/*

 * 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.

 *

 */

// Low Memory Detection Support

// Two memory alarms in the JDK (we called them sensors).

//   - Heap memory sensor

//   - Non-heap memory sensor

// When the VM detects if the memory usage of a memory pool has reached

// or exceeded its threshold, it will trigger the sensor for the type

// of the memory pool (heap or nonheap or both).

//

// If threshold == -1, no low memory detection is supported and

// the threshold value is not allowed to be changed.

// If threshold == 0, no low memory detection is performed for

// that memory pool.  The threshold can be set to any non-negative

// value.

//

// The default threshold of the Hotspot memory pools are:

//   Eden space        -1

//   Survivor space 1  -1

//   Survivor space 2  -1

//   Old generation    0

//   Perm generation   0

//   CodeCache         0

//

// For heap memory, detection will be performed when GC finishes

// and also in the slow path allocation.

// For Code cache, detection will be performed in the allocation

// and deallocation.

//

// May need to deal with hysteresis effect.

//

class LowMemoryDetectorThread;

class OopClosure;

class MemoryPool;

class ThresholdSupport : public CHeapObj {

 private:

  bool            _support_high_threshold;

  bool            _support_low_threshold;

  size_t          _high_threshold;

  size_t          _low_threshold;

 public:

  ThresholdSupport(bool support_high, bool support_low) {

    _support_high_threshold = support_high;

    _support_low_threshold = support_low;

    _high_threshold = 0;

    _low_threshold= 0;

  }

  size_t      high_threshold() const        { return _high_threshold; }

  size_t      low_threshold()  const        { return _low_threshold; }

  bool        is_high_threshold_supported() { return _support_high_threshold; }

  bool        is_low_threshold_supported()  { return _support_low_threshold; }

  bool        is_high_threshold_crossed(MemoryUsage usage) {

    if (_support_high_threshold && _high_threshold > 0) {

      return (usage.used() >= _high_threshold);

    }

    return false;

  }

  bool        is_low_threshold_crossed(MemoryUsage usage) {

    if (_support_low_threshold && _low_threshold > 0) {

      return (usage.used() < _low_threshold);

    }

    return false;

  }

  size_t      set_high_threshold(size_t new_threshold) {

    assert(_support_high_threshold, "can only be set if supported");

    assert(new_threshold >= _low_threshold, "new_threshold must be >= _low_threshold");

    size_t prev = _high_threshold;

    _high_threshold = new_threshold;

    return prev;

  }

  size_t      set_low_threshold(size_t new_threshold) {

    assert(_support_low_threshold, "can only be set if supported");

    assert(new_threshold <= _high_threshold, "new_threshold must be <= _high_threshold");

    size_t prev = _low_threshold;

    _low_threshold = new_threshold;

    return prev;

  }

};

class SensorInfo : public CHeapObj {

private:

  instanceOop     _sensor_obj;

  bool            _sensor_on;

  size_t          _sensor_count;

  // before the actual sensor on flag and sensor count are set

  // we maintain the number of pending triggers and clears.

  // _pending_trigger_count means the number of pending triggers

  // and the sensor count should be incremented by the same number.

  int             _pending_trigger_count;

  // _pending_clear_count takes precedence if it's > 0 which

  // indicates the resulting sensor will be off

  // Sensor trigger requests will reset this clear count to

  // indicate the resulting flag should be on.

  int             _pending_clear_count;

  MemoryUsage     _usage;

  void clear(int count, TRAPS);

  void trigger(int count, TRAPS);

public:

  SensorInfo();

  void set_sensor(instanceOop sensor) {

    assert(_sensor_obj == NULL, "Should be set only once");

    _sensor_obj = sensor;

  }

  bool has_pending_requests() {

    return (_pending_trigger_count > 0 || _pending_clear_count > 0);

  }

  int pending_trigger_count()      { return _pending_trigger_count; }

  int pending_clear_count()        { return _pending_clear_count; }

  // When this method is used, the memory usage is monitored

  // as a gauge attribute.  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 set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold);

  // 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.

  //

  // 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 set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold);

  void process_pending_requests(TRAPS);

  void oops_do(OopClosure* f);

#ifndef PRODUCT

  // printing on default output stream;

  void print();

#endif // PRODUCT

};

class LowMemoryDetector : public AllStatic {

friend class LowMemoryDetectorDisabler;

private:

  // true if any collected heap has low memory detection enabled

  static volatile bool _enabled_for_collected_pools;

  // > 0 if temporary disabed

  static volatile jint _disabled_count;

  static LowMemoryDetectorThread* _detector_thread;

  static void low_memory_detector_thread_entry(JavaThread* thread, TRAPS);

  static void check_memory_usage();

  static bool has_pending_requests();

  static bool temporary_disabled() { return _disabled_count > 0; }

  static void disable() { Atomic::inc(&_disabled_count); }

  static void enable() { Atomic::dec(&_disabled_count); }

public:

  static void initialize();

  static void detect_low_memory();

  static void detect_low_memory(MemoryPool* pool);

  static void detect_after_gc_memory(MemoryPool* pool);

  static bool is_enabled(MemoryPool* pool) {

    // low memory detection is enabled for collected memory pools

    // iff one of the collected memory pool has a sensor and the

    // threshold set non-zero

    if (pool->usage_sensor() == NULL) {

      return false;

    } else {

      ThresholdSupport* threshold_support = pool->usage_threshold();

      return (threshold_support->is_high_threshold_supported() ?

               (threshold_support->high_threshold() > 0) : false);

    }

  }

  // indicates if low memory detection is enabled for any collected

  // memory pools

  static inline bool is_enabled_for_collected_pools() {

    return !temporary_disabled() && _enabled_for_collected_pools;

  }

  // recompute enabled flag

  static void recompute_enabled_for_collected_pools();

  // low memory detection for collected memory pools.

  static inline void detect_low_memory_for_collected_pools() {

    // no-op if low memory detection not enabled

    if (!is_enabled_for_collected_pools()) {

      return;

    }

    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 low memory detection is enabled then check if the

      // current used exceeds the high threshold

      if (pool->is_collected_pool() && is_enabled(pool)) {

        size_t used = pool->used_in_bytes();

        size_t high = pool->usage_threshold()->high_threshold();

        if (used > high) {

          detect_low_memory(pool);

        }

      }

    }

  }

};

class LowMemoryDetectorDisabler: public StackObj {

public:

  LowMemoryDetectorDisabler()

  {

    LowMemoryDetector::disable();

  }

  ~LowMemoryDetectorDisabler()

  {

    assert(LowMemoryDetector::temporary_disabled(), "should be disabled!");

    LowMemoryDetector::enable();

  }

};