210 lines
6.9 KiB
C++
210 lines
6.9 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MOZSTORAGEHELPER_H
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#define MOZSTORAGEHELPER_H
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#include "nsAutoPtr.h"
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#include "nsStringGlue.h"
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#include "mozilla/DebugOnly.h"
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#include "mozIStorageAsyncConnection.h"
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#include "mozIStorageConnection.h"
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#include "mozIStorageStatement.h"
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#include "mozIStoragePendingStatement.h"
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#include "nsError.h"
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/**
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* This class wraps a transaction inside a given C++ scope, guaranteeing that
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* the transaction will be completed even if you have an exception or
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* return early.
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*
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* A common use is to create an instance with aCommitOnComplete = false (rollback),
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* then call Commit() on this object manually when your function completes
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* successfully.
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*
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* @note nested transactions are not supported by Sqlite, so if a transaction
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* is already in progress, this object does nothing. Note that in this case,
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* you may not get the transaction type you asked for, and you won't be able
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* to rollback.
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*
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* @param aConnection
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* The connection to create the transaction on.
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* @param aCommitOnComplete
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* Controls whether the transaction is committed or rolled back when
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* this object goes out of scope.
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* @param aType [optional]
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* The transaction type, as defined in mozIStorageConnection. Defaults
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* to TRANSACTION_DEFERRED.
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* @param aAsyncCommit [optional]
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* Whether commit should be executed asynchronously on the helper thread.
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* This is a special option introduced as an interim solution to reduce
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* main-thread fsyncs in Places. Can only be used on main-thread.
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*
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* WARNING: YOU SHOULD _NOT_ WRITE NEW MAIN-THREAD CODE USING THIS!
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*
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* Notice that async commit might cause synchronous statements to fail
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* with SQLITE_BUSY. A possible mitigation strategy is to use
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* PRAGMA busy_timeout, but notice that might cause main-thread jank.
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* Finally, if the database is using WAL journaling mode, other
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* connections won't see the changes done in async committed transactions
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* until commit is complete.
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*
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* For all of the above reasons, this should only be used as an interim
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* solution and avoided completely if possible.
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*/
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class mozStorageTransaction
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{
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public:
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mozStorageTransaction(mozIStorageConnection* aConnection,
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bool aCommitOnComplete,
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int32_t aType = mozIStorageConnection::TRANSACTION_DEFERRED,
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bool aAsyncCommit = false)
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: mConnection(aConnection),
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mHasTransaction(false),
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mCommitOnComplete(aCommitOnComplete),
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mCompleted(false),
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mAsyncCommit(aAsyncCommit)
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{
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if (mConnection) {
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nsAutoCString query("BEGIN");
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switch(aType) {
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case mozIStorageConnection::TRANSACTION_IMMEDIATE:
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query.AppendLiteral(" IMMEDIATE");
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break;
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case mozIStorageConnection::TRANSACTION_EXCLUSIVE:
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query.AppendLiteral(" EXCLUSIVE");
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break;
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case mozIStorageConnection::TRANSACTION_DEFERRED:
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query.AppendLiteral(" DEFERRED");
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break;
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default:
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MOZ_ASSERT(false, "Unknown transaction type");
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}
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// If a transaction is already in progress, this will fail, since Sqlite
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// doesn't support nested transactions.
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mHasTransaction = NS_SUCCEEDED(mConnection->ExecuteSimpleSQL(query));
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}
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}
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~mozStorageTransaction()
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{
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if (mConnection && mHasTransaction && !mCompleted) {
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if (mCommitOnComplete) {
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mozilla::DebugOnly<nsresult> rv = Commit();
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NS_WARN_IF_FALSE(NS_SUCCEEDED(rv),
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"A transaction didn't commit correctly");
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}
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else {
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mozilla::DebugOnly<nsresult> rv = Rollback();
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NS_WARN_IF_FALSE(NS_SUCCEEDED(rv),
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"A transaction didn't rollback correctly");
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}
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}
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}
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/**
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* Commits the transaction if one is in progress. If one is not in progress,
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* this is a NOP since the actual owner of the transaction outside of our
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* scope is in charge of finally committing or rolling back the transaction.
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*/
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nsresult Commit()
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{
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if (!mConnection || mCompleted || !mHasTransaction)
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return NS_OK;
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mCompleted = true;
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// TODO (bug 559659): this might fail with SQLITE_BUSY, but we don't handle
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// it, thus the transaction might stay open until the next COMMIT.
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nsresult rv;
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if (mAsyncCommit) {
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nsCOMPtr<mozIStoragePendingStatement> ps;
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rv = mConnection->ExecuteSimpleSQLAsync(NS_LITERAL_CSTRING("COMMIT"),
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nullptr, getter_AddRefs(ps));
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}
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else {
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rv = mConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING("COMMIT"));
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}
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if (NS_SUCCEEDED(rv))
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mHasTransaction = false;
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return rv;
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}
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/**
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* Rolls back the transaction if one is in progress. If one is not in progress,
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* this is a NOP since the actual owner of the transaction outside of our
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* scope is in charge of finally rolling back the transaction.
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*/
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nsresult Rollback()
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{
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if (!mConnection || mCompleted || !mHasTransaction)
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return NS_OK;
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mCompleted = true;
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// TODO (bug 1062823): from Sqlite 3.7.11 on, rollback won't ever return
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// a busy error, so this handling can be removed.
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nsresult rv = NS_OK;
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do {
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rv = mConnection->ExecuteSimpleSQL(NS_LITERAL_CSTRING("ROLLBACK"));
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if (rv == NS_ERROR_STORAGE_BUSY)
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(void)PR_Sleep(PR_INTERVAL_NO_WAIT);
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} while (rv == NS_ERROR_STORAGE_BUSY);
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if (NS_SUCCEEDED(rv))
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mHasTransaction = false;
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return rv;
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}
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protected:
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nsCOMPtr<mozIStorageConnection> mConnection;
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bool mHasTransaction;
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bool mCommitOnComplete;
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bool mCompleted;
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bool mAsyncCommit;
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};
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/**
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* This class wraps a statement so that it is guaraneed to be reset when
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* this object goes out of scope.
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*
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* Note that this always just resets the statement. If the statement doesn't
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* need resetting, the reset operation is inexpensive.
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*/
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class MOZ_STACK_CLASS mozStorageStatementScoper
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{
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public:
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explicit mozStorageStatementScoper(mozIStorageStatement* aStatement)
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: mStatement(aStatement)
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{
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}
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~mozStorageStatementScoper()
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{
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if (mStatement)
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mStatement->Reset();
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}
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/**
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* Call this to make the statement not reset. You might do this if you know
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* that the statement has been reset.
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*/
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void Abandon()
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{
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mStatement = nullptr;
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}
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protected:
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nsCOMPtr<mozIStorageStatement> mStatement;
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};
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// Use this to make queries uniquely identifiable in telemetry
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// statistics, especially PRAGMAs. We don't include __LINE__ so that
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// queries are stable in the face of source code changes.
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#define MOZ_STORAGE_UNIQUIFY_QUERY_STR "/* " __FILE__ " */ "
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#endif /* MOZSTORAGEHELPER_H */
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