From af6b33f2331c8e6e658fe42c6c9cc83e7d81151e Mon Sep 17 00:00:00 2001
From: James Vanneman <james.vanneman@reddit.com>
Date: Tue, 30 Dec 2025 11:03:50 -0500
Subject: [PATCH] PR 2402 added support for CompletableFuture which
 accidentally introduced a double registration bug in HttpJettySolrClient by
 calling onRequestQueued/onComplete twice with
 asyncListener.queuedListener/completeListener

This introduces three undesirable scenarios:

Potential deadlock due to a surge in requests that all acquire 1 permit and cannot acquire a second
 Unnecessary system throttling when a request acquires a single permit but can't acquire a second due to in flight requests and new requests that arrived after the first token acquisition but before the second.
Half the number of permits available
---
 ...SOLR-18051-fix-double-registration-bug.yml |  8 ++
 .../solrj/jetty/HttpJettySolrClient.java      | 86 +++++++++----------
 2 files changed, 49 insertions(+), 45 deletions(-)
 create mode 100644 changelog/unreleased/SOLR-18051-fix-double-registration-bug.yml

diff --git a/changelog/unreleased/SOLR-18051-fix-double-registration-bug.yml b/changelog/unreleased/SOLR-18051-fix-double-registration-bug.yml
new file mode 100644
index 00000000000..0181f211698
--- /dev/null
+++ b/changelog/unreleased/SOLR-18051-fix-double-registration-bug.yml
@@ -0,0 +1,8 @@
+# See https://github.com/apache/solr/blob/main/dev-docs/changelog.adoc
+title: Fix phaser/semaphore double registration bug in HttpJettySolrClient
+type: fixed # added, changed, fixed, deprecated, removed, dependency_update, security, other
+authors:
+  - name: James Vanneman
+links:
+  - name: SOLR-18051
+    url: https://issues.apache.org/jira/browse/SOLR-18051
diff --git a/solr/solrj/src/java/org/apache/solr/client/solrj/jetty/HttpJettySolrClient.java b/solr/solrj/src/java/org/apache/solr/client/solrj/jetty/HttpJettySolrClient.java
index 072a2add953..cac90ba4670 100644
--- a/solr/solrj/src/java/org/apache/solr/client/solrj/jetty/HttpJettySolrClient.java
+++ b/solr/solrj/src/java/org/apache/solr/client/solrj/jetty/HttpJettySolrClient.java
@@ -401,51 +401,47 @@ public CompletableFuture<NamedList<Object>> requestAsync(
       future.completeExceptionally(e);
       return future;
     }
-    mrrv.request
-        .onRequestQueued(asyncTracker.queuedListener)
-        .onComplete(asyncTracker.completeListener)
-        .send(
-            new InputStreamResponseListener() {
-              // MDC snapshot from requestAsync's thread
-              MDCCopyHelper mdcCopyHelper = new MDCCopyHelper();
-
-              @Override
-              public void onHeaders(Response response) {
-                super.onHeaders(response);
-                InputStreamResponseListener listener = this;
-                executor.execute(
-                    () -> {
-                      InputStream is = listener.getInputStream();
-                      try {
-                        NamedList<Object> body =
-                            processErrorsAndResponse(solrRequest, response, is, url);
-                        mdcCopyHelper.onBegin(null);
-                        log.debug("response processing success");
-                        future.complete(body);
-                      } catch (CancellationException e) {
-                        mdcCopyHelper.onBegin(null);
-                        log.debug("response processing cancelled", e);
-                        if (!future.isDone()) {
-                          future.cancel(true);
-                        }
-                      } catch (Throwable e) {
-                        mdcCopyHelper.onBegin(null);
-                        log.debug("response processing failed", e);
-                        future.completeExceptionally(e);
-                      } finally {
-                        log.debug("response processing completed");
-                        mdcCopyHelper.onComplete(null);
-                      }
-                    });
-              }
-
-              @Override
-              public void onFailure(Response response, Throwable failure) {
-                super.onFailure(response, failure);
-                future.completeExceptionally(
-                    new SolrServerException(failure.getMessage(), failure));
-              }
-            });
+    mrrv.request.send(
+        new InputStreamResponseListener() {
+          // MDC snapshot from requestAsync's thread
+          MDCCopyHelper mdcCopyHelper = new MDCCopyHelper();
+
+          @Override
+          public void onHeaders(Response response) {
+            super.onHeaders(response);
+            InputStreamResponseListener listener = this;
+            executor.execute(
+                () -> {
+                  InputStream is = listener.getInputStream();
+                  try {
+                    NamedList<Object> body =
+                        processErrorsAndResponse(solrRequest, response, is, url);
+                    mdcCopyHelper.onBegin(null);
+                    log.debug("response processing success");
+                    future.complete(body);
+                  } catch (CancellationException e) {
+                    mdcCopyHelper.onBegin(null);
+                    log.debug("response processing cancelled", e);
+                    if (!future.isDone()) {
+                      future.cancel(true);
+                    }
+                  } catch (Throwable e) {
+                    mdcCopyHelper.onBegin(null);
+                    log.debug("response processing failed", e);
+                    future.completeExceptionally(e);
+                  } finally {
+                    log.debug("response processing completed");
+                    mdcCopyHelper.onComplete(null);
+                  }
+                });
+          }
+
+          @Override
+          public void onFailure(Response response, Throwable failure) {
+            super.onFailure(response, failure);
+            future.completeExceptionally(new SolrServerException(failure.getMessage(), failure));
+          }
+        });
 
     // SOLR-17916: Disable request aborting
     // future.exceptionally(