1 /*
   2  * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  22  *
  23  */
  24 
  25 #ifndef SHARE_GC_G1_G1FREEIDSET_HPP
  26 #define SHARE_GC_G1_G1FREEIDSET_HPP
  27 
  28 #include "runtime/semaphore.hpp"
  29 #include "utilities/globalDefinitions.hpp"
  30 #include "utilities/macros.hpp"
  31 
  32 // Represents a set of small integer ids, from which elements can be
  33 // temporarily allocated for exclusive use.  The ids are in a
  34 // contiguous range from 'start' to 'start + size'.  Used to obtain a
  35 // distinct worker_id value for a mutator thread that doesn't normally
  36 // have such an id.
  37 class G1FreeIdSet {
  38   Semaphore _sem;
  39   uint* _next;
  40   uint _start;
  41   uint _size;
  42   uintx _head_index_mask;
  43   volatile uintx _head;
  44 
  45   uint head_index(uintx head) const;
  46   uintx make_head(uint index, uintx old_head) const;
  47 
  48   NONCOPYABLE(G1FreeIdSet);
  49 
  50 public:
  51   G1FreeIdSet(uint start, uint size);
  52   ~G1FreeIdSet();
  53 
  54   // Returns an unclaimed parallel id (waiting for one to be released if
  55   // necessary).  Must not safepoint while holding a claimed id.
  56   uint claim_par_id();
  57 
  58   void release_par_id(uint id);
  59 
  60   struct TestSupport;           // For unit test access.
  61 };
  62 
  63 #endif // SHARE_GC_G1_G1FREEIDSET_HPP