ChrisHegarty opened a new issue, #15317:
URL: https://github.com/apache/lucene/issues/15317
Potential hang with initialisation of `TermsEnum` and `BaseTermsEnum`.
The static `TermsEnum.EMPTY` initialises to an implementation of
`BaseTermsEnum`. `TermsEnum` is a superclass of `BaseTermsEnum`, so there is a
clear dependency between these classes. If a subclass of `BaseTermsEnum` is
initialising it may grab the lock on `BaseTermsEnum`, and prevent `TermsEnum`
from initialising. E.g.
```
"main" #3 [8963] prio=5 os_prio=31 cpu=30.57ms elapsed=2.19s
tid=0x0000000123815a00 nid=8963 in Object.wait() [0x000000016b24e000]
java.lang.Thread.State: RUNNABLE
at TermsEnumClinitHang.main(TermsEnumClinitHang.java:22)
- waiting on the Class initialization monitor for
org.apache.lucene.index.TermsEnum
"TEST_THREAD" #25 [27395] prio=5 os_prio=31 cpu=1.54ms elapsed=2.17s
tid=0x000000012382e800 nid=27395 in Object.wait() [0x000000016d632000]
java.lang.Thread.State: RUNNABLE
at org.apache.lucene.index.TermsEnum.<clinit>(TermsEnum.java:199)
- waiting on the Class initialization monitor for
org.apache.lucene.index.BaseTermsEnum
at TermsEnumClinitHang$1.run(TermsEnumClinitHang.java:15)
...
```
```
import org.apache.lucene.index.BaseTermsEnum;
import org.apache.lucene.index.ImpactsEnum;
import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.util.BytesRef;
public class TermsEnumClinitHang {
public static void main(String... args) throws Exception {
Thread t = new Thread() {
public void run() {
System.out.println("Test thread about to access TermsEnum.EMPTY");
// This will block until the main thread completes static
initialization of MyBaseTermsEnum
var empty = TermsEnum.EMPTY;
System.out.println("Test thread done - empty=" + empty);
}
};
t.setName("TEST_THREAD");
t.start();
var myBaseTermsEnum = new MyBaseTermsEnum();
System.out.println("Test thread done - myBaseTermsEnum=" +
myBaseTermsEnum);
}
static class MyBaseTermsEnum extends BaseTermsEnum {
@Override public SeekStatus seekCeil(BytesRef text) { return null; }
@Override public void seekExact(long ord) { }
@Override public BytesRef term() { return null; }
@Override public long ord() { return 0; }
@Override public int docFreq() { return 0;}
@Override public long totalTermFreq() { return 0;}
@Override public PostingsEnum postings(PostingsEnum reuse, int flags) {
return null; }
@Override public ImpactsEnum impacts(int flags) { return null; }
@Override public BytesRef next() { return null; }
}
}
```
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