storage/mozStorageHelper.h
author J. Ryan Stinnett <jryans@gmail.com>
Wed, 09 Sep 2015 15:41:20 -0500
changeset 294193 c638ef3e2f2077dde2c1d9a174bf4bddc2e20714
parent 275452 ad01543457e739b4eee7a245e16734a3ecfd10ad
child 353688 93657f8dedaafa384bcd49c71b52e195ec968de8
permissions -rw-r--r--
Bug 1165599 - Restore basic external view source. r=jsantell CLOSED TREE This restores external view source after changes in bug 1025146. It does function in e10s, however the page descriptor is not used, so viewing a POST result will GET the page instead. This is the same as it was before bug 1025146. Follow ups will add usage tracking and improve e10s behavior if there is enough usage.

/* -*- 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 "nsAutoPtr.h"
#include "nsStringGlue.h"
#include "mozilla/DebugOnly.h"

#include "mozIStorageAsyncConnection.h"
#include "mozIStorageConnection.h"
#include "mozIStorageStatement.h"
#include "mozIStoragePendingStatement.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, so if a transaction
 * is already in progress, this object does nothing.  Note that in this case,
 * you may not get the transaction type you asked for, and you won't be able
 * to rollback.
 *
 * @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.  Defaults
 *        to TRANSACTION_DEFERRED.
 * @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
{
public:
  mozStorageTransaction(mozIStorageConnection* aConnection,
                        bool aCommitOnComplete,
                        int32_t aType = mozIStorageConnection::TRANSACTION_DEFERRED,
                        bool aAsyncCommit = false)
    : mConnection(aConnection),
      mHasTransaction(false),
      mCommitOnComplete(aCommitOnComplete),
      mCompleted(false),
      mAsyncCommit(aAsyncCommit)
  {
    if (mConnection) {
      nsAutoCString query("BEGIN");
      switch(aType) {
        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");
      }
      // If a transaction is already in progress, this will fail, since Sqlite
      // doesn't support nested transactions.
      mHasTransaction = NS_SUCCEEDED(mConnection->ExecuteSimpleSQL(query));
    }
  }

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

  /**
   * 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()
  {
    if (!mConnection || mCompleted || !mHasTransaction)
      return NS_OK;
    mCompleted = true;

    // 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.
    nsresult rv;
    if (mAsyncCommit) {
      nsCOMPtr<mozIStoragePendingStatement> ps;
      rv = mConnection->ExecuteSimpleSQLAsync(NS_LITERAL_CSTRING("COMMIT"),
                                              nullptr, getter_AddRefs(ps));
    }
    else {
      rv = mConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING("COMMIT"));
    }

    if (NS_SUCCEEDED(rv))
      mHasTransaction = false;

    return rv;
  }

  /**
   * 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()
  {
    if (!mConnection || mCompleted || !mHasTransaction)
      return NS_OK;
    mCompleted = true;

    // TODO (bug 1062823): from Sqlite 3.7.11 on, rollback won't ever return
    // a busy error, so this handling can be removed.
    nsresult rv = NS_OK;
    do {
      rv = mConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING("ROLLBACK"));
      if (rv == NS_ERROR_STORAGE_BUSY)
        (void)PR_Sleep(PR_INTERVAL_NO_WAIT);
    } while (rv == NS_ERROR_STORAGE_BUSY);

    if (NS_SUCCEEDED(rv))
      mHasTransaction = false;

    return rv;
  }

protected:
  nsCOMPtr<mozIStorageConnection> mConnection;
  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();
  }

  /**
   * 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 */