1 /*
   2  * Copyright (c) 2017, 2018, Red Hat, Inc. All rights reserved.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This code is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  11  * version 2 for more details (a copy is included in the LICENSE file that
  12  * accompanied this code).
  13  *
  14  * You should have received a copy of the GNU General Public License version
  15  * 2 along with this work; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  17  *
  18  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  19  * or visit www.oracle.com if you need additional information or have any
  20  * questions.
  21  *
  22  */
  23 
  24 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP
  25 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP
  26 
  27 #include "gc_implementation/shenandoah/shenandoahPadding.hpp"
  28 #include "memory/allocation.hpp"
  29 #include "runtime/safepoint.hpp"
  30 #include "runtime/thread.hpp"
  31 
  32 class ShenandoahLock  {
  33 private:
  34   enum LockState { unlocked = 0, locked = 1 };
  35 
  36   shenandoah_padding(0);
  37   volatile int _state;
  38   shenandoah_padding(1);
  39   volatile Thread* _owner;
  40   shenandoah_padding(2);
  41 
  42 public:
  43   ShenandoahLock() : _state(unlocked), _owner(NULL) {};
  44 
  45   void lock() {
  46 #ifdef ASSERT
  47     assert(_owner != Thread::current(), "reentrant locking attempt, would deadlock");
  48 #endif
  49     Thread::SpinAcquire(&_state, "Shenandoah Heap Lock");
  50 #ifdef ASSERT
  51     assert(_state == locked, "must be locked");
  52     assert(_owner == NULL, "must not be owned");
  53     _owner = Thread::current();
  54 #endif
  55   }
  56 
  57   void unlock() {
  58 #ifdef ASSERT
  59     assert (_owner == Thread::current(), "sanity");
  60     _owner = NULL;
  61 #endif
  62     Thread::SpinRelease(&_state);
  63   }
  64 
  65   bool owned_by_self() {
  66 #ifdef ASSERT
  67     return _state == locked && _owner == Thread::current();
  68 #else
  69     ShouldNotReachHere();
  70     return false;
  71 #endif
  72   }
  73 };
  74 
  75 class ShenandoahLocker : public StackObj {
  76 private:
  77   ShenandoahLock* _lock;
  78 public:
  79   ShenandoahLocker(ShenandoahLock* lock) {
  80     _lock = lock;
  81     _lock->lock();
  82   }
  83 
  84   ~ShenandoahLocker() {
  85     _lock->unlock();
  86   }
  87 };
  88 
  89 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP