1 /*
  2  * Copyright (c) 2017, 2019, Red Hat, Inc. 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
 21  * questions.
 22  *
 23  */
 24 
 25 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHLOCK_HPP
 26 #define SHARE_GC_SHENANDOAH_SHENANDOAHLOCK_HPP
 27 
 28 #include "gc/shenandoah/shenandoahPadding.hpp"
 29 #include "memory/allocation.hpp"
 30 #include "runtime/javaThread.hpp"
 31 #include "runtime/safepoint.hpp"
 32 
 33 class ShenandoahLock  {
 34 private:
 35   enum LockState { unlocked = 0, locked = 1 };
 36 
 37   shenandoah_padding(0);
 38   volatile LockState _state;
 39   shenandoah_padding(1);
 40   Thread* volatile _owner;
 41   shenandoah_padding(2);
 42 
 43   template<bool ALLOW_BLOCK>
 44   void contended_lock_internal(JavaThread* java_thread);
 45 public:
 46   ShenandoahLock() : _state(unlocked), _owner(nullptr) {};
 47 
 48   void lock(bool allow_block_for_safepoint) {
 49     assert(Atomic::load(&_owner) != Thread::current(), "reentrant locking attempt, would deadlock");
 50 
 51     if ((allow_block_for_safepoint && SafepointSynchronize::is_synchronizing()) ||
 52         (Atomic::cmpxchg(&_state, unlocked, locked) != unlocked)) {
 53       // 1. Java thread, and there is a pending safepoint. Dive into contended locking
 54       //    immediately without trying anything else, and block.
 55       // 2. Fast lock fails, dive into contended lock handling.
 56       contended_lock(allow_block_for_safepoint);
 57     }
 58 
 59     assert(Atomic::load(&_state) == locked, "must be locked");
 60     assert(Atomic::load(&_owner) == nullptr, "must not be owned");
 61     DEBUG_ONLY(Atomic::store(&_owner, Thread::current());)
 62   }
 63 
 64   void unlock() {
 65     assert(Atomic::load(&_owner) == Thread::current(), "sanity");
 66     DEBUG_ONLY(Atomic::store(&_owner, (Thread*)nullptr);)
 67     OrderAccess::fence();
 68     Atomic::store(&_state, unlocked);
 69   }
 70 
 71   void contended_lock(bool allow_block_for_safepoint);
 72 
 73   bool owned_by_self() {
 74 #ifdef ASSERT
 75     return _state == locked && _owner == Thread::current();
 76 #else
 77     ShouldNotReachHere();
 78     return false;
 79 #endif
 80   }
 81 };
 82 
 83 class ShenandoahLocker : public StackObj {
 84 private:
 85   ShenandoahLock* const _lock;
 86 public:
 87   ShenandoahLocker(ShenandoahLock* lock, bool allow_block_for_safepoint = false) : _lock(lock) {
 88     if (_lock != nullptr) {
 89       _lock->lock(allow_block_for_safepoint);
 90     }
 91   }
 92 
 93   ~ShenandoahLocker() {
 94     if (_lock != nullptr) {
 95       _lock->unlock();
 96     }
 97   }
 98 };
 99 
100 class ShenandoahSimpleLock {
101 private:
102   PlatformMonitor   _lock; // native lock
103 public:
104   ShenandoahSimpleLock();
105 
106   virtual void lock();
107   virtual void unlock();
108 };
109 
110 class ShenandoahReentrantLock : public ShenandoahSimpleLock {
111 private:
112   Thread* volatile      _owner;
113   uint64_t              _count;
114 
115 public:
116   ShenandoahReentrantLock();
117   ~ShenandoahReentrantLock();
118 
119   virtual void lock();
120   virtual void unlock();
121 
122   // If the lock already owned by this thread
123   bool owned_by_self() const ;
124 };
125 
126 class ShenandoahReentrantLocker : public StackObj {
127 private:
128   ShenandoahReentrantLock* const _lock;
129 
130 public:
131   ShenandoahReentrantLocker(ShenandoahReentrantLock* lock) :
132     _lock(lock) {
133     if (_lock != nullptr) {
134       _lock->lock();
135     }
136   }
137 
138   ~ShenandoahReentrantLocker() {
139     if (_lock != nullptr) {
140       assert(_lock->owned_by_self(), "Must be owner");
141       _lock->unlock();
142     }
143   }
144 };
145 
146 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHLOCK_HPP