1 /*
   2  * Copyright (c) 2017, Red Hat, Inc. and/or its affiliates.
   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/shenandoahHeap.hpp"
  28 #include "memory/allocation.hpp"
  29 #include "runtime/thread.hpp"
  30 
  31 class ShenandoahHeapLock  {
  32 private:
  33   enum LockState { unlocked = 0, locked = 1 };
  34 
  35   char _pad0[DEFAULT_CACHE_LINE_SIZE];
  36   volatile int _state;
  37   char _pad1[DEFAULT_CACHE_LINE_SIZE];
  38   volatile Thread* _owner;
  39   char _pad2[DEFAULT_CACHE_LINE_SIZE];
  40 
  41 public:
  42   ShenandoahHeapLock() : _state(unlocked), _owner(NULL) {};
  43 
  44   void lock() {
  45     Thread::SpinAcquire(&_state, "Shenandoah Heap Lock");
  46 #ifdef ASSERT
  47     assert(_state == locked, "must be locked");
  48     assert(_owner == NULL, "must not be owned");
  49     _owner = Thread::current();
  50 #endif
  51   }
  52 
  53   void unlock() {
  54 #ifdef ASSERT
  55     assert (_owner == Thread::current(), "sanity");
  56     _owner = NULL;
  57 #endif
  58     Thread::SpinRelease(&_state);
  59   }
  60 
  61 #ifdef ASSERT
  62   void assert_owned_by_current_thread() {
  63     assert(_state == locked, "must be locked");
  64     assert(_owner == Thread::current(), "must be owned by current thread");
  65   }
  66 
  67   void assert_not_owned_by_current_thread() {
  68     assert(_owner != Thread::current(), "must be not owned by current thread");
  69   }
  70 
  71   void assert_owned_by_current_thread_or_safepoint() {
  72     Thread* thr = Thread::current();
  73     assert((_state == locked && _owner == thr) ||
  74            (SafepointSynchronize::is_at_safepoint() && thr->is_VM_thread()),
  75            "must own heap lock or by VM thread at safepoint");
  76   }
  77 #endif
  78 };
  79 
  80 class ShenandoahHeapLocker : public StackObj {
  81 private:
  82   ShenandoahHeapLock* _lock;
  83 public:
  84   ShenandoahHeapLocker(ShenandoahHeapLock* lock) {
  85     _lock = lock;
  86     _lock->lock();
  87   }
  88 
  89   ~ShenandoahHeapLocker() {
  90     _lock->unlock();
  91   }
  92 };
  93 
  94 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP