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/*
Copyright (c) 2007, 2015, Oracle and/or its affiliates. All rights reserved.
The MySQL Connector/J is licensed under the terms of the GPLv2
<http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
this software, see the FOSS License Exception
<http://www.mysql.com/about/legal/licensing/foss-exception.html>.
This program is free software; you can redistribute it and/or modify it under the terms
of the GNU General Public License as published by the Free Software Foundation; version 2
of the License.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License along with this
program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
Floor, Boston, MA 02110-1301 USA
*/
package com.mysql.jdbc;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;
import java.util.Properties;
/**
* A balancing strategy that starts at a random point, and then advances in the list (wrapping around) for each new pickConnection() call.
*
* The initial point selection, and subsequent point selections are blacklist-aware.
*/
public class SequentialBalanceStrategy implements BalanceStrategy {
private int currentHostIndex = -1;
public SequentialBalanceStrategy() {
}
public void destroy() {
// we don't have anything to clean up
}
public void init(Connection conn, Properties props) throws SQLException {
// we don't have anything to initialize
}
public ConnectionImpl pickConnection(LoadBalancedConnectionProxy proxy, List<String> configuredHosts, Map<String, ConnectionImpl> liveConnections,
long[] responseTimes, int numRetries) throws SQLException {
int numHosts = configuredHosts.size();
SQLException ex = null;
Map<String, Long> blackList = proxy.getGlobalBlacklist();
for (int attempts = 0; attempts < numRetries;) {
if (numHosts == 1) {
this.currentHostIndex = 0; // pathological case
} else if (this.currentHostIndex == -1) {
int random = (int) Math.floor((Math.random() * numHosts));
for (int i = random; i < numHosts; i++) {
if (!blackList.containsKey(configuredHosts.get(i))) {
this.currentHostIndex = i;
break;
}
}
if (this.currentHostIndex == -1) {
for (int i = 0; i < random; i++) {
if (!blackList.containsKey(configuredHosts.get(i))) {
this.currentHostIndex = i;
break;
}
}
}
if (this.currentHostIndex == -1) {
blackList = proxy.getGlobalBlacklist(); // it may have changed
// and the proxy returns a copy
try {
Thread.sleep(250);
} catch (InterruptedException e) {
}
continue; // retry
}
} else {
int i = this.currentHostIndex + 1;
boolean foundGoodHost = false;
for (; i < numHosts; i++) {
if (!blackList.containsKey(configuredHosts.get(i))) {
this.currentHostIndex = i;
foundGoodHost = true;
break;
}
}
if (!foundGoodHost) {
for (i = 0; i < this.currentHostIndex; i++) {
if (!blackList.containsKey(configuredHosts.get(i))) {
this.currentHostIndex = i;
foundGoodHost = true;
break;
}
}
}
if (!foundGoodHost) {
blackList = proxy.getGlobalBlacklist(); // it may have changed
// and the proxy returns a copy
try {
Thread.sleep(250);
} catch (InterruptedException e) {
}
continue; // retry
}
}
String hostPortSpec = configuredHosts.get(this.currentHostIndex);
ConnectionImpl conn = liveConnections.get(hostPortSpec);
if (conn == null) {
try {
conn = proxy.createConnectionForHost(hostPortSpec);
} catch (SQLException sqlEx) {
ex = sqlEx;
if (proxy.shouldExceptionTriggerConnectionSwitch(sqlEx)) {
proxy.addToGlobalBlacklist(hostPortSpec);
try {
Thread.sleep(250);
} catch (InterruptedException e) {
}
continue;
}
throw sqlEx;
}
}
return conn;
}
if (ex != null) {
throw ex;
}
return null; // we won't get here, compiler can't tell
}
}