Incorrect initialization of thread local variable inside IOContext (
implementation is not threadsafe )
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Key: HIVE-1647
URL: https://issues.apache.org/jira/browse/HIVE-1647
Project: Hadoop Hive
Issue Type: Bug
Components: Server Infrastructure
Affects Versions: 0.5.0
Reporter: Raman Grover
Fix For: 0.3.1
Bug in org.apache.hadoop.hive.ql.io.IOContext
in relation to initialization of thread local variable.
public class IOContext {
private static ThreadLocal<IOContext> threadLocal = new
ThreadLocal<IOContext>(){ };
static {
if (threadLocal.get() == null) {
threadLocal.set(new IOContext());
}
}
In a multi-threaded environment, the thread that gets to load the class first
for the JVM (assuming threads share the classloader),
gets to initialize itself correctly by executing the code in the static block.
Once the class is loaded,
any subsequent threads would have their respective threadlocal variable as
null. Since IOContext
is set during initialization of HiveRecordReader, In a scenario where multiple
threads get to acquire
an instance of HiveRecordReader, it would result in a NPE for all but the
first thread that gets to load the class in the VM.
Is the above scenario of multiple threads initializing HiveRecordReader a
typical one ? or we could just provide the following fix...
private static ThreadLocal<IOContext> threadLocal = new
ThreadLocal<IOContext>(){
protected synchronized IOContext initialValue() {
return new IOContext();
}
};
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