dweiss commented on code in PR #12199:
URL: https://github.com/apache/lucene/pull/12199#discussion_r1132698882


##########
lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThreadPool.java:
##########
@@ -113,15 +113,19 @@ private synchronized DocumentsWriterPerThread newWriter() 
{
    * operation (add/updateDocument).
    */
   DocumentsWriterPerThread getAndLock() {
-    synchronized (this) {
-      ensureOpen();
-      DocumentsWriterPerThread dwpt = 
freeList.poll(DocumentsWriterPerThread::tryLock);
-      if (dwpt == null) {
-        dwpt = newWriter();
+    ensureOpen();
+    DocumentsWriterPerThread dwpt = 
freeList.poll(DocumentsWriterPerThread::tryLock);
+    if (dwpt == null) {

Review Comment:
   It's not about the poll. It's about whether dwpt = newWriter(); can be 
expanded and reordered by the compiler so that dwpt gets assigned a value 
before the constructor (or whatever initialization inside newWriter) takes 
place. Any thread checking dwpt == null outside synchronized could, at least in 
theory, see such a "partially constructed" object.



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