gecko-dev/storage/public/mozStorageHelper.h

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5.3 KiB
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 "nsAutoPtr.h"
#include "mozIStorageAsyncConnection.h"
#include "mozIStorageConnection.h"
#include "mozIStorageStatement.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.
*
* aCommitOnComplete controls whether the transaction is committed or rolled
* back when it goes out of scope. A common use is to create an instance with
* commitOnComplete = FALSE (rollback), then call Commit on this object manually
* when your function completes successfully.
*
* Note that 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 ask for, and you won't be able
* to rollback.
*
* Note: This class is templatized to be also usable with internal data
* structures. External users of this class should generally use
* |mozStorageTransaction| instead.
*/
template<typename T, typename U>
class mozStorageTransactionBase
{
public:
mozStorageTransactionBase(T* aConnection,
bool aCommitOnComplete,
int32_t aType = mozIStorageConnection::TRANSACTION_DEFERRED)
: mConnection(aConnection),
mHasTransaction(false),
mCommitOnComplete(aCommitOnComplete),
mCompleted(false)
{
// We won't try to get a transaction if one is already in progress.
if (mConnection)
mHasTransaction = NS_SUCCEEDED(mConnection->BeginTransactionAs(aType));
}
~mozStorageTransactionBase()
{
if (mConnection && mHasTransaction && ! mCompleted) {
if (mCommitOnComplete)
mConnection->CommitTransaction();
else
mConnection->RollbackTransaction();
}
}
/**
* 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 comitting or rolling back the transaction.
*/
nsresult Commit()
{
if (!mConnection || mCompleted)
return NS_OK; // no connection, or already done
mCompleted = true;
if (! mHasTransaction)
return NS_OK; // transaction not ours, ignore
nsresult rv = mConnection->CommitTransaction();
if (NS_SUCCEEDED(rv))
mHasTransaction = false;
return rv;
}
/**
* Rolls back the transaction in progress. You should only call this function
* if this object has a real transaction (HasTransaction() = true) because
* otherwise, there is no transaction to roll back.
*/
nsresult Rollback()
{
if (!mConnection || mCompleted)
return NS_OK; // no connection, or already done
mCompleted = true;
if (! mHasTransaction)
return NS_ERROR_FAILURE;
// It is possible that a rollback will return busy, so we busy wait...
nsresult rv = NS_OK;
do {
rv = mConnection->RollbackTransaction();
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;
}
/**
* Returns whether this object wraps a real transaction. False means that
* this object doesn't do anything because there was already a transaction in
* progress when it was created.
*/
bool HasTransaction()
{
return mHasTransaction;
}
/**
* This sets the default action (commit or rollback) when this object goes
* out of scope.
*/
void SetDefaultAction(bool aCommitOnComplete)
{
mCommitOnComplete = aCommitOnComplete;
}
protected:
U mConnection;
bool mHasTransaction;
bool mCommitOnComplete;
bool mCompleted;
};
/**
* An instance of the mozStorageTransaction<> family dedicated
* to |mozIStorageConnection|.
*/
typedef mozStorageTransactionBase<mozIStorageConnection,
nsCOMPtr<mozIStorageConnection> >
mozStorageTransaction;
/**
* 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:
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 */