/*

 * Copyright (c) 2003, 2019, 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 "memory/allocation.inline.hpp"

#include "prims/jvmtiRawMonitor.hpp"

#include "runtime/atomic.hpp"

#include "runtime/interfaceSupport.inline.hpp"

#include "runtime/orderAccess.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::replace_if_null(Self, &_owner)) {

       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::replace_if_null(Self, &_owner)) {

        _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(&_owner, (void*)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") ;

      // Once we set TState to TS_RUN the waiting thread can complete

      // SimpleEnter and 'w' is pointing into random stack space. So we have

      // to ensure we extract the ParkEvent (which is in type-stable memory)

      // before we set the state, and then don't access 'w'.

      ParkEvent * ev = w->_event ;

      OrderAccess::loadstore();

      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 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) {

  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(THREAD, &_owner, (void*)NULL);

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

  } else {

    Contended = Atomic::cmpxchg(THREAD, &_owner, (void*)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) {

  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) {

  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

  }

  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") ;

  }

  return OM_OK ;

}

int JvmtiRawMonitor::raw_notify(TRAPS) {

  if (THREAD != _owner) {

    return OM_ILLEGAL_MONITOR_STATE;

  }

  SimpleNotify (THREAD, false) ;

  return OM_OK;

}

int JvmtiRawMonitor::raw_notifyAll(TRAPS) {

  if (THREAD != _owner) {

    return OM_ILLEGAL_MONITOR_STATE;

  }

  SimpleNotify (THREAD, true) ;

  return OM_OK;

}