storage/public/mozStorageHelper.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* ***** BEGIN LICENSE BLOCK *****
   3  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   4  *
   5  * The contents of this file are subject to the Mozilla Public License Version
   6  * 1.1 (the "License"); you may not use this file except in compliance with
   7  * the License. You may obtain a copy of the License at
   8  * http://www.mozilla.org/MPL/
   9  *
  10  * Software distributed under the License is distributed on an "AS IS" basis,
  11  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  12  * for the specific language governing rights and limitations under the
  13  * License.
  14  *
  15  * The Original Code is Storage code
  16  *
  17  * The Initial Developer of the Original Code is
  18  * Google Inc.
  19  * Portions created by the Initial Developer are Copyright (C) 2005
  20  * the Initial Developer. All Rights Reserved.
  21  *
  22  * Contributor(s):
  23  *   Brett Wilson <brettw@gmail.com>
  24  *
  25  * Alternatively, the contents of this file may be used under the terms of
  26  * either the GNU General Public License Version 2 or later (the "GPL"), or
  27  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  28  * in which case the provisions of the GPL or the LGPL are applicable instead
  29  * of those above. If you wish to allow use of your version of this file only
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  31  * use your version of this file under the terms of the MPL, indicate your
  32  * decision by deleting the provisions above and replace them with the notice
  33  * and other provisions required by the GPL or the LGPL. If you do not delete
  34  * the provisions above, a recipient may use your version of this file under
  35  * the terms of any one of the MPL, the GPL or the LGPL.
  36  *
  37  * ***** END LICENSE BLOCK ***** */
  38
  39 #ifndef _MOZSTORAGEHELPER_H_
  40 #define _MOZSTORAGEHELPER_H_
  41
  42 #include "mozIStorageConnection.h"
  43 #include "mozIStorageStatement.h"
  44 #include "mozStorage.h"
  45
  46
  47 /**
  48  * This class wraps a transaction inside a given C++ scope, guaranteeing that
  49  * the transaction will be completed even if you have an exception or
  50  * return early.
  51  *
  52  * aCommitOnComplete controls whether the transaction is committed or rolled
  53  * back when it goes out of scope. A common use is to create an instance with
  54  * commitOnComplete = FALSE (rollback), then call Commit on this object manually
  55  * when your function completes successfully.
  56  *
  57  * Note that nested transactions are not supported by sqlite, so if a transaction
  58  * is already in progress, this object does nothing. Note that in this case,
  59  * you may not get the transaction type you ask for, and you won't be able
  60  * to rollback.
  61  */
  62 class mozStorageTransaction
  63 {
  64 public:
  65   mozStorageTransaction(mozIStorageConnection* aConnection,
  66                         PRBool aCommitOnComplete,
  67                         PRInt32 aType = mozIStorageConnection::TRANSACTION_DEFERRED)
  68     : mConnection(aConnection),
  69       mHasTransaction(PR_FALSE),
  70       mCommitOnComplete(aCommitOnComplete),
  71       mCompleted(PR_FALSE)
  72   {
  73     // We won't try to get a transaction if one is already in progress.
  74     if (mConnection)
  75       mHasTransaction = NS_SUCCEEDED(mConnection->BeginTransactionAs(aType));
  76   }
  77   ~mozStorageTransaction()
  78   {
  79     if (mConnection && mHasTransaction && ! mCompleted) {
  80       if (mCommitOnComplete)
  81         mConnection->CommitTransaction();
  82       else
  83         mConnection->RollbackTransaction();
  84     }
  85   }
  86
  87   /**
  88    * Commits the transaction if one is in progress. If one is not in progress,
  89    * this is a NOP since the actual owner of the transaction outside of our
  90    * scope is in charge of finally comitting or rolling back the transaction.
  91    */
  92   nsresult Commit()
  93   {
  94     if (!mConnection || mCompleted)
  95       return NS_OK; // no connection, or already done
  96     mCompleted = PR_TRUE;
  97     if (! mHasTransaction)
  98       return NS_OK; // transaction not ours, ignore
  99     return mConnection->CommitTransaction();
 100   }
 101
 102   /**
 103    * Rolls back the transaction in progress. You should only call this function
 104    * if this object has a real transaction (HasTransaction() = true) because
 105    * otherwise, there is no transaction to roll back.
 106    */
 107   nsresult Rollback()
 108   {
 109     if (!mConnection || mCompleted)
 110       return NS_OK; // no connection, or already done
 111     mCompleted = PR_TRUE;
 112     if (! mHasTransaction)
 113       return NS_ERROR_FAILURE;
 114
 115     // It is possible that a rollback will return busy, so we busy wait...
 116     nsresult rv = NS_OK;
 117     do {
 118       rv = mConnection->RollbackTransaction();
 119       if (rv == NS_ERROR_STORAGE_BUSY)
 120         (void)PR_Sleep(PR_INTERVAL_NO_WAIT);
 121     } while (rv == NS_ERROR_STORAGE_BUSY);
 122
 123     return rv;
 124   }
 125
 126   /**
 127    * Returns whether this object wraps a real transaction. False means that
 128    * this object doesn't do anything because there was already a transaction in
 129    * progress when it was created.
 130    */
 131   PRBool HasTransaction()
 132   {
 133     return mHasTransaction;
 134   }
 135
 136   /**
 137    * This sets the default action (commit or rollback) when this object goes
 138    * out of scope.
 139    */
 140   void SetDefaultAction(PRBool aCommitOnComplete)
 141   {
 142     mCommitOnComplete = aCommitOnComplete;
 143   }
 144
 145 protected:
 146   nsCOMPtr<mozIStorageConnection> mConnection;
 147   PRBool mHasTransaction;
 148   PRBool mCommitOnComplete;
 149   PRBool mCompleted;
 150 };
 151
 152
 153 /**
 154  * This class wraps a statement so that it is guaraneed to be reset when
 155  * this object goes out of scope.
 156  *
 157  * Note that this always just resets the statement. If the statement doesn't
 158  * need resetting, the reset operation is inexpensive.
 159  */
 160 class NS_STACK_CLASS mozStorageStatementScoper
 161 {
 162 public:
 163   mozStorageStatementScoper(mozIStorageStatement* aStatement)
 164       : mStatement(aStatement)
 165   {
 166   }
 167   ~mozStorageStatementScoper()
 168   {
 169     if (mStatement)
 170       mStatement->Reset();
 171   }
 172
 173   /**
 174    * Call this to make the statement not reset. You might do this if you know
 175    * that the statement has been reset.
 176    */
 177   void Abandon()
 178   {
 179     mStatement = nsnull;
 180   }
 181
 182 protected:
 183   nsCOMPtr<mozIStorageStatement> mStatement;
 184 };
 185
 186 #endif /* _MOZSTORAGEHELPER_H_ */