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