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 /*

  * Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "prims/jvmtiRawMonitor.hpp"

 #include "runtime/interfaceSupport.hpp"

 #include "runtime/orderAccess.inline.hpp"

 #include "runtime/thread.inline.hpp"

 GrowableArray<JvmtiRawMonitor*> *JvmtiPendingMonitors::_monitors = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<JvmtiRawMonitor*>(1,true);

 void JvmtiPendingMonitors::transition_raw_monitors() {

   assert((Threads::number_of_threads()==1),

          "Java thread has not created yet or more than one java thread \

 is running. Raw monitor transition will not work");

   JavaThread *current_java_thread = JavaThread::current();

   assert(current_java_thread->thread_state() == _thread_in_vm, "Must be in vm");

   {

     ThreadBlockInVM __tbivm(current_java_thread);

     for(int i=0; i< count(); i++) {

       JvmtiRawMonitor *rmonitor = monitors()->at(i);

       int r = rmonitor->raw_enter(current_java_thread);

       assert(r == ObjectMonitor::OM_OK, "raw_enter should have worked");

     }

   }

   // pending monitors are converted to real monitor so delete them all.

   dispose();

 }

 //

 // class JvmtiRawMonitor

 //

 JvmtiRawMonitor::JvmtiRawMonitor(const char *name) {

 #ifdef ASSERT

   _name = strcpy(NEW_C_HEAP_ARRAY(char, strlen(name) + 1, mtInternal), name);

 #else

   _name = NULL;

 #endif

   _magic = JVMTI_RM_MAGIC;

 }

 JvmtiRawMonitor::~JvmtiRawMonitor() {

 #ifdef ASSERT

   FreeHeap(_name);

 #endif

   _magic = 0;

 }

 bool

 JvmtiRawMonitor::is_valid() {

   int value = 0;

   // This object might not be a JvmtiRawMonitor so we can't assume

   // the _magic field is properly aligned. Get the value in a safe

   // way and then check against JVMTI_RM_MAGIC.

   switch (sizeof(_magic)) {

   case 2:

     value = Bytes::get_native_u2((address)&_magic);

     break;

   case 4:

     value = Bytes::get_native_u4((address)&_magic);

     break;

   case 8:

     value = Bytes::get_native_u8((address)&_magic);

     break;

   default:

     guarantee(false, "_magic field is an unexpected size");

   }

   return value == JVMTI_RM_MAGIC;

 }

 // -------------------------------------------------------------------------

 // The raw monitor subsystem is entirely distinct from normal

 // java-synchronization or jni-synchronization.  raw monitors are not

 // associated with objects.  They can be implemented in any manner

 // that makes sense.  The original implementors decided to piggy-back

 // the raw-monitor implementation on the existing Java objectMonitor mechanism.

 // This flaw needs to fixed.  We should reimplement raw monitors as sui-generis.

 // Specifically, we should not implement raw monitors via java monitors.

 // Time permitting, we should disentangle and deconvolve the two implementations

 // and move the resulting raw monitor implementation over to the JVMTI directories.

 // Ideally, the raw monitor implementation would be built on top of

 // park-unpark and nothing else.

 //

 // raw monitors are used mainly by JVMTI

 // The raw monitor implementation borrows the ObjectMonitor structure,

 // but the operators are degenerate and extremely simple.

 //

 // Mixed use of a single objectMonitor instance -- as both a raw monitor

 // and a normal java monitor -- is not permissible.

 //

 // Note that we use the single RawMonitor_lock to protect queue operations for

 // _all_ raw monitors.  This is a scalability impediment, but since raw monitor usage

 // is deprecated and rare, this is not of concern.  The RawMonitor_lock can not

 // be held indefinitely.  The critical sections must be short and bounded.

 //

 // -------------------------------------------------------------------------

 int JvmtiRawMonitor::SimpleEnter (Thread * Self) {

   for (;;) {

     if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {

        return OS_OK ;

     }

     ObjectWaiter Node (Self) ;

     Self->_ParkEvent->reset() ;     // strictly optional

     Node.TState = ObjectWaiter::TS_ENTER ;

     RawMonitor_lock->lock_without_safepoint_check() ;

     Node._next  = _EntryList ;

     _EntryList  = &Node ;

     OrderAccess::fence() ;

     if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {

         _EntryList = Node._next ;

         RawMonitor_lock->unlock() ;

         return OS_OK ;

     }

     RawMonitor_lock->unlock() ;

     while (Node.TState == ObjectWaiter::TS_ENTER) {

        Self->_ParkEvent->park() ;

     }

   }

 }

 int JvmtiRawMonitor::SimpleExit (Thread * Self) {

   guarantee (_owner == Self, "invariant") ;

   OrderAccess::release_store_ptr (&_owner, NULL) ;

   OrderAccess::fence() ;

   if (_EntryList == NULL) return OS_OK ;

   ObjectWaiter * w ;

   RawMonitor_lock->lock_without_safepoint_check() ;

   w = _EntryList ;

   if (w != NULL) {

       _EntryList = w->_next ;

   }

   RawMonitor_lock->unlock() ;

   if (w != NULL) {

       guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;

       ParkEvent * ev = w->_event ;

       w->TState = ObjectWaiter::TS_RUN ;

       OrderAccess::fence() ;

       ev->unpark() ;

   }

   return OS_OK ;

 }

 int JvmtiRawMonitor::SimpleWait (Thread * Self, jlong millis) {

   guarantee (_owner == Self  , "invariant") ;

   guarantee (_recursions == 0, "invariant") ;

   ObjectWaiter Node (Self) ;

   Node._notified = 0 ;

   Node.TState    = ObjectWaiter::TS_WAIT ;

   RawMonitor_lock->lock_without_safepoint_check() ;

   Node._next     = _WaitSet ;

   _WaitSet       = &Node ;

   RawMonitor_lock->unlock() ;

   SimpleExit (Self) ;

   guarantee (_owner != Self, "invariant") ;

   int ret = OS_OK ;

   if (millis <= 0) {

     Self->_ParkEvent->park();

   } else {

     ret = Self->_ParkEvent->park(millis);

   }

   // If thread still resides on the waitset then unlink it.

   // Double-checked locking -- the usage is safe in this context

   // as we TState is volatile and the lock-unlock operators are

   // serializing (barrier-equivalent).

   if (Node.TState == ObjectWaiter::TS_WAIT) {

     RawMonitor_lock->lock_without_safepoint_check() ;

     if (Node.TState == ObjectWaiter::TS_WAIT) {

       // Simple O(n) unlink, but performance isn't critical here.

       ObjectWaiter * p ;

       ObjectWaiter * q = NULL ;

       for (p = _WaitSet ; p != &Node; p = p->_next) {

          q = p ;

       }

       guarantee (p == &Node, "invariant") ;

       if (q == NULL) {

         guarantee (p == _WaitSet, "invariant") ;

         _WaitSet = p->_next ;

       } else {

         guarantee (p == q->_next, "invariant") ;

         q->_next = p->_next ;

       }

       Node.TState = ObjectWaiter::TS_RUN ;

     }

     RawMonitor_lock->unlock() ;

   }

   guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;

   SimpleEnter (Self) ;

   guarantee (_owner == Self, "invariant") ;

   guarantee (_recursions == 0, "invariant") ;

   return ret ;

 }

 int JvmtiRawMonitor::SimpleNotify (Thread * Self, bool All) {

   guarantee (_owner == Self, "invariant") ;

   if (_WaitSet == NULL) return OS_OK ;

   // We have two options:

   // A. Transfer the threads from the WaitSet to the EntryList

   // B. Remove the thread from the WaitSet and unpark() it.

   //

   // We use (B), which is crude and results in lots of futile

   // context switching.  In particular (B) induces lots of contention.

   ParkEvent * ev = NULL ;       // consider using a small auto array ...

   RawMonitor_lock->lock_without_safepoint_check() ;

   for (;;) {

       ObjectWaiter * w = _WaitSet ;

       if (w == NULL) break ;

       _WaitSet = w->_next ;

       if (ev != NULL) { ev->unpark(); ev = NULL; }

       ev = w->_event ;

       OrderAccess::loadstore() ;

       w->TState = ObjectWaiter::TS_RUN ;

       OrderAccess::storeload();

       if (!All) break ;

   }

   RawMonitor_lock->unlock() ;

   if (ev != NULL) ev->unpark();

   return OS_OK ;

 }

 // Any JavaThread will enter here with state _thread_blocked

 int JvmtiRawMonitor::raw_enter(TRAPS) {

   TEVENT (raw_enter) ;

   void * Contended ;

   // don't enter raw monitor if thread is being externally suspended, it will

   // surprise the suspender if a "suspended" thread can still enter monitor

   JavaThread * jt = (JavaThread *)THREAD;

   if (THREAD->is_Java_thread()) {

     jt->SR_lock()->lock_without_safepoint_check();

     while (jt->is_external_suspend()) {

       jt->SR_lock()->unlock();

       jt->java_suspend_self();

       jt->SR_lock()->lock_without_safepoint_check();

     }

     // guarded by SR_lock to avoid racing with new external suspend requests.

     Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;

     jt->SR_lock()->unlock();

   } else {

     Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;

   }

   if (Contended == THREAD) {

      _recursions ++ ;

      return OM_OK ;

   }

   if (Contended == NULL) {

      guarantee (_owner == THREAD, "invariant") ;

      guarantee (_recursions == 0, "invariant") ;

      return OM_OK ;

   }

   THREAD->set_current_pending_monitor(this);

   if (!THREAD->is_Java_thread()) {

      // No other non-Java threads besides VM thread would acquire

      // a raw monitor.

      assert(THREAD->is_VM_thread(), "must be VM thread");

      SimpleEnter (THREAD) ;

    } else {

      guarantee (jt->thread_state() == _thread_blocked, "invariant") ;

      for (;;) {

        jt->set_suspend_equivalent();

        // cleared by handle_special_suspend_equivalent_condition() or

        // java_suspend_self()

        SimpleEnter (THREAD) ;

        // were we externally suspended while we were waiting?

        if (!jt->handle_special_suspend_equivalent_condition()) break ;

        // This thread was externally suspended

        //

        // This logic isn't needed for JVMTI raw monitors,

        // but doesn't hurt just in case the suspend rules change. This

            // logic is needed for the JvmtiRawMonitor.wait() reentry phase.

            // We have reentered the contended monitor, but while we were

            // waiting another thread suspended us. We don't want to reenter

            // the monitor while suspended because that would surprise the

            // thread that suspended us.

            //

            // Drop the lock -

        SimpleExit (THREAD) ;

            jt->java_suspend_self();

          }

      assert(_owner == THREAD, "Fatal error with monitor owner!");

      assert(_recursions == 0, "Fatal error with monitor recursions!");

   }

   THREAD->set_current_pending_monitor(NULL);

   guarantee (_recursions == 0, "invariant") ;

   return OM_OK;

 }

 // Used mainly for JVMTI raw monitor implementation

 // Also used for JvmtiRawMonitor::wait().

 int JvmtiRawMonitor::raw_exit(TRAPS) {

   TEVENT (raw_exit) ;

   if (THREAD != _owner) {

     return OM_ILLEGAL_MONITOR_STATE;

   }

   if (_recursions > 0) {

     --_recursions ;

     return OM_OK ;

   }

   void * List = _EntryList ;

   SimpleExit (THREAD) ;

   return OM_OK;

 }

 // Used for JVMTI raw monitor implementation.

 // All JavaThreads will enter here with state _thread_blocked

 int JvmtiRawMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {

   TEVENT (raw_wait) ;

   if (THREAD != _owner) {

     return OM_ILLEGAL_MONITOR_STATE;

   }

   // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.

   // The caller must be able to tolerate spurious returns from raw_wait().

   THREAD->_ParkEvent->reset() ;

   OrderAccess::fence() ;

   // check interrupt event

   if (interruptible && Thread::is_interrupted(THREAD, true)) {

     return OM_INTERRUPTED;

   }

   intptr_t save = _recursions ;

   _recursions = 0 ;

   _waiters ++ ;

   if (THREAD->is_Java_thread()) {

     guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;

     ((JavaThread *)THREAD)->set_suspend_equivalent();

   }

   int rv = SimpleWait (THREAD, millis) ;

   _recursions = save ;

   _waiters -- ;

   guarantee (THREAD == _owner, "invariant") ;

   if (THREAD->is_Java_thread()) {

      JavaThread * jSelf = (JavaThread *) THREAD ;

      for (;;) {

         if (!jSelf->handle_special_suspend_equivalent_condition()) break ;

         SimpleExit (THREAD) ;

         jSelf->java_suspend_self();

         SimpleEnter (THREAD) ;

         jSelf->set_suspend_equivalent() ;

      }

   }

   guarantee (THREAD == _owner, "invariant") ;

   if (interruptible && Thread::is_interrupted(THREAD, true)) {

     return OM_INTERRUPTED;

   }

   return OM_OK ;

 }

 int JvmtiRawMonitor::raw_notify(TRAPS) {

   TEVENT (raw_notify) ;

   if (THREAD != _owner) {

     return OM_ILLEGAL_MONITOR_STATE;

   }

   SimpleNotify (THREAD, false) ;

   return OM_OK;

 }

 int JvmtiRawMonitor::raw_notifyAll(TRAPS) {

   TEVENT (raw_notifyAll) ;

   if (THREAD != _owner) {

     return OM_ILLEGAL_MONITOR_STATE;

   }

   SimpleNotify (THREAD, true) ;

   return OM_OK;

 }