From 5acbf8baea3f1a982bdba29b51c8531caa919748 Mon Sep 17 00:00:00 2001
From: Patrick Fontanilla <pfon@amazon.com>
Date: Wed, 15 Apr 2026 19:02:28 +0000
Subject: [PATCH] 8381871: GenShen: ShenandoahGCHeuristics flag not reset after
 ignoring non-adaptive value

Reviewed-by: xpeng, kdnilsen, ysr, serb, wkemper
---
 .../gc/shenandoah/shenandoahArguments.cpp     |  1 +
 .../options/TestGenerationalHeuristics.java   | 84 +++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 test/hotspot/jtreg/gc/shenandoah/options/TestGenerationalHeuristics.java

diff --git a/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp b/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp
index c1fa4b964b7..e9d6a686694 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp
@@ -200,6 +200,7 @@ void ShenandoahArguments::initialize() {
       && strcmp(ShenandoahGCHeuristics, "adaptive") != 0) {
     log_warning(gc)("Ignoring -XX:ShenandoahGCHeuristics input: %s, because generational shenandoah only"
       " supports adaptive heuristics", ShenandoahGCHeuristics);
+    FLAG_SET_ERGO(ShenandoahGCHeuristics, "adaptive");
   }
 
   FullGCForwarding::initialize_flags(MaxHeapSize);
diff --git a/test/hotspot/jtreg/gc/shenandoah/options/TestGenerationalHeuristics.java b/test/hotspot/jtreg/gc/shenandoah/options/TestGenerationalHeuristics.java
new file mode 100644
index 00000000000..822c3806347
--- /dev/null
+++ b/test/hotspot/jtreg/gc/shenandoah/options/TestGenerationalHeuristics.java
@@ -0,0 +1,84 @@
+/*
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+/*
+ * @test id=generational
+ * @bug 8381871
+ * @summary Test that ShenandoahGCHeuristics is always adaptive in generational mode
+ * @requires vm.gc.Shenandoah
+ * @library /test/lib
+ * @run driver TestGenerationalHeuristics
+ */
+
+import jdk.test.lib.process.ProcessTools;
+import jdk.test.lib.process.OutputAnalyzer;
+
+public class TestGenerationalHeuristics {
+    public static void main(String[] args) throws Exception {
+        {
+            OutputAnalyzer output = ProcessTools.executeLimitedTestJava(
+                "-XX:+UseShenandoahGC",
+                "-XX:ShenandoahGCMode=generational",
+                "-XX:ShenandoahGCHeuristics=adaptive",
+                "-XX:+PrintFlagsFinal",
+                "-version");
+            output.shouldMatch("ShenandoahGCHeuristics(.*)= adaptive ");
+            output.shouldHaveExitValue(0);
+        }
+
+        {
+            OutputAnalyzer output = ProcessTools.executeLimitedTestJava(
+                "-XX:+UseShenandoahGC",
+                "-XX:ShenandoahGCMode=generational",
+                "-XX:ShenandoahGCHeuristics=static",
+                "-XX:+PrintFlagsFinal",
+                "-version");
+            output.shouldMatch("ShenandoahGCHeuristics(.*)= adaptive ");
+            output.shouldHaveExitValue(0);
+        }
+
+        {
+            OutputAnalyzer output = ProcessTools.executeLimitedTestJava(
+                "-XX:+UseShenandoahGC",
+                "-XX:ShenandoahGCMode=generational",
+                "-XX:ShenandoahGCHeuristics=aggressive",
+                "-XX:+PrintFlagsFinal",
+                "-version");
+            output.shouldMatch("ShenandoahGCHeuristics(.*)= adaptive ");
+            output.shouldHaveExitValue(0);
+        }
+
+        {
+            OutputAnalyzer output = ProcessTools.executeLimitedTestJava(
+                "-XX:+UseShenandoahGC",
+                "-XX:ShenandoahGCMode=generational",
+                "-XX:ShenandoahGCHeuristics=compact",
+                "-XX:+PrintFlagsFinal",
+                "-version");
+            output.shouldMatch("ShenandoahGCHeuristics(.*)= adaptive ");
+            output.shouldHaveExitValue(0);
+        }
+    }
+
+}