8267185: Add string deduplication support to ParallelGC

Reviewed-by: kbarrett, ayang

src/hotspot/share/gc/parallel/psStringDedup.hpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2021, Oracle and/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.
+ *
+ */
+
+#ifndef SHARE_GC_PARALLEL_PSSTRINGDEDUP_HPP
+#define SHARE_GC_PARALLEL_PSSTRINGDEDUP_HPP
+
+#include "gc/parallel/psScavenge.hpp"
+#include "gc/shared/stringdedup/stringDedup.hpp"
+#include "memory/allStatic.hpp"
+#include "oops/oopsHierarchy.hpp"
+
+class psStringDedup : AllStatic {
+public:
+  static bool is_candidate_from_mark(oop java_string) {
+    // Candidate if string is being evacuated from young to old but has not
+    // reached the deduplication age threshold, i.e. has not previously been a
+    // candidate during its life in the young generation.
+    return PSScavenge::is_obj_in_young(java_string) &&
+           StringDedup::is_below_threshold_age(java_string->age());
+  }
+
+  static bool is_candidate_from_evacuation(oop obj,
+                                           bool obj_is_tenured) {
+    return obj_is_tenured ?
+           StringDedup::is_below_threshold_age(obj->age()) :
+           StringDedup::is_threshold_age(obj->age());
+  }
+};
+#endif // SHARE_GC_PARALLEL_PSSTRINGDEDUP_HPP