--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/memory/metaspace/chunkHeaderPool.hpp	Tue Sep 10 09:24:05 2019 +0200
@@ -0,0 +1,140 @@
+/*
+ * Copyright (c) 2019, SAP SE. All rights reserved.
+ * Copyright (c) 2019, 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_MEMORY_METASPACE_CHUNKHEADERPOOL_HPP
+#define SHARE_MEMORY_METASPACE_CHUNKHEADERPOOL_HPP
+
+#include "memory/metaspace/internStat.hpp"
+#include "memory/metaspace/metachunk.hpp"
+#include "utilities/debug.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+namespace metaspace {
+
+// A simple helper class; A pool of unused chunk headers.
+
+class ChunkHeaderPool {
+
+  static const int slab_capacity = 128;
+
+  struct slab_t {
+    slab_t* next;
+    int top;
+    Metachunk elems [slab_capacity]; // var sized;
+  };
+
+  IntCounter _num_slabs;
+  slab_t* _first_slab;
+  slab_t* _current_slab;
+
+  IntCounter _num_handed_out;
+
+  MetachunkList _freelist;
+
+  const bool _delete_on_destruction;
+
+  void allocate_new_slab();
+
+  static ChunkHeaderPool _chunkHeaderPool;
+
+
+public:
+
+  ChunkHeaderPool(bool delete_on_destruction);
+
+  ~ChunkHeaderPool();
+
+  // Allocates a Metachunk structure. The structure is uninitialized.
+  Metachunk* allocate_chunk_header() {
+
+    Metachunk* c = NULL;
+
+    DEBUG_ONLY(verify(false));
+
+    c = _freelist.remove_first();
+    assert(c == NULL || c->is_dead(), "Not a freelist chunk header?");
+
+    if (c == NULL) {
+
+      if (_current_slab == NULL ||
+          _current_slab->top == slab_capacity) {
+        allocate_new_slab();
+        assert(_current_slab->top < slab_capacity, "Sanity");
+      }
+
+      c = _current_slab->elems + _current_slab->top;
+      _current_slab->top ++;
+
+    }
+
+    _num_handed_out.increment();
+
+    // By contract, the returned structure is uninitialized.
+    // Zap to make this clear.
+    DEBUG_ONLY(c->zap_header(0xBB);)
+
+    return c;
+
+  }
+
+  void return_chunk_header(Metachunk* c) {
+    // We only ever should return free chunks, since returning chunks
+    // happens only on merging and merging only works with free chunks.
+    assert(c != NULL && c->is_free(), "Sanity");
+#ifdef ASSERT
+    // In debug, fill dead header with pattern.
+    c->zap_header(0xCC);
+    c->set_next(NULL);
+    c->set_prev(NULL);
+#endif
+    c->set_dead();
+    _freelist.add(c);
+    _num_handed_out.decrement();
+
+  }
+
+  // Returns number of allocated elements.
+  int used() const                   { return _num_handed_out.get(); }
+
+  // Returns number of elements in free list.
+  int freelist_size() const          { return _freelist.size(); }
+
+  // Returns size of memory used.
+  size_t memory_footprint_words() const;
+
+  DEBUG_ONLY(void verify(bool slow) const;)
+
+  // Returns reference to the one global chunk header pool.
+  static ChunkHeaderPool& pool() { return _chunkHeaderPool; }
+
+};
+
+
+} // namespace metaspace
+
+
+
+
+#endif // SHARE_MEMORY_METASPACE_CHUNKHEADERPOOL_HPP