/*

 * Copyright (c) 1998, 2017, 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 "compiler/compileBroker.hpp"

#include "gc/shared/collectedHeap.hpp"

#include "jfr/jfrEvents.hpp"

#include "jfr/support/jfrThreadId.hpp"

#include "logging/log.hpp"

#include "logging/logConfiguration.hpp"

#include "memory/resourceArea.hpp"

#include "oops/method.hpp"

#include "oops/oop.inline.hpp"

#include "oops/verifyOopClosure.hpp"

#include "runtime/interfaceSupport.inline.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/os.hpp"

#include "runtime/safepoint.hpp"

#include "runtime/thread.inline.hpp"

#include "runtime/vmThread.hpp"

#include "runtime/vm_operations.hpp"

#include "services/runtimeService.hpp"

#include "utilities/dtrace.hpp"

#include "utilities/events.hpp"

#include "utilities/vmError.hpp"

#include "utilities/xmlstream.hpp"

// Dummy VM operation to act as first element in our circular double-linked list

class VM_Dummy: public VM_Operation {

  VMOp_Type type() const { return VMOp_Dummy; }

  void  doit() {};

};

VMOperationQueue::VMOperationQueue() {

  // The queue is a circular doubled-linked list, which always contains

  // one element (i.e., one element means empty).

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

    _queue_length[i] = 0;

    _queue_counter = 0;

    _queue[i] = new VM_Dummy();

    _queue[i]->set_next(_queue[i]);

    _queue[i]->set_prev(_queue[i]);

  }

  _drain_list = NULL;

}

bool VMOperationQueue::queue_empty(int prio) {

  // It is empty if there is exactly one element

  bool empty = (_queue[prio] == _queue[prio]->next());

  assert( (_queue_length[prio] == 0 && empty) ||

          (_queue_length[prio] > 0  && !empty), "sanity check");

  return _queue_length[prio] == 0;

}

// Inserts an element to the right of the q element

void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {

  assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");

  n->set_prev(q);

  n->set_next(q->next());

  q->next()->set_prev(n);

  q->set_next(n);

}

void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {

  _queue_length[prio]++;

  insert(_queue[prio]->next(), op);

}

void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {

  _queue_length[prio]++;

  insert(_queue[prio]->prev(), op);

}

void VMOperationQueue::unlink(VM_Operation* q) {

  assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");

  q->prev()->set_next(q->next());

  q->next()->set_prev(q->prev());

}

VM_Operation* VMOperationQueue::queue_remove_front(int prio) {

  if (queue_empty(prio)) return NULL;

  assert(_queue_length[prio] >= 0, "sanity check");

  _queue_length[prio]--;

  VM_Operation* r = _queue[prio]->next();

  assert(r != _queue[prio], "cannot remove base element");

  unlink(r);

  return r;

}

VM_Operation* VMOperationQueue::queue_drain(int prio) {

  if (queue_empty(prio)) return NULL;

  DEBUG_ONLY(int length = _queue_length[prio];);

  assert(length >= 0, "sanity check");

  _queue_length[prio] = 0;

  VM_Operation* r = _queue[prio]->next();

  assert(r != _queue[prio], "cannot remove base element");

  // remove links to base element from head and tail

  r->set_prev(NULL);

  _queue[prio]->prev()->set_next(NULL);

  // restore queue to empty state

  _queue[prio]->set_next(_queue[prio]);

  _queue[prio]->set_prev(_queue[prio]);

  assert(queue_empty(prio), "drain corrupted queue");

#ifdef ASSERT

  int len = 0;

  VM_Operation* cur;

  for(cur = r; cur != NULL; cur=cur->next()) len++;

  assert(len == length, "drain lost some ops");

#endif

  return r;

}

void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {

  VM_Operation* cur = _queue[queue];

  cur = cur->next();

  while (cur != _queue[queue]) {

    cur->oops_do(f);

    cur = cur->next();

  }

}

void VMOperationQueue::drain_list_oops_do(OopClosure* f) {

  VM_Operation* cur = _drain_list;

  while (cur != NULL) {

    cur->oops_do(f);

    cur = cur->next();

  }

}

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

// High-level interface

bool VMOperationQueue::add(VM_Operation *op) {

  HOTSPOT_VMOPS_REQUEST(

                   (char *) op->name(), strlen(op->name()),

                   op->evaluation_mode());

  // Encapsulates VM queue policy. Currently, that

  // only involves putting them on the right list

  if (op->evaluate_at_safepoint()) {

    queue_add_back(SafepointPriority, op);

    return true;

  }

  queue_add_back(MediumPriority, op);

  return true;

}

VM_Operation* VMOperationQueue::remove_next() {

  // Assuming VMOperation queue is two-level priority queue. If there are

  // more than two priorities, we need a different scheduling algorithm.

  assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,

         "current algorithm does not work");

  // simple counter based scheduling to prevent starvation of lower priority

  // queue. -- see 4390175

  int high_prio, low_prio;

  if (_queue_counter++ < 10) {

      high_prio = SafepointPriority;

      low_prio  = MediumPriority;

  } else {

      _queue_counter = 0;

      high_prio = MediumPriority;

      low_prio  = SafepointPriority;

  }

  return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);

}

void VMOperationQueue::oops_do(OopClosure* f) {

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

    queue_oops_do(i, f);

  }

  drain_list_oops_do(f);

}

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

// Implementation of VMThread stuff

bool                VMThread::_should_terminate   = false;

bool              VMThread::_terminated         = false;

Monitor*          VMThread::_terminate_lock     = NULL;

VMThread*         VMThread::_vm_thread          = NULL;

VM_Operation*     VMThread::_cur_vm_operation   = NULL;

VMOperationQueue* VMThread::_vm_queue           = NULL;

PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = NULL;

const char*       VMThread::_no_op_reason       = NULL;

void VMThread::create() {

  assert(vm_thread() == NULL, "we can only allocate one VMThread");

  _vm_thread = new VMThread();

  // Create VM operation queue

  _vm_queue = new VMOperationQueue();

  guarantee(_vm_queue != NULL, "just checking");

  _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,

                                Monitor::_safepoint_check_never);

  if (UsePerfData) {

    // jvmstat performance counters

    Thread* THREAD = Thread::current();

    _perf_accumulated_vm_operation_time =

                 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",

                                                 PerfData::U_Ticks, CHECK);

  }

}

VMThread::VMThread() : NamedThread() {

  set_name("VM Thread");

}

void VMThread::destroy() {

  _vm_thread = NULL;      // VM thread is gone

}

void VMThread::run() {

  assert(this == vm_thread(), "check");

  this->initialize_named_thread();

  this->record_stack_base_and_size();

  // Notify_lock wait checks on active_handles() to rewait in

  // case of spurious wakeup, it should wait on the last

  // value set prior to the notify

  this->set_active_handles(JNIHandleBlock::allocate_block());

  {

    MutexLocker ml(Notify_lock);

    Notify_lock->notify();

  }

  // Notify_lock is destroyed by Threads::create_vm()

  int prio = (VMThreadPriority == -1)

    ? os::java_to_os_priority[NearMaxPriority]

    : VMThreadPriority;

  // Note that I cannot call os::set_priority because it expects Java

  // priorities and I am *explicitly* using OS priorities so that it's

  // possible to set the VM thread priority higher than any Java thread.

  os::set_native_priority( this, prio );

  // Wait for VM_Operations until termination

  this->loop();

  // Note the intention to exit before safepointing.

  // 6295565  This has the effect of waiting for any large tty

  // outputs to finish.

  if (xtty != NULL) {

    ttyLocker ttyl;

    xtty->begin_elem("destroy_vm");

    xtty->stamp();

    xtty->end_elem();

    assert(should_terminate(), "termination flag must be set");

  }

  // 4526887 let VM thread exit at Safepoint

  _no_op_reason = "Halt";

  SafepointSynchronize::begin();

  if (VerifyBeforeExit) {

    HandleMark hm(VMThread::vm_thread());

    // Among other things, this ensures that Eden top is correct.

    Universe::heap()->prepare_for_verify();

    // Silent verification so as not to pollute normal output,

    // unless we really asked for it.

    Universe::verify();

  }

  CompileBroker::set_should_block();

  // wait for threads (compiler threads or daemon threads) in the

  // _thread_in_native state to block.

  VM_Exit::wait_for_threads_in_native_to_block();

  // signal other threads that VM process is gone

  {

    // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows

    // VM thread to enter any lock at Safepoint as long as its _owner is NULL.

    // If that happens after _terminate_lock->wait() has unset _owner

    // but before it actually drops the lock and waits, the notification below

    // may get lost and we will have a hang. To avoid this, we need to use

    // Mutex::lock_without_safepoint_check().

    MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);

    _terminated = true;

    _terminate_lock->notify();

  }

  // We are now racing with the VM termination being carried out in

  // another thread, so we don't "delete this". Numerous threads don't

  // get deleted when the VM terminates

}

// Notify the VMThread that the last non-daemon JavaThread has terminated,

// and wait until operation is performed.

void VMThread::wait_for_vm_thread_exit() {

  { MutexLocker mu(VMOperationQueue_lock);

    _should_terminate = true;

    VMOperationQueue_lock->notify();

  }

  // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint

  // because this thread has been removed from the threads list. But anything

  // that could get blocked by Safepoint should not be used after this point,

  // otherwise we will hang, since there is no one can end the safepoint.

  // Wait until VM thread is terminated

  // Note: it should be OK to use Terminator_lock here. But this is called

  // at a very delicate time (VM shutdown) and we are operating in non- VM

  // thread at Safepoint. It's safer to not share lock with other threads.

  { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);

    while(!VMThread::is_terminated()) {

        _terminate_lock->wait(Mutex::_no_safepoint_check_flag);

    }

  }

}

static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {

  assert(event != NULL, "invariant");

  assert(event->should_commit(), "invariant");

  assert(op != NULL, "invariant");

  const bool is_concurrent = op->evaluate_concurrently();

  const bool evaluate_at_safepoint = op->evaluate_at_safepoint();

  event->set_operation(op->type());

  event->set_safepoint(evaluate_at_safepoint);

  event->set_blocking(!is_concurrent);

  // Only write caller thread information for non-concurrent vm operations.

  // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.

  // This is because the caller thread could have exited already.

  event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));

  event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);

  event->commit();

}

void VMThread::evaluate_operation(VM_Operation* op) {

  ResourceMark rm;

  {

    PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());

    HOTSPOT_VMOPS_BEGIN(

                     (char *) op->name(), strlen(op->name()),

                     op->evaluation_mode());

    EventExecuteVMOperation event;

    op->evaluate();

    if (event.should_commit()) {

      post_vm_operation_event(&event, op);

    }

    HOTSPOT_VMOPS_END(

                     (char *) op->name(), strlen(op->name()),

                     op->evaluation_mode());

  }

  // Last access of info in _cur_vm_operation!

  bool c_heap_allocated = op->is_cheap_allocated();

  // Mark as completed

  if (!op->evaluate_concurrently()) {

    op->calling_thread()->increment_vm_operation_completed_count();

  }

  // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,

  // since if it is stack allocated the calling thread might have deallocated

  if (c_heap_allocated) {

    delete _cur_vm_operation;

  }

}

bool VMThread::no_op_safepoint_needed(bool check_time) {

  if (SafepointALot) {

    _no_op_reason = "SafepointALot";

    return true;

  }

  if (!SafepointSynchronize::is_cleanup_needed()) {

    return false;

  }

  if (check_time) {

    long interval = SafepointSynchronize::last_non_safepoint_interval();

    bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&

                             (interval > GuaranteedSafepointInterval);

    if (!max_time_exceeded) {

      return false;

    }

  }

  _no_op_reason = "Cleanup";

  return true;

}

void VMThread::loop() {

  assert(_cur_vm_operation == NULL, "no current one should be executing");

  while(true) {

    VM_Operation* safepoint_ops = NULL;

    //

    // Wait for VM operation

    //

    // use no_safepoint_check to get lock without attempting to "sneak"

    { MutexLockerEx mu_queue(VMOperationQueue_lock,

                             Mutex::_no_safepoint_check_flag);

      // Look for new operation

      assert(_cur_vm_operation == NULL, "no current one should be executing");

      _cur_vm_operation = _vm_queue->remove_next();

      // Stall time tracking code

      if (PrintVMQWaitTime && _cur_vm_operation != NULL &&

          !_cur_vm_operation->evaluate_concurrently()) {

        long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();

        if (stall > 0)

          tty->print_cr("%s stall: %ld",  _cur_vm_operation->name(), stall);

      }

      while (!should_terminate() && _cur_vm_operation == NULL) {

        // wait with a timeout to guarantee safepoints at regular intervals

        bool timedout =

          VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,

                                      GuaranteedSafepointInterval);

        // Support for self destruction

        if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&

            (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {

          tty->print_cr("VM self-destructed");

          exit(-1);

        }

        if (timedout && VMThread::no_op_safepoint_needed(false)) {

          MutexUnlockerEx mul(VMOperationQueue_lock,

                              Mutex::_no_safepoint_check_flag);

          // Force a safepoint since we have not had one for at least

          // 'GuaranteedSafepointInterval' milliseconds.  This will run all

          // the clean-up processing that needs to be done regularly at a

          // safepoint

          SafepointSynchronize::begin();

          #ifdef ASSERT

            if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();

          #endif

          SafepointSynchronize::end();

        }

        _cur_vm_operation = _vm_queue->remove_next();

        // If we are at a safepoint we will evaluate all the operations that

        // follow that also require a safepoint

        if (_cur_vm_operation != NULL &&

            _cur_vm_operation->evaluate_at_safepoint()) {

          safepoint_ops = _vm_queue->drain_at_safepoint_priority();

        }

      }

      if (should_terminate()) break;

    } // Release mu_queue_lock

    //

    // Execute VM operation

    //

    { HandleMark hm(VMThread::vm_thread());

      EventMark em("Executing VM operation: %s", vm_operation()->name());

      assert(_cur_vm_operation != NULL, "we should have found an operation to execute");

      // Give the VM thread an extra quantum.  Jobs tend to be bursty and this

      // helps the VM thread to finish up the job.

      // FIXME: When this is enabled and there are many threads, this can degrade

      // performance significantly.

      if( VMThreadHintNoPreempt )

        os::hint_no_preempt();

      // If we are at a safepoint we will evaluate all the operations that

      // follow that also require a safepoint

      if (_cur_vm_operation->evaluate_at_safepoint()) {

        log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());

        _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned

        SafepointSynchronize::begin();

        evaluate_operation(_cur_vm_operation);

        // now process all queued safepoint ops, iteratively draining

        // the queue until there are none left

        do {

          _cur_vm_operation = safepoint_ops;

          if (_cur_vm_operation != NULL) {

            do {

              log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());

              // evaluate_operation deletes the op object so we have

              // to grab the next op now

              VM_Operation* next = _cur_vm_operation->next();

              _vm_queue->set_drain_list(next);

              evaluate_operation(_cur_vm_operation);

              _cur_vm_operation = next;

              if (PrintSafepointStatistics) {

                SafepointSynchronize::inc_vmop_coalesced_count();

              }

            } while (_cur_vm_operation != NULL);