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/* -*- 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 */