lowMemoryDetector.cpp

/*
 * Copyright 2003-2007 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 */

# include "incls/_precompiled.incl"
# include "incls/_lowMemoryDetector.cpp.incl"

LowMemoryDetectorThread* LowMemoryDetector::_detector_thread = NULL;
volatile bool LowMemoryDetector::_enabled_for_collected_pools = false;
volatile jint LowMemoryDetector::_disabled_count = 0;

void LowMemoryDetector::initialize() {
  EXCEPTION_MARK;

  instanceKlassHandle klass (THREAD,  SystemDictionary::thread_klass());
  instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);

  const char thread_name[] = "Low Memory Detector";
  Handle string = java_lang_String::create_from_str(thread_name, CHECK);

  // Initialize thread_oop to put it into the system threadGroup
  Handle thread_group (THREAD, Universe::system_thread_group());
  JavaValue result(T_VOID);
  JavaCalls::call_special(&result, thread_oop,
                          klass,
                          vmSymbolHandles::object_initializer_name(),
                          vmSymbolHandles::threadgroup_string_void_signature(),
                          thread_group,
                          string,
                          CHECK);

  {
    MutexLocker mu(Threads_lock);
    _detector_thread = new LowMemoryDetectorThread(&low_memory_detector_thread_entry);

    // At this point it may be possible that no osthread was created for the
    // JavaThread due to lack of memory. We would have to throw an exception
    // in that case. However, since this must work and we do not allow
    // exceptions anyway, check and abort if this fails.
    if (_detector_thread == NULL || _detector_thread->osthread() == NULL) {
      vm_exit_during_initialization("java.lang.OutOfMemoryError",
                                    "unable to create new native thread");
    }

    java_lang_Thread::set_thread(thread_oop(), _detector_thread);
    java_lang_Thread::set_priority(thread_oop(), NearMaxPriority);
    java_lang_Thread::set_daemon(thread_oop());
    _detector_thread->set_threadObj(thread_oop());

    Threads::add(_detector_thread);
    Thread::start(_detector_thread);
  }
}

bool LowMemoryDetector::has_pending_requests() {
  assert(LowMemory_lock->owned_by_self(), "Must own LowMemory_lock");
  bool has_requests = false;
  int num_memory_pools = MemoryService::num_memory_pools();
  for (int i = 0; i < num_memory_pools; i++) {
    MemoryPool* pool = MemoryService::get_memory_pool(i);
    SensorInfo* sensor = pool->usage_sensor();
    if (sensor != NULL) {
      has_requests = has_requests || sensor->has_pending_requests();
    }

    SensorInfo* gc_sensor = pool->gc_usage_sensor();
    if (gc_sensor != NULL) {
      has_requests = has_requests || gc_sensor->has_pending_requests();
    }
  }
  return has_requests;
}

void LowMemoryDetector::low_memory_detector_thread_entry(JavaThread* jt, TRAPS) {
  while (true) {
    bool   sensors_changed = false;

    {
      // _no_safepoint_check_flag is used here as LowMemory_lock is a
      // special lock and the VMThread may acquire this lock at safepoint.
      // Need state transition ThreadBlockInVM so that this thread
      // will be handled by safepoint correctly when this thread is
      // notified at a safepoint.

      // This ThreadBlockInVM object is not also considered to be
      // suspend-equivalent because LowMemoryDetector threads are
      // not visible to external suspension.

      ThreadBlockInVM tbivm(jt);

      MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
      while (!(sensors_changed = has_pending_requests())) {
        // wait until one of the sensors has pending requests
        LowMemory_lock->wait(Mutex::_no_safepoint_check_flag);
      }
    }

    {
      ResourceMark rm(THREAD);
      HandleMark hm(THREAD);

      // No need to hold LowMemory_lock to call out to Java
      int num_memory_pools = MemoryService::num_memory_pools();
      for (int i = 0; i < num_memory_pools; i++) {
        MemoryPool* pool = MemoryService::get_memory_pool(i);
        SensorInfo* sensor = pool->usage_sensor();
        SensorInfo* gc_sensor = pool->gc_usage_sensor();
        if (sensor != NULL && sensor->has_pending_requests()) {
          sensor->process_pending_requests(CHECK);
        }
        if (gc_sensor != NULL && gc_sensor->has_pending_requests()) {
          gc_sensor->process_pending_requests(CHECK);
        }
      }
    }
  }
}

// This method could be called from any Java threads
// and also VMThread.
void LowMemoryDetector::detect_low_memory() {
  MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);

  bool has_pending_requests = false;
  int num_memory_pools = MemoryService::num_memory_pools();
  for (int i = 0; i < num_memory_pools; i++) {
    MemoryPool* pool = MemoryService::get_memory_pool(i);
    SensorInfo* sensor = pool->usage_sensor();
    if (sensor != NULL &&
        pool->usage_threshold()->is_high_threshold_supported() &&
        pool->usage_threshold()->high_threshold() != 0) {
      MemoryUsage usage = pool->get_memory_usage();
      sensor->set_gauge_sensor_level(usage,
                                     pool->usage_threshold());
      has_pending_requests = has_pending_requests || sensor->has_pending_requests();
    }
  }

  if (has_pending_requests) {
    LowMemory_lock->notify_all();
  }
}

// This method could be called from any Java threads
// and also VMThread.
void LowMemoryDetector::detect_low_memory(MemoryPool* pool) {
  SensorInfo* sensor = pool->usage_sensor();
  if (sensor == NULL ||
      !pool->usage_threshold()->is_high_threshold_supported() ||
      pool->usage_threshold()->high_threshold() == 0) {
    return;
  }

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

    MemoryUsage usage = pool->get_memory_usage();
    sensor->set_gauge_sensor_level(usage,
                                   pool->usage_threshold());
    if (sensor->has_pending_requests()) {
      // notify sensor state update
      LowMemory_lock->notify_all();
    }
  }
}

// Only called by VMThread at GC time
void LowMemoryDetector::detect_after_gc_memory(MemoryPool* pool) {
  SensorInfo* sensor = pool->gc_usage_sensor();
  if (sensor == NULL ||
      !pool->gc_usage_threshold()->is_high_threshold_supported() ||
      pool->gc_usage_threshold()->high_threshold() == 0) {
    return;
  }

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

    MemoryUsage usage = pool->get_last_collection_usage();
    sensor->set_counter_sensor_level(usage, pool->gc_usage_threshold());

    if (sensor->has_pending_requests()) {
      // notify sensor state update
      LowMemory_lock->notify_all();
    }
  }
}

// recompute enabled flag
void LowMemoryDetector::recompute_enabled_for_collected_pools() {
  bool enabled = false;
  int num_memory_pools = MemoryService::num_memory_pools();
  for (int i=0; i<num_memory_pools; i++) {
    MemoryPool* pool = MemoryService::get_memory_pool(i);
    if (pool->is_collected_pool() && is_enabled(pool)) {
      enabled = true;
      break;
    }
  }
  _enabled_for_collected_pools = enabled;
}

SensorInfo::SensorInfo() {
  _sensor_obj = NULL;
  _sensor_on = false;
  _sensor_count = 0;
  _pending_trigger_count = 0;
  _pending_clear_count = 0;
}

// When this method is used, the memory usage is monitored
// as a gauge attribute.  Sensor notifications (trigger or
// clear) is only emitted at the first time it crosses
// a threshold.
//
// High and low thresholds are designed to provide a
// hysteresis mechanism to avoid repeated triggering
// of notifications when the attribute value makes small oscillations
// around the high or low threshold value.
//
// The sensor will be triggered if:
//  (1) the usage is crossing above the high threshold and
//      the sensor is currently off and no pending
//      trigger requests; or
//  (2) the usage is crossing above the high threshold and
//      the sensor will be off (i.e. sensor is currently on
//      and has pending clear requests).
//
// Subsequent crossings of the high threshold value do not cause
// any triggers unless the usage becomes less than the low threshold.
//
// The sensor will be cleared if:
//  (1) the usage is crossing below the low threshold and
//      the sensor is currently on and no pending
//      clear requests; or
//  (2) the usage is crossing below the low threshold and
//      the sensor will be on (i.e. sensor is currently off
//      and has pending trigger requests).
//
// Subsequent crossings of the low threshold value do not cause
// any clears unless the usage becomes greater than or equal
// to the high threshold.
//
// If the current level is between high and low threhsold, no change.
//
void SensorInfo::set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold) {
  assert(high_low_threshold->is_high_threshold_supported(), "just checking");

  bool is_over_high = high_low_threshold->is_high_threshold_crossed(usage);
  bool is_below_low = high_low_threshold->is_low_threshold_crossed(usage);

  assert(!(is_over_high && is_below_low), "Can't be both true");

  if (is_over_high &&
        ((!_sensor_on && _pending_trigger_count == 0) ||
         _pending_clear_count > 0)) {
    // low memory detected and need to increment the trigger pending count
    // if the sensor is off or will be off due to _pending_clear_ > 0
    // Request to trigger the sensor
    _pending_trigger_count++;
    _usage = usage;

    if (_pending_clear_count > 0) {
      // non-zero pending clear requests indicates that there are
      // pending requests to clear this sensor.
      // This trigger request needs to clear this clear count
      // since the resulting sensor flag should be on.
      _pending_clear_count = 0;
    }
  } else if (is_below_low &&
               ((_sensor_on && _pending_clear_count == 0) ||
                (_pending_trigger_count > 0 && _pending_clear_count == 0))) {
    // memory usage returns below the threshold
    // Request to clear the sensor if the sensor is on or will be on due to
    // _pending_trigger_count > 0 and also no clear request
    _pending_clear_count++;
  }
}

// When this method is used, the memory usage is monitored as a
// simple counter attribute.  The sensor will be triggered
// whenever the usage is crossing the threshold to keep track
// of the number of times the VM detects such a condition occurs.
//
// High and low thresholds are designed to provide a
// hysteresis mechanism to avoid repeated triggering
// of notifications when the attribute value makes small oscillations
// around the high or low threshold value.
//
// The sensor will be triggered if:
//   - the usage is crossing above the high threshold regardless
//     of the current sensor state.
//
// The sensor will be cleared if:
//  (1) the usage is crossing below the low threshold and
//      the sensor is currently on; or
//  (2) the usage is crossing below the low threshold and
//      the sensor will be on (i.e. sensor is currently off
//      and has pending trigger requests).
void SensorInfo::set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold) {
  assert(counter_threshold->is_high_threshold_supported(), "just checking");

  bool is_over_high = counter_threshold->is_high_threshold_crossed(usage);
  bool is_below_low = counter_threshold->is_low_threshold_crossed(usage);

  assert(!(is_over_high && is_below_low), "Can't be both true");

  if (is_over_high) {
    _pending_trigger_count++;
    _usage = usage;
    _pending_clear_count = 0;
  } else if (is_below_low && (_sensor_on || _pending_trigger_count > 0)) {
    _pending_clear_count++;
  }
}

void SensorInfo::oops_do(OopClosure* f) {
  f->do_oop((oop*) &_sensor_obj);
}

void SensorInfo::process_pending_requests(TRAPS) {
  if (!has_pending_requests()) {
    return;
  }

  int pending_count = pending_trigger_count();
  if (pending_clear_count() > 0) {
    clear(pending_count, CHECK);
  } else {
    trigger(pending_count, CHECK);
  }

}

void SensorInfo::trigger(int count, TRAPS) {
  assert(count <= _pending_trigger_count, "just checking");

  if (_sensor_obj != NULL) {
    klassOop k = Management::sun_management_Sensor_klass(CHECK);
    instanceKlassHandle sensorKlass (THREAD, k);
    Handle sensor_h(THREAD, _sensor_obj);
    Handle usage_h = MemoryService::create_MemoryUsage_obj(_usage, CHECK);

    JavaValue result(T_VOID);
    JavaCallArguments args(sensor_h);
    args.push_int((int) count);
    args.push_oop(usage_h);

    JavaCalls::call_virtual(&result,
                            sensorKlass,
                            vmSymbolHandles::trigger_name(),
                            vmSymbolHandles::trigger_method_signature(),
                            &args,
                            CHECK);
  }

  {
    // Holds LowMemory_lock and update the sensor state
    MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
    _sensor_on = true;
    _sensor_count += count;
    _pending_trigger_count = _pending_trigger_count - count;
  }
}

void SensorInfo::clear(int count, TRAPS) {
  if (_sensor_obj != NULL) {
    klassOop k = Management::sun_management_Sensor_klass(CHECK);
    instanceKlassHandle sensorKlass (THREAD, k);
    Handle sensor(THREAD, _sensor_obj);

    JavaValue result(T_VOID);
    JavaCallArguments args(sensor);
    args.push_int((int) count);
    JavaCalls::call_virtual(&result,
                            sensorKlass,
                            vmSymbolHandles::clear_name(),
                            vmSymbolHandles::int_void_signature(),
                            &args,
                            CHECK);
  }

  {
    // Holds LowMemory_lock and update the sensor state
    MutexLockerEx ml(LowMemory_lock, Mutex::_no_safepoint_check_flag);
    _sensor_on = false;
    _pending_clear_count = 0;
    _pending_trigger_count = _pending_trigger_count - count;
  }
}

//--------------------------------------------------------------
// Non-product code

#ifndef PRODUCT
void SensorInfo::print() {
  tty->print_cr("%s count = %ld pending_triggers = %ld pending_clears = %ld",
                (_sensor_on ? "on" : "off"),
                _sensor_count, _pending_trigger_count, _pending_clear_count);
}

#endif // PRODUCT