Exception when using SharedPoolDataSource concurrently
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Key: DBCP-369
URL: https://issues.apache.org/jira/browse/DBCP-369
Project: Commons Dbcp
Issue Type: Bug
Affects Versions: 1.4
Environment: Java Hotspot Server VM 1.6.0_07, Linux
Reporter: Michael Pradel
Hi,
I get a ConcurrentModificationException when using instances of
SharedPoolDataSource concurrently. The problem occurs when one thread calls
setDataSourceName() while another thread calls close(), either on the same
instance of SharedPoolDataSource or on different instances. I'll attach a short
example program that leads to an exception for almost every run on my machine.
The cause of the exception seems to be in InstanceKeyObjectFactory.
registerNewInstance() is synchronized, but removeInstance() isn't. This allows
concurrent accesses to the non-thread-safe 'instanceMap'.
Is this a bug? Or are SharedPoolDataSource and InstanceKeyObjectFactory not
supposed to be thread-safe?
Thanks!
import java.util.ArrayList;
import org.apache.commons.dbcp.datasources.SharedPoolDataSource;
public class SharedPoolDataSourceTest {
public static void main(String[] args) {
new SharedPoolDataSourceTest().run();
}
private void run() {
final ArrayList<SharedPoolDataSource> dataSources = new
ArrayList<SharedPoolDataSource>();
for (int j = 0; j < 10000; j++) {
SharedPoolDataSource dataSource = new
SharedPoolDataSource();
dataSources.add(dataSource);
}
Thread t1 = new Thread(new Runnable() {
public void run() {
for (SharedPoolDataSource dataSource :
dataSources) {
dataSource.setDataSourceName("a");
}
}
});
Thread t2 = new Thread(new Runnable() {
public void run() {
for (SharedPoolDataSource dataSource :
dataSources) {
try { dataSource.close(); } catch
(Exception e) {}
}
}
});
t1.start();
t2.start();
try {
t1.join();
t2.join();
} catch (InterruptedException ie) {}
}
}
Exception in thread "Thread-0" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
at java.util.HashMap$KeyIterator.next(HashMap.java:828)
at
org.apache.commons.dbcp.datasources.InstanceKeyObjectFactory.registerNewInstance(InstanceKeyObjectFactory.java:51)
at
org.apache.commons.dbcp.datasources.InstanceKeyDataSource.setDataSourceName(InstanceKeyDataSource.java:246)
at
potentialBugs.SharedPoolDataSourceTest$1.run(SharedPoolDataSourceTest.java:23)
at java.lang.Thread.run(Thread.java:619)
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