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轻量级锁释放后的状态

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轻量级锁加锁成功后的状态

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interpreterRuntime.cpp

  1. //%note monitor_1
  2. IRT_ENTRY_NO_ASYNC(void, InterpreterRuntime::monitorenter(JavaThread* thread, BasicObjectLock* elem))
  3. #ifdef ASSERT
  4.   thread->last_frame().interpreter_frame_verify_monitor(elem);
  5. #endif
  6.   if (PrintBiasedLockingStatistics) {
  7.     Atomic::inc(BiasedLocking::slow_path_entry_count_addr());
  8.   }
  9.   Handle h_obj(thread, elem->obj());
  10.   assert(Universe::heap()->is_in_reserved_or_null(h_obj()),
  11.          "must be NULL or an object");
  12.   //是否开启了偏向锁模式
  13.   if (UseBiasedLocking) {
  14.     // Retry fast entry if bias is revoked to avoid unnecessary inflation
  15.     ObjectSynchronizer::fast_enter(h_obj, elem->lock(), true, CHECK);
  16.   } else {
  17.     ObjectSynchronizer::slow_enter(h_obj, elem->lock(), CHECK);
  18.   }
  19.   assert(Universe::heap()->is_in_reserved_or_null(elem->obj()),
  20.          "must be NULL or an object");
  21. #ifdef ASSERT
  22.   thread->last_frame().interpreter_frame_verify_monitor(elem);
  23. #endif
  24. IRT_END

synchronizer.cpp

  1. void ObjectSynchronizer::fast_enter(Handle obj, BasicLock *lock,
  2.                                     bool attempt_rebias, TRAPS) {
  3.     if (UseBiasedLocking) {
  4.         if (!SafepointSynchronize::is_at_safepoint()) {
  5.             //撤销偏向锁或者重偏向
  6.             BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
  7.             if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
  8.                 return;
  9.             }
  10.         } else {
  11.             assert(!attempt_rebias, "can not rebias toward VM thread");
  12.             BiasedLocking::revoke_at_safepoint(obj);
  13.         }
  14.         assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
  15.     }
  17.     slow_enter(obj, lock, THREAD);
  18. }
  20. void ObjectSynchronizer::slow_enter(Handle obj, BasicLock *lock, TRAPS) {
  21.     markOop mark = obj->mark();
  22.     assert(!mark->has_bias_pattern(), "should not see bias pattern here");
  24.     if (mark->is_neutral()) {
  25.         // Anticipate successful CAS -- the ST of the displaced mark must
  26.         // be visible <= the ST performed by the CAS.
  27.         lock->set_displaced_header(mark);
  28.         //在markword中存入 lockRecord的引用 
  29.         if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
  30.             //轻量级锁加锁成功
  31.             return;
  32.         }
  33.         // Fall through to inflate() ...
  34.     } else if (mark->has_locker() &&
  35.                THREAD->is_lock_owned((address) mark->locker())) {
  36.         assert(lock != mark->locker(), "must not re-lock the same lock");
  37.         assert(lock != (BasicLock *) obj->mark(), "don't relock with same BasicLock");
  38.         lock->set_displaced_header(NULL);
  39.         return;
  40.     }
  42.     // The object header will never be displaced to this lock,
  43.     // so it does not matter what the value is, except that it
  44.     // must be non-zero to avoid looking like a re-entrant lock,
  45.     // and must not look locked either.
  46.     lock->set_displaced_header(markOopDesc::unused_mark());
  47.     //开始膨胀成重量级锁 10
  48.     ObjectSynchronizer::inflate(THREAD,obj(),inflate_cause_monitor_enter)->enter(THREAD);
  49. }