENSURE_SUCCESS(rv, rv);

    autoFinishTransaction.release();

    return NS_OK;
  }

  /**
   * Commits the transaction if one is in progress. If one is not in progress,
   * this is a NOP since the actual owner of the transaction outside of our
   * scope is in charge of finally committing or rolling back the transaction.
   */
  nsresult Commit() {
    // XXX Assert instead of returning NS_OK if the transaction hasn't been
    // started.
    if (!mConnection || mCompleted || !mHasTransaction) return NS_OK;

    SQLiteMutexAutoLock lock(mConnection->GetSharedDBMutex());

#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
    MOZ_DIAGNOSTIC_ASSERT(CurrentTransaction(lock));
#else
    if (!CurrentTransaction(lock)) {
      return NS_ERROR_NOT_AVAILABLE;
    }
#endif

    mCompleted = true;

    nsresult rv;

    if (TopLevelTransaction(lock)) {
      // TODO (bug 559659): this might fail with SQLITE_BUSY, but we don't
      // handle it, thus the transaction might stay open until the next COMMIT.
      if (mAsyncCommit) {
        nsCOMPtr<mozIStoragePendingStatement> ps;
        rv = mConnection->ExecuteSimpleSQLAsync("COMMIT"_ns, nullptr,
                                                getter_AddRefs(ps));
      } else {
        rv = mConnection->ExecuteSimpleSQL("COMMIT"_ns);
      }
    } else {
      rv = mConnection->ExecuteSimpleSQL("RELEASE sp"_ns +
                                         IntToCString(mNestingLevel));
    }

    NS_ENSURE_SUCCESS(rv, rv);

    TransactionFinished(lock);

    return NS_OK;
  }

  /**
   * Rolls back the transaction if one is in progress. If one is not in
   * progress, this is a NOP since the actual owner of the transaction outside
   * of our scope is in charge of finally rolling back the transaction.
   */
  nsresult Rollback() {
    // XXX Assert instead of returning NS_OK if the transaction hasn't been
    // started.
    if (!mConnection || mCompleted || !mHasTransaction) return NS_OK;

    SQLiteMutexAutoLock lock(mConnection->GetSharedDBMutex());

#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
    MOZ_DIAGNOSTIC_ASSERT(CurrentTransaction(lock));
#else
    if (!CurrentTransaction(lock)) {
      return NS_ERROR_NOT_AVAILABLE;
    }
#endif

    mCompleted = true;

    nsresult rv;

    if (TopLevelTransaction(lock)) {
      // TODO (bug 1062823): from Sqlite 3.7.11 on, rollback won't ever return
      // a busy error, so this handling can be removed.
      do {
        rv = mConnection->ExecuteSimpleSQL("ROLLBACK"_ns);
        if (rv == NS_ERROR_STORAGE_BUSY) (void)PR_Sleep(PR_INTERVAL_NO_WAIT);
      } while (rv == NS_ERROR_STORAGE_BUSY);
    } else {
      const auto nestingLevelCString = IntToCString(mNestingLevel);
      rv = mConnection->ExecuteSimpleSQL(
          "ROLLBACK TO sp"_ns + nestingLevelCString + "; RELEASE sp"_ns +
          nestingLevelCString);
    }

    NS_ENSURE_SUCCESS(rv, rv);

    TransactionFinished(lock);

    return NS_OK;
  }

protected:
  void TransactionStarted(const SQLiteMutexAutoLock& aProofOfLock) {
    MOZ_ASSERT(mConnection);
    MOZ_ASSERT(!mHasTransaction);
    MOZ_ASSERT(mNestingLevel == 0);
    mHasTransaction = true;
    mNestingLevel = mConnection->IncreaseTransactionNestingLevel(aProofOfLock);
  }

  bool CurrentTransaction(const SQLiteMutexAutoLock& aProofOfLock) const {
    MOZ_ASSERT(mConnection);
    MOZ_ASSERT(mHasTransaction);
    MOZ_ASSERT(mNestingLevel > 0);
    return mNestingLevel ==
           mConnection->GetTransactionNestingLevel(aProofOfLock);
  }

  bool TopLevelTransaction(const SQLiteMutexAutoLock& aProofOfLock) const {
    MOZ_ASSERT(mConnection);
    MOZ_ASSERT(mHasTransaction);
    MOZ_ASSERT(mNestingLevel > 0);
    MOZ_ASSERT(CurrentTransaction(aProofOfLock));
    return mNestingLevel == 1;
  }

  void TransactionFinished(const SQLiteMutexAutoLock& aProofOfLock) {
    MOZ_ASSERT(mConnection);
    MOZ_ASSERT(mHasTransaction);
    MOZ_ASSERT(mNestingLevel > 0);
    MOZ_ASSERT(CurrentTransaction(aProofOfLock));
    mConnection->DecreaseTransactionNestingLevel(aProofOfLock);
    mNestingLevel = 0;
    mHasTransaction = false;
  }

  nsCOMPtr<mozIStorageConnection> mConnection;
  int32_t mType;
  uint32_t mNestingLevel;
  bool mHasTransaction;
  bool mCommitOnComplete;
  bool mCompleted;
  bool mAsyncCommit;
};

/**
* This class wraps a statement so that it is guaraneed to be reset when
* this object goes out of scope.
*
* Note that this always just resets the statement. If the statement doesn't
* need resetting, the reset operation is inexpensive.
*/
class MOZ_STACK_CLASS mozStorageStatementScoper {
public:
  explicit mozStorageStatementScoper(mozIStorageStatement* aStatement)
      : mStatement(aStatement) {}
  ~mozStorageStatementScoper() {
    if (mStatement) mStatement->Reset();
  }

  mozStorageStatementScoper(mozStorageStatementScoper&&) = default;
  mozStorageStatementScoper& operator=(mozStorageStatementScoper&&) = default;
  mozStorageStatementScoper(const mozStorageStatementScoper&) = delete;
  mozStorageStatementScoper& operator=(const mozStorageStatementScoper&) =
      delete;

  /**
   * Call this to make the statement not reset. You might do this if you know
   * that the statement has been reset.
   */
  void Abandon() { mStatement = nullptr; }

protected:
  nsCOMPtr<mozIStorageStatement> mStatement;
};

// Use this to make queries uniquely identifiable in telemetry
// statistics, especially PRAGMAs.  We don't include __LINE__ so that
// queries are stable in the face of source code changes.
#define MOZ_STORAGE_UNIQUIFY_QUERY_STR "/* " __FILE__ " */ "

#endif /* MOZSTORAGEHELPER_H */

quality96%

¤ Dauer der Verarbeitung: 0.1 Sekunden (vorverarbeitet) ¤

Wurzel

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.