remove IndexReader.registerParentReader() (#15002)

Remove this function and associated WeakhashMap: it is not needed any
more. The tests still pass, user still gets ACE (just slightly different
exception message).

Closes #14999

Author: rmuir

lucene/CHANGES.txt

@@ -50,6 +50,10 @@ Improvements
   global queue min-score checking. Improves performance and consistency. (Mike Sokolov, Dzung Bui,
   Ben Trent)
 
+* GITHUB#15002: Remove synchronized WeakHashMap from IndexReader. This was added to help prevent
+  SIGSEGV with the old unsafe "mmap hack", which has been replaced by MemorySegments.
+  (Uwe Schindler, Robert Muir)
+
 Optimizations
 ---------------------
 * GITHUB#14011: Reduce allocation rate in HNSW concurrent merge. (Viliam Durina)

lucene/core/src/java/org/apache/lucene/index/BaseCompositeReader.java

@@ -84,7 +84,6 @@ protected BaseCompositeReader(R[] subReaders, Comparator<R> subReadersSorter) th
       starts[i] = (int) maxDoc;
       final IndexReader r = subReaders[i];
       maxDoc += r.maxDoc(); // compute maxDocs
-      r.registerParentReader(this);
     }
 
     if (maxDoc > IndexWriter.getActualMaxDocs()) {

lucene/core/src/java/org/apache/lucene/index/FilterLeafReader.java

@@ -334,7 +334,6 @@ protected FilterLeafReader(LeafReader in) {
       throw new NullPointerException("incoming LeafReader must not be null");
     }
     this.in = in;
-    in.registerParentReader(this);
   }
 
   @Override

lucene/core/src/java/org/apache/lucene/index/IndexReader.java

@@ -18,10 +18,7 @@
 
 import java.io.Closeable;
 import java.io.IOException;
-import java.util.Collections;
 import java.util.List;
-import java.util.Set;
-import java.util.WeakHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 import org.apache.lucene.store.AlreadyClosedException;
 
@@ -146,24 +143,6 @@ public interface ClosedListener {
     void onClose(CacheKey key) throws IOException;
   }
 
-  private final Set<IndexReader> parentReaders =
-      Collections.synchronizedSet(
-          Collections.newSetFromMap(new WeakHashMap<IndexReader, Boolean>()));
-
-  /**
-   * Expert: This method is called by {@code IndexReader}s which wrap other readers (e.g. {@link
-   * CompositeReader} or {@link FilterLeafReader}) to register the parent at the child (this reader)
-   * on construction of the parent. When this reader is closed, it will mark all registered parents
-   * as closed, too. The references to parent readers are weak only, so they can be GCed once they
-   * are no longer in use.
-   *
-   * @lucene.experimental
-   */
-  public final void registerParentReader(IndexReader reader) {
-    ensureOpen();
-    parentReaders.add(reader);
-  }
-
   /**
    * For test framework use only.
    *
@@ -173,18 +152,6 @@ protected void notifyReaderClosedListeners() throws IOException {
     // nothing to notify in the base impl
   }
 
-  private void reportCloseToParentReaders() throws IOException {
-    synchronized (parentReaders) {
-      for (IndexReader parent : parentReaders) {
-        parent.closedByChild = true;
-        // cross memory barrier by a fake write:
-        parent.refCount.addAndGet(0);
-        // recurse:
-        parent.reportCloseToParentReaders();
-      }
-    }
-  }
-
   /** Expert: returns the current refCount for this reader */
   public final int getRefCount() {
     // NOTE: don't ensureOpen, so that callers can see
@@ -253,8 +220,7 @@ public final void decRef() throws IOException {
     final int rc = refCount.decrementAndGet();
     if (rc == 0) {
       closed = true;
-      try (Closeable _ = this::reportCloseToParentReaders;
-          Closeable _ = this::notifyReaderClosedListeners) {
+      try (Closeable _ = this::notifyReaderClosedListeners) {
         doClose();
       }
     } else if (rc < 0) {

lucene/core/src/java/org/apache/lucene/index/ParallelLeafReader.java

@@ -196,7 +196,6 @@ public ParallelLeafReader(
       if (!closeSubReaders) {
         reader.incRef();
       }
-      reader.registerParentReader(this);
     }
   }
 

lucene/core/src/test/org/apache/lucene/index/TestReaderClosed.java

@@ -25,7 +25,6 @@
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.tests.analysis.MockAnalyzer;
 import org.apache.lucene.tests.analysis.MockTokenizer;
-import org.apache.lucene.tests.index.OwnCacheKeyMultiReader;
 import org.apache.lucene.tests.index.RandomIndexWriter;
 import org.apache.lucene.tests.util.LuceneTestCase;
 import org.apache.lucene.tests.util.TestUtil;
@@ -81,39 +80,6 @@ public void test() throws Exception {
     }
   }
 
-  // LUCENE-3800
-  public void testReaderChaining() throws Exception {
-    assertTrue(reader.getRefCount() > 0);
-    LeafReader wrappedReader = new ParallelLeafReader(getOnlyLeafReader(reader));
-
-    // We wrap with a OwnCacheKeyMultiReader so that closing the underlying reader
-    // does not terminate the threadpool (if that index searcher uses one)
-    IndexSearcher searcher = newSearcher(new OwnCacheKeyMultiReader(wrappedReader));
-
-    TermRangeQuery query = TermRangeQuery.newStringRange("field", "a", "z", true, true);
-    searcher.search(query, 5);
-    reader.close(); // close original child reader
-    try {
-      searcher.search(query, 5);
-    } catch (Exception e) {
-      AlreadyClosedException ace = null;
-      for (Throwable t = e; t != null; t = t.getCause()) {
-        if (t instanceof AlreadyClosedException) {
-          ace = (AlreadyClosedException) t;
-        }
-      }
-      if (ace == null) {
-        throw new AssertionError("Query failed, but not due to an AlreadyClosedException", e);
-      }
-      assertEquals(
-          "this IndexReader cannot be used anymore as one of its child readers was closed",
-          ace.getMessage());
-    } finally {
-      // close executor: in case of wrap-wrap-wrapping
-      searcher.getIndexReader().close();
-    }
-  }
-
   @Override
   public void tearDown() throws Exception {
     dir.close();