117 lines
4.1 KiB
C++
117 lines
4.1 KiB
C++
/***********************************************************************
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deadlock.cpp - Demonstrates how MySQL's deadlock detection interacts
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with MySQL++'s Transaction class an exception handling mechanism.
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Run one copy of this program with the -m1 command line switch, then
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while it's waiting for you to press Enter, run another copy with -m2
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instead.
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Copyright (c) 2007 by Jim Wallace and (c) 2007-2009 by Educational
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Technology Resources, Inc. Others may also hold copyrights on code
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in this file. See the CREDITS.txt file in the top directory of the
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distribution for details.
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This file is part of MySQL++.
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MySQL++ is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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MySQL++ is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with MySQL++; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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***********************************************************************/
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#include "cmdline.h"
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#include <mysql++.h>
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#include <mysqld_error.h>
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#include <iostream>
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using namespace std;
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// Bring in global holding the value given to the -m switch
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extern int run_mode;
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int
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main(int argc, char *argv[])
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{
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// Get database access parameters from command line
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mysqlpp::examples::CommandLine cmdline(argc, argv);
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if (!cmdline) {
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return 1;
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}
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// Check that the mode parameter was also given and it makes sense
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const int run_mode = cmdline.run_mode();
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if ((run_mode != 1) && (run_mode != 2)) {
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cerr << argv[0] << " must be run with -m1 or -m2 as one of "
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"its command-line arguments." << endl;
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return 1;
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}
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mysqlpp::Connection con;
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try {
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// Establish the connection to the database server
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mysqlpp::Connection con(mysqlpp::examples::db_name,
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cmdline.server(), cmdline.user(), cmdline.pass());
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// Start a transaction set. Transactions create mutex locks on
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// modified rows, so if two programs both touch the same pair of
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// rows but in opposite orders at the wrong time, one of the two
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// programs will deadlock. The MySQL server knows how to detect
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// this situation, and its error return causes MySQL++ to throw
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// a BadQuery exception. The point of this example is that if
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// you want to detect this problem, you would check the value of
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// BadQuery::errnum(), not Connection::errnum(), because the
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// transaction rollback process executes a query which succeeds,
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// setting the MySQL C API's "last error number" value to 0.
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// The exception object carries its own copy of the error number
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// at the point the exception was thrown for this very reason.
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mysqlpp::Query query = con.query();
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mysqlpp::Transaction trans(con);
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// Build and run the queries, with the order depending on the -m
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// flag, so that a second copy of the program will deadlock if
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// run while the first is waiting for Enter.
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char dummy[100];
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for (int i = 0; i < 2; ++i) {
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int lock = run_mode + (run_mode == 1 ? i : -i);
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cout << "Trying lock " << lock << "..." << endl;
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query << "select * from deadlock_test" << lock <<
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" where x = " << lock << " for update";
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query.store();
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cout << "Acquired lock " << lock << ". Press Enter to ";
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cout << (i == 0 ? "try next lock" : "exit");
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cout << ": " << flush;
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cin.getline(dummy, sizeof(dummy));
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}
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}
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catch (mysqlpp::BadQuery e) {
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if (e.errnum() == ER_LOCK_DEADLOCK) {
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cerr << "Transaction deadlock detected!" << endl;
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cerr << "Connection::errnum = " << con.errnum() <<
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", BadQuery::errnum = " << e.errnum() << endl;
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}
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else {
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cerr << "Unexpected query error: " << e.what() << endl;
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}
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return 1;
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}
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catch (mysqlpp::Exception e) {
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cerr << "General error: " << e.what() << endl;
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return 1;
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}
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return 0;
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}
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